/**
 * @fileoverview Util class to find config files.
 * @author Aliaksei Shytkin
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const fs = require("fs"),
    path = require("path");

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

/**
 * Get the entries for a directory. Including a try-catch may be detrimental to
 * function performance, so move it out here a separate function.
 * @param {string} directory The directory to search in.
 * @returns {string[]} The entries in the directory or an empty array on error.
 * @private
 */
function getDirectoryEntries(directory) {
    try {

        return fs.readdirSync(directory);
    } catch (ex) {
        return [];
    }
}

/**
 * Create a hash of filenames from a directory listing
 * @param {string[]} entries Array of directory entries.
 * @param {string} directory Path to a current directory.
 * @param {string[]} supportedConfigs List of support filenames.
 * @returns {Object} Hashmap of filenames
 */
function normalizeDirectoryEntries(entries, directory, supportedConfigs) {
    const fileHash = {};

    entries.forEach(entry => {
        if (supportedConfigs.indexOf(entry) >= 0) {
            const resolvedEntry = path.resolve(directory, entry);

            if (fs.statSync(resolvedEntry).isFile()) {
                fileHash[entry] = resolvedEntry;
            }
        }
    });
    return fileHash;
}

//------------------------------------------------------------------------------
// API
//------------------------------------------------------------------------------

/**
 * FileFinder class
 */
class FileFinder {

    /**
     * @param {string[]} files The basename(s) of the file(s) to find.
     * @param {stirng} cwd Current working directory
     */
    constructor(files, cwd) {
        this.fileNames = Array.isArray(files) ? files : [files];
        this.cwd = cwd || process.cwd();
        this.cache = {};
    }

    /**
     * Find all instances of files with the specified file names, in directory and
     * parent directories. Cache the results.
     * Does not check if a matching directory entry is a file.
     * Searches for all the file names in this.fileNames.
     * Is currently used by lib/config.js to find .eslintrc and package.json files.
     * @param  {string} directory The directory to start the search from.
     * @returns {GeneratorFunction} to iterate the file paths found
     */
    *findAllInDirectoryAndParents(directory) {
        const cache = this.cache;

        if (directory) {
            directory = path.resolve(this.cwd, directory);
        } else {
            directory = this.cwd;
        }

        if (cache.hasOwnProperty(directory)) {
            yield* cache[directory];
            return; // to avoid doing the normal loop afterwards
        }

        const dirs = [];
        const fileNames = this.fileNames;
        let searched = 0;

        do {
            dirs[searched++] = directory;
            cache[directory] = [];

            const filesMap = normalizeDirectoryEntries(getDirectoryEntries(directory), directory, fileNames);

            if (Object.keys(filesMap).length) {
                for (let k = 0; k < fileNames.length; k++) {

                    if (filesMap[fileNames[k]]) {
                        const filePath = filesMap[fileNames[k]];

                        // Add the file path to the cache of each directory searched.
                        for (let j = 0; j < searched; j++) {
                            cache[dirs[j]].push(filePath);
                        }
                        yield filePath;
                        break;
                    }
                }
            }

            const child = directory;

            // Assign parent directory to directory.
            directory = path.dirname(directory);

            if (directory === child) {
                return;
            }

        } while (!cache.hasOwnProperty(directory));

        // Add what has been cached previously to the cache of each directory searched.
        for (let i = 0; i < searched; i++) {
            dirs.push.apply(cache[dirs[i]], cache[directory]);
        }

        yield* cache[dirs[0]];
    }
}

module.exports = FileFinder;