scontainers/dist/decorators/take_while.js

A container/collection/iterator library for JavaScript, comfortable to use, performant and versatile.

"use strict";

function _implSymbol(target, sym, value) {
  Object.defineProperty(target, sym, {
    value,
    configurable: true
  });
  return target[sym];
}

function _getSymbol(targetSymName, ...traitSets) {
  let symbol;
  traitSets.forEach(traitSet => {
    const sym = traitSet[targetSymName];

    if (typeof sym === 'symbol') {
      if (!!symbol && symbol !== sym) {
        throw new Error(`Symbol ${targetSymName} offered by multiple trait sets.`);
      }

      symbol = sym;
    }
  });

  if (!symbol) {
    throw new Error(`No trait set is providing symbol ${targetSymName}.`);
  }

  return symbol;
}

function _testTraitSet(traitSet) {
  if (!traitSet || typeof traitSet === 'boolean' || typeof traitSet === 'number' || typeof traitSet === 'string') {
    throw new Error(`${traitSet} cannot be used as a trait set.`);
  }
}

const {
  traits,
  id
} = require('../utils.js');

_testTraitSet(traits.utils);

_testTraitSet(traits.scontainers);

_testTraitSet(traits.semantics);

const _describeScontainer = _getSymbol("describeScontainer", traits.utils, traits.scontainers, traits.semantics);

const _implCoreTraits = _getSymbol("implCoreTraits", traits.utils, traits.scontainers, traits.semantics);

const _kvIterator = _getSymbol("kvIterator", traits.utils, traits.scontainers, traits.semantics);

const _reverse = _getSymbol("reverse", traits.utils, traits.scontainers, traits.semantics);

const _takeWhile = _getSymbol("takeWhile", traits.utils, traits.scontainers, traits.semantics);

module.exports = function (ParentCollection) {
  const parentProto = ParentCollection.prototype;
  return function () {
    class TakeWhile {
      static get name() {
        return `${ParentCollection.name}::TakeWhile`;
      }

      constructor(coll, fn) {
        this.wrapped = coll;
        this.fn = fn;
      }

      toString() {
        return `${this.wrapped}.takeWhile(${this.fn.name || 'ƒ'})`;
      }

    }

    TakeWhile[_describeScontainer]({
      InnerCollection: ParentCollection,
      innerCollectionKey: id`wrapped`,
      argKeys: [id`fn`]
    });

    TakeWhile[_implCoreTraits]({
      kvIterator() {
        return function kvIterator() {
          return {
            collection: this.wrapped,
            fn: this.fn,
            it: this.wrapped[_kvIterator](),

            next() {
              const next = this.it.next();

              if (!next) {
                return;
              }

              const {
                key,
                value,
                n
              } = next;

              if (this.fn(value, key, n)) {
                return next;
              }

              this.next = function next() {};
            }

          };
        };
      },

      reverse() {
        if (parentProto[_reverse]) {
          return function reverse() {
            return this.wrapped[_reverse]()[_takeWhile](this.fn);
          };
        }
      }

    });

    return TakeWhile;
  };
};