const GIS_SCRIPT_SRC = 'https://accounts.google.com/gsi/client';
const GIS_SCRIPT_ID = 'ehandyhire-google-gis';

export function getGoogleClientId(): string {
  return process.env.NEXT_PUBLIC_GOOGLE_CLIENT_ID?.trim() || '';
}

export function isGoogleSignInConfigured(): boolean {
  return Boolean(getGoogleClientId());
}

declare global {
  interface Window {
    google?: {
      accounts: {
        id: {
          initialize: (config: {
            client_id: string;
            callback: (response: { credential?: string }) => void;
            auto_select?: boolean;
            cancel_on_tap_outside?: boolean;
            use_fedcm_for_prompt?: boolean;
          }) => void;
          renderButton: (
            parent: HTMLElement,
            options: {
              theme?: 'outline' | 'filled_blue' | 'filled_black';
              size?: 'large' | 'medium' | 'small';
              text?: 'signin_with' | 'signup_with' | 'continue_with' | 'signin';
              shape?: 'rectangular' | 'pill' | 'circle' | 'square';
              logo_alignment?: 'left' | 'center';
              width?: number | string;
              locale?: string;
            }
          ) => void;
          prompt: (momentListener?: (notification: {
            isNotDisplayed: () => boolean;
            isSkippedMoment: () => boolean;
          }) => void) => void;
        };
      };
    };
  }
}

let loadPromise: Promise<void> | null = null;

export function loadGoogleIdentityServices(): Promise<void> {
  if (typeof window === 'undefined') {
    return Promise.reject(new Error('Google Sign-In is only available in the browser'));
  }

  if (window.google?.accounts?.id) {
    return Promise.resolve();
  }

  if (loadPromise) return loadPromise;

  loadPromise = new Promise((resolve, reject) => {
    const existing = document.getElementById(GIS_SCRIPT_ID) as HTMLScriptElement | null;
    if (existing) {
      existing.addEventListener('load', () => resolve(), { once: true });
      existing.addEventListener('error', () => reject(new Error('Failed to load Google Sign-In')), {
        once: true,
      });
      return;
    }

    const script = document.createElement('script');
    script.id = GIS_SCRIPT_ID;
    script.src = GIS_SCRIPT_SRC;
    script.async = true;
    script.defer = true;
    script.onload = () => resolve();
    script.onerror = () => {
      loadPromise = null;
      reject(new Error('Failed to load Google Sign-In'));
    };
    document.head.appendChild(script);
  });

  return loadPromise;
}