scontainers/dist/decorators/reverse.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 _nth = _getSymbol("nth", traits.utils, traits.scontainers, traits.semantics);

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

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

const _len = _getSymbol("len", traits.utils, traits.scontainers, traits.semantics);

module.exports = function (ParentCollection) {
  if (!ParentCollection.prototype[_nth]) {
    return;
  }

  return function () {
    class Reverse {
      static get name() {
        return `${ParentCollection.name}::Reverse`;
      }

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

      toString() {
        return `${this.wrapped}.reverse()`;
      }

    }

    Reverse[_describeScontainer]({
      InnerCollection: ParentCollection,
      innerCollectionKey: id`wrapped`,
      argKeys: [],
      mappingOnly: true
    });

    Reverse[_implCoreTraits]({
      nStage(kvn) {
        return kvn;
      },

      nToParentN(n) {
        return this[_len]() - n - 1;
      },

      reverse() {
        return this.wrapped;
      }

    });

    return Reverse;
  };
};