# @title Uniswap Exchange Interface V1
# @notice Source code found at https://github.com/uniswap
# @notice Use at your own risk

contract Factory():
    def getExchange(token_addr: address) -> address: constant

contract Exchange():
    def getEthToTokenOutputPrice(tokens_bought: uint256) -> uint256(wei): constant
    def ethToTokenTransferInput(min_tokens: uint256, deadline: timestamp, recipient: address) -> uint256: modifying
    def ethToTokenTransferOutput(tokens_bought: uint256, deadline: timestamp, recipient: address) -> uint256(wei): modifying

TokenPurchase: event({buyer: indexed(address), eth_sold: indexed(uint256(wei)), tokens_bought: indexed(uint256)})
EthPurchase: event({buyer: indexed(address), tokens_sold: indexed(uint256), eth_bought: indexed(uint256(wei))})
AddLiquidity: event({provider: indexed(address), eth_amount: indexed(uint256(wei)), token_amount: indexed(uint256)})
RemoveLiquidity: event({provider: indexed(address), eth_amount: indexed(uint256(wei)), token_amount: indexed(uint256)})
Transfer: event({_from: indexed(address), _to: indexed(address), _value: uint256})
Approval: event({_owner: indexed(address), _spender: indexed(address), _value: uint256})

name: public(bytes32)                             # Uniswap V1
symbol: public(bytes32)                           # UNI-V1
decimals: public(uint256)                         # 18
totalSupply: public(uint256)                      # total number of UNI in existence
balances: uint256[address]                        # UNI balance of an address
allowances: (uint256[address])[address]           # UNI allowance of one address on another
token: address(ERC20)                             # address of the ERC20 token traded on this contract
factory: Factory                                  # interface for the factory that created this contract

# @dev This function acts as a contract constructor which is not currently supported in contracts deployed
#      using create_with_code_of(). It is called once by the factory during contract creation.
@public
def setup(token_addr: address):
    assert (self.factory == ZERO_ADDRESS and self.token == ZERO_ADDRESS) and token_addr != ZERO_ADDRESS
    self.factory = msg.sender
    self.token = token_addr
    self.name = 0x556e697377617020563100000000000000000000000000000000000000000000
    self.symbol = 0x554e492d56310000000000000000000000000000000000000000000000000000
    self.decimals = 18

# @notice Deposit ETH and Tokens (self.token) at current ratio to mint UNI tokens.
# @dev min_liquidity does nothing when total UNI supply is 0.
# @param min_liquidity Minimum number of UNI sender will mint if total UNI supply is greater than 0.
# @param max_tokens Maximum number of tokens deposited. Deposits max amount if total UNI supply is 0.
# @param deadline Time after which this transaction can no longer be executed.
# @return The amount of UNI minted.
@public
@payable
def addLiquidity(min_liquidity: uint256, max_tokens: uint256, deadline: timestamp) -> uint256:
    assert deadline > block.timestamp and (max_tokens > 0 and msg.value > 0)
    total_liquidity: uint256 = self.totalSupply
    if total_liquidity > 0:
        assert min_liquidity > 0
        eth_reserve: uint256(wei) = self.balance - msg.value
        token_reserve: uint256 = self.token.balanceOf(self)
        token_amount: uint256 = msg.value * token_reserve / eth_reserve + 1
        liquidity_minted: uint256 = msg.value * total_liquidity / eth_reserve
        assert max_tokens >= token_amount and liquidity_minted >= min_liquidity
        self.balances[msg.sender] += liquidity_minted
        self.totalSupply = total_liquidity + liquidity_minted
        assert self.token.transferFrom(msg.sender, self, token_amount)
        log.AddLiquidity(msg.sender, msg.value, token_amount)
        log.Transfer(ZERO_ADDRESS, msg.sender, liquidity_minted)
        return liquidity_minted
    else:
        assert (self.factory != ZERO_ADDRESS and self.token != ZERO_ADDRESS) and msg.value >= 1000000000
        assert self.factory.getExchange(self.token) == self
        token_amount: uint256 = max_tokens
        initial_liquidity: uint256 = as_unitless_number(self.balance)
        self.totalSupply = initial_liquidity
        self.balances[msg.sender] = initial_liquidity
        assert self.token.transferFrom(msg.sender, self, token_amount)
        log.AddLiquidity(msg.sender, msg.value, token_amount)
        log.Transfer(ZERO_ADDRESS, msg.sender, initial_liquidity)
        return initial_liquidity

# @dev Burn UNI tokens to withdraw ETH and Tokens at current ratio.
# @param amount Amount of UNI burned.
# @param min_eth Minimum ETH withdrawn.
# @param min_tokens Minimum Tokens withdrawn.
# @param deadline Time after which this transaction can no longer be executed.
# @return The amount of ETH and Tokens withdrawn.
@public
def removeLiquidity(amount: uint256, min_eth: uint256(wei), min_tokens: uint256, deadline: timestamp) -> (uint256(wei), uint256):
    assert (amount > 0 and deadline > block.timestamp) and (min_eth > 0 and min_tokens > 0)
    total_liquidity: uint256 = self.totalSupply
    assert total_liquidity > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_amount: uint256(wei) = amount * self.balance / total_liquidity
    token_amount: uint256 = amount * token_reserve / total_liquidity
    assert eth_amount >= min_eth and token_amount >= min_tokens
    self.balances[msg.sender] -= amount
    self.totalSupply = total_liquidity - amount
    send(msg.sender, eth_amount)
    assert self.token.transfer(msg.sender, token_amount)
    log.RemoveLiquidity(msg.sender, eth_amount, token_amount)
    log.Transfer(msg.sender, ZERO_ADDRESS, amount)
    return eth_amount, token_amount

# @dev Pricing function for converting between ETH and Tokens.
# @param input_amount Amount of ETH or Tokens being sold.
# @param input_reserve Amount of ETH or Tokens (input type) in exchange reserves.
# @param output_reserve Amount of ETH or Tokens (output type) in exchange reserves.
# @return Amount of ETH or Tokens bought.
@private
@constant
def getInputPrice(input_amount: uint256, input_reserve: uint256, output_reserve: uint256) -> uint256:
    assert input_reserve > 0 and output_reserve > 0
    input_amount_with_fee: uint256 = input_amount * 997
    numerator: uint256 = input_amount_with_fee * output_reserve
    denominator: uint256 = (input_reserve * 1000) + input_amount_with_fee
    return numerator / denominator

# @dev Pricing function for converting between ETH and Tokens.
# @param output_amount Amount of ETH or Tokens being bought.
# @param input_reserve Amount of ETH or Tokens (input type) in exchange reserves.
# @param output_reserve Amount of ETH or Tokens (output type) in exchange reserves.
# @return Amount of ETH or Tokens sold.
@private
@constant
def getOutputPrice(output_amount: uint256, input_reserve: uint256, output_reserve: uint256) -> uint256:
    assert input_reserve > 0 and output_reserve > 0
    numerator: uint256 = input_reserve * output_amount * 1000
    denominator: uint256 = (output_reserve - output_amount) * 997
    return numerator / denominator + 1

@private
def ethToTokenInput(eth_sold: uint256(wei), min_tokens: uint256, deadline: timestamp, buyer: address, recipient: address) -> uint256:
    assert deadline >= block.timestamp and (eth_sold > 0 and min_tokens > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_bought: uint256 = self.getInputPrice(as_unitless_number(eth_sold), as_unitless_number(self.balance - eth_sold), token_reserve)
    assert tokens_bought >= min_tokens
    assert self.token.transfer(recipient, tokens_bought)
    log.TokenPurchase(buyer, eth_sold, tokens_bought)
    return tokens_bought

# @notice Convert ETH to Tokens.
# @dev User specifies exact input (msg.value).
# @dev User cannot specify minimum output or deadline.
@public
@payable
def __default__():
    self.ethToTokenInput(msg.value, 1, block.timestamp, msg.sender, msg.sender)

# @notice Convert ETH to Tokens.
# @dev User specifies exact input (msg.value) and minimum output.
# @param min_tokens Minimum Tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of Tokens bought.
@public
@payable
def ethToTokenSwapInput(min_tokens: uint256, deadline: timestamp) -> uint256:
    return self.ethToTokenInput(msg.value, min_tokens, deadline, msg.sender, msg.sender)

# @notice Convert ETH to Tokens and transfers Tokens to recipient.
# @dev User specifies exact input (msg.value) and minimum output
# @param min_tokens Minimum Tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output Tokens.
# @return Amount of Tokens bought.
@public
@payable
def ethToTokenTransferInput(min_tokens: uint256, deadline: timestamp, recipient: address) -> uint256:
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.ethToTokenInput(msg.value, min_tokens, deadline, msg.sender, recipient)

@private
def ethToTokenOutput(tokens_bought: uint256, max_eth: uint256(wei), deadline: timestamp, buyer: address, recipient: address) -> uint256(wei):
    assert deadline >= block.timestamp and (tokens_bought > 0 and max_eth > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_sold: uint256 = self.getOutputPrice(tokens_bought, as_unitless_number(self.balance - max_eth), token_reserve)
    # Throws if eth_sold > max_eth
    eth_refund: uint256(wei) = max_eth - as_wei_value(eth_sold, 'wei')
    if eth_refund > 0:
        send(buyer, eth_refund)
    assert self.token.transfer(recipient, tokens_bought)
    log.TokenPurchase(buyer, as_wei_value(eth_sold, 'wei'), tokens_bought)
    return as_wei_value(eth_sold, 'wei')

# @notice Convert ETH to Tokens.
# @dev User specifies maximum input (msg.value) and exact output.
# @param tokens_bought Amount of tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of ETH sold.
@public
@payable
def ethToTokenSwapOutput(tokens_bought: uint256, deadline: timestamp) -> uint256(wei):
    return self.ethToTokenOutput(tokens_bought, msg.value, deadline, msg.sender, msg.sender)

# @notice Convert ETH to Tokens and transfers Tokens to recipient.
# @dev User specifies maximum input (msg.value) and exact output.
# @param tokens_bought Amount of tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output Tokens.
# @return Amount of ETH sold.
@public
@payable
def ethToTokenTransferOutput(tokens_bought: uint256, deadline: timestamp, recipient: address) -> uint256(wei):
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.ethToTokenOutput(tokens_bought, msg.value, deadline, msg.sender, recipient)

@private
def tokenToEthInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp, buyer: address, recipient: address) -> uint256(wei):
    assert deadline >= block.timestamp and (tokens_sold > 0 and min_eth > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    wei_bought: uint256(wei) = as_wei_value(eth_bought, 'wei')
    assert wei_bought >= min_eth
    send(recipient, wei_bought)
    assert self.token.transferFrom(buyer, self, tokens_sold)
    log.EthPurchase(buyer, tokens_sold, wei_bought)
    return wei_bought


# @notice Convert Tokens to ETH.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_eth Minimum ETH purchased.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of ETH bought.
@public
def tokenToEthSwapInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp) -> uint256(wei):
    return self.tokenToEthInput(tokens_sold, min_eth, deadline, msg.sender, msg.sender)

# @notice Convert Tokens to ETH and transfers ETH to recipient.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_eth Minimum ETH purchased.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @return Amount of ETH bought.
@public
def tokenToEthTransferInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp, recipient: address) -> uint256(wei):
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.tokenToEthInput(tokens_sold, min_eth, deadline, msg.sender, recipient)

@private
def tokenToEthOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp, buyer: address, recipient: address) -> uint256:
    assert deadline >= block.timestamp and eth_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_sold: uint256 = self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))
    # tokens sold is always > 0
    assert max_tokens >= tokens_sold
    send(recipient, eth_bought)
    assert self.token.transferFrom(buyer, self, tokens_sold)
    log.EthPurchase(buyer, tokens_sold, eth_bought)
    return tokens_sold

# @notice Convert Tokens to ETH.
# @dev User specifies maximum input and exact output.
# @param eth_bought Amount of ETH purchased.
# @param max_tokens Maximum Tokens sold.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of Tokens sold.
@public
def tokenToEthSwapOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp) -> uint256:
    return self.tokenToEthOutput(eth_bought, max_tokens, deadline, msg.sender, msg.sender)

# @notice Convert Tokens to ETH and transfers ETH to recipient.
# @dev User specifies maximum input and exact output.
# @param eth_bought Amount of ETH purchased.
# @param max_tokens Maximum Tokens sold.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @return Amount of Tokens sold.
@public
def tokenToEthTransferOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp, recipient: address) -> uint256:
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.tokenToEthOutput(eth_bought, max_tokens, deadline, msg.sender, recipient)

@private
def tokenToTokenInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
    assert (deadline >= block.timestamp and tokens_sold > 0) and (min_tokens_bought > 0 and min_eth_bought > 0)
    assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    wei_bought: uint256(wei) = as_wei_value(eth_bought, 'wei')
    assert wei_bought >= min_eth_bought
    assert self.token.transferFrom(buyer, self, tokens_sold)
    tokens_bought: uint256 = Exchange(exchange_addr).ethToTokenTransferInput(min_tokens_bought, deadline, recipient, value=wei_bought)
    log.EthPurchase(buyer, tokens_sold, wei_bought)
    return tokens_bought

# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
#         Tokens (token_addr) to recipient.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)

@private
def tokenToTokenOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
    assert deadline >= block.timestamp and (tokens_bought > 0 and max_eth_sold > 0)
    assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
    eth_bought: uint256(wei) = Exchange(exchange_addr).getEthToTokenOutputPrice(tokens_bought)
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_sold: uint256 = self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))
    # tokens sold is always > 0
    assert max_tokens_sold >= tokens_sold and max_eth_sold >= eth_bought
    assert self.token.transferFrom(buyer, self, tokens_sold)
    eth_sold: uint256(wei) = Exchange(exchange_addr).ethToTokenTransferOutput(tokens_bought, deadline, recipient, value=eth_bought)
    log.EthPurchase(buyer, tokens_sold, eth_bought)
    return tokens_sold

# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
#         Tokens (token_addr) to recipient.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
#         Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
    assert recipient != self
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
#         Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
    assert recipient != self
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)

# @notice Public price function for ETH to Token trades with an exact input.
# @param eth_sold Amount of ETH sold.
# @return Amount of Tokens that can be bought with input ETH.
@public
@constant
def getEthToTokenInputPrice(eth_sold: uint256(wei)) -> uint256:
    assert eth_sold > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    return self.getInputPrice(as_unitless_number(eth_sold), as_unitless_number(self.balance), token_reserve)

# @notice Public price function for ETH to Token trades with an exact output.
# @param tokens_bought Amount of Tokens bought.
# @return Amount of ETH needed to buy output Tokens.
@public
@constant
def getEthToTokenOutputPrice(tokens_bought: uint256) -> uint256(wei):
    assert tokens_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_sold: uint256 = self.getOutputPrice(tokens_bought, as_unitless_number(self.balance), token_reserve)
    return as_wei_value(eth_sold, 'wei')

# @notice Public price function for Token to ETH trades with an exact input.
# @param tokens_sold Amount of Tokens sold.
# @return Amount of ETH that can be bought with input Tokens.
@public
@constant
def getTokenToEthInputPrice(tokens_sold: uint256) -> uint256(wei):
    assert tokens_sold > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    return as_wei_value(eth_bought, 'wei')

# @notice Public price function for Token to ETH trades with an exact output.
# @param eth_bought Amount of output ETH.
# @return Amount of Tokens needed to buy output ETH.
@public
@constant
def getTokenToEthOutputPrice(eth_bought: uint256(wei)) -> uint256:
    assert eth_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    return self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))

# @return Address of Token that is sold on this exchange.
@public
@constant
def tokenAddress() -> address:
    return self.token

# @return Address of factory that created this exchange.
@public
@constant
def factoryAddress() -> address(Factory):
    return self.factory

# ERC20 compatibility for exchange liquidity modified from
# https://github.com/ethereum/vyper/blob/master/examples/tokens/ERC20.vy
@public
@constant
def balanceOf(_owner : address) -> uint256:
    return self.balances[_owner]

@public
def transfer(_to : address, _value : uint256) -> bool:
    self.balances[msg.sender] -= _value
    self.balances[_to] += _value
    log.Transfer(msg.sender, _to, _value)
    return True

@public
def transferFrom(_from : address, _to : address, _value : uint256) -> bool:
    self.balances[_from] -= _value
    self.balances[_to] += _value
    self.allowances[_from][msg.sender] -= _value
    log.Transfer(_from, _to, _value)
    return True

@public
def approve(_spender : address, _value : uint256) -> bool:
    self.allowances[msg.sender][_spender] = _value
    log.Approval(msg.sender, _spender, _value)
    return True

@public
@constant
def allowance(_owner : address, _spender : address) -> uint256:
    return self.allowances[_owner][_spender]

# @title Uniswap Exchange Interface V1
# @notice Source code found at https://github.com/uniswap
# @notice Use at your own risk

contract Factory():
    def getExchange(token_addr: address) -> address: constant

contract Exchange():
    def getEthToTokenOutputPrice(tokens_bought: uint256) -> uint256(wei): constant
    def ethToTokenTransferInput(min_tokens: uint256, deadline: timestamp, recipient: address) -> uint256: modifying
    def ethToTokenTransferOutput(tokens_bought: uint256, deadline: timestamp, recipient: address) -> uint256(wei): modifying

TokenPurchase: event({buyer: indexed(address), eth_sold: indexed(uint256(wei)), tokens_bought: indexed(uint256)})
EthPurchase: event({buyer: indexed(address), tokens_sold: indexed(uint256), eth_bought: indexed(uint256(wei))})
AddLiquidity: event({provider: indexed(address), eth_amount: indexed(uint256(wei)), token_amount: indexed(uint256)})
RemoveLiquidity: event({provider: indexed(address), eth_amount: indexed(uint256(wei)), token_amount: indexed(uint256)})
Transfer: event({_from: indexed(address), _to: indexed(address), _value: uint256})
Approval: event({_owner: indexed(address), _spender: indexed(address), _value: uint256})

name: public(bytes32)                             # Uniswap V1
symbol: public(bytes32)                           # UNI-V1
decimals: public(uint256)                         # 18
totalSupply: public(uint256)                      # total number of UNI in existence
balances: uint256[address]                        # UNI balance of an address
allowances: (uint256[address])[address]           # UNI allowance of one address on another
token: address(ERC20)                             # address of the ERC20 token traded on this contract
factory: Factory                                  # interface for the factory that created this contract

# @dev This function acts as a contract constructor which is not currently supported in contracts deployed
#      using create_with_code_of(). It is called once by the factory during contract creation.
@public
def setup(token_addr: address):
    assert (self.factory == ZERO_ADDRESS and self.token == ZERO_ADDRESS) and token_addr != ZERO_ADDRESS
    self.factory = msg.sender
    self.token = token_addr
    self.name = 0x556e697377617020563100000000000000000000000000000000000000000000
    self.symbol = 0x554e492d56310000000000000000000000000000000000000000000000000000
    self.decimals = 18

# @notice Deposit ETH and Tokens (self.token) at current ratio to mint UNI tokens.
# @dev min_liquidity does nothing when total UNI supply is 0.
# @param min_liquidity Minimum number of UNI sender will mint if total UNI supply is greater than 0.
# @param max_tokens Maximum number of tokens deposited. Deposits max amount if total UNI supply is 0.
# @param deadline Time after which this transaction can no longer be executed.
# @return The amount of UNI minted.
@public
@payable
def addLiquidity(min_liquidity: uint256, max_tokens: uint256, deadline: timestamp) -> uint256:
    assert deadline > block.timestamp and (max_tokens > 0 and msg.value > 0)
    total_liquidity: uint256 = self.totalSupply
    if total_liquidity > 0:
        assert min_liquidity > 0
        eth_reserve: uint256(wei) = self.balance - msg.value
        token_reserve: uint256 = self.token.balanceOf(self)
        token_amount: uint256 = msg.value * token_reserve / eth_reserve + 1
        liquidity_minted: uint256 = msg.value * total_liquidity / eth_reserve
        assert max_tokens >= token_amount and liquidity_minted >= min_liquidity
        self.balances[msg.sender] += liquidity_minted
        self.totalSupply = total_liquidity + liquidity_minted
        assert self.token.transferFrom(msg.sender, self, token_amount)
        log.AddLiquidity(msg.sender, msg.value, token_amount)
        log.Transfer(ZERO_ADDRESS, msg.sender, liquidity_minted)
        return liquidity_minted
    else:
        assert (self.factory != ZERO_ADDRESS and self.token != ZERO_ADDRESS) and msg.value >= 1000000000
        assert self.factory.getExchange(self.token) == self
        token_amount: uint256 = max_tokens
        initial_liquidity: uint256 = as_unitless_number(self.balance)
        self.totalSupply = initial_liquidity
        self.balances[msg.sender] = initial_liquidity
        assert self.token.transferFrom(msg.sender, self, token_amount)
        log.AddLiquidity(msg.sender, msg.value, token_amount)
        log.Transfer(ZERO_ADDRESS, msg.sender, initial_liquidity)
        return initial_liquidity

# @dev Burn UNI tokens to withdraw ETH and Tokens at current ratio.
# @param amount Amount of UNI burned.
# @param min_eth Minimum ETH withdrawn.
# @param min_tokens Minimum Tokens withdrawn.
# @param deadline Time after which this transaction can no longer be executed.
# @return The amount of ETH and Tokens withdrawn.
@public
def removeLiquidity(amount: uint256, min_eth: uint256(wei), min_tokens: uint256, deadline: timestamp) -> (uint256(wei), uint256):
    assert (amount > 0 and deadline > block.timestamp) and (min_eth > 0 and min_tokens > 0)
    total_liquidity: uint256 = self.totalSupply
    assert total_liquidity > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_amount: uint256(wei) = amount * self.balance / total_liquidity
    token_amount: uint256 = amount * token_reserve / total_liquidity
    assert eth_amount >= min_eth and token_amount >= min_tokens
    self.balances[msg.sender] -= amount
    self.totalSupply = total_liquidity - amount
    send(msg.sender, eth_amount)
    assert self.token.transfer(msg.sender, token_amount)
    log.RemoveLiquidity(msg.sender, eth_amount, token_amount)
    log.Transfer(msg.sender, ZERO_ADDRESS, amount)
    return eth_amount, token_amount

# @dev Pricing function for converting between ETH and Tokens.
# @param input_amount Amount of ETH or Tokens being sold.
# @param input_reserve Amount of ETH or Tokens (input type) in exchange reserves.
# @param output_reserve Amount of ETH or Tokens (output type) in exchange reserves.
# @return Amount of ETH or Tokens bought.
@private
@constant
def getInputPrice(input_amount: uint256, input_reserve: uint256, output_reserve: uint256) -> uint256:
    assert input_reserve > 0 and output_reserve > 0
    input_amount_with_fee: uint256 = input_amount * 997
    numerator: uint256 = input_amount_with_fee * output_reserve
    denominator: uint256 = (input_reserve * 1000) + input_amount_with_fee
    return numerator / denominator

# @dev Pricing function for converting between ETH and Tokens.
# @param output_amount Amount of ETH or Tokens being bought.
# @param input_reserve Amount of ETH or Tokens (input type) in exchange reserves.
# @param output_reserve Amount of ETH or Tokens (output type) in exchange reserves.
# @return Amount of ETH or Tokens sold.
@private
@constant
def getOutputPrice(output_amount: uint256, input_reserve: uint256, output_reserve: uint256) -> uint256:
    assert input_reserve > 0 and output_reserve > 0
    numerator: uint256 = input_reserve * output_amount * 1000
    denominator: uint256 = (output_reserve - output_amount) * 997
    return numerator / denominator + 1

@private
def ethToTokenInput(eth_sold: uint256(wei), min_tokens: uint256, deadline: timestamp, buyer: address, recipient: address) -> uint256:
    assert deadline >= block.timestamp and (eth_sold > 0 and min_tokens > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_bought: uint256 = self.getInputPrice(as_unitless_number(eth_sold), as_unitless_number(self.balance - eth_sold), token_reserve)
    assert tokens_bought >= min_tokens
    assert self.token.transfer(recipient, tokens_bought)
    log.TokenPurchase(buyer, eth_sold, tokens_bought)
    return tokens_bought

# @notice Convert ETH to Tokens.
# @dev User specifies exact input (msg.value).
# @dev User cannot specify minimum output or deadline.
@public
@payable
def __default__():
    self.ethToTokenInput(msg.value, 1, block.timestamp, msg.sender, msg.sender)

# @notice Convert ETH to Tokens.
# @dev User specifies exact input (msg.value) and minimum output.
# @param min_tokens Minimum Tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of Tokens bought.
@public
@payable
def ethToTokenSwapInput(min_tokens: uint256, deadline: timestamp) -> uint256:
    return self.ethToTokenInput(msg.value, min_tokens, deadline, msg.sender, msg.sender)

# @notice Convert ETH to Tokens and transfers Tokens to recipient.
# @dev User specifies exact input (msg.value) and minimum output
# @param min_tokens Minimum Tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output Tokens.
# @return Amount of Tokens bought.
@public
@payable
def ethToTokenTransferInput(min_tokens: uint256, deadline: timestamp, recipient: address) -> uint256:
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.ethToTokenInput(msg.value, min_tokens, deadline, msg.sender, recipient)

@private
def ethToTokenOutput(tokens_bought: uint256, max_eth: uint256(wei), deadline: timestamp, buyer: address, recipient: address) -> uint256(wei):
    assert deadline >= block.timestamp and (tokens_bought > 0 and max_eth > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_sold: uint256 = self.getOutputPrice(tokens_bought, as_unitless_number(self.balance - max_eth), token_reserve)
    # Throws if eth_sold > max_eth
    eth_refund: uint256(wei) = max_eth - as_wei_value(eth_sold, 'wei')
    if eth_refund > 0:
        send(buyer, eth_refund)
    assert self.token.transfer(recipient, tokens_bought)
    log.TokenPurchase(buyer, as_wei_value(eth_sold, 'wei'), tokens_bought)
    return as_wei_value(eth_sold, 'wei')

# @notice Convert ETH to Tokens.
# @dev User specifies maximum input (msg.value) and exact output.
# @param tokens_bought Amount of tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of ETH sold.
@public
@payable
def ethToTokenSwapOutput(tokens_bought: uint256, deadline: timestamp) -> uint256(wei):
    return self.ethToTokenOutput(tokens_bought, msg.value, deadline, msg.sender, msg.sender)

# @notice Convert ETH to Tokens and transfers Tokens to recipient.
# @dev User specifies maximum input (msg.value) and exact output.
# @param tokens_bought Amount of tokens bought.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output Tokens.
# @return Amount of ETH sold.
@public
@payable
def ethToTokenTransferOutput(tokens_bought: uint256, deadline: timestamp, recipient: address) -> uint256(wei):
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.ethToTokenOutput(tokens_bought, msg.value, deadline, msg.sender, recipient)

@private
def tokenToEthInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp, buyer: address, recipient: address) -> uint256(wei):
    assert deadline >= block.timestamp and (tokens_sold > 0 and min_eth > 0)
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    wei_bought: uint256(wei) = as_wei_value(eth_bought, 'wei')
    assert wei_bought >= min_eth
    send(recipient, wei_bought)
    assert self.token.transferFrom(buyer, self, tokens_sold)
    log.EthPurchase(buyer, tokens_sold, wei_bought)
    return wei_bought


# @notice Convert Tokens to ETH.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_eth Minimum ETH purchased.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of ETH bought.
@public
def tokenToEthSwapInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp) -> uint256(wei):
    return self.tokenToEthInput(tokens_sold, min_eth, deadline, msg.sender, msg.sender)

# @notice Convert Tokens to ETH and transfers ETH to recipient.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_eth Minimum ETH purchased.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @return Amount of ETH bought.
@public
def tokenToEthTransferInput(tokens_sold: uint256, min_eth: uint256(wei), deadline: timestamp, recipient: address) -> uint256(wei):
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.tokenToEthInput(tokens_sold, min_eth, deadline, msg.sender, recipient)

@private
def tokenToEthOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp, buyer: address, recipient: address) -> uint256:
    assert deadline >= block.timestamp and eth_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_sold: uint256 = self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))
    # tokens sold is always > 0
    assert max_tokens >= tokens_sold
    send(recipient, eth_bought)
    assert self.token.transferFrom(buyer, self, tokens_sold)
    log.EthPurchase(buyer, tokens_sold, eth_bought)
    return tokens_sold

# @notice Convert Tokens to ETH.
# @dev User specifies maximum input and exact output.
# @param eth_bought Amount of ETH purchased.
# @param max_tokens Maximum Tokens sold.
# @param deadline Time after which this transaction can no longer be executed.
# @return Amount of Tokens sold.
@public
def tokenToEthSwapOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp) -> uint256:
    return self.tokenToEthOutput(eth_bought, max_tokens, deadline, msg.sender, msg.sender)

# @notice Convert Tokens to ETH and transfers ETH to recipient.
# @dev User specifies maximum input and exact output.
# @param eth_bought Amount of ETH purchased.
# @param max_tokens Maximum Tokens sold.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @return Amount of Tokens sold.
@public
def tokenToEthTransferOutput(eth_bought: uint256(wei), max_tokens: uint256, deadline: timestamp, recipient: address) -> uint256:
    assert recipient != self and recipient != ZERO_ADDRESS
    return self.tokenToEthOutput(eth_bought, max_tokens, deadline, msg.sender, recipient)

@private
def tokenToTokenInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
    assert (deadline >= block.timestamp and tokens_sold > 0) and (min_tokens_bought > 0 and min_eth_bought > 0)
    assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    wei_bought: uint256(wei) = as_wei_value(eth_bought, 'wei')
    assert wei_bought >= min_eth_bought
    assert self.token.transferFrom(buyer, self, tokens_sold)
    tokens_bought: uint256 = Exchange(exchange_addr).ethToTokenTransferInput(min_tokens_bought, deadline, recipient, value=wei_bought)
    log.EthPurchase(buyer, tokens_sold, wei_bought)
    return tokens_bought

# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
#         Tokens (token_addr) to recipient.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)

@private
def tokenToTokenOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
    assert deadline >= block.timestamp and (tokens_bought > 0 and max_eth_sold > 0)
    assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
    eth_bought: uint256(wei) = Exchange(exchange_addr).getEthToTokenOutputPrice(tokens_bought)
    token_reserve: uint256 = self.token.balanceOf(self)
    tokens_sold: uint256 = self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))
    # tokens sold is always > 0
    assert max_tokens_sold >= tokens_sold and max_eth_sold >= eth_bought
    assert self.token.transferFrom(buyer, self, tokens_sold)
    eth_sold: uint256(wei) = Exchange(exchange_addr).ethToTokenTransferOutput(tokens_bought, deadline, recipient, value=eth_bought)
    log.EthPurchase(buyer, tokens_sold, eth_bought)
    return tokens_sold

# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
#         Tokens (token_addr) to recipient.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
    exchange_addr: address = self.factory.getExchange(token_addr)
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
#         Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
    assert recipient != self
    return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)

# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
#         Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
    assert recipient != self
    return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)

# @notice Public price function for ETH to Token trades with an exact input.
# @param eth_sold Amount of ETH sold.
# @return Amount of Tokens that can be bought with input ETH.
@public
@constant
def getEthToTokenInputPrice(eth_sold: uint256(wei)) -> uint256:
    assert eth_sold > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    return self.getInputPrice(as_unitless_number(eth_sold), as_unitless_number(self.balance), token_reserve)

# @notice Public price function for ETH to Token trades with an exact output.
# @param tokens_bought Amount of Tokens bought.
# @return Amount of ETH needed to buy output Tokens.
@public
@constant
def getEthToTokenOutputPrice(tokens_bought: uint256) -> uint256(wei):
    assert tokens_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_sold: uint256 = self.getOutputPrice(tokens_bought, as_unitless_number(self.balance), token_reserve)
    return as_wei_value(eth_sold, 'wei')

# @notice Public price function for Token to ETH trades with an exact input.
# @param tokens_sold Amount of Tokens sold.
# @return Amount of ETH that can be bought with input Tokens.
@public
@constant
def getTokenToEthInputPrice(tokens_sold: uint256) -> uint256(wei):
    assert tokens_sold > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
    return as_wei_value(eth_bought, 'wei')

# @notice Public price function for Token to ETH trades with an exact output.
# @param eth_bought Amount of output ETH.
# @return Amount of Tokens needed to buy output ETH.
@public
@constant
def getTokenToEthOutputPrice(eth_bought: uint256(wei)) -> uint256:
    assert eth_bought > 0
    token_reserve: uint256 = self.token.balanceOf(self)
    return self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))

# @return Address of Token that is sold on this exchange.
@public
@constant
def tokenAddress() -> address:
    return self.token

# @return Address of factory that created this exchange.
@public
@constant
def factoryAddress() -> address(Factory):
    return self.factory

# ERC20 compatibility for exchange liquidity modified from
# https://github.com/ethereum/vyper/blob/master/examples/tokens/ERC20.vy
@public
@constant
def balanceOf(_owner : address) -> uint256:
    return self.balances[_owner]

@public
def transfer(_to : address, _value : uint256) -> bool:
    self.balances[msg.sender] -= _value
    self.balances[_to] += _value
    log.Transfer(msg.sender, _to, _value)
    return True

@public
def transferFrom(_from : address, _to : address, _value : uint256) -> bool:
    self.balances[_from] -= _value
    self.balances[_to] += _value
    self.allowances[_from][msg.sender] -= _value
    log.Transfer(_from, _to, _value)
    return True

@public
def approve(_spender : address, _value : uint256) -> bool:
    self.allowances[msg.sender][_spender] = _value
    log.Approval(msg.sender, _spender, _value)
    return True

@public
@constant
def allowance(_owner : address, _spender : address) -> uint256:
    return self.allowances[_owner][_spender]

pragma solidity ^0.4.24;


contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function safeMul(uint a, uint b) public pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function safeDiv(uint a, uint b) public pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}


// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}


// ----------------------------------------------------------------------------
// Contract function to receive approval and execute function in one call
//
// Borrowed from MiniMeToken
// ----------------------------------------------------------------------------
contract ApproveAndCallFallBack {
    function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
}


contract Owned {
    address public owner;
    // address public newOwner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    // function transferOwnership(address _newOwner) public onlyOwner {
    //     newOwner = _newOwner;
    // }

    // function acceptOwnership() public {
    //     require(msg.sender == newOwner);
    //     emit OwnershipTransferred(owner, newOwner);
    //     owner = newOwner;
    //     newOwner = address(0);
    // }
}


contract VXV is ERC20Interface, Owned, SafeMath {
    string public symbol;
    string public name;
    uint8 public decimals;
    uint public totalSupply;
    uint public rate;

    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;

    constructor() public {
        symbol = "VXV";
        name = "VectorspaceAI";
        decimals = 18;
        totalSupply = 50000000 * 10 ** uint256(decimals);
        rate = 203;
        balances[owner] = totalSupply;
        emit Transfer(address(0), owner, totalSupply);
    }

    function changeRate(uint newRate) public onlyOwner {
        require(newRate > 0);
        rate = newRate;
    }

    function totalSupply() public view returns (uint) {
        return totalSupply - balances[address(0)];
    }

    function balanceOf(address tokenOwner) public view returns (uint balance) {
        return balances[tokenOwner];
    }

    modifier validTo(address to) {
        require(to != address(0));
        require(to != address(this));
        _;
    }

    function transferInternal(address from, address to, uint tokens) internal {
        balances[from] = safeSub(balances[from], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
    }

    function transfer(address to, uint tokens) public validTo(to) returns (bool success) {
        transferInternal(msg.sender, to, tokens);
        return true;
    }

    // ------------------------------------------------------------------------
    // Transfer `tokens` from the `from` account to the `to` account
    //
    // The calling account must already have sufficient tokens approve(...)-d
    // for spending from the `from` account and
    // - From account must have sufficient balance to transfer
    // - Spender must have sufficient allowance to transfer
    // - 0 value transfers are allowed
    // ------------------------------------------------------------------------
    function transferFrom(address from, address to, uint tokens) public validTo(to) returns (bool success) {
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        transferInternal(from, to, tokens);
        return true;
    }

    // ------------------------------------------------------------------------
    // Token owner can approve for `spender` to transferFrom(...) `tokens`
    // from the token owner's account
    //
    // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
    // recommends that there are no checks for the approval double-spend attack
    // as this should be implemented in user interfaces
    // ------------------------------------------------------------------------
    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function allowance(address tokenOwner, address spender) public view returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }

    // ------------------------------------------------------------------------
    // Token owner can approve for `spender` to transferFrom(...) `tokens`
    // from the token owner's account. The `spender` contract function
    // `receiveApproval(...)` is then executed
    // ------------------------------------------------------------------------
    function approveAndCall(address spender, uint tokens, bytes data) public returns (bool success) {
        if (approve(spender, tokens)) {
            ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
            return true;
        }
    }

    function () public payable {
        uint tokens;
        tokens = safeMul(msg.value, rate);

        balances[owner] = safeSub(balances[owner], tokens);
        balances[msg.sender] = safeAdd(balances[msg.sender], tokens);

        emit Transfer(address(0), msg.sender, tokens);
        owner.transfer(msg.value);
    }

    // ------------------------------------------------------------------------
    // Owner can transfer out any accidentally sent ERC20 tokens
    // ------------------------------------------------------------------------
    // function transferAnyERC20Token(address tokenAddress, uint tokens) public onlyOwner returns (bool success) {
    //     return ERC20Interface(tokenAddress).transfer(owner, tokens);
    // }
}

// File: contracts/interfaces/IUniswapV2Pair.sol

pragma solidity >=0.5.0;

interface IUniswapV2Pair {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
    function price0CumulativeLast() external view returns (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}

// File: contracts/interfaces/IUniswapV2ERC20.sol

pragma solidity >=0.5.0;

interface IUniswapV2ERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;
}

// File: contracts/libraries/SafeMath.sol

pragma solidity =0.5.16;

// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)

library SafeMath {
    function add(uint x, uint y) internal pure returns (uint z) {
        require((z = x + y) >= x, 'ds-math-add-overflow');
    }

    function sub(uint x, uint y) internal pure returns (uint z) {
        require((z = x - y) <= x, 'ds-math-sub-underflow');
    }

    function mul(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x, 'ds-math-mul-overflow');
    }
}

// File: contracts/UniswapV2ERC20.sol

pragma solidity =0.5.16;



contract UniswapV2ERC20 is IUniswapV2ERC20 {
    using SafeMath for uint;

    string public constant name = 'Uniswap V2';
    string public constant symbol = 'UNI-V2';
    uint8 public constant decimals = 18;
    uint  public totalSupply;
    mapping(address => uint) public balanceOf;
    mapping(address => mapping(address => uint)) public allowance;

    bytes32 public DOMAIN_SEPARATOR;
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
    mapping(address => uint) public nonces;

    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    constructor() public {
        uint chainId;
        assembly {
            chainId := chainid
        }
        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
                keccak256(bytes(name)),
                keccak256(bytes('1')),
                chainId,
                address(this)
            )
        );
    }

    function _mint(address to, uint value) internal {
        totalSupply = totalSupply.add(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(address(0), to, value);
    }

    function _burn(address from, uint value) internal {
        balanceOf[from] = balanceOf[from].sub(value);
        totalSupply = totalSupply.sub(value);
        emit Transfer(from, address(0), value);
    }

    function _approve(address owner, address spender, uint value) private {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    function _transfer(address from, address to, uint value) private {
        balanceOf[from] = balanceOf[from].sub(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(from, to, value);
    }

    function approve(address spender, uint value) external returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function transfer(address to, uint value) external returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    function transferFrom(address from, address to, uint value) external returns (bool) {
        if (allowance[from][msg.sender] != uint(-1)) {
            allowance[from][msg.sender] = allowance[from][msg.sender].sub(value);
        }
        _transfer(from, to, value);
        return true;
    }

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        require(deadline >= block.timestamp, 'UniswapV2: EXPIRED');
        bytes32 digest = keccak256(
            abi.encodePacked(
                '\x19\x01',
                DOMAIN_SEPARATOR,
                keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))
            )
        );
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress != address(0) && recoveredAddress == owner, 'UniswapV2: INVALID_SIGNATURE');
        _approve(owner, spender, value);
    }
}

// File: contracts/libraries/Math.sol

pragma solidity =0.5.16;

// a library for performing various math operations

library Math {
    function min(uint x, uint y) internal pure returns (uint z) {
        z = x < y ? x : y;
    }

    // babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
    function sqrt(uint y) internal pure returns (uint z) {
        if (y > 3) {
            z = y;
            uint x = y / 2 + 1;
            while (x < z) {
                z = x;
                x = (y / x + x) / 2;
            }
        } else if (y != 0) {
            z = 1;
        }
    }
}

// File: contracts/libraries/UQ112x112.sol

pragma solidity =0.5.16;

// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))

// range: [0, 2**112 - 1]
// resolution: 1 / 2**112

library UQ112x112 {
    uint224 constant Q112 = 2**112;

    // encode a uint112 as a UQ112x112
    function encode(uint112 y) internal pure returns (uint224 z) {
        z = uint224(y) * Q112; // never overflows
    }

    // divide a UQ112x112 by a uint112, returning a UQ112x112
    function uqdiv(uint224 x, uint112 y) internal pure returns (uint224 z) {
        z = x / uint224(y);
    }
}

// File: contracts/interfaces/IERC20.sol

pragma solidity >=0.5.0;

interface IERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);
}

// File: contracts/interfaces/IUniswapV2Factory.sol

pragma solidity >=0.5.0;

interface IUniswapV2Factory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint);

    function feeTo() external view returns (address);
    function feeToSetter() external view returns (address);

    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function allPairs(uint) external view returns (address pair);
    function allPairsLength() external view returns (uint);

    function createPair(address tokenA, address tokenB) external returns (address pair);

    function setFeeTo(address) external;
    function setFeeToSetter(address) external;
}

// File: contracts/interfaces/IUniswapV2Callee.sol

pragma solidity >=0.5.0;

interface IUniswapV2Callee {
    function uniswapV2Call(address sender, uint amount0, uint amount1, bytes calldata data) external;
}

// File: contracts/UniswapV2Pair.sol

pragma solidity =0.5.16;








contract UniswapV2Pair is IUniswapV2Pair, UniswapV2ERC20 {
    using SafeMath  for uint;
    using UQ112x112 for uint224;

    uint public constant MINIMUM_LIQUIDITY = 10**3;
    bytes4 private constant SELECTOR = bytes4(keccak256(bytes('transfer(address,uint256)')));

    address public factory;
    address public token0;
    address public token1;

    uint112 private reserve0;           // uses single storage slot, accessible via getReserves
    uint112 private reserve1;           // uses single storage slot, accessible via getReserves
    uint32  private blockTimestampLast; // uses single storage slot, accessible via getReserves

    uint public price0CumulativeLast;
    uint public price1CumulativeLast;
    uint public kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event

    uint private unlocked = 1;
    modifier lock() {
        require(unlocked == 1, 'UniswapV2: LOCKED');
        unlocked = 0;
        _;
        unlocked = 1;
    }

    function getReserves() public view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast) {
        _reserve0 = reserve0;
        _reserve1 = reserve1;
        _blockTimestampLast = blockTimestampLast;
    }

    function _safeTransfer(address token, address to, uint value) private {
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'UniswapV2: TRANSFER_FAILED');
    }

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    constructor() public {
        factory = msg.sender;
    }

    // called once by the factory at time of deployment
    function initialize(address _token0, address _token1) external {
        require(msg.sender == factory, 'UniswapV2: FORBIDDEN'); // sufficient check
        token0 = _token0;
        token1 = _token1;
    }

    // update reserves and, on the first call per block, price accumulators
    function _update(uint balance0, uint balance1, uint112 _reserve0, uint112 _reserve1) private {
        require(balance0 <= uint112(-1) && balance1 <= uint112(-1), 'UniswapV2: OVERFLOW');
        uint32 blockTimestamp = uint32(block.timestamp % 2**32);
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
        if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
            // * never overflows, and + overflow is desired
            price0CumulativeLast += uint(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) * timeElapsed;
            price1CumulativeLast += uint(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) * timeElapsed;
        }
        reserve0 = uint112(balance0);
        reserve1 = uint112(balance1);
        blockTimestampLast = blockTimestamp;
        emit Sync(reserve0, reserve1);
    }

    // if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
    function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
        address feeTo = IUniswapV2Factory(factory).feeTo();
        feeOn = feeTo != address(0);
        uint _kLast = kLast; // gas savings
        if (feeOn) {
            if (_kLast != 0) {
                uint rootK = Math.sqrt(uint(_reserve0).mul(_reserve1));
                uint rootKLast = Math.sqrt(_kLast);
                if (rootK > rootKLast) {
                    uint numerator = totalSupply.mul(rootK.sub(rootKLast));
                    uint denominator = rootK.mul(5).add(rootKLast);
                    uint liquidity = numerator / denominator;
                    if (liquidity > 0) _mint(feeTo, liquidity);
                }
            }
        } else if (_kLast != 0) {
            kLast = 0;
        }
    }

    // this low-level function should be called from a contract which performs important safety checks
    function mint(address to) external lock returns (uint liquidity) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        uint balance0 = IERC20(token0).balanceOf(address(this));
        uint balance1 = IERC20(token1).balanceOf(address(this));
        uint amount0 = balance0.sub(_reserve0);
        uint amount1 = balance1.sub(_reserve1);

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
        if (_totalSupply == 0) {
            liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
           _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
        } else {
            liquidity = Math.min(amount0.mul(_totalSupply) / _reserve0, amount1.mul(_totalSupply) / _reserve1);
        }
        require(liquidity > 0, 'UniswapV2: INSUFFICIENT_LIQUIDITY_MINTED');
        _mint(to, liquidity);

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Mint(msg.sender, amount0, amount1);
    }

    // this low-level function should be called from a contract which performs important safety checks
    function burn(address to) external lock returns (uint amount0, uint amount1) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        address _token0 = token0;                                // gas savings
        address _token1 = token1;                                // gas savings
        uint balance0 = IERC20(_token0).balanceOf(address(this));
        uint balance1 = IERC20(_token1).balanceOf(address(this));
        uint liquidity = balanceOf[address(this)];

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
        amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
        amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
        require(amount0 > 0 && amount1 > 0, 'UniswapV2: INSUFFICIENT_LIQUIDITY_BURNED');
        _burn(address(this), liquidity);
        _safeTransfer(_token0, to, amount0);
        _safeTransfer(_token1, to, amount1);
        balance0 = IERC20(_token0).balanceOf(address(this));
        balance1 = IERC20(_token1).balanceOf(address(this));

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Burn(msg.sender, amount0, amount1, to);
    }

    // this low-level function should be called from a contract which performs important safety checks
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external lock {
        require(amount0Out > 0 || amount1Out > 0, 'UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT');
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        require(amount0Out < _reserve0 && amount1Out < _reserve1, 'UniswapV2: INSUFFICIENT_LIQUIDITY');

        uint balance0;
        uint balance1;
        { // scope for _token{0,1}, avoids stack too deep errors
        address _token0 = token0;
        address _token1 = token1;
        require(to != _token0 && to != _token1, 'UniswapV2: INVALID_TO');
        if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
        if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
        if (data.length > 0) IUniswapV2Callee(to).uniswapV2Call(msg.sender, amount0Out, amount1Out, data);
        balance0 = IERC20(_token0).balanceOf(address(this));
        balance1 = IERC20(_token1).balanceOf(address(this));
        }
        uint amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
        uint amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
        require(amount0In > 0 || amount1In > 0, 'UniswapV2: INSUFFICIENT_INPUT_AMOUNT');
        { // scope for reserve{0,1}Adjusted, avoids stack too deep errors
        uint balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
        uint balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
        require(balance0Adjusted.mul(balance1Adjusted) >= uint(_reserve0).mul(_reserve1).mul(1000**2), 'UniswapV2: K');
        }

        _update(balance0, balance1, _reserve0, _reserve1);
        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
    }

    // force balances to match reserves
    function skim(address to) external lock {
        address _token0 = token0; // gas savings
        address _token1 = token1; // gas savings
        _safeTransfer(_token0, to, IERC20(_token0).balanceOf(address(this)).sub(reserve0));
        _safeTransfer(_token1, to, IERC20(_token1).balanceOf(address(this)).sub(reserve1));
    }

    // force reserves to match balances
    function sync() external lock {
        _update(IERC20(token0).balanceOf(address(this)), IERC20(token1).balanceOf(address(this)), reserve0, reserve1);
    }
}