/*!
 * @license
 * Copyright 2019 Alfresco Software, 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.
 */

import { Inject, Injectable, InjectionToken, Optional } from '@angular/core';
import { TranslateService } from '@ngx-translate/core';
import { Observable } from 'rxjs';
import { TranslateLoaderService } from './translate-loader.service';
import { UserPreferencesService, UserPreferenceValues } from './user-preferences.service';

export const TRANSLATION_PROVIDER = new InjectionToken('Injection token for translation providers.');

export interface TranslationProvider {
    name: string;
    source: string;
}

@Injectable({
    providedIn: 'root'
})
export class TranslationService {
    defaultLang: string;
    userLang: string;
    customLoader: TranslateLoaderService;

    constructor(public translate: TranslateService,
                userPreferencesService: UserPreferencesService,
                @Optional() @Inject(TRANSLATION_PROVIDER) providers: TranslationProvider[]) {
        this.customLoader = <TranslateLoaderService> this.translate.currentLoader;

        this.defaultLang = 'en';
        translate.setDefaultLang(this.defaultLang);
        this.customLoader.setDefaultLang(this.defaultLang);

        if (providers && providers.length > 0) {
            for (const provider of providers) {
                this.addTranslationFolder(provider.name, provider.source);
            }
        }

        userPreferencesService.select(UserPreferenceValues.Locale).subscribe((locale) => {
            if (locale) {
                this.userLang = locale;
                this.use(this.userLang);
            }
        });
    }

    /**
     * Adds a new folder of translation source files.
     * @param name Name for the translation provider
     * @param path Path to the folder
     */
    addTranslationFolder(name: string = '', path: string = '') {
        if (!this.customLoader.providerRegistered(name)) {
            this.customLoader.registerProvider(name, path);

            if (this.userLang) {
                this.loadTranslation(this.userLang, this.defaultLang);
            } else {
                this.loadTranslation(this.defaultLang);
            }
        }
    }

    /**
     * Loads a translation file.
     * @param lang Language code for the language to load
     * @param fallback Language code to fall back to if the first one was unavailable
     */
    loadTranslation(lang: string, fallback?: string) {
        this.translate.getTranslation(lang).subscribe(
            () => {
                this.translate.use(lang);
                this.onTranslationChanged(lang);
            },
            () => {
                if (fallback && fallback !== lang) {
                    this.loadTranslation(fallback);
                }
            }
        );
    }

    /**
     * Triggers a notification callback when the translation language changes.
     * @param lang The new language code
     */
    onTranslationChanged(lang: string): void {
        this.translate.onTranslationChange.next({
            lang: lang,
            translations: this.customLoader.getFullTranslationJSON(lang)
        });
    }

    /**
     * Sets the target language for translations.
     * @param lang Code name for the language
     * @returns Translations available for the language
     */
    use(lang: string): Observable<any> {
        this.customLoader.init(lang);
        return this.translate.use(lang);
    }

    /**
     * Gets the translation for the supplied key.
     * @param key Key to translate
     * @param interpolateParams String(s) to be interpolated into the main message
     * @returns Translated text
     */
    get(key: string | Array<string>, interpolateParams?: Object): Observable<string | any> {
        return this.translate.get(key, interpolateParams);
    }

    /**
     * Directly returns the translation for the supplied key.
     * @param key Key to translate
     * @param interpolateParams String(s) to be interpolated into the main message
     * @returns Translated text
     */
    instant(key: string | Array<string>, interpolateParams?: Object): string | any {
        return key ? this.translate.instant(key, interpolateParams) : '';
    }
}