// (C) Copyright 2015 Moodle Pty Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

const gulp = require('gulp');
const slash = require('gulp-slash');
const clipEmptyFiles = require('gulp-clip-empty-files');
const through = require('through');
const bufferFrom = require('buffer-from');
const File = require('vinyl');
const pathLib = require('path');

/**
 * Task to build the language files into a single file per language.
 */
class BuildLangTask {

    /**
     * Copy a property from one object to another, adding a prefix to the key if needed.
     *
     * @param target Object to copy the properties to.
     * @param source Object to copy the properties from.
     * @param prefix Prefix to add to the keys.
     */
    addProperties(target, source, prefix) {
        for (let property in source) {
            target[prefix + property] = source[property];
        }
    }

    /**
     * Run the task.
     *
     * @param language Language to treat.
     * @param langPaths Paths to the possible language files.
     * @param done Function to call when done.
     */
    run(language, langPaths, done) {
        const filename = language + '.json';
        const data = {};
        let firstFile = null;
        const self = this;

        const paths = langPaths.map((path) => {
            if (path.slice(-1) != '/') {
                path = path + '/';
            }

            return path + language + '.json';
        });

        gulp.src(paths, { allowEmpty: true })
            .pipe(slash())
            .pipe(clipEmptyFiles())
            .pipe(through(function(file) {
                if (!firstFile) {
                    firstFile = file;
                }

                return self.treatFile(file, data);
            }, function() {
                /* This implementation is based on gulp-jsoncombine module.
                 * https://github.com/reflog/gulp-jsoncombine */
                if (firstFile) {
                    const joinedPath = pathLib.join(firstFile.base, language + '.json');

                    const joinedFile = new File({
                        cwd: firstFile.cwd,
                        base: firstFile.base,
                        path: joinedPath,
                        contents: self.treatMergedData(data),
                    });

                    this.emit('data', joinedFile);
                }

                this.emit('end');
            }))
            .pipe(gulp.dest(pathLib.join('./src/assets', 'lang')))
            .on('end', done);
    }

    /**
     * Treats a file to merge JSONs. This function is based on gulp-jsoncombine module.
     * https://github.com/reflog/gulp-jsoncombine
     *
     * @param file File treated.
     * @param data Object where to store the data.
     */
    treatFile(file, data) {
        if (file.isNull() || file.isStream()) {
            return; // ignore
        }

        try {
            let srcPos = file.path.lastIndexOf('/src/');
            if (srcPos == -1) {
                // It's probably a Windows environment.
                srcPos = file.path.lastIndexOf('\\src\\');
            }

            const path = file.path.substr(srcPos + 5);
            data[path] = JSON.parse(file.contents.toString());
        } catch (err) {
            console.log('Error parsing JSON: ' + err);
        }
    }

    /**
     * Treats the merged JSON data, adding prefixes depending on the component.
     *
     * @param data Merged data.
     * @return Buffer with the treated data.
     */
    treatMergedData(data) {
        const merged = {};
        const mergedOrdered = {};

        for (let filepath in data) {
            const pathSplit = filepath.split(/[\/\\]/);
            let prefix;

            pathSplit.pop();

            switch (pathSplit[0]) {
                case 'lang':
                    prefix = 'core';
                    break;
                case 'core':
                    if (pathSplit[1] == 'lang') {
                        // Not used right now.
                        prefix = 'core';
                    } else {
                        prefix = 'core.' + pathSplit[1];
                    }
                    break;
                case 'addon':
                    // Remove final item 'lang'.
                    pathSplit.pop();
                    // Remove first item 'addon'.
                    pathSplit.shift();

                    // For subplugins. We'll use plugin_subfolder_subfolder2_...
                    // E.g. 'mod_assign_feedback_comments'.
                    prefix = 'addon.' + pathSplit.join('_');
                    break;
                case 'assets':
                    prefix = 'assets.' + pathSplit[1];
                    break;
            }

            if (prefix) {
                this.addProperties(merged, data[filepath], prefix + '.');
            }
        }

        // Force ordering by string key.
        Object.keys(merged).sort().forEach((key) => {
            mergedOrdered[key] = merged[key];
        });

        return bufferFrom(JSON.stringify(mergedOrdered, null, 4));
    }
}

module.exports = BuildLangTask;