/**
 * Copyright (c) 2017-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

const fs = require('fs');

const Metadata = require('../core/metadata.js');

const CWD = process.cwd();
let languages;
if (fs.existsSync(CWD + '/languages.js')) {
  languages = require(CWD + '/languages.js');
} else {
  languages = [
    {
      enabled: true,
      name: 'English',
      tag: 'en',
    },
  ];
}

// returns data broken up into categories for a sidebar
function readCategories(sidebar) {
  const enabledLanguages = languages
    .filter(lang => lang.enabled)
    .map(lang => lang.tag);

  const allCategories = {};

  for (let k = 0; k < enabledLanguages.length; ++k) {
    const language = enabledLanguages[k];

    const metadatas = [];
    Object.keys(Metadata).forEach(id => {
      const metadata = Metadata[id];
      if (metadata.sidebar === sidebar && metadata.language === language) {
        metadatas.push(metadata);
      }
    });

    // Build a hashmap of article_id -> metadata
    const articles = {};
    for (let i = 0; i < metadatas.length; ++i) {
      const metadata = metadatas[i];
      articles[metadata.id] = metadata;
    }

    // Build a hashmap of article_id -> previous_id
    const previous = {};
    for (let i = 0; i < metadatas.length; ++i) {
      const metadata = metadatas[i];
      if (metadata.next) {
        if (!articles[metadata.next]) {
          throw new Error(
            metadata.version
              ? `Improper sidebars file for version ${
                  metadata.version
                }, document with id '${
                  metadata.next
                }' not found. Make sure that all documents with ids specified in this version's sidebar file exist and that no ids are repeated.`
              : `Improper sidebars.json file, document with id '${
                  metadata.next
                }' not found. Make sure that documents with the ids specified in sidebars.json exist and that no ids are repeated.`
          );
        }
        previous[articles[metadata.next].id] = metadata.id;
      }
    }

    // Find the first element which doesn't have any previous
    let first = null;
    for (let i = 0; i < metadatas.length; ++i) {
      const metadata = metadatas[i];
      if (!previous[metadata.id]) {
        first = metadata;
        break;
      }
    }

    const categories = [];
    let currentCategory = null;

    let metadata = first;
    let i = 0;
    while (metadata && i++ < 1000) {
      if (!currentCategory || metadata.category !== currentCategory.name) {
        if (currentCategory) {
          categories.push(currentCategory);
        }
        currentCategory = {
          name: metadata.category,
          links: [],
        };
      }
      currentCategory.links.push(metadata);
      metadata = articles[metadata.next];
    }
    categories.push(currentCategory);

    allCategories[language] = categories;
  }

  return allCategories;
}

module.exports = readCategories;