# 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

$ git pull
$ brownie run scripts/uniswap.py -I
...
>>> factory
<Factory Contract '0xb5F338E1397D646AFFf707DD47ea94eAacdBa45D'>

>>> token = ERCToken.deploy(1000, "A")
<ERCToken Contract '0xcFf3e49D8947D75Fa04115cFD3f9343c95956eb7'>

>>> factory.createExchange(token.address)
>>> factory.getExchange(token.address)
'0x0bEf07F1fF27538ee5C7D64e7582A42867069f4e'

# or simply
>>> exchange = new_exchange(factory, token)
<Exchange Contract '0x0bEf07F1fF27538ee5C7D64e7582A42867069f4e'>

# Note.
#   min_liquidity will be ignored for the very first setup
#   max_tokens indicates #tokens to be put
#   msg.value should be provided as part of the invocation
def addLiquidity(min_liquidity: uint256, max_tokens: uint256, 
                 deadline: timestamp) -> uint256:

# allow the exchange to spend 100 tokens
>>> token.approve(exchange.address, 100)

# add liquidity of (100 tokens, 1000000000 wei)
>>> exchange.addLiquidity(0, 100, time.time() + 1000, {"value": 1000000000})

>>> exchange.balance()
1000000000
>>> token.balanceOf(exchange.address)
100

  # @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')

# selling one token (input) and ether as output
>>> exchange.getTokenToEthInputPrice(1)
9871580

>>> 10000000 - 9871580
128420

# getting cheaper when putting more tokens
>>> exchange.getTokenToEthInputPrice(10)/10
9066108.9

def getEthToTokenOutputPrice(tokens_bought) 
    -> uint256(wei)
def ethToTokenTransferInput(min_tokens, deadline, recipient)
    -> uint256
def ethToTokenTransferOutput(tokens_bought, deadline, recipient)
    -> uint256(wei)

>>> token.approve(exchange.address, 1)
>>> exchange.tokenToEthSwapInput(1, ethPerToken, int(time.time())+1000)

├── General ERC20 Token (0xe0aA552A10d7EC8760Fc6c246D391E698a82dDf9)
│   ├── Approval
│   │   ├── owner: 0x66aB6D9362d4F35596279692F0251Db635165871
│   │   ├── spender: 0x87e23022F31814f835C052A9e280608bdE7aE3f9
│   │   └── value: 0
│   └── Transfer
│       ├── from: 0x66aB6D9362d4F35596279692F0251Db635165871
│       ├── to: 0x87e23022F31814f835C052A9e280608bdE7aE3f9
│       └── value: 1
│
└── 0x87e23022F31814f835C052A9e280608bdE7aE3f9
    └── EthPurchase
        ├── buyer: 0x66aB6D9362d4F35596279692F0251Db635165871
        ├── tokens_sold: 1
        └── eth_bought: 9871580