/**
 * utils.js
 * @file General purpose utilities
 * @description General purpose utilities.
 */

const path = require('path');
const fs = require('fs').promises;

/**
 * The general purpose utilities.
 */
class Utils {
  /**
   * @function getLocalizedPath
   * @description Returns a localized file path accoring to the locale.
   *
   * Localized files are searched in subfolders of a given path, e.g.
   *
   * root/
   * ├── base/                    // base path to files
   * │   ├── example.html         // default file
   * │   └── de/                  // de language folder
   * │   │   └── example.html     // de localized file
   * │   └── de-AT/               // de-AT locale folder
   * │   │   └── example.html     // de-AT localized file
   *
   * Files are matched with the locale in the following order:
   * 1. Locale match, e.g. locale `de-AT` matches file in folder `de-AT`.
   * 2. Language match, e.g. locale `de-AT` matches file in folder `de`.
   * 3. Default; file in base folder is returned.
   *
   * @param {String} defaultPath The absolute file path, which is also
   * the default path returned if localization is not available.
   * @param {String} locale The locale.
   * @returns {Promise<Object>} The object contains:
   * - `path`: The path to the localized file, or the original path if
   *   localization is not available.
   * - `subdir`: The subdirectory of the localized file, or undefined if
   *   there is no matching localized file.
   */
  static async getLocalizedPath(defaultPath, locale) {
    // Get file name and paths
    const file = path.basename(defaultPath);
    const basePath = path.dirname(defaultPath);

    // If locale is not set return default file
    if (!locale) {
      return { path: defaultPath };
    }

    // Check file for locale exists
    const localePath = path.join(basePath, locale, file);
    const localeFileExists = await Utils.fileExists(localePath);

    // If file for locale exists return file
    if (localeFileExists) {
      return { path: localePath, subdir: locale };
    }

    // Check file for language exists
    const language = locale.split('-')[0];
    const languagePath = path.join(basePath, language, file);
    const languageFileExists = await Utils.fileExists(languagePath);

    // If file for language exists return file
    if (languageFileExists) {
      return { path: languagePath, subdir: language };
    }

    // Return default file
    return { path: defaultPath };
  }

  /**
   * @function fileExists
   * @description Checks whether a file exists.
   * @param {String} path The file path.
   * @returns {Promise<Boolean>} Is true if the file can be accessed, false otherwise.
   */
  static async fileExists(path) {
    try {
      await fs.access(path);
      return true;
    } catch (e) {
      return false;
    }
  }

  /**
   * @function isPath
   * @description Evaluates whether a string is a file path (as opposed to a URL for example).
   * @param {String} s The string to evaluate.
   * @returns {Boolean} Returns true if the evaluated string is a path.
   */
  static isPath(s) {
    return /(^\/)|(^\.\/)|(^\.\.\/)/.test(s);
  }

  /**
   * Flattens an object and crates new keys with custom delimiters.
   * @param {Object} obj The object to flatten.
   * @param {String} [delimiter='.'] The delimiter of the newly generated keys.
   * @param {Object} result
   * @returns {Object} The flattened object.
   **/
  static flattenObject(obj, parentKey, delimiter = '.', result = {}) {
    for (const key in obj) {
      if (Object.prototype.hasOwnProperty.call(obj, key)) {
        const newKey = parentKey ? parentKey + delimiter + key : key;

        if (typeof obj[key] === 'object' && obj[key] !== null) {
          this.flattenObject(obj[key], newKey, delimiter, result);
        } else {
          result[newKey] = obj[key];
        }
      }
    }
    return result;
  }

  /**
   * Determines whether an object is a Promise.
   * @param {any} object The object to validate.
   * @returns {Boolean} Returns true if the object is a promise.
   */
  static isPromise(object) {
    return object instanceof Promise;
  }

  /**
   * Creates an object with all permutations of the original keys.
   * For example, this definition:
   * ```
   * {
   *   a: [true, false],
   *   b: [1, 2],
   *   c: ['x']
   * }
   * ```
   * permutates to:
   * ```
   * [
   *   { a: true, b: 1, c: 'x' },
   *   { a: true, b: 2, c: 'x' },
   *   { a: false, b: 1, c: 'x' },
   *   { a: false, b: 2, c: 'x' }
   * ]
   * ```
   * @param {Object} object The object to permutate.
   * @param {Integer} [index=0] The current key index.
   * @param {Object} [current={}] The current result entry being composed.
   * @param {Array} [results=[]] The resulting array of permutations.
   */
  static getObjectKeyPermutations(object, index = 0, current = {}, results = []) {
    const keys = Object.keys(object);
    const key = keys[index];
    const values = object[key];

    for (const value of values) {
      current[key] = value;
      const nextIndex = index + 1;

      if (nextIndex < keys.length) {
        Utils.getObjectKeyPermutations(object, nextIndex, current, results);
      } else {
        const result = Object.assign({}, current);
        results.push(result);
      }
    }
    return results;
  }

  /**
   * Validates parameters and throws if a parameter is invalid.
   * Example parameter types syntax:
   * ```
   * {
   *   parameterName: {
   *      t: 'boolean',
   *      v: isBoolean,
   *      o: true
   *   },
   *   ...
   * }
   * ```
   * @param {Object} params The parameters to validate.
   * @param {Array<Object>} types The parameter types used for validation.
   * @param {Object} types.t The parameter type; used for error message, not for validation.
   * @param {Object} types.v The function to validate the parameter value.
   * @param {Boolean} [types.o=false] Is true if the parameter is optional.
   */
  static validateParams(params, types) {
    for (const key of Object.keys(params)) {
      const type = types[key];
      const isOptional = !!type.o;
      const param = params[key];
      if (!(isOptional && param == null) && !type.v(param)) {
        throw `Invalid parameter ${key} must be of type ${type.t} but is ${typeof param}`;
      }
    }
  }
}

module.exports = Utils;