OMG Network custom transaction example part 2

deliverableWithFee.js

/*
*    deliverableWithFee.js
*
*    Storefront application where user purchases ERC20, 721 and
*    pays fees in the network's native fee curency.
*    Modified version of community-points::transaction.js
*    See also
*    keny@eastcoastbands.com
 */

/*
  Copyright 2020 OmiseGO Pte Ltd

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

const BN = require('bn.js');
const {transaction} = require('@omisego/omg-js-util');

const NULL_METADATA = '0x0000000000000000000000000000000000000000000000000000000000000000';

module.exports = {
  create: function (
    from,
    to,
    spendUtxos,
    spendAmount,
    metadata,
    spendToken,
    feeUtxos,
    feeAmount,
    feeOwner,
    markupOwner,
    markupAmount
  ) {
    if (!spendUtxos || spendUtxos.length === 0) {
      throw new Error('spendUtxos is empty')
    }
    if (!feeUtxos || feeUtxos.length === 0) {
      throw new Error('feeUtxos is empty')
    }

    spendAmount = BN.isBN(spendAmount) ? spendAmount : new BN(spendAmount.toString());
    feeAmount = BN.isBN(feeAmount) ? feeAmount : new BN(feeAmount.toString());
    markupAmount = BN.isBN(markupAmount) ? markupAmount : new BN(markupAmount.toString());


    const spendTotal = this.totalAmount(spendUtxos);
    if (spendTotal.lt(spendAmount)) {
      throw new Error('Insufficient inputs to cover spend')
    }

    const markupTotal = this.totalAmount(feeUtxos);
    if (markupTotal.lt(markupAmount)) {
      throw new Error('Insufficient inputs to cover markup')
    }

    const feeFunds = this.totalAmount(feeUtxos);

    const encodedMetadata = metadata
      ? transaction.encodeMetadata(metadata)
      : NULL_METADATA;

    // Construct the tx body
    const txBody = {
      inputs: [...spendUtxos, ...feeUtxos],
      outputs: [
        {
          outputType: 1,
          outputGuard: to,
          currency: spendToken,
          amount: spendAmount
        },
        {
          outputType: 1,
          outputGuard: markupOwner,
          currency: feeUtxos[0].currency,
          amount: markupAmount
        }
      ],
      metadata: encodedMetadata
    };

    // change output erc20
    if (spendTotal.gt(spendAmount)) {
      const changeAmount = spendTotal.sub(spendAmount);
      txBody.outputs.push({
        outputType: 1,
        outputGuard: from,
        currency: spendToken,
        amount: changeAmount
      })
    }

    // fee change output
    const feeChange = feeFunds.sub(markupAmount).sub(feeAmount);
    if (feeChange > 0){
      txBody.outputs.push({
        outputType: 1,
        outputGuard: feeOwner,
        currency: feeUtxos[0].currency,
        amount: feeChange
      })
    }

    return txBody
  },

  totalAmount: (utxos) => {
    return utxos.reduce((prev, curr) => {
      return prev.add(new BN(curr.amount.toString()))
    }, new BN(0))
  },

  getTypedData: (txBody, verifyingContract) => {
    return transaction.getTypedData(txBody, verifyingContract)
  },
};