/**
 * 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-extra');
const _ = require('lodash');
const path = require('path');

const CONFIG_FILE_NAME = 'docusaurus.config.js';

const REQUIRED_FIELDS = [
  'baseUrl',
  'favicon',
  'headerLinks',
  'headerIcon',
  'organizationName',
  'projectName',
  'title',
  'tagline',
  'url',
];

const OPTIONAL_FIELDS = [
  'algolia',
  'chainWebpack',
  'configureWebpack',
  'customDocsPath',
  'customFields',
  'defaultLanguage',
  'docsUrl',
  'githubHost',
  'highlight',
  'markdownPlugins',
];

const DEFAULT_CONFIG = {
  customDocsPath: 'docs',
  docsUrl: 'docs',
};

function formatFields(fields) {
  return fields.map(field => `'${field}'`).join(', ');
}

function loadConfig(siteDir, deleteCache = true) {
  const configPath = path.resolve(siteDir, CONFIG_FILE_NAME);
  if (deleteCache) {
    delete require.cache[configPath];
  }
  let loadedConfig = {};
  if (fs.existsSync(configPath)) {
    loadedConfig = require(configPath); // eslint-disable-line
  }

  const missingFields = REQUIRED_FIELDS.filter(
    field => !_.has(loadedConfig, field),
  );
  if (missingFields.length > 0) {
    throw new Error(
      `The required field(s) ${formatFields(
        missingFields,
      )} are missing from ${CONFIG_FILE_NAME}`,
    );
  }

  // Merge default config with loaded config.
  const config = {...DEFAULT_CONFIG, ...loadedConfig};

  // Build final headerLinks based on siteConfig.
  const {headerLinks} = config;

  // Add language dropdown to end if location not specified.
  let languages = false;
  headerLinks.forEach(link => {
    if (link.languages) {
      languages = true;
    }
  });
  if (!languages) {
    headerLinks.push({languages: true});
  }
  let search = false;
  headerLinks.forEach(link => {
    // Append search bar if location not specified.
    if (link.search) {
      search = true;
    }
  });
  if (!search && config.algolia) {
    headerLinks.push({search: true});
  }
  config.headerLinks = headerLinks;

  /*
    User's own array of custom fields,
    e.g: if they want to include some field so they can access it later from `props.siteConfig`
  */
  const {customFields = []} = config;

  // Don't allow unrecognized fields.
  const allowedFields = [
    ...REQUIRED_FIELDS,
    ...OPTIONAL_FIELDS,
    ...customFields,
  ];
  const unrecognizedFields = Object.keys(config).filter(
    field => !allowedFields.includes(field),
  );
  if (unrecognizedFields && unrecognizedFields.length > 0) {
    throw new Error(
      `The field(s) ${formatFields(
        unrecognizedFields,
      )} are not recognized in ${CONFIG_FILE_NAME}`,
    );
  }

  return config;
}

module.exports = {
  configFileName: CONFIG_FILE_NAME,
  loadConfig,
};