iter-tools-es/impls/$window-ahead/window-ahead.js

The iterable toolbox

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

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

function* __windowAhead(source, size, {
  filler = undefined,
  useFiller = true
} = {}) {
  const buffer = new CircularBuffer(size);
  const bufferReadProxy = new ReadOnlyCircularBuffer(buffer);
  let len = 0;

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

    if (buffer.isFull()) {
      yield bufferReadProxy;
    }

    len++;
  }

  if (useFiller) {
    for (let i = len; i < size; i++) {
      buffer.push(filler);
    }
  }

  if (len > 0 && len < size) yield bufferReadProxy;

  for (let i = 0; i < Math.min(size, len) - 1; i++) {
    buffer.shift();

    if (useFiller) {
      buffer.push(filler);
    }

    yield bufferReadProxy;
  }
}

exports.__windowAhead = __windowAhead;
const windowAhead = /*#__PURE__*/iterableCurry(__windowAhead, {
  minArgs: 1,
  maxArgs: 2,

  validateArgs(args) {
    if (typeof args[1] !== 'number') {
      throw new Error(`${'windowAhead'} must be passed a numeric size`);
    }
  }

});
exports.windowAhead = windowAhead;