iterama/node/take-async.js

Composable functional (async) iterable helpers

var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.takeAsync = void 0;

var _circularr = _interopRequireDefault(require("circularr"));

var _iterate = require("./iterate");

const takeFirstAsync = n => iterable => ({
  async *[Symbol.asyncIterator]() {
    if (n <= 0) {
      return;
    }

    let i = 0;

    for await (const value of iterable) {
      yield value;

      if (++i >= n) {
        break;
      }
    }
  }

});

const takeLastAsync = n => iterable => ({
  async *[Symbol.asyncIterator]() {
    const last = new _circularr.default(n);
    let numValues = 0;

    for await (const value of iterable) {
      last.shift(value);
      numValues++;
    }

    const iterator = (0, _iterate.iterate)(last);
    const offset = last.length - numValues;

    for (let i = 0; i < offset; i++) {
      iterator.next();
    }

    for (const value of iterator) {
      yield value;
    }
  }

});

const takeAsync = n => n < 0 ? takeLastAsync(-n) : takeFirstAsync(n);

exports.takeAsync = takeAsync;