iter-tools-es/impls/$slice/slice.js

The iterable toolbox

const {
  CircularBuffer
} = require('../../internal/circular-buffer.js');

const {
  iterableCurry
} = require('../../internal/iterable.js');

const {
  makeValidateArgs
} = require('./internal/validate-args.js');

function* __sliceFromStart(source, start = 0, end = Infinity, step = 1) {
  let currentPos = 0;
  let nextValidPos = start;
  const bufferSize = Math.abs(end);
  let buffer;
  let counter = 0;

  if (end < 0) {
    buffer = new CircularBuffer(bufferSize);
  }

  for (let value of source) {
    if (buffer) {
      value = buffer.push(value);
      counter++;

      if (counter <= bufferSize) {
        continue;
      }
    }

    if (currentPos >= end && end >= 0) {
      break;
    }

    if (nextValidPos === currentPos) {
      yield value;
      nextValidPos += step;
    }

    currentPos++;
  }
}

exports.__sliceFromStart = __sliceFromStart;

function bufferedSlice(source, start, end, step) {
  const bufferSize = Math.abs(start);
  const buffer = new CircularBuffer(bufferSize);
  let counter = 0;

  for (const value of source) {
    buffer.push(value);
    counter++;
  }

  let newEnd;

  if (isFinite(end) && end > 0) {
    newEnd = end - (counter - buffer.size);
    if (newEnd < 0) return [];
  } else {
    newEnd = end;
  }

  return __sliceFromStart(buffer, 0, newEnd, step);
}

function* __slice(source, start = 0, end = Infinity, step = 1) {
  if (start >= 0) {
    yield* __sliceFromStart(source, start, end, step);
  } else {
    yield* bufferedSlice(source, start, end, step);
  }
}

exports.__slice = __slice;
const slice = /*#__PURE__*/iterableCurry(__slice, {
  validateArgs: /*#__PURE__*/makeValidateArgs('slice'),
  growRight: true,
  minArgs: 0,
  maxArgs: 3
});
exports.slice = slice;