bitcoinjs-lib/ts_src/transaction_builder.ts

import { Network } from './networks';
import * as networks from './networks';
import { reverseBuffer } from './bufferutils';
import { Transaction, Output } from './transaction';
import { ECPairInterface } from './ecpair';
import * as ECPair from './ecpair';
import * as types from './types';
import * as baddress from './address';
import * as bcrypto from './crypto';
import * as bscript from './script';
import { Payment } from './payments';
import * as payments from './payments';
import * as classify from './classify';
import { OPS as ops } from './script';
const typeforce = require('typeforce');

const SCRIPT_TYPES = classify.types;

type TxbSignatures = Array<Buffer> | Array<Buffer | undefined>;
type TxbPubkeys = Array<Buffer | undefined>;
type TxbWitness = Array<Buffer>;
type TxbScriptType = string;
type TxbScript = Buffer;

interface TxbInput {
  value?: number;
  hasWitness?: boolean;
  signScript?: TxbScript;
  signType?: TxbScriptType;
  prevOutScript?: TxbScript;
  redeemScript?: TxbScript;
  redeemScriptType?: TxbScriptType;
  prevOutType?: TxbScriptType;
  pubkeys?: TxbPubkeys;
  signatures?: TxbSignatures;
  witness?: TxbWitness;
  witnessScript?: TxbScript;
  witnessScriptType?: TxbScriptType;
  script?: TxbScript;
  sequence?: number;
  scriptSig?: TxbScript;
  maxSignatures?: number;
}

interface TxbOutput {
  type: string;
  pubkeys?: TxbPubkeys;
  signatures?: TxbSignatures;
  maxSignatures?: number;
}

function txIsString(tx: Buffer | string | Transaction): tx is string {
  return typeof tx === 'string' || tx instanceof String;
}

function txIsTransaction(tx: Buffer | string | Transaction): tx is Transaction {
  return tx instanceof Transaction;
}

export class TransactionBuilder {
  network: Network;
  maximumFeeRate: number;
  private __prevTxSet: { [index: string]: boolean };
  private __inputs: Array<TxbInput>;
  private __tx: Transaction;

  constructor(network?: Network, maximumFeeRate?: number) {
    this.__prevTxSet = {};
    this.network = network || networks.bitcoin;

    // WARNING: This is __NOT__ to be relied on, its just another potential safety mechanism (safety in-depth)
    this.maximumFeeRate = maximumFeeRate || 2500;

    this.__inputs = [];
    this.__tx = new Transaction();
    this.__tx.version = 2;
  }

  static fromTransaction(
    transaction: Transaction,
    network?: Network,
  ): TransactionBuilder {
    const txb = new TransactionBuilder(network);

    // Copy transaction fields
    txb.setVersion(transaction.version);
    txb.setLockTime(transaction.locktime);

    // Copy outputs (done first to avoid signature invalidation)
    transaction.outs.forEach(txOut => {
      txb.addOutput(txOut.script, (<Output>txOut).value);
    });

    // Copy inputs
    transaction.ins.forEach(txIn => {
      txb.__addInputUnsafe(txIn.hash, txIn.index, {
        sequence: txIn.sequence,
        script: txIn.script,
        witness: txIn.witness,
      });
    });

    // fix some things not possible through the public API
    txb.__inputs.forEach((input, i) => {
      fixMultisigOrder(input, transaction, i);
    });

    return txb;
  }

  setLockTime(locktime: number): void {
    typeforce(types.UInt32, locktime);

    // if any signatures exist, throw
    if (
      this.__inputs.some(input => {
        if (!input.signatures) return false;

        return input.signatures.some(s => s !== undefined);
      })
    ) {
      throw new Error('No, this would invalidate signatures');
    }

    this.__tx.locktime = locktime;
  }

  setVersion(version: number): void {
    typeforce(types.UInt32, version);

    // XXX: this might eventually become more complex depending on what the versions represent
    this.__tx.version = version;
  }

  addInput(
    txHash: Buffer | string | Transaction,
    vout: number,
    sequence: number,
    prevOutScript: Buffer,
  ): number {
    if (!this.__canModifyInputs()) {
      throw new Error('No, this would invalidate signatures');
    }

    let value: number | undefined = undefined;

    // is it a hex string?
    if (txIsString(txHash)) {
      // transaction hashs's are displayed in reverse order, un-reverse it
      txHash = reverseBuffer(Buffer.from(txHash, 'hex'));

      // is it a Transaction object?
    } else if (txIsTransaction(txHash)) {
      const txOut = txHash.outs[vout];
      prevOutScript = txOut.script;
      value = (<Output>txOut).value;

      txHash = <Buffer>txHash.getHash(false);
    }

    return this.__addInputUnsafe(txHash, vout, {
      sequence: sequence,
      prevOutScript: prevOutScript,
      value: value,
    });
  }

  private __addInputUnsafe(
    txHash: Buffer,
    vout: number,
    options: TxbInput,
  ): number {
    if (Transaction.isCoinbaseHash(txHash)) {
      throw new Error('coinbase inputs not supported');
    }

    const prevTxOut = txHash.toString('hex') + ':' + vout;
    if (this.__prevTxSet[prevTxOut] !== undefined)
      throw new Error('Duplicate TxOut: ' + prevTxOut);

    let input = <TxbInput>{};

    // derive what we can from the scriptSig
    if (options.script !== undefined) {
      input = expandInput(options.script, options.witness || []);
    }

    // if an input value was given, retain it
    if (options.value !== undefined) {
      input.value = options.value;
    }

    // derive what we can from the previous transactions output script
    if (!input.prevOutScript && options.prevOutScript) {
      let prevOutType;

      if (!input.pubkeys && !input.signatures) {
        const expanded = expandOutput(options.prevOutScript);
        if (expanded.pubkeys) {
          input.pubkeys = expanded.pubkeys;
          input.signatures = expanded.signatures;
        }

        prevOutType = expanded.type;
      }

      input.prevOutScript = options.prevOutScript;
      input.prevOutType = prevOutType || classify.output(options.prevOutScript);
    }

    const vin = this.__tx.addInput(
      txHash,
      vout,
      options.sequence,
      options.scriptSig,
    );
    this.__inputs[vin] = input;
    this.__prevTxSet[prevTxOut] = true;
    return vin;
  }

  addOutput(scriptPubKey: string | Buffer, value: number): number {
    if (!this.__canModifyOutputs()) {
      throw new Error('No, this would invalidate signatures');
    }

    // Attempt to get a script if it's a base58 or bech32 address string
    if (typeof scriptPubKey === 'string') {
      scriptPubKey = baddress.toOutputScript(scriptPubKey, this.network);
    }

    return this.__tx.addOutput(scriptPubKey, value);
  }

  build(): Transaction {
    return this.__build(false);
  }

  buildIncomplete(): Transaction {
    return this.__build(true);
  }

  private __build(allowIncomplete?: boolean): Transaction {
    if (!allowIncomplete) {
      if (!this.__tx.ins.length) throw new Error('Transaction has no inputs');
      if (!this.__tx.outs.length) throw new Error('Transaction has no outputs');
    }

    const tx = this.__tx.clone();

    // create script signatures from inputs
    this.__inputs.forEach((input, i) => {
      if (!input.prevOutType && !allowIncomplete)
        throw new Error('Transaction is not complete');

      const result = build(input.prevOutType!, input, allowIncomplete);
      if (!result) {
        if (!allowIncomplete && input.prevOutType === SCRIPT_TYPES.NONSTANDARD)
          throw new Error('Unknown input type');
        if (!allowIncomplete) throw new Error('Not enough information');
        return;
      }

      tx.setInputScript(i, result.input!);
      tx.setWitness(i, result.witness!);
    });

    if (!allowIncomplete) {
      // do not rely on this, its merely a last resort
      if (this.__overMaximumFees(tx.virtualSize())) {
        throw new Error('Transaction has absurd fees');
      }
    }

    return tx;
  }

  sign(
    vin: number,
    keyPair: ECPairInterface,
    redeemScript: Buffer,
    hashType: number,
    witnessValue: number,
    witnessScript: Buffer,
  ) {
    // TODO: remove keyPair.network matching in 4.0.0
    if (keyPair.network && keyPair.network !== this.network)
      throw new TypeError('Inconsistent network');
    if (!this.__inputs[vin]) throw new Error('No input at index: ' + vin);

    hashType = hashType || Transaction.SIGHASH_ALL;
    if (this.__needsOutputs(hashType))
      throw new Error('Transaction needs outputs');

    const input = this.__inputs[vin];

    // if redeemScript was previously provided, enforce consistency
    if (
      input.redeemScript !== undefined &&
      redeemScript &&
      !input.redeemScript.equals(redeemScript)
    ) {
      throw new Error('Inconsistent redeemScript');
    }

    const ourPubKey = keyPair.publicKey || keyPair.getPublicKey!();
    if (!canSign(input)) {
      if (witnessValue !== undefined) {
        if (input.value !== undefined && input.value !== witnessValue)
          throw new Error("Input didn't match witnessValue");
        typeforce(types.Satoshi, witnessValue);
        input.value = witnessValue;
      }

      if (!canSign(input)) {
        const prepared = prepareInput(
          input,
          ourPubKey,
          redeemScript,
          witnessScript,
        );

        // updates inline
        Object.assign(input, prepared);
      }

      if (!canSign(input)) throw Error(input.prevOutType + ' not supported');
    }

    // ready to sign
    let signatureHash: Buffer;
    if (input.hasWitness) {
      signatureHash = this.__tx.hashForWitnessV0(
        vin,
        <Buffer>input.signScript,
        <number>input.value,
        hashType,
      );
    } else {
      signatureHash = this.__tx.hashForSignature(
        vin,
        <Buffer>input.signScript,
        hashType,
      );
    }

    // enforce in order signing of public keys
    const signed = input.pubkeys!.some((pubKey, i) => {
      if (!ourPubKey.equals(pubKey!)) return false;
      if (input.signatures![i]) throw new Error('Signature already exists');

      // TODO: add tests
      if (ourPubKey.length !== 33 && input.hasWitness) {
        throw new Error(
          'BIP143 rejects uncompressed public keys in P2WPKH or P2WSH',
        );
      }

      const signature = keyPair.sign(signatureHash);
      input.signatures![i] = bscript.signature.encode(signature, hashType);
      return true;
    });

    if (!signed) throw new Error('Key pair cannot sign for this input');
  }

  private __canModifyInputs(): boolean {
    return this.__inputs.every(input => {
      if (!input.signatures) return true;

      return input.signatures.every(signature => {
        if (!signature) return true;
        const hashType = signatureHashType(signature);

        // if SIGHASH_ANYONECANPAY is set, signatures would not
        // be invalidated by more inputs
        return (hashType & Transaction.SIGHASH_ANYONECANPAY) !== 0;
      });
    });
  }

  private __needsOutputs(signingHashType: number): boolean {
    if (signingHashType === Transaction.SIGHASH_ALL) {
      return this.__tx.outs.length === 0;
    }

    // if inputs are being signed with SIGHASH_NONE, we don't strictly need outputs
    // .build() will fail, but .buildIncomplete() is OK
    return (
      this.__tx.outs.length === 0 &&
      this.__inputs.some(input => {
        if (!input.signatures) return false;

        return input.signatures.some(signature => {
          if (!signature) return false; // no signature, no issue
          const hashType = signatureHashType(signature);
          if (hashType & Transaction.SIGHASH_NONE) return false; // SIGHASH_NONE doesn't care about outputs
          return true; // SIGHASH_* does care
        });
      })
    );
  }

  private __canModifyOutputs(): boolean {
    const nInputs = this.__tx.ins.length;
    const nOutputs = this.__tx.outs.length;

    return this.__inputs.every(input => {
      if (input.signatures === undefined) return true;

      return input.signatures.every(signature => {
        if (!signature) return true;
        const hashType = signatureHashType(signature);

        const hashTypeMod = hashType & 0x1f;
        if (hashTypeMod === Transaction.SIGHASH_NONE) return true;
        if (hashTypeMod === Transaction.SIGHASH_SINGLE) {
          // if SIGHASH_SINGLE is set, and nInputs > nOutputs
          // some signatures would be invalidated by the addition
          // of more outputs
          return nInputs <= nOutputs;
        }
        return false;
      });
    });
  }

  private __overMaximumFees(bytes: number): boolean {
    // not all inputs will have .value defined
    const incoming = this.__inputs.reduce((a, x) => a + (x.value! >>> 0), 0);

    // but all outputs do, and if we have any input value
    // we can immediately determine if the outputs are too small
    const outgoing = this.__tx.outs.reduce((a, x) => a + (<Output>x).value, 0);
    const fee = incoming - outgoing;
    const feeRate = fee / bytes;

    return feeRate > this.maximumFeeRate;
  }
}

function expandInput(
  scriptSig: Buffer,
  witnessStack: Array<Buffer>,
  type?: string,
  scriptPubKey?: Buffer,
): TxbInput {
  if (scriptSig.length === 0 && witnessStack.length === 0) return {};
  if (!type) {
    let ssType: string | undefined = classify.input(scriptSig, true);
    let wsType: string | undefined = classify.witness(witnessStack, true);
    if (ssType === SCRIPT_TYPES.NONSTANDARD) ssType = undefined;
    if (wsType === SCRIPT_TYPES.NONSTANDARD) wsType = undefined;
    type = ssType || wsType;
  }

  switch (type) {
    case SCRIPT_TYPES.P2WPKH: {
      const { output, pubkey, signature } = payments.p2wpkh({
        witness: witnessStack,
      });

      return {
        prevOutScript: output,
        prevOutType: SCRIPT_TYPES.P2WPKH,
        pubkeys: [pubkey],
        signatures: [signature],
      };
    }

    case SCRIPT_TYPES.P2PKH: {
      const { output, pubkey, signature } = payments.p2pkh({
        input: scriptSig,
      });

      return {
        prevOutScript: output,
        prevOutType: SCRIPT_TYPES.P2PKH,
        pubkeys: [pubkey],
        signatures: [signature],
      };
    }

    case SCRIPT_TYPES.P2PK: {
      const { signature } = payments.p2pk({ input: scriptSig });

      return {
        prevOutType: SCRIPT_TYPES.P2PK,
        pubkeys: [undefined],
        signatures: [signature],
      };
    }

    case SCRIPT_TYPES.P2MS: {
      const { m, pubkeys, signatures } = payments.p2ms(
        {
          input: scriptSig,
          output: scriptPubKey,
        },
        { allowIncomplete: true },
      );

      return {
        prevOutType: SCRIPT_TYPES.P2MS,
        pubkeys: pubkeys,
        signatures: signatures,
        maxSignatures: m,
      };
    }
  }

  if (type === SCRIPT_TYPES.P2SH) {
    const { output, redeem } = payments.p2sh({
      input: scriptSig,
      witness: witnessStack,
    });

    const outputType = classify.output(redeem!.output!);
    const expanded = expandInput(
      redeem!.input!,
      redeem!.witness!,
      outputType,
      redeem!.output,
    );
    if (!expanded.prevOutType) return {};

    return {
      prevOutScript: output,
      prevOutType: SCRIPT_TYPES.P2SH,
      redeemScript: redeem!.output,
      redeemScriptType: expanded.prevOutType,
      witnessScript: expanded.witnessScript,
      witnessScriptType: expanded.witnessScriptType,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
    };
  }

  if (type === SCRIPT_TYPES.P2WSH) {
    const { output, redeem } = payments.p2wsh({
      input: scriptSig,
      witness: witnessStack,
    });
    const outputType = classify.output(redeem!.output!);
    let expanded;
    if (outputType === SCRIPT_TYPES.P2WPKH) {
      expanded = expandInput(redeem!.input!, redeem!.witness!, outputType);
    } else {
      expanded = expandInput(
        bscript.compile(redeem!.witness!),
        [],
        outputType,
        redeem!.output,
      );
    }
    if (!expanded.prevOutType) return {};

    return {
      prevOutScript: output,
      prevOutType: SCRIPT_TYPES.P2WSH,
      witnessScript: redeem!.output,
      witnessScriptType: expanded.prevOutType,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
    };
  }

  return {
    prevOutType: SCRIPT_TYPES.NONSTANDARD,
    prevOutScript: scriptSig,
  };
}

// could be done in expandInput, but requires the original Transaction for hashForSignature
function fixMultisigOrder(
  input: TxbInput,
  transaction: Transaction,
  vin: number,
): void {
  if (input.redeemScriptType !== SCRIPT_TYPES.P2MS || !input.redeemScript)
    return;
  if (input.pubkeys!.length === input.signatures!.length) return;

  const unmatched = input.signatures!.concat();

  input.signatures = input.pubkeys!.map(pubKey => {
    const keyPair = ECPair.fromPublicKey(pubKey!);
    let match: Buffer | undefined;

    // check for a signature
    unmatched.some((signature, i) => {
      // skip if undefined || OP_0
      if (!signature) return false;

      // TODO: avoid O(n) hashForSignature
      const parsed = bscript.signature.decode(signature);
      const hash = transaction.hashForSignature(
        vin,
        input.redeemScript!,
        parsed.hashType,
      );

      // skip if signature does not match pubKey
      if (!keyPair.verify(hash, parsed.signature)) return false;

      // remove matched signature from unmatched
      unmatched[i] = undefined;
      match = signature;

      return true;
    });

    return match;
  });
}

function expandOutput(script: Buffer, ourPubKey?: Buffer): TxbOutput {
  typeforce(types.Buffer, script);
  const type = classify.output(script);

  switch (type) {
    case SCRIPT_TYPES.P2PKH: {
      if (!ourPubKey) return { type };

      // does our hash160(pubKey) match the output scripts?
      const pkh1 = payments.p2pkh({ output: script }).hash;
      const pkh2 = bcrypto.hash160(ourPubKey);
      if (!pkh1!.equals(pkh2)) return { type };

      return {
        type,
        pubkeys: [ourPubKey],
        signatures: [undefined],
      };
    }

    case SCRIPT_TYPES.P2WPKH: {
      if (!ourPubKey) return { type };

      // does our hash160(pubKey) match the output scripts?
      const wpkh1 = payments.p2wpkh({ output: script }).hash;
      const wpkh2 = bcrypto.hash160(ourPubKey);
      if (!wpkh1!.equals(wpkh2)) return { type };

      return {
        type,
        pubkeys: [ourPubKey],
        signatures: [undefined],
      };
    }

    case SCRIPT_TYPES.P2PK: {
      const p2pk = payments.p2pk({ output: script });
      return {
        type,
        pubkeys: [p2pk.pubkey],
        signatures: [undefined],
      };
    }

    case SCRIPT_TYPES.P2MS: {
      const p2ms = payments.p2ms({ output: script });
      return {
        type,
        pubkeys: p2ms.pubkeys,
        signatures: p2ms.pubkeys!.map((): undefined => undefined),
        maxSignatures: p2ms.m,
      };
    }
  }

  return { type };
}

function prepareInput(
  input: TxbInput,
  ourPubKey: Buffer,
  redeemScript: Buffer,
  witnessScript: Buffer,
): TxbInput {
  if (redeemScript && witnessScript) {
    const p2wsh = <Payment>(
      payments.p2wsh({ redeem: { output: witnessScript } })
    );
    const p2wshAlt = <Payment>payments.p2wsh({ output: redeemScript });
    const p2sh = <Payment>payments.p2sh({ redeem: { output: redeemScript } });
    const p2shAlt = <Payment>payments.p2sh({ redeem: p2wsh });

    // enforces P2SH(P2WSH(...))
    if (!p2wsh.hash!.equals(p2wshAlt.hash!))
      throw new Error('Witness script inconsistent with prevOutScript');
    if (!p2sh.hash!.equals(p2shAlt.hash!))
      throw new Error('Redeem script inconsistent with prevOutScript');

    const expanded = expandOutput(p2wsh.redeem!.output!, ourPubKey);
    if (!expanded.pubkeys)
      throw new Error(
        expanded.type +
          ' not supported as witnessScript (' +
          bscript.toASM(witnessScript) +
          ')',
      );
    if (input.signatures && input.signatures.some(x => x !== undefined)) {
      expanded.signatures = input.signatures;
    }

    let signScript = witnessScript;
    if (expanded.type === SCRIPT_TYPES.P2WPKH)
      throw new Error('P2SH(P2WSH(P2WPKH)) is a consensus failure');

    return {
      redeemScript,
      redeemScriptType: SCRIPT_TYPES.P2WSH,

      witnessScript,
      witnessScriptType: expanded.type,

      prevOutType: SCRIPT_TYPES.P2SH,
      prevOutScript: p2sh.output,

      hasWitness: true,
      signScript,
      signType: expanded.type,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
      maxSignatures: expanded.maxSignatures,
    };
  }

  if (redeemScript) {
    const p2sh = <Payment>payments.p2sh({ redeem: { output: redeemScript } });

    if (input.prevOutScript) {
      let p2shAlt;
      try {
        p2shAlt = <Payment>payments.p2sh({ output: input.prevOutScript });
      } catch (e) {
        throw new Error('PrevOutScript must be P2SH');
      }
      if (!p2sh.hash!.equals(p2shAlt.hash!))
        throw new Error('Redeem script inconsistent with prevOutScript');
    }

    const expanded = expandOutput(p2sh.redeem!.output!, ourPubKey);
    if (!expanded.pubkeys)
      throw new Error(
        expanded.type +
          ' not supported as redeemScript (' +
          bscript.toASM(redeemScript) +
          ')',
      );
    if (input.signatures && input.signatures.some(x => x !== undefined)) {
      expanded.signatures = input.signatures;
    }

    let signScript = redeemScript;
    if (expanded.type === SCRIPT_TYPES.P2WPKH) {
      signScript = payments.p2pkh({ pubkey: expanded.pubkeys[0] }).output!;
    }

    return {
      redeemScript,
      redeemScriptType: expanded.type,

      prevOutType: SCRIPT_TYPES.P2SH,
      prevOutScript: p2sh.output,

      hasWitness: expanded.type === SCRIPT_TYPES.P2WPKH,
      signScript,
      signType: expanded.type,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
      maxSignatures: expanded.maxSignatures,
    };
  }

  if (witnessScript) {
    const p2wsh = payments.p2wsh({ redeem: { output: witnessScript } });

    if (input.prevOutScript) {
      const p2wshAlt = payments.p2wsh({ output: input.prevOutScript });
      if (!p2wsh.hash!.equals(p2wshAlt.hash!))
        throw new Error('Witness script inconsistent with prevOutScript');
    }

    const expanded = expandOutput(p2wsh.redeem!.output!, ourPubKey);
    if (!expanded.pubkeys)
      throw new Error(
        expanded.type +
          ' not supported as witnessScript (' +
          bscript.toASM(witnessScript) +
          ')',
      );
    if (input.signatures && input.signatures.some(x => x !== undefined)) {
      expanded.signatures = input.signatures;
    }

    let signScript = witnessScript;
    if (expanded.type === SCRIPT_TYPES.P2WPKH)
      throw new Error('P2WSH(P2WPKH) is a consensus failure');

    return {
      witnessScript,
      witnessScriptType: expanded.type,

      prevOutType: SCRIPT_TYPES.P2WSH,
      prevOutScript: p2wsh.output,

      hasWitness: true,
      signScript,
      signType: expanded.type,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
      maxSignatures: expanded.maxSignatures,
    };
  }

  if (input.prevOutType && input.prevOutScript) {
    // embedded scripts are not possible without extra information
    if (input.prevOutType === SCRIPT_TYPES.P2SH)
      throw new Error(
        'PrevOutScript is ' + input.prevOutType + ', requires redeemScript',
      );
    if (input.prevOutType === SCRIPT_TYPES.P2WSH)
      throw new Error(
        'PrevOutScript is ' + input.prevOutType + ', requires witnessScript',
      );
    if (!input.prevOutScript) throw new Error('PrevOutScript is missing');

    const expanded = expandOutput(input.prevOutScript, ourPubKey);
    if (!expanded.pubkeys)
      throw new Error(
        expanded.type +
          ' not supported (' +
          bscript.toASM(input.prevOutScript) +
          ')',
      );
    if (input.signatures && input.signatures.some(x => x !== undefined)) {
      expanded.signatures = input.signatures;
    }

    let signScript = input.prevOutScript;
    if (expanded.type === SCRIPT_TYPES.P2WPKH) {
      signScript = <Buffer>(
        payments.p2pkh({ pubkey: expanded.pubkeys[0] }).output
      );
    }

    return {
      prevOutType: expanded.type,
      prevOutScript: input.prevOutScript,

      hasWitness: expanded.type === SCRIPT_TYPES.P2WPKH,
      signScript,
      signType: expanded.type,

      pubkeys: expanded.pubkeys,
      signatures: expanded.signatures,
      maxSignatures: expanded.maxSignatures,
    };
  }

  const prevOutScript = payments.p2pkh({ pubkey: ourPubKey }).output;
  return {
    prevOutType: SCRIPT_TYPES.P2PKH,
    prevOutScript: prevOutScript,

    hasWitness: false,
    signScript: prevOutScript,
    signType: SCRIPT_TYPES.P2PKH,

    pubkeys: [ourPubKey],
    signatures: [undefined],
  };
}

function build(
  type: string,
  input: TxbInput,
  allowIncomplete?: boolean,
): Payment | undefined {
  const pubkeys = <Array<Buffer>>(input.pubkeys || []);
  let signatures = <Array<Buffer>>(input.signatures || []);

  switch (type) {
    case SCRIPT_TYPES.P2PKH: {
      if (pubkeys.length === 0) break;
      if (signatures.length === 0) break;

      return payments.p2pkh({ pubkey: pubkeys[0], signature: signatures[0] });
    }
    case SCRIPT_TYPES.P2WPKH: {
      if (pubkeys.length === 0) break;
      if (signatures.length === 0) break;

      return payments.p2wpkh({ pubkey: pubkeys[0], signature: signatures[0] });
    }
    case SCRIPT_TYPES.P2PK: {
      if (pubkeys.length === 0) break;
      if (signatures.length === 0) break;

      return payments.p2pk({ signature: signatures[0] });
    }
    case SCRIPT_TYPES.P2MS: {
      const m = input.maxSignatures;
      if (allowIncomplete) {
        signatures = signatures.map(x => x || ops.OP_0);
      } else {
        signatures = signatures.filter(x => x);
      }

      // if the transaction is not not complete (complete), or if signatures.length === m, validate
      // otherwise, the number of OP_0's may be >= m, so don't validate (boo)
      const validate = !allowIncomplete || m === signatures.length;
      return payments.p2ms(
        { m, pubkeys, signatures },
        { allowIncomplete, validate },
      );
    }
    case SCRIPT_TYPES.P2SH: {
      const redeem = build(input.redeemScriptType!, input, allowIncomplete);
      if (!redeem) return;

      return payments.p2sh({
        redeem: {
          output: redeem.output || input.redeemScript,
          input: redeem.input,
          witness: redeem.witness,
        },
      });
    }
    case SCRIPT_TYPES.P2WSH: {
      const redeem = build(input.witnessScriptType!, input, allowIncomplete);
      if (!redeem) return;

      return payments.p2wsh({
        redeem: {
          output: input.witnessScript,
          input: redeem.input,
          witness: redeem.witness,
        },
      });
    }
  }
}

function canSign(input: TxbInput): boolean {
  return (
    input.signScript !== undefined &&
    input.signType !== undefined &&
    input.pubkeys !== undefined &&
    input.signatures !== undefined &&
    input.signatures.length === input.pubkeys.length &&
    input.pubkeys.length > 0 &&
    (input.hasWitness === false || input.value !== undefined)
  );
}

function signatureHashType(buffer: Buffer): number {
  return buffer.readUInt8(buffer.length - 1);
}