import { useEffect, useMemo, useState } from 'react'
import { AsyncBatcher } from '@tanstack/pacer/async-batcher'
import { shallow, useSelector } from '@tanstack/react-store'
import { useDefaultPacerOptions } from '../provider/PacerProvider'
import type {
  AsyncBatcherOptions,
  AsyncBatcherState,
} from '@tanstack/pacer/async-batcher'
import type { Store } from '@tanstack/react-store'
import type { FunctionComponent, ReactNode } from 'react'

export interface ReactAsyncBatcherOptions<
  TValue,
  TSelected = {},
> extends AsyncBatcherOptions<TValue> {
  /**
   * Optional callback invoked when the component unmounts. Receives the batcher instance.
   * When provided, replaces the default cleanup (cancel + abort); use it to call flush(), reset(), cancel(), add logging, etc.
   */
  onUnmount?: (batcher: ReactAsyncBatcher<TValue, TSelected>) => void
}

export interface ReactAsyncBatcher<TValue, TSelected = {}> extends Omit<
  AsyncBatcher<TValue>,
  'store'
> {
  /**
   * A React HOC (Higher Order Component) that allows you to subscribe to the batcher state.
   *
   * This is useful for opting into state re-renders for specific parts of the batcher state
   * deep in your component tree without needing to pass a selector to the hook.
   *
   * @example
   * <batcher.Subscribe selector={(state) => ({ size: state.size, isExecuting: state.isExecuting })}>
   *   {({ size, isExecuting }) => (
   *     <div>Batch: {size} items, {isExecuting ? 'Processing' : 'Ready'}</div>
   *   )}
   * </batcher.Subscribe>
   */
  Subscribe: <TSelected>(props: {
    selector: (state: AsyncBatcherState<TValue>) => TSelected
    children: ((state: TSelected) => ReactNode) | ReactNode
  }) => ReturnType<FunctionComponent>
  /**
   * Reactive state that will be updated and re-rendered when the batcher state changes
   *
   * Use this instead of `batcher.store.state`
   */
  readonly state: Readonly<TSelected>
  /**
   * @deprecated Use `batcher.state` instead of `batcher.store.state` if you want to read reactive state.
   * The state on the store object is not reactive, as it has not been wrapped in a `useSelector` hook internally.
   * Although, you can make the state reactive by using the `useSelector` in your own usage.
   */
  readonly store: Store<Readonly<AsyncBatcherState<TValue>>>
}

/**
 * A React hook that creates an `AsyncBatcher` instance for managing asynchronous batches of items.
 *
 * This is the async version of the useBatcher hook. Unlike the sync version, this async batcher:
 * - Handles promises and returns results from batch executions
 * - Provides error handling with configurable error behavior
 * - Tracks success, error, and settle counts separately
 * - Has state tracking for when batches are executing
 * - Returns the result of the batch function execution
 *
 * Features:
 * - Configurable batch size and wait time
 * - Custom batch processing logic via getShouldExecute
 * - Event callbacks for monitoring batch operations
 * - Error handling for failed batch operations
 * - Automatic or manual batch processing
 *
 * The batcher collects items and processes them in batches based on:
 * - Maximum batch size (number of items per batch)
 * - Time-based batching (process after X milliseconds)
 * - Custom batch processing logic via getShouldExecute
 *
 * Error Handling:
 * - If an `onError` handler is provided, it will be called with the error and batcher instance
 * - If `throwOnError` is true (default when no onError handler is provided), the error will be thrown
 * - If `throwOnError` is false (default when onError handler is provided), the error will be swallowed
 * - Both onError and throwOnError can be used together - the handler will be called before any error is thrown
 * - The error state can be checked using the underlying AsyncBatcher instance
 *
 * ## State Management and Selector
 *
 * The hook uses TanStack Store for reactive state management. You can subscribe to state changes
 * in two ways:
 *
 * **1. Using `batcher.Subscribe` HOC (Recommended for component tree subscriptions)**
 *
 * Use the `Subscribe` HOC to subscribe to state changes deep in your component tree without
 * needing to pass a selector to the hook. This is ideal when you want to subscribe to state
 * in child components.
 *
 * **2. Using the `selector` parameter (For hook-level subscriptions)**
 *
 * The `selector` parameter allows you to specify which state changes will trigger a re-render
 * at the hook level, optimizing performance by preventing unnecessary re-renders when irrelevant
 * state changes occur.
 *
 * **By default, there will be no reactive state subscriptions** and you must opt-in to state
 * tracking by providing a selector function or using the `Subscribe` HOC. This prevents unnecessary
 * re-renders and gives you full control over when your component updates.
 *
 * Available state properties:
 * - `errorCount`: Number of batch executions that have resulted in errors
 * - `failedItems`: Array of items that failed during batch processing
 * - `isEmpty`: Whether the batcher has no items to process
 * - `isExecuting`: Whether a batch is currently being processed asynchronously
 * - `isPending`: Whether the batcher is waiting for the timeout to trigger batch processing
 * - `isRunning`: Whether the batcher is active and will process items automatically
 * - `items`: Array of items currently queued for batch processing
 * - `lastResult`: The result from the most recent batch execution
 * - `settleCount`: Number of batch executions that have completed (success or error)
 * - `size`: Number of items currently in the batch queue
 * - `status`: Current processing status ('idle' | 'pending' | 'executing' | 'populated')
 * - `successCount`: Number of batch executions that have completed successfully
 * - `totalItemsProcessed`: Total number of items processed across all batches
 * - `totalItemsFailed`: Total number of items that have failed processing
 *
 * ## Unmount behavior
 *
 * By default, the hook cancels any pending batch and aborts any in-flight execution when the component unmounts.
 * Abort only cancels underlying operations (e.g. fetch) when the abort signal from `getAbortSignal()` is passed to them.
 * Use the `onUnmount` option to customize this. For example, to flush pending work instead:
 *
 * ```tsx
 * const batcher = useAsyncBatcher(fn, {
 *   maxSize: 10,
 *   wait: 2000,
 *   onUnmount: (b) => b.flush()
 * });
 * ```
 *
 * Note: For async utils, `flush()` returns a Promise and runs fire-and-forget in the cleanup.
 * If your batch function updates React state, those updates may run after the component has
 * unmounted, which can cause "setState on unmounted component" warnings. Guard your callbacks
 * accordingly when using onUnmount with flush.
 *
 * @example
 * ```tsx
 * // Basic async batcher for API requests - no reactive state subscriptions
 * const asyncBatcher = useAsyncBatcher(
 *   async (items) => {
 *     const results = await Promise.all(items.map(item => processItem(item)));
 *     return results;
 *   },
 *   { maxSize: 10, wait: 2000 }
 * );
 *
 * // Subscribe to state changes deep in component tree using Subscribe HOC
 * <asyncBatcher.Subscribe selector={(state) => ({ size: state.size, isExecuting: state.isExecuting })}>
 *   {({ size, isExecuting }) => (
 *     <div>Batch: {size} items, {isExecuting ? 'Processing' : 'Ready'}</div>
 *   )}
 * </asyncBatcher.Subscribe>
 *
 * // Opt-in to re-render when execution state changes at hook level (optimized for loading indicators)
 * const asyncBatcher = useAsyncBatcher(
 *   async (items) => {
 *     const results = await Promise.all(items.map(item => processItem(item)));
 *     return results;
 *   },
 *   { maxSize: 10, wait: 2000 },
 *   (state) => ({
 *     isExecuting: state.isExecuting,
 *     isPending: state.isPending,
 *     status: state.status
 *   })
 * );
 *
 * // Opt-in to re-render when results are available (optimized for data display)
 * const asyncBatcher = useAsyncBatcher(
 *   async (items) => {
 *     const results = await Promise.all(items.map(item => processItem(item)));
 *     return results;
 *   },
 *   { maxSize: 10, wait: 2000 },
 *   (state) => ({
 *     lastResult: state.lastResult,
 *     successCount: state.successCount,
 *     totalItemsProcessed: state.totalItemsProcessed
 *   })
 * );
 *
 * // Opt-in to re-render when error state changes (optimized for error handling)
 * const asyncBatcher = useAsyncBatcher(
 *   async (items) => {
 *     const results = await Promise.all(items.map(item => processItem(item)));
 *     return results;
 *   },
 *   {
 *     maxSize: 10,
 *     wait: 2000,
 *     onError: (error) => console.error('Batch processing failed:', error)
 *   },
 *   (state) => ({
 *     errorCount: state.errorCount,
 *     failedItems: state.failedItems,
 *     totalItemsFailed: state.totalItemsFailed
 *   })
 * );
 *
 * // Complete example with all callbacks
 * const asyncBatcher = useAsyncBatcher(
 *   async (items) => {
 *     const results = await Promise.all(items.map(item => processItem(item)));
 *     return results;
 *   },
 *   {
 *     maxSize: 10,
 *     wait: 2000,
 *     onSuccess: (result) => {
 *       console.log('Batch processed successfully:', result);
 *     },
 *     onError: (error) => {
 *       console.error('Batch processing failed:', error);
 *     }
 *   }
 * );
 *
 * // Add items to batch
 * asyncBatcher.addItem(newItem);
 *
 * // Manually execute batch
 * const result = await asyncBatcher.execute();
 *
 * // Access the selected state (will be empty object {} unless selector provided)
 * const { isExecuting, lastResult, size } = asyncBatcher.state;
 * ```
 */
export function useAsyncBatcher<TValue, TSelected = {}>(
  fn: (items: Array<TValue>) => Promise<any>,
  options: ReactAsyncBatcherOptions<TValue, TSelected> = {},
  selector: (state: AsyncBatcherState<TValue>) => TSelected = () =>
    ({}) as TSelected,
): ReactAsyncBatcher<TValue, TSelected> {
  const mergedOptions = {
    ...useDefaultPacerOptions().asyncBatcher,
    ...options,
  } as ReactAsyncBatcherOptions<TValue, TSelected>
  const [asyncBatcher] = useState(() => {
    const asyncBatcherInstance = new AsyncBatcher<TValue>(
      fn,
      mergedOptions,
    ) as unknown as ReactAsyncBatcher<TValue, TSelected>

    /* eslint-disable-next-line @eslint-react/component-hook-factories -- Subscribe attached once in useState lazy init; stable per instance */
    asyncBatcherInstance.Subscribe = function Subscribe<TSelected>(props: {
      selector: (state: AsyncBatcherState<TValue>) => TSelected
      children: ((state: TSelected) => ReactNode) | ReactNode
    }) {
      const selected = useSelector(asyncBatcherInstance.store, props.selector, {
        compare: shallow,
      })

      return typeof props.children === 'function'
        ? props.children(selected)
        : props.children
    }

    return asyncBatcherInstance
  })

  asyncBatcher.fn = fn
  asyncBatcher.setOptions(mergedOptions)

  /* eslint-disable react-hooks/exhaustive-deps, @eslint-react/exhaustive-deps, react-compiler/react-compiler -- unmount cleanup only; empty deps keep teardown stable */
  useEffect(() => {
    return () => {
      if (mergedOptions.onUnmount) {
        mergedOptions.onUnmount(asyncBatcher)
      } else {
        asyncBatcher.cancel()
        asyncBatcher.abort()
      }
    }
  }, [])
  /* eslint-enable react-hooks/exhaustive-deps, @eslint-react/exhaustive-deps, react-compiler/react-compiler */

  const state = useSelector(asyncBatcher.store, selector, { compare: shallow })

  return useMemo(
    () =>
      ({
        ...asyncBatcher,
        state,
      }) as ReactAsyncBatcher<TValue, TSelected>, // omit `store` in favor of `state`
    [asyncBatcher, state],
  )
}