import "txUtil.scrypt";

struct SHPreimage {
  bytes txVer;
  bytes nLockTime;
  bytes hashPrevouts;
  bytes hashSpentAmounts;
  bytes hashSpentScripts;
  bytes hashSequences;
  bytes hashOutputs;
  bytes spendType;
  bytes inputIndex;
  bytes hashTapLeaf;
  bytes keyVer;
  bytes codeSeparator;
  bytes _e;
  int eLastByte;
}

struct PrevoutsCtx {
  bytes[6] prevouts;
  int inputIndexVal;
  int outputIndexVal;
  bytes spentTxhash;
  bytes outputIndex;
}

library SigHashUtils {
  static const PubKey Gx = PubKey(b'79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798');
  static const bytes ePreimagePrefix = b'7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48d37c7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48d37c79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f8179879be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798';
  static const bytes preimagePrefix = b'f40a48df4b2a70c8b4924bf2654661ed3d95fd66a313eb87237597c628e4a031f40a48df4b2a70c8b4924bf2654661ed3d95fd66a313eb87237597c628e4a0310000';
  static function checkSHPreimage(SHPreimage shPreimage) : Sig {
    Sha256 sigHash = sha256(SigHashUtils.preimagePrefix + shPreimage.txVer + shPreimage.nLockTime + shPreimage.hashPrevouts + shPreimage.hashSpentAmounts + shPreimage.hashSpentScripts + shPreimage.hashSequences + shPreimage.hashOutputs + shPreimage.spendType + shPreimage.inputIndex + shPreimage.hashTapLeaf + shPreimage.keyVer + shPreimage.codeSeparator);
    Sha256 e = sha256(SigHashUtils.ePreimagePrefix + sigHash);
    require(shPreimage.eLastByte < 127);
    bytes eLastByte = shPreimage.eLastByte == 0 ? b'00' : pack(shPreimage.eLastByte);
    require(e == shPreimage._e + eLastByte);
    bytes s = SigHashUtils.Gx + shPreimage._e + pack(shPreimage.eLastByte + 1);
    return Sig(s);
  }
  static function checkPrevoutsCtx(PrevoutsCtx prevoutsCtx, bytes hashPrevouts, bytes inputIndex) : bool {
    require(sha256(TxUtil.mergePrevouts(prevoutsCtx.prevouts)) == hashPrevouts);
    require(TxUtil.checkIndex(prevoutsCtx.inputIndexVal, inputIndex));
    require(TxUtil.checkIndex(prevoutsCtx.outputIndexVal, prevoutsCtx.outputIndex));
    require(prevoutsCtx.prevouts[(prevoutsCtx.inputIndexVal)] == prevoutsCtx.spentTxhash + prevoutsCtx.outputIndex);
    return true;
  }
  static function checkSpentScriptsCtx(bytes[6] spentScriptsCtx, bytes hashSpentScripts) : bool {
    require(sha256(TxUtil.mergeSpentScripts(spentScriptsCtx)) == hashSpentScripts);
    return true;
  }
}