import type { LoadProgress } from "./shared/types";

const CACHE = "laya-webgpu-v1";

async function sha256(bytes: ArrayBuffer): Promise<string> {
  const hash = await crypto.subtle.digest("SHA-256", bytes);
  return [...new Uint8Array(hash)].map((part) => part.toString(16).padStart(2, "0")).join("");
}

export async function fetchVerified(
  url: string,
  expectedHash?: string,
  onProgress?: (progress: LoadProgress) => void,
  signal?: AbortSignal,
): Promise<ArrayBuffer> {
  const cache = "caches" in globalThis ? await caches.open(CACHE).catch(() => undefined) : undefined;
  const cached = await cache?.match(url).catch(() => undefined);
  if (cached) {
    const bytes = await cached.arrayBuffer();
    if (!expectedHash || await sha256(bytes) === expectedHash.toLowerCase()) return bytes;
    await cache?.delete(url).catch(() => false);
  }

  const response = await fetch(url, { signal });
  if (!response.ok) throw new Error(`Download failed (${response.status}) for ${url}`);
  const total = Number(response.headers.get("content-length")) || undefined;
  if (!response.body) {
    const bytes = await response.arrayBuffer();
    if (expectedHash && await sha256(bytes) !== expectedHash.toLowerCase()) throw new Error(`SHA-256 mismatch for ${url}`);
    return bytes;
  }
  const reader = response.body.getReader();
  const chunks: Uint8Array[] = [];
  let loaded = 0;
  while (true) {
    const { done, value } = await reader.read();
    if (done) break;
    chunks.push(value);
    loaded += value.byteLength;
    onProgress?.({ phase: "model", loaded, total, detail: url });
  }
  const joined = new Uint8Array(loaded);
  let offset = 0;
  for (const chunk of chunks) { joined.set(chunk, offset); offset += chunk.length; }
  if (expectedHash && await sha256(joined.buffer) !== expectedHash.toLowerCase()) throw new Error(`SHA-256 mismatch for ${url}`);
  await cache?.put(url, new Response(joined, { headers: response.headers })).catch(() => undefined);
  return joined.buffer;
}

export async function clearModelCache(): Promise<void> {
  if ("caches" in globalThis) await caches.delete(CACHE);
}