/**
 * Copyright since 2025 Mifos Initiative
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

import { ApplicationRef, Injectable, inject } from '@angular/core';
import { BehaviorSubject } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class ThemingService {
  private ref = inject(ApplicationRef);

  private darkModeOn = false;

  themes = [
    'dark-theme',
    'light-theme'
  ]; // <- list all themes in this array
  theme = new BehaviorSubject('light-theme'); // <- initial theme

  constructor() {
    // The user's own choice, kept in localStorage by the theme toggle, is the only thing that
    // decides the theme.
    //
    // The OS preference used to decide it instead, and a media-query listener kept it in step with
    // Windows. That is what turned a page black after printing: Chrome re-evaluates
    // prefers-color-scheme around the print dialog, the listener fired on the way back, and the app
    // flipped to dark against the user's saved choice — on every screen, and only after a print,
    // which is exactly how it was reported. A member of staff who set the app light does not expect
    // printing a report to change it, and the toggle they used had no way to win against the OS.
    //
    // Nothing here reads the OS any more, so there is no listener to fire and nothing to fight the
    // toggle. isDarkMode() still reports the OS preference for the one caller that offers it as a
    // default on first use.
    this.darkModeOn = !!this.storedPreference();
    this.setDarkMode(this.darkModeOn);
  }

  /** The saved choice, or null when the user has never set one. */
  private storedPreference(): boolean | null {
    try {
      const raw = localStorage.getItem('mifosXThemeDarkEnabled');
      return raw === null ? null : JSON.parse(raw);
    } catch {
      // A blocked or corrupt localStorage must not stop the app from rendering; light is the
      // default the rest of the stylesheet already assumes.
      return null;
    }
  }

  /**
   * Whether the app is currently in dark mode.
   *
   * Reports the app's own state, not the OS preference. It used to read the media query and assign
   * the result to darkModeOn on the way past — so merely asking the question overwrote the user's
   * saved choice, and setInitialDarkMode() then applied whatever the OS happened to say.
   */
  isDarkMode(): boolean {
    return this.darkModeOn;
  }

  /** The OS preference, offered as a starting point when the user has never chosen for themselves. */
  isSystemDarkMode(): boolean {
    return !!(window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches);
  }

  setDarkMode(isDarkMode: boolean) {
    this.darkModeOn = isDarkMode;
    if (isDarkMode) {
      document.body.classList.add('dark-theme');
      document.body.classList.remove('light-theme');
      this.theme.next('dark-theme');
    } else {
      document.body.classList.add('light-theme');
      document.body.classList.remove('dark-theme');
      this.theme.next('light-theme');
    }
  }

  setInitialDarkMode(): void {
    this.setDarkMode(this.darkModeOn);
  }
}