///
/// Copyright © 2016-2022 The Thingsboard Authors
///
/// 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 { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { TranslateService } from '@ngx-translate/core';
import { Observable, of } from 'rxjs';
import { catchError, map, mergeMap, tap } from 'rxjs/operators';
import { helpBaseUrl as siteBaseUrl } from '@shared/models/constants';
import { UiSettingsService } from '@core/http/ui-settings.service';

const localHelpBaseUrl = '/assets';

const NOT_FOUND_CONTENT: HelpData = {
  content: '## Not found',
  helpBaseUrl: localHelpBaseUrl
};

@Injectable({
  providedIn: 'root'
})
export class HelpService {

  private siteBaseUrl = siteBaseUrl;
  private helpCache: {[lang: string]: {[key: string]: string}} = {};

  constructor(
    private translate: TranslateService,
    private http: HttpClient,
    private uiSettingsService: UiSettingsService
  ) {}

  getHelpContent(key: string): Observable<string> {
    const lang = this.translate.currentLang;
    if (this.helpCache[lang] && this.helpCache[lang][key]) {
      return of(this.helpCache[lang][key]);
    } else {
      return this.loadHelpContent(lang, key).pipe(
        catchError(() => {
          const defaultLang = this.translate.getDefaultLang();
          if (lang !== defaultLang) {
            return this.loadHelpContent(defaultLang, key).pipe(
              catchError(() => {
                return of(NOT_FOUND_CONTENT);
              })
            );
          } else {
            return of(NOT_FOUND_CONTENT);
          }
        }),
        mergeMap((content) => {
          return this.processIncludes(this.processVariables(content));
        }),
        tap((content) => {
          let langContent = this.helpCache[lang];
          if (!langContent) {
            langContent = {};
            this.helpCache[lang] = langContent;
          }
          langContent[key] = content;
        })
      );
    }
  }

  private loadHelpContent(lang: string, key: string): Observable<HelpData> {
    return this.uiSettingsService.getHelpBaseUrl().pipe(
      mergeMap((helpBaseUrl) => {
        return this.loadHelpContentFromBaseUrl(helpBaseUrl, lang, key).pipe(
          catchError((e) => {
            if (localHelpBaseUrl !== helpBaseUrl) {
              return this.loadHelpContentFromBaseUrl(localHelpBaseUrl, lang, key);
            } else {
              throw e;
            }
          })
        );
      })
    );
  }

  private loadHelpContentFromBaseUrl(helpBaseUrl: string, lang: string, key: string): Observable<HelpData> {
    return this.http.get(`${helpBaseUrl}/help/${lang}/${key}.md`, {responseType: 'text'} ).pipe(
      map((content) => {
        return {
          content,
          helpBaseUrl
        };
      })
    );
  }

  private processVariables(helpData: HelpData): string {
    const baseUrlReg = /\${siteBaseUrl}/g;
    helpData.content = helpData.content.replace(baseUrlReg, this.siteBaseUrl);
    const helpBaseUrlReg = /\${helpBaseUrl}/g;
    return helpData.content.replace(helpBaseUrlReg, helpData.helpBaseUrl);
  }

  private processIncludes(content: string): Observable<string> {
    const includesRule = /{% include (.*) %}/;
    const match = includesRule.exec(content);
    if (match) {
      const key = match[1];
      return this.getHelpContent(key).pipe(
        mergeMap((include) => {
          content = content.replace(match[0], include);
          return this.processIncludes(content);
        })
      );
    } else {
      return of(content);
    }
  }

}

interface HelpData {
  content: string;
  helpBaseUrl: string;
}
