import { renderFull } from "@/lib/image-pipeline/bridge";
import {
  renderPreview,
  type PreviewRenderResult,
} from "@/lib/image-pipeline/preview-renderer";
import type { PipelineStep } from "@/lib/image-pipeline/contracts";
import type { HistogramData } from "@/lib/image-pipeline/histogram";
import type { RenderFullOptions, RenderFullResult } from "@/lib/image-pipeline/render-types";

export type { PreviewRenderResult };

type PreviewWorkerPayload = {
  sourceUrl: string;
  steps: readonly PipelineStep[];
  previewWidth: number;
};

type WorkerRequestMessage =
  | {
      kind: "preview";
      requestId: number;
      payload: PreviewWorkerPayload;
    }
  | {
      kind: "full";
      requestId: number;
      payload: RenderFullOptions;
    }
  | {
      kind: "cancel";
      requestId: number;
    };

type WorkerResultPreviewPayload = {
  width: number;
  height: number;
  histogram: HistogramData;
  pixels: ArrayBuffer;
};

type WorkerResponseMessage =
  | {
      kind: "preview-result";
      requestId: number;
      payload: WorkerResultPreviewPayload;
    }
  | {
      kind: "full-result";
      requestId: number;
      payload: RenderFullResult;
    }
  | {
      kind: "error";
      requestId: number;
      payload: {
        name: string;
        message: string;
      };
    };

class WorkerUnavailableError extends Error {
  constructor(causeMessage?: string) {
    super(causeMessage ?? "Image pipeline worker is unavailable.");
    this.name = "WorkerUnavailableError";
  }
}

type PendingRequest = {
  kind: "preview" | "full";
  resolve: (value: PreviewRenderResult | RenderFullResult) => void;
  reject: (reason?: unknown) => void;
};

let workerInstance: Worker | null = null;
let workerInitError: Error | null = null;
let requestIdCounter = 0;
const pendingRequests = new Map<number, PendingRequest>();

function nextRequestId(): number {
  requestIdCounter += 1;
  return requestIdCounter;
}

function makeAbortError(): DOMException {
  return new DOMException("The operation was aborted.", "AbortError");
}

function isAbortError(error: unknown): boolean {
  if (error instanceof DOMException && error.name === "AbortError") {
    return true;
  }

  if (error instanceof Error && error.name === "AbortError") {
    return true;
  }

  return false;
}

function handleWorkerFailure(error: Error): void {
  workerInitError = error;

  if (workerInstance) {
    workerInstance.terminate();
    workerInstance = null;
  }

  for (const [requestId, pending] of pendingRequests.entries()) {
    pending.reject(error);
    pendingRequests.delete(requestId);
  }
}

function getWorker(): Worker {
  if (typeof window === "undefined" || typeof Worker === "undefined") {
    throw new WorkerUnavailableError("Worker API is not available.");
  }

  if (workerInitError) {
    throw new WorkerUnavailableError(workerInitError.message);
  }

  if (workerInstance) {
    return workerInstance;
  }

  try {
    const created = new Worker(new URL("./image-pipeline.worker.ts", import.meta.url), {
      type: "module",
    });

    created.onmessage = (event: MessageEvent<WorkerResponseMessage>) => {
      const message = event.data;
      const pending = pendingRequests.get(message.requestId);
      if (!pending) {
        return;
      }

      pendingRequests.delete(message.requestId);

      if (message.kind === "error") {
        const workerError = new Error(message.payload.message);
        workerError.name = message.payload.name;
        pending.reject(workerError);
        return;
      }

      if (pending.kind === "preview" && message.kind === "preview-result") {
        const pixels = new Uint8ClampedArray(message.payload.pixels);
        pending.resolve({
          width: message.payload.width,
          height: message.payload.height,
          imageData: new ImageData(pixels, message.payload.width, message.payload.height),
          histogram: message.payload.histogram,
        });
        return;
      }

      if (pending.kind === "full" && message.kind === "full-result") {
        pending.resolve(message.payload);
        return;
      }

      pending.reject(new Error("Image pipeline worker response type mismatch."));
    };

    created.onerror = () => {
      handleWorkerFailure(new Error("Image pipeline worker crashed."));
    };

    created.onmessageerror = () => {
      handleWorkerFailure(new Error("Image pipeline worker message deserialization failed."));
    };

    workerInstance = created;
    return created;
  } catch (error: unknown) {
    const normalized = error instanceof Error ? error : new Error("Worker initialization failed.");
    workerInitError = normalized;
    throw new WorkerUnavailableError(normalized.message);
  }
}

function runWorkerRequest<TResponse extends PreviewRenderResult | RenderFullResult>(args: {
  kind: "preview" | "full";
  payload: PreviewWorkerPayload | RenderFullOptions;
  signal?: AbortSignal;
}): Promise<TResponse> {
  if (args.signal?.aborted) {
    return Promise.reject(makeAbortError());
  }

  const worker = getWorker();
  const requestId = nextRequestId();

  return new Promise<TResponse>((resolve, reject) => {
    let isSettled = false;
    const settleOnce = (callback: () => void): void => {
      if (isSettled) {
        return;
      }

      isSettled = true;
      callback();
    };

    const abortHandler = () => {
      settleOnce(() => {
        pendingRequests.delete(requestId);
        worker.postMessage({ kind: "cancel", requestId } satisfies WorkerRequestMessage);
        reject(makeAbortError());
      });
    };

    if (args.signal) {
      args.signal.addEventListener("abort", abortHandler, { once: true });
    }

    const wrappedResolve = (value: TResponse) => {
      settleOnce(() => {
        if (args.signal) {
          args.signal.removeEventListener("abort", abortHandler);
        }
        resolve(value);
      });
    };

    const wrappedReject = (error: unknown) => {
      settleOnce(() => {
        if (args.signal) {
          args.signal.removeEventListener("abort", abortHandler);
        }
        reject(error);
      });
    };

    pendingRequests.set(requestId, {
      kind: args.kind,
      resolve: wrappedResolve as PendingRequest["resolve"],
      reject: wrappedReject,
    });

    if (args.kind === "preview") {
      worker.postMessage({
        kind: "preview",
        requestId,
        payload: args.payload as PreviewWorkerPayload,
      } satisfies WorkerRequestMessage);
      return;
    }

    worker.postMessage({
      kind: "full",
      requestId,
      payload: args.payload as RenderFullOptions,
    } satisfies WorkerRequestMessage);
  });
}

export async function renderPreviewWithWorkerFallback(options: {
  sourceUrl: string;
  steps: readonly PipelineStep[];
  previewWidth: number;
  signal?: AbortSignal;
}): Promise<PreviewRenderResult> {
  try {
    return await runWorkerRequest<PreviewRenderResult>({
      kind: "preview",
      payload: {
        sourceUrl: options.sourceUrl,
        steps: options.steps,
        previewWidth: options.previewWidth,
      },
      signal: options.signal,
    });
  } catch (error: unknown) {
    if (isAbortError(error)) {
      throw error;
    }

    return await renderPreview(options);
  }
}

export async function renderFullWithWorkerFallback(
  options: RenderFullOptions,
): Promise<RenderFullResult> {
  try {
    return await runWorkerRequest<RenderFullResult>({
      kind: "full",
      payload: options,
      signal: options.signal,
    });
  } catch (error: unknown) {
    if (isAbortError(error)) {
      throw error;
    }

    return await renderFull(options);
  }
}

export function isPipelineAbortError(error: unknown): boolean {
  return isAbortError(error);
}