/**
 * Fetches product images for invoice line items and returns them as
 * `data:` URLs ready to embed in the PDF.
 *
 * Uses a simple in-process LRU-ish Map keyed by URL. Images are typically
 * served from Shopify's CDN so re-fetching is cheap, but caching avoids
 * hammering the network when regenerating an invoice multiple times.
 */
const MAX_BYTES = 2 * 1024 * 1024; // 2 MB cap per image
const CACHE_MAX_ENTRIES = 200;

const cache = new Map<string, string>(); // url -> data URL

function rememberInCache(url: string, dataUrl: string) {
  if (cache.size >= CACHE_MAX_ENTRIES) {
    // Drop the oldest entry (Map preserves insertion order).
    const oldest = cache.keys().next().value;
    if (oldest) cache.delete(oldest);
  }
  cache.set(url, dataUrl);
}

function guessContentType(url: string, headerCt: string | null): string {
  if (headerCt && headerCt.startsWith("image/")) return headerCt;
  const lower = url.toLowerCase();
  if (lower.includes(".jpg") || lower.includes(".jpeg")) return "image/jpeg";
  if (lower.includes(".webp")) return "image/webp";
  if (lower.includes(".gif")) return "image/gif";
  return "image/png";
}

export async function fetchProductImageDataUrl(url: string): Promise<string | undefined> {
  if (!url) return undefined;
  const hit = cache.get(url);
  if (hit) return hit;

  // Request a small Shopify CDN variant when possible to keep the PDF lean.
  // Shopify image URLs accept a `width=` query param; fall back to the original URL.
  const requestUrl = url.includes("cdn.shopify.com") && !/[?&](width|height|crop)=/.test(url)
    ? `${url}${url.includes("?") ? "&" : "?"}width=128`
    : url;

  let res: Response;
  try {
    res = await fetch(requestUrl);
  } catch (err) {
    console.warn(`Product image fetch failed for ${url}:`, err);
    return undefined;
  }
  if (!res.ok) {
    console.warn(`Product image HTTP ${res.status} for ${url}`);
    return undefined;
  }
  const buf = await res.arrayBuffer();
  if (buf.byteLength === 0 || buf.byteLength > MAX_BYTES) return undefined;

  const contentType = guessContentType(url, res.headers.get("content-type"));
  // @react-pdf supports png/jpeg natively; webp/gif are unreliable. Skip those.
  if (contentType !== "image/png" && contentType !== "image/jpeg") return undefined;

  const b64 = Buffer.from(buf).toString("base64");
  const dataUrl = `data:${contentType};base64,${b64}`;
  rememberInCache(url, dataUrl);
  return dataUrl;
}

/**
 * Resolves images for every line in parallel, mutating `imageDataUrl` in place.
 * Failures are swallowed (the row simply renders without an icon).
 */
export async function attachLineItemImages(
  lines: { imageUrl?: string; imageDataUrl?: string }[],
): Promise<void> {
  await Promise.all(
    lines.map(async (line) => {
      if (!line.imageUrl) return;
      const dataUrl = await fetchProductImageDataUrl(line.imageUrl);
      if (dataUrl) line.imageDataUrl = dataUrl;
    }),
  );
}