/** Immutable font descriptor shared by clinical and patient document renderers. */
export interface DocumentFont {
  id: string;
  name: string;
  regularSha256: string;
  boldSha256: string | null;
}

const loaded = new Map<string, Promise<string>>();

export function loadDocumentFont(
  font: DocumentFont | null,
  apiBase: string,
): Promise<string> {
  if (!font) return Promise.resolve("");
  const key = `${apiBase}:${font.id}:${font.regularSha256}:${font.boldSha256 ?? ""}`;
  const existing = loaded.get(key);
  if (existing) return existing;
  const family = `Medisign-${font.regularSha256}-${font.boldSha256 ?? "regular"}`;
  const load = async () => {
    const descriptors = [
      { sha: font.regularSha256, weight: "400" },
      { sha: font.boldSha256 ?? font.regularSha256, weight: "700" },
    ];
    const faces = await Promise.all(
      descriptors.map(async ({ sha, weight }) => {
        const url = `${apiBase.replace(/\/$/, "")}/v1/document-fonts/${encodeURIComponent(font.id)}/${sha}.ttf`;
        const response = await fetch(url, {
          signal: AbortSignal.timeout(30000),
        });
        if (!response.ok)
          throw new Error("文书字体加载失败，请重试或联系管理员。");
        const bytes = await response.arrayBuffer();
        // The URL names an immutable digest; verify before registering the face.
        if (globalThis.crypto?.subtle) {
          const digest = await crypto.subtle.digest("SHA-256", bytes);
          const actual = Array.from(new Uint8Array(digest), (byte) =>
            byte.toString(16).padStart(2, "0"),
          ).join("");
          if (actual !== sha) throw new Error("文书字体校验失败。");
        }
        return new FontFace(family, bytes, { weight }).load();
      }),
    );
    for (const face of faces) document.fonts.add(face);
    return `"${family}"`;
  };
  const promise = load().catch((error: unknown) => {
    loaded.delete(key);
    throw error;
  });
  loaded.set(key, promise);
  return promise;
}