Function compose

src/static/js/Changeset.ts:755–784

(cs1: string, cs2:string, pool: AttributePool)

 * @returns {string}
 */
export const compose = (cs1: string, cs2:string, pool: AttributePool): string => {
  const unpacked1 = unpack(cs1);
  const unpacked2 = unpack(cs2);
  const len1 = unpacked1.oldLen;
  const len2 = unpacked1.newLen;
  assert(len2 === unpacked2.oldLen, 'mismatched composition of two changesets');
  const len3 = unpacked2.newLen;
  const bankIter1 = new StringIterator(unpacked1.charBank);
  const bankIter2 = new StringIterator(unpacked2.charBank);
  const bankAssem = new StringAssembler();

  const newOps = applyZip(unpacked1.ops, unpacked2.ops, (op1: Op, op2: Op) => {
    const op1code = op1.opcode;
    const op2code = op2.opcode;
    if (op1code === '+' && op2code === '-') {
      bankIter1.skip(Math.min(op1.chars, op2.chars));
    }
    const opOut = slicerZipperFunc(op1, op2, pool);
    if (opOut.opcode === '+') {
      if (op2code === '+') {
        bankAssem.append(bankIter2.take(opOut.chars));
      } else {
        bankAssem.append(bankIter1.take(opOut.chars));
      }
    }
    return opOut;
  });

  return pack(len1, len3, newOps, bankAssem.toString());
};

/**
 * Returns a function that tests if a string of attributes (e.g. '*3*4') contains a given attribute