import type { WebEngineVariantV2 } from "../../../protocol/manifest";
import type {
  EngineVariantResourceState,
  EngineVariantSession,
} from "./engine-variant-bootstrap";
import { EngineVariantLoadError } from "./engine-variant-bootstrap";

interface EmscriptenPThreadRuntime {
  unusedWorkers: Worker[];
  runningWorkers: Worker[];
  terminateAllThreads(): void;
}

interface BrowserVariantModule {
  HEAPU8: Uint8Array;
  _malloc(size: number): number;
  _free(pointer: number): void;
  _web_engine_create(): number;
  _web_engine_destroy(handle: number): void;
  _web_engine_get_live_handles(): number;
  _web_engine_open_blend(handle: number, data: number, length: number): number;
  PThread?: EmscriptenPThreadRuntime;
}

type BrowserVariantFactory = (options: { wasmBinary: ArrayBuffer }) => Promise<BrowserVariantModule>;

async function verifiedBytes(url: string, expectedSha256: string, controllers: Set<AbortController>): Promise<ArrayBuffer> {
  const controller = new AbortController();
  controllers.add(controller);
  try {
    const response = await fetch(url, { cache: "no-store", signal: controller.signal });
    if (!response.ok) {
      throw new EngineVariantLoadError(
        "ENGINE_VARIANT_RESOURCE_REQUEST_FAILED",
        `${url} returned ${response.status}`,
      );
    }
    const bytes = await response.arrayBuffer();
    const digest = await crypto.subtle.digest("SHA-256", bytes);
    const actual = [...new Uint8Array(digest)]
      .map((byte) => byte.toString(16).padStart(2, "0"))
      .join("");
    if (actual !== expectedSha256) {
      throw new EngineVariantLoadError("ENGINE_VARIANT_RESOURCE_HASH_MISMATCH", url);
    }
    return bytes;
  }
  finally {
    controllers.delete(controller);
  }
}

class BrowserEngineVariantSession implements EngineVariantSession<ArrayBuffer> {
  readonly variant: WebEngineVariantV2;
  private readonly module: BrowserVariantModule;
  private readonly pendingRequests: Set<AbortController>;
  private readonly timers = new Set<ReturnType<typeof setTimeout>>();
  private handle: number;

  constructor(
    variant: WebEngineVariantV2,
    module: BrowserVariantModule,
    handle: number,
    pendingRequests: Set<AbortController>,
  ) {
    this.variant = variant;
    this.module = module;
    this.handle = handle;
    this.pendingRequests = pendingRequests;
  }

  async openProject(project: ArrayBuffer): Promise<void> {
    if (this.handle <= 0) throw new Error("ENGINE_VARIANT_SESSION_DISPOSED");
    const pointer = this.module._malloc(project.byteLength);
    if (project.byteLength > 0 && pointer <= 0) throw new Error("ENGINE_VARIANT_PROJECT_ALLOCATION_FAILED");
    try {
      if (project.byteLength > 0) this.module.HEAPU8.set(new Uint8Array(project), pointer);
      const result = this.module._web_engine_open_blend(this.handle, pointer, project.byteLength);
      if (result !== 0) throw new Error(`ENGINE_VARIANT_PROJECT_OPEN_FAILED: ${result}`);
    }
    finally {
      if (pointer > 0) this.module._free(pointer);
    }
  }

  resourceState(): EngineVariantResourceState {
    const pthread = this.module.PThread;
    return {
      handles: this.handle > 0 ? this.module._web_engine_get_live_handles() : 0,
      workers: pthread ? pthread.unusedWorkers.length + pthread.runningWorkers.length : 0,
      timers: this.timers.size,
      pendingRequests: this.pendingRequests.size,
    };
  }

  testOnlySeedTrackedResources(): void {
    this.pendingRequests.add(new AbortController());
    const timer = setTimeout(() => this.timers.delete(timer), 60_000);
    this.timers.add(timer);
  }

  async dispose(): Promise<EngineVariantResourceState> {
    for (const controller of this.pendingRequests) controller.abort();
    this.pendingRequests.clear();
    for (const timer of this.timers) clearTimeout(timer);
    this.timers.clear();
    if (this.handle > 0) {
      this.module._web_engine_destroy(this.handle);
      this.handle = 0;
    }
    this.module.PThread?.terminateAllThreads();
    return this.resourceState();
  }
}

export async function createBrowserEngineVariantSession(
  variant: WebEngineVariantV2,
): Promise<EngineVariantSession<ArrayBuffer>> {
  const controllers = new Set<AbortController>();
  const verifiedResources = new Map<string, ArrayBuffer>();
  const verify = async (resource: { url: string; sha256: string }): Promise<ArrayBuffer> => {
    const existing = verifiedResources.get(resource.url);
    if (existing) return existing;
    const bytes = await verifiedBytes(resource.url, resource.sha256, controllers);
    verifiedResources.set(resource.url, bytes);
    return bytes;
  };
  await verify(variant.resources.js);
  const wasmBinary = await verify(variant.resources.wasm);
  if (variant.id === "pthread") await verify(variant.resources.pthreadWorker);
  const imported = await import(/* @vite-ignore */ variant.resources.js.url) as { default: BrowserVariantFactory };
  const module = await imported.default({ wasmBinary });
  const handle = module._web_engine_create();
  if (handle <= 0) {
    module.PThread?.terminateAllThreads();
    throw new Error("ENGINE_VARIANT_HANDLE_CREATION_FAILED");
  }
  return new BrowserEngineVariantSession(variant, module, handle, controllers);
}