import { err, type Result } from "../types/result.ts";

export function debounce<T extends (...args: Parameters<T>) => void>(
  fn: T,
  ms: number,
): T & { cancel: () => void } {
  let timeoutId: ReturnType<typeof setTimeout> | null = null;

  const debounced = ((...args: Parameters<T>) => {
    if (timeoutId) clearTimeout(timeoutId);
    timeoutId = setTimeout(() => {
      fn(...args);
      timeoutId = null;
    }, ms);
  }) as T & { cancel: () => void };

  debounced.cancel = () => {
    if (timeoutId) {
      clearTimeout(timeoutId);
      timeoutId = null;
    }
  };

  return debounced;
}

export function throttle<T extends (...args: Parameters<T>) => void>(
  fn: T,
  ms: number,
): T {
  let lastCall = 0;
  let timeoutId: ReturnType<typeof setTimeout> | null = null;

  return ((...args: Parameters<T>) => {
    const now = Date.now();
    const remaining = ms - (now - lastCall);

    if (remaining <= 0) {
      if (timeoutId) {
        clearTimeout(timeoutId);
        timeoutId = null;
      }
      lastCall = now;
      fn(...args);
    } else if (!timeoutId) {
      timeoutId = setTimeout(() => {
        lastCall = Date.now();
        timeoutId = null;
        fn(...args);
      }, remaining);
    }
  }) as T;
}

export function sleep(ms: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

export async function retry<T>(
  fn: () => Promise<T>,
  options: {
    attempts?: number;
    delay?: number;
    backoff?: number;
    shouldRetry?: (error: unknown, attempt: number) => boolean;
  } = {},
): Promise<T> {
  const {
    attempts = 3,
    delay = 1000,
    backoff = 2,
    shouldRetry = () => true,
  } = options;

  let lastError: unknown;
  let currentDelay = delay;

  for (let attempt = 1; attempt <= attempts; attempt++) {
    try {
      return await fn();
    } catch (error) {
      lastError = error;
      if (attempt === attempts || !shouldRetry(error, attempt)) {
        throw error;
      }
      await sleep(currentDelay);
      currentDelay *= backoff;
    }
  }

  throw lastError;
}

export async function retryResult<T, E>(
  fn: () => Promise<Result<T, E>>,
  options: {
    attempts?: number;
    delay?: number;
    backoff?: number;
    shouldRetry?: (error: E, attempt: number) => boolean;
  } = {},
): Promise<Result<T, E>> {
  const {
    attempts = 3,
    delay = 1000,
    backoff = 2,
    shouldRetry = () => true,
  } = options;

  let lastResult: Result<T, E> | null = null;
  let currentDelay = delay;

  for (let attempt = 1; attempt <= attempts; attempt++) {
    const result = await fn();
    lastResult = result;

    if (result.ok) {
      return result;
    }

    if (attempt === attempts || !shouldRetry(result.error, attempt)) {
      return result;
    }

    await sleep(currentDelay);
    currentDelay *= backoff;
  }

  return lastResult!;
}

export function timeout<T>(promise: Promise<T>, ms: number): Promise<T> {
  return new Promise((resolve, reject) => {
    const timeoutId = setTimeout(() => {
      reject(new Error(`Timeout after ${ms}ms`));
    }, ms);

    promise
      .then((value) => {
        clearTimeout(timeoutId);
        resolve(value);
      })
      .catch((error) => {
        clearTimeout(timeoutId);
        reject(error);
      });
  });
}

export async function timeoutResult<T>(
  promise: Promise<Result<T, Error>>,
  ms: number,
): Promise<Result<T, Error>> {
  try {
    return await timeout(promise, ms);
  } catch (e) {
    return err(e instanceof Error ? e : new Error(String(e)));
  }
}

export async function parallel<T>(
  tasks: (() => Promise<T>)[],
  concurrency: number,
): Promise<T[]> {
  const results: T[] = [];
  const executing: Promise<void>[] = [];

  for (const task of tasks) {
    const p = task().then((result) => {
      results.push(result);
    });

    executing.push(p);

    if (executing.length >= concurrency) {
      await Promise.race(executing);
      executing.splice(
        executing.findIndex((e) => e === p),
        1,
      );
    }
  }

  await Promise.all(executing);
  return results;
}

export async function mapParallel<T, U>(
  items: T[],
  fn: (item: T, index: number) => Promise<U>,
  concurrency: number,
): Promise<U[]> {
  const results: U[] = new Array(items.length);
  const executing: Promise<void>[] = [];

  for (let i = 0; i < items.length; i++) {
    const index = i;
    const p = fn(items[index], index).then((result) => {
      results[index] = result;
    });

    executing.push(p);

    if (executing.length >= concurrency) {
      await Promise.race(executing);
      const doneIndex = executing.findIndex(
        (e) => (e as Promise<void> & { _done?: boolean })._done !== false,
      );
      if (doneIndex >= 0) {
        executing.splice(doneIndex, 1);
      }
    }
  }

  await Promise.all(executing);
  return results;
}

export function createAbortable<T>(
  fn: (signal: AbortSignal) => Promise<T>,
): { promise: Promise<T>; abort: () => void } {
  const controller = new AbortController();
  return {
    promise: fn(controller.signal),
    abort: () => controller.abort(),
  };
}

export interface Deferred<T> {
  promise: Promise<T>;
  resolve: (value: T) => void;
  reject: (error: unknown) => void;
}

export function deferred<T>(): Deferred<T> {
  let resolve!: (value: T) => void;
  let reject!: (error: unknown) => void;

  const promise = new Promise<T>((res, rej) => {
    resolve = res;
    reject = rej;
  });

  return { promise, resolve, reject };
}