import {
  AngularNodeAppEngine,
  createNodeRequestHandler,
  isMainModule,
  writeResponseToNodeResponse,
} from '@angular/ssr/node';
import * as fs from 'node:fs';
import * as http from 'node:http';
import * as https from 'node:https';
import * as path from 'node:path';
import { isSpider, getUserAgent } from './spider_detection';

/**
 * Manually import and register the Angular app engine manifest.
 * The Angular 21 builder generates angular-app-engine-manifest.mjs at build time
 * but does NOT automatically inject the import into server.mjs.
 * Without this, AngularNodeAppEngine fails with "Angular app engine manifest is not set"
 * and every SSR request returns 404.
 */
// @ts-ignore — generated at build time by @angular/build
import engineManifest from './angular-app-engine-manifest.mjs';
import { ɵsetAngularAppEngineManifest } from '@angular/ssr';
ɵsetAngularAppEngineManifest(engineManifest);

const appEngine = new AngularNodeAppEngine();

/**
 * Station config shape — mirrors the backend API response.
 * Only the color fields are used for theme injection; the rest are
 * passed through verbatim for the client-side StationConfigService.
 */
interface StationConfig {
  color_primary: string;
  color_primary_light: string;
  color_primary_dark: string;
  color_primary_muted: string;
  color_accent: string;
  color_accent_light: string;
  color_accent_dark: string;
  color_accent_muted: string;
  color_background: string;
  color_text: string;
  color_success: string;
  color_danger: string;
  color_info: string;
  color_white: string;
  color_light: string;
  color_medium: string;
  color_black: string;
  [key: string]: unknown;
}

/** CSS custom property names mapped from StationConfig color fields. */
const COLOR_MAP: ReadonlyArray<{ field: keyof StationConfig; prop: string }> = [
  { field: 'color_primary', prop: '--color-primary' },
  { field: 'color_primary_light', prop: '--color-primary-light' },
  { field: 'color_primary_dark', prop: '--color-primary-dark' },
  { field: 'color_primary_muted', prop: '--color-primary-muted' },
  { field: 'color_accent', prop: '--color-accent' },
  { field: 'color_accent_light', prop: '--color-accent-light' },
  { field: 'color_accent_dark', prop: '--color-accent-dark' },
  { field: 'color_accent_muted', prop: '--color-accent-muted' },
  { field: 'color_background', prop: '--color-cream' },
  { field: 'color_text', prop: '--color-dark' },
  { field: 'color_success', prop: '--color-success' },
  { field: 'color_danger', prop: '--color-danger' },
  { field: 'color_info', prop: '--color-info' },
  { field: 'color_white', prop: '--color-white' },
  { field: 'color_light', prop: '--color-light' },
  { field: 'color_medium', prop: '--color-medium' },
  { field: 'color_black', prop: '--color-black' },
];

/**
 * Resolve the static CSR shell path (index.csr.html).
 *
 * IMPORTANT: We MUST prefer index.csr.html over index.html.
 * The Angular build with prerender config produces both:
 * - index.html: prerendered at build time with stale DEFAULT_CONFIG baked in
 * - index.csr.html: pure CSR shell with empty <app-root> — Angular hydrates client-side
 *
 * Serving index.html to regular users causes the flash: the prerendered DOM
 * shows stale build-time content until Angular re-renders with fresh data.
 * Even with window.__STATION_CONFIG injection, the prerendered innerHTML inside
 * <app-root> still shows old content on the first paint.
 *
 * Production (Docker): browser files are copied to /usr/share/nginx/html/
 * Local dev (ng build): browser files live in dist/radio-station/browser/
 * Try each candidate in order and return the first that exists.
 */
function browserIndexPath(): string {
  // Production path — Dockerfile copies browser output here
  // CSR shell first — avoid prerendered index.html with stale content
  const productionPaths = [
    '/usr/share/nginx/html/index.csr.html',
    '/usr/share/nginx/html/index.html',
    '/var/www/html/index.csr.html',
    '/var/www/html/index.html',
  ];

  // Local dev path — relative to the compiled server directory
  const dir = typeof __dirname !== 'undefined' ? __dirname : path.dirname(new URL(import.meta.url).pathname);
  const localPaths = [
    path.join(dir, 'browser', 'index.csr.html'),
    path.join(dir, 'browser', 'index.html'),
    path.join(dir, '..', 'browser', 'index.csr.html'),
    path.join(dir, '..', 'browser', 'index.html'),
  ];

  const allCandidates = [...productionPaths, ...localPaths];
  for (const candidate of allCandidates) {
    try {
      if (fs.existsSync(candidate)) return candidate;
    } catch {
      // ignore — keep trying
    }
  }
  // Return the first candidate so the error path has a sensible value to log
  return allCandidates[0];
}

/**
 * Build an inline `<script>` that seeds `window.__STATION_CONFIG` so the
 * client-side StationConfigService can read fresh config synchronously
 * during bootstrap — no async API round-trip needed, no DEFAULT_CONFIG flash.
 */
function buildConfigScript(config: StationConfig): string {
  const json = JSON.stringify(config);
  return `<script>window.__STATION_CONFIG=${json};</script>`;
}

/** Build a gradient CSS value from three color stops. */
function gradient(from: string, mid: string, to: string): string {
  return `linear-gradient(135deg, ${from} 0%, ${mid} 40%, ${to} 100%)`;
}

/**
 * Build inline CSS custom properties on `:root` so the first paint carries
 * the correct color scheme — eliminates the color flash that occurs when
 * ThemeService.apply() runs asynchronously after the API call.
 *
 * Includes both flat color properties AND derived gradient variables
 * (--sky-gradient, --sunset-gradient, --mixed-gradient) so components
 * using var() for backgrounds render correctly on the very first paint.
 */
function buildThemeStyle(config: StationConfig): string {
  const props: string[] = [];

  for (const { field, prop } of COLOR_MAP) {
    const value = (config as any)[field];
    if (value && typeof value === 'string') {
      props.push(`${prop}: ${value}`);
    }
  }

  // Derived gradients — mirror the same formulas ThemeService.apply() uses.
  // These must be injected server-side; otherwise components referencing
  // var(--sky-gradient) etc. fall back to their SCSS build-time defaults
  // on first paint, causing a visible color flash.
  const cp = (field: keyof StationConfig): string => (config as any)[field] || '';
  props.push(`--sky-gradient: ${gradient(cp('color_primary_dark'), cp('color_primary'), cp('color_primary_light'))}`);
  props.push(`--sunset-gradient: ${gradient(cp('color_accent_dark'), cp('color_accent'), cp('color_accent_light'))}`);
  props.push(`--mixed-gradient: linear-gradient(135deg, ${cp('color_primary_dark')} 0%, ${cp('color_primary')} 50%, ${cp('color_accent')} 100%)`);

  if (props.length === 0) return '';

  const css = `:root{${props.join(';')}}`;
  return `<style>${css}</style>`;
}

/**
 * Fetch fresh station config from the backend API.
 * This runs server-side — it goes through the nginx proxy chain to the
 * upstream FastAPI backend. On failure we fall back to serving the shell
 * unmodified (client-side fetch picks up the slack).
 */
async function fetchStationConfig(): Promise<StationConfig | null> {
  // SSR_API_BASE_URL points at nginx (localhost:80) which proxies /api/ to
  // the upstream FastAPI backend. This avoids cross-origin issues and reuses
  // the same proxy chain the SSR engine itself would use.
  const baseUrl = process.env['SSR_API_BASE_URL'] || 'http://localhost:80';
  const url = `${baseUrl}/api/station-config`;

  try {
    const client = baseUrl.startsWith('https') ? https : http;
    const data = await new Promise<string>((resolve, reject) => {
      const req = client.get(url, {
        headers: { 'Accept': 'application/json' },
      }, (res) => {
        const chunks: Buffer[] = [];
        res.on('data', (chunk: Buffer) => chunks.push(chunk));
        res.on('end', () => resolve(Buffer.concat(chunks).toString('utf-8')));
        res.on('error', reject);
      });
      req.on('error', reject);
      req.setTimeout(2000, () => { req.destroy(new Error('Station config fetch timed out')); });
    });
    return JSON.parse(data) as StationConfig;
  } catch (err) {
    console.warn(`[SSR] Failed to fetch station config from ${url}: ${err}`);
    return null;
  }
}

/**
 * Serve the CSR app shell, enhanced with fresh station config injected at
 * runtime so the client bootstraps with real data — no DEFAULT_CONFIG flash.
 *
 * Strategy:
 * 1. Read CSR shell HTML from disk
 * 2. Fetch live station config from the backend API
 * 3. Inject window.__STATION_CONFIG as an inline <script> before </head>
 * 4. Inject theme CSS custom properties as an inline <style> before </head>
 * 5. The client-side StationConfigService reads window.__STATION_CONFIG
 *    synchronously on construction — it skips the API call when seeded.
 */
async function serveCsrShell(res: http.ServerResponse): Promise<void> {
  const indexPath = browserIndexPath();

  let html: string;
  try {
    html = fs.readFileSync(indexPath, 'utf-8');
  } catch {
    res.statusCode = 500;
    res.end('Internal server error — index.html not found');
    return;
  }

  // Attempt to fetch fresh config to inject into the shell.
  const config = await fetchStationConfig();

  let enhanced = html;
  if (config) {
    const script = buildConfigScript(config);
    const style = buildThemeStyle(config);
    const injection = `${style}\n${script}`;
    enhanced = html.replace('</head>', `${injection}</head>`);
  }

  res.setHeader('Content-Type', 'text/html; charset=utf-8');
  res.setHeader('X-Render-Mode', 'CSR');
  res.setHeader('Cache-Control', 'no-cache, no-store, must-revalidate');
  res.setHeader('Pragma', 'no-cache');
  res.end(enhanced);
}

const requestHandler = createNodeRequestHandler(async (req, res, next) => {
  try {
    const response = await appEngine.handle(req);

    if (response) {
      await writeResponseToNodeResponse(response, res);
    } else {
      next();
    }
  } catch (error) {
    next(error);
  }
});

if (isMainModule(import.meta.url)) {
  console.log('Node.js SSR server ready');
  const server = http.createServer();
  server.on('request', async (req, res) => {
    try {
      // ── Spider detection gate ──────────────────────────
      // Only search engine spiders get full SSR rendering.
      // Regular users receive the CSR app shell from disk,
      // enhanced with fresh station config injected at runtime.
      const userAgent = getUserAgent(req.headers);
      if (!isSpider(userAgent)) {
        await serveCsrShell(res);
        return;
      }

      // Spider — render full HTML via Angular SSR with live API data
      await requestHandler(req, res, () => {
        res.statusCode = 404;
        res.end('Not Found');
      });
    } catch (error) {
      console.error('SSR error:', error);
      res.statusCode = 500;
      res.end('Internal server error');
    }
  });
  server.listen(4200, () => {
    console.log('SSR server listening on http://localhost:4200');
  });
}

export { requestHandler };