status-im/status-go

package paraswap

import (
    "context"
    "encoding/json"
    "errors"
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
)

const transactionsURL = "https://apiv5.paraswap.io/transactions/%d"

type Transaction struct {
    From     string `json:"from"`
    To       string `json:"to"`
    Value    string `json:"value"`
    Data     string `json:"data"`
    GasPrice string `json:"gasPrice"`
    Gas      string `json:"gas"`
    ChainID  uint64 `json:"chainId"`
    Error    string `json:"error"`
}

func (c *ClientV5) BuildTransaction(ctx context.Context, srcTokenAddress common.Address, srcTokenDecimals uint, srcAmountWei *big.Int,
    destTokenAddress common.Address, destTokenDecimals uint, destAmountWei *big.Int, slippageBasisPoints uint,
    addressFrom common.Address, addressTo common.Address, priceRoute json.RawMessage, side SwapSide) (Transaction, error) {

    params := map[string]interface{}{}
    params["srcToken"] = srcTokenAddress.Hex()
    params["srcDecimals"] = srcTokenDecimals
    params["destToken"] = destTokenAddress.Hex()
    params["destDecimals"] = destTokenDecimals
    params["userAddress"] = addressFrom.Hex()
    // params["receiver"] = addressTo.Hex() // at this point paraswap doesn't allow swap and transfer transaction
    params["priceRoute"] = priceRoute

    if slippageBasisPoints > 0 {
        params["slippage"] = slippageBasisPoints
        if side == SellSide {
            params["srcAmount"] = srcAmountWei.String()
        } else {
            params["destAmount"] = destAmountWei.String()
        }
    } else {
        params["srcAmount"] = srcAmountWei.String()
        params["destAmount"] = destAmountWei.String()
    }

    url := fmt.Sprintf(transactionsURL, c.chainID)
    response, err := c.httpClient.DoPostRequest(ctx, url, params)
    if err != nil {
        return Transaction{}, err
    }

    tx, err := handleBuildTransactionResponse(response)
    if err != nil {
        return Transaction{}, err
    }

    return tx, nil
}

func handleBuildTransactionResponse(response []byte) (Transaction, error) {
    var transactionResponse Transaction
    err := json.Unmarshal(response, &transactionResponse)
    if err != nil {
        return Transaction{}, err
    }
    if transactionResponse.Error != "" {
        return Transaction{}, errors.New(transactionResponse.Error)
    }
    return transactionResponse, nil
}