/**
 * Server-only Bild-Helfer: Asset-Meta vom CMS, Blurhash-LQIP, Responsive-Srcset.
 * Nur in `+page.server.ts` / `+layout.server.ts` importieren — nutzt sharp + blurhash.
 */

import { env } from '$env/dynamic/public';
import {
  getCmsImageUrl,
  type RustyImageTransformParams,
  type CmsImageField,
} from './rusty-image';

function getCmsBaseUrl(): string {
  return (env.PUBLIC_CMS_URL || 'http://localhost:3000').replace(/\/$/, '');
}

export interface AssetMeta {
  width: number;
  height: number;
  hasAlpha: boolean;
  mimeType: string;
  blurhash?: string;
}

const metaCache = new Map<string, Promise<AssetMeta | null>>();

function toMetaEndpoint(url: string): string | null {
  try {
    const u = new URL(url);
    const base = getCmsBaseUrl();
    const baseHost = new URL(base).host;
    if (u.host !== baseHost && !/^127\.0\.0\.1|localhost/.test(u.host)) {
      return null;
    }
    u.searchParams.set('meta', 'true');
    return `${base}${u.pathname}${u.search}`;
  } catch {
    return null;
  }
}

/**
 * Holt AssetInfo vom CMS: `/api/assets/<path>?meta=true`.
 * Cached per URL für die Prozess-Lebensdauer.
 */
export async function fetchAssetMeta(url: string): Promise<AssetMeta | null> {
  const endpoint = toMetaEndpoint(url);
  if (!endpoint) return null;
  const cached = metaCache.get(endpoint);
  if (cached) return cached;
  const p = (async () => {
    try {
      const res = await fetch(endpoint);
      if (!res.ok) return null;
      const json = (await res.json()) as {
        width?: number;
        height?: number;
        has_alpha?: boolean;
        mime_type?: string;
        blurhash?: string;
      };
      if (
        typeof json?.width !== 'number' ||
        typeof json?.height !== 'number' ||
        json.width <= 0 ||
        json.height <= 0
      ) {
        return null;
      }
      return {
        width: json.width,
        height: json.height,
        hasAlpha: Boolean(json.has_alpha),
        mimeType: json.mime_type ?? 'image/jpeg',
        ...(typeof json.blurhash === 'string' && json.blurhash.trim()
          ? { blurhash: json.blurhash }
          : {}),
      } satisfies AssetMeta;
    } catch {
      return null;
    }
  })();
  metaCache.set(endpoint, p);
  return p;
}

const blurhashCache = new Map<string, Promise<string | null>>();

/**
 * Dekodiert Blurhash → 32×32 RGBA → JPEG Q40 → base64 data-URL.
 * Liefert kompakten LQIP (~300–500 B) für CSS-`background-image`.
 */
export async function blurhashToDataUrl(
  hash: string,
  width = 32,
  height = 32,
): Promise<string | null> {
  const key = `${hash}|${width}x${height}`;
  const cached = blurhashCache.get(key);
  if (cached) return cached;
  const p = (async () => {
    try {
      const [{ decode }, sharpMod] = await Promise.all([
        import('blurhash'),
        import('sharp'),
      ]);
      const pixels = decode(hash, width, height);
      const sharp = sharpMod.default;
      const jpeg = await sharp(Buffer.from(pixels), {
        raw: { width, height, channels: 4 },
      })
        .jpeg({ quality: 40 })
        .toBuffer();
      return `data:image/jpeg;base64,${jpeg.toString('base64')}`;
    } catch {
      return null;
    }
  })();
  blurhashCache.set(key, p);
  return p;
}

export interface ResponsiveImage {
  sources: { type: string; srcset: string }[];
  fallback: string;
  width: number;
  height: number;
  widths: number[];
  lqip?: string;
}

export interface ResponsiveImageOptions {
  widths?: number[];
  ar?: string;
  fit?: RustyImageTransformParams['fit'];
  formats?: Array<'avif' | 'webp' | 'jpeg'>;
  quality?: number;
  focal?: CmsImageField['focal'];
  lqip?: boolean;
}

const DEFAULT_WIDTHS = [640, 960, 1280, 1600, 1920, 2400];
const DEFAULT_FORMATS: Array<'avif' | 'webp' | 'jpeg'> = ['webp', 'jpeg'];
const MIME_FOR_FORMAT: Record<'avif' | 'webp' | 'jpeg', string> = {
  avif: 'image/avif',
  webp: 'image/webp',
  jpeg: 'image/jpeg',
};

function parseAr(ar: string | undefined): number | null {
  if (!ar) return null;
  const m = ar.match(/^(\d+(?:\.\d+)?)\s*[/:x]\s*(\d+(?:\.\d+)?)$/);
  if (!m) return null;
  const w = Number(m[1]);
  const h = Number(m[2]);
  if (!Number.isFinite(w) || !Number.isFinite(h) || w <= 0 || h <= 0) return null;
  return w / h;
}

/**
 * Baut `<picture>`-Daten (AVIF/WebP/JPEG srcset + Fallback + LQIP).
 * Breiten werden gegen die echte Bildbreite aus `fetchAssetMeta` geclampt (kein Upscaling).
 * Alle URLs zeigen auf `/cms-images?…` (erst bei Client-Request wird gerendert & gecached).
 */
export async function buildResponsiveImage(
  url: string,
  opts: ResponsiveImageOptions = {},
): Promise<ResponsiveImage | null> {
  const meta = await fetchAssetMeta(url);

  const widthsRaw = (opts.widths ?? DEFAULT_WIDTHS).filter((w) => Number.isFinite(w) && w > 0);
  if (widthsRaw.length === 0) return null;

  const maxW = meta?.width ?? Math.max(...widthsRaw);
  const widths = [...new Set(widthsRaw.map((w) => Math.min(w, maxW)).filter((w) => w > 0))].sort(
    (a, b) => a - b,
  );
  if (widths.length === 0) return null;

  const ar =
    parseAr(opts.ar) ??
    (meta?.width && meta?.height ? meta.width / meta.height : null);

  const formats = opts.formats ?? DEFAULT_FORMATS;
  const fit = opts.fit ?? 'cover';
  const quality = opts.quality ?? 78;

  const baseParams: RustyImageTransformParams = {
    fit,
    quality,
    ...(opts.ar ? { ar: opts.ar } : {}),
    ...(opts.focal
      ? { focalX: opts.focal.x, focalY: opts.focal.y }
      : {}),
  };

  const sources = formats.map((fmt) => {
    const srcset = widths
      .map((w) => {
        const u = getCmsImageUrl(url, { ...baseParams, width: w, format: fmt });
        return `${u} ${w}w`;
      })
      .join(', ');
    return { type: MIME_FOR_FORMAT[fmt], srcset };
  });

  const fallbackWidth = widths[widths.length - 1] ?? maxW;
  const fallbackFormat: 'jpeg' | 'webp' = formats.includes('jpeg') ? 'jpeg' : 'webp';
  const fallback = getCmsImageUrl(url, {
    ...baseParams,
    width: fallbackWidth,
    format: fallbackFormat,
  });

  const width = fallbackWidth;
  const height = ar ? Math.round(width / ar) : meta?.height ?? Math.round(width * 0.5625);

  const lqip =
    opts.lqip !== false && meta?.blurhash
      ? ((await blurhashToDataUrl(meta.blurhash)) ?? undefined)
      : undefined;

  return {
    sources,
    fallback,
    width,
    height,
    widths,
    ...(lqip ? { lqip } : {}),
  };
}

/**
 * Fire-and-forget Cache-Warmup: alle srcset-Varianten + Fallback parallel anrequesten.
 * Nutzt SvelteKit's `event.fetch` für Self-Calls (keine echten HTTP-Roundtrips in Prod-SSR).
 * Blockiert den Response NICHT — läuft im Hintergrund weiter.
 */
export function warmResponsiveImage(
  responsive: ResponsiveImage | null,
  fetchFn: typeof fetch,
): void {
  if (!responsive) return;
  const urls = new Set<string>();
  urls.add(responsive.fallback);
  for (const s of responsive.sources) {
    for (const entry of s.srcset.split(',')) {
      const url = entry.trim().split(/\s+/)[0];
      if (url) urls.add(url);
    }
  }
  for (const u of urls) {
    void fetchFn(u).catch(() => {});
  }
}

/**
 * Fire-and-forget Warmup für PostCard-Bilder (Grid: 400px base, 2x density, webp+jpeg).
 * Spiegelt die URLs, die <RustyImage width={400} aspect="3/2"/> zur Laufzeit anfragt.
 */
export function warmPostCardImages(
  posts: Array<{ _rawImageUrl?: string; _imageFocal?: { x: number; y: number } | null }>,
  fetchFn: typeof fetch,
  limit = 6,
): void {
  const widths = [400, 800];
  const formats: Array<'webp' | 'jpeg'> = ['webp', 'jpeg'];
  for (const post of posts.slice(0, limit)) {
    const raw = post._rawImageUrl;
    if (!raw) continue;
    const focal = post._imageFocal ?? undefined;
    for (const w of widths) {
      for (const format of formats) {
        const url = getCmsImageUrl(raw, {
          width: w,
          height: Math.round((w / 3) * 2),
          fit: 'cover',
          format,
          quality: 75,
          ar: '3/2',
          ...(focal ? { focalX: focal.x, focalY: focal.y } : {}),
        });
        void fetchFn(url).catch(() => {});
      }
    }
  }
}