erc20 token swap contract example needed

Question

is there a contract example which allows to exchange one erc20 for another?

i have 2 tokens

i want to exchange from tokenA to tokenB 1:1 and keep 1% as a fee

the sender should just make a normal erc20-send to the contracts address and receive back the other token.

the contract will have a pool of tokens, A and B

if someone pays 1 tokenA to the contract, the contract should send 0.99 tokenB back to the sending address and keep 0.01 tokenA in the pool.

i saw uniswap is doing something like this but with variable rates and more complex.

please point me to an example of such a contract or even point me to some good solidity programmer who could make this for me.

thanks for your time

Answer 1

It is fairly easy if you assume some simplifications:

• both tokens have the same decimals
• no error checking
• Swap contract have enough funds of tokenB

function swapA(uint256 amountA) {

    // Tranfer tokens from sender to this contract
    tokenA.transferFrom(msg.sender, address(this), amountA);

    // Calculate fees
    uint256 fee = amountA / 100;
    uint256 amountB = amountA - fee;

    // Transfer amount minus fees to sender
    tokenB.transfer(msg.sender, amountB);
}