/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

import {createListActions, ListData, ListState} from './useListData';
import {Key, LoadingState, Selection, SortDescriptor} from '@react-types/shared';
import {useEffect, useReducer, useRef} from 'react';

export interface AsyncListOptions<T, C> {
  /** The keys for the initially selected items. */
  initialSelectedKeys?: Iterable<Key>,
  /** The initial sort descriptor. */
  initialSortDescriptor?: SortDescriptor,
  /** The initial filter text. */
  initialFilterText?: string,
  /** A function that returns a unique key for an item object. */
  getKey?: (item: T) => Key,
  /** A function that loads the data for the items in the list. */
  load: AsyncListLoadFunction<T, C>,
  /**
   * An optional function that performs sorting. If not provided,
   * then `sortDescriptor` is passed to the `load` function.
   */
  sort?: AsyncListLoadFunction<T, C, AsyncListLoadOptions<T, C> & {sortDescriptor: SortDescriptor}>
}

type AsyncListLoadFunction<T, C, S extends AsyncListLoadOptions<T, C> = AsyncListLoadOptions<T, C>> = (state: S) => AsyncListStateUpdate<T, C> | Promise<AsyncListStateUpdate<T, C>>;

interface AsyncListLoadOptions<T, C> {
  /** The items currently in the list. */
  items: T[],
  /** The keys of the currently selected items in the list. */
  selectedKeys: Selection,
  /** The current sort descriptor for the list. */
  sortDescriptor?: SortDescriptor,
  /** An abort signal used to notify the load function that the request has been aborted. */
  signal: AbortSignal,
  /** The pagination cursor returned from the last page load. */
  cursor?: C,
  /** The current filter text used to perform server side filtering. */
  filterText?: string,
  /** The current loading state of the list. */
  loadingState?: LoadingState
}

interface AsyncListStateUpdate<T, C> {
  /** The new items to append to the list. */
  items: Iterable<T>,
  /** The keys to add to the selection. */
  selectedKeys?: Iterable<Key>,
  /** The sort descriptor to set. */
  sortDescriptor?: SortDescriptor,
  /** The pagination cursor to be used for the next page load. */
  cursor?: C,
  /** The updated filter text for the list. */
  filterText?: string
}

interface AsyncListState<T, C> extends ListState<T> {
  state: LoadingState,
  items: T[],
  // disabledKeys?: Iterable<Key>,
  selectedKeys: Selection,
  // selectedKey?: Key,
  // expandedKeys?: Iterable<Key>,
  sortDescriptor?: SortDescriptor,
  error?: Error,
  abortController?: AbortController,
  cursor?: C
}

type ActionType = 'success' | 'error' | 'loading' | 'loadingMore' | 'sorting' | 'update' | 'filtering';
interface Action<T, C> {
  type: ActionType,
  items?: Iterable<T>,
  selectedKeys?: Iterable<Key>,
  sortDescriptor?: SortDescriptor,
  error?: Error,
  abortController?: AbortController,
  updater?: (state: ListState<T>) => ListState<T>,
  cursor?: C,
  filterText?: string
}

export interface AsyncListData<T> extends ListData<T> {
  /** Whether data is currently being loaded. */
  isLoading: boolean,
  /** If loading data failed, then this contains the error that occurred. */
  error?: Error,
  // disabledKeys?: Set<Key>,
  // selectedKey?: Key,
  // expandedKeys?: Set<Key>,
  /** The current sort descriptor for the list. */
  sortDescriptor?: SortDescriptor,

  /** Reloads the data in the list. */
  reload(): void,
  /** Loads the next page of data in the list. */
  loadMore(): void,
  /** Triggers sorting for the list. */
  sort(descriptor: SortDescriptor): void,
  /** The current loading state for the list. */
  loadingState: LoadingState
}

function reducer<T, C>(data: AsyncListState<T, C>, action: Action<T, C>): AsyncListState<T, C> {
  let selectedKeys;
  switch (data.state) {
    case 'idle':
    case 'error':
      switch (action.type) {
        case 'loading':
        case 'loadingMore':
        case 'sorting':
        case 'filtering':
          return {
            ...data,
            filterText: action.filterText ?? data.filterText,
            state: action.type,
            // Reset items to an empty list if loading, but not when sorting.
            items: action.type === 'loading' ? [] : data.items,
            sortDescriptor: action.sortDescriptor ?? data.sortDescriptor,
            abortController: action.abortController
          };
        case 'update':
          return {
            ...data,
            ...action.updater?.(data)
          };
        case 'success':
        case 'error':
          return data;
        default:
          throw new Error(`Invalid action "${action.type}" in state "${data.state}"`);
      }
    case 'loading':
    case 'sorting':
    case 'filtering':
      switch (action.type) {
        case 'success':
          // Ignore if there is a newer abortcontroller in state.
          // This means that multiple requests were going at once.
          // We want to take only the latest result.
          if (action.abortController !== data.abortController) {
            return data;
          }

          selectedKeys = action.selectedKeys ?? data.selectedKeys;
          return {
            ...data,
            filterText: action.filterText ?? data.filterText,
            state: 'idle',
            items: [...(action.items) ?? []],
            selectedKeys: selectedKeys === 'all' ? 'all' : new Set(selectedKeys),
            sortDescriptor: action.sortDescriptor ?? data.sortDescriptor,
            abortController: undefined,
            cursor: action.cursor
          };
        case 'error':
          if (action.abortController !== data.abortController) {
            return data;
          }

          return {
            ...data,
            state: 'error',
            error: action.error,
            abortController: undefined
          };
        case 'loading':
        case 'loadingMore':
        case 'sorting':
        case 'filtering':
          // We're already loading, and another load was triggered at the same time.
          // We need to abort the previous load and start a new one.
          data.abortController?.abort('aborting current load and starting new one');
          return {
            ...data,
            filterText: action.filterText ?? data.filterText,
            state: action.type,
            // Reset items to an empty list if loading, but not when sorting.
            items: action.type === 'loading' ? [] : data.items,
            abortController: action.abortController
          };
        case 'update':
          // We're already loading, and an update happened at the same time (e.g. selectedKey changed).
          // Update data but don't abort previous load.
          return {
            ...data,
            ...action.updater?.(data)
          };
        default:
          throw new Error(`Invalid action "${action.type}" in state "${data.state}"`);
      }
    case 'loadingMore':
      switch (action.type) {
        case 'success':
          selectedKeys = (data.selectedKeys === 'all' || action.selectedKeys === 'all')
            ? 'all'
            : new Set([...data.selectedKeys, ...(action.selectedKeys ?? [])]);
          // Append the new items
          return {
            ...data,
            state: 'idle',
            items: [...data.items, ...(action.items ?? [])],
            selectedKeys,
            sortDescriptor: action.sortDescriptor ?? data.sortDescriptor,
            abortController: undefined,
            cursor: action.cursor
          };
        case 'error':
          if (action.abortController !== data.abortController) {
            return data;
          }

          return {
            ...data,
            state: 'error',
            error: action.error
          };
        case 'loading':
        case 'sorting':
        case 'filtering':
          // We're already loading more, and another load was triggered at the same time.
          // We need to abort the previous load more and start a new one.
          data.abortController?.abort();
          return {
            ...data,
            filterText: action.filterText ?? data.filterText,
            state: action.type,
            // Reset items to an empty list if loading, but not when sorting.
            items: action.type === 'loading' ? [] : data.items,
            abortController: action.abortController
          };
        case 'loadingMore':
          // If already loading more and another loading more is triggered, abort the new load more since
          // it is a duplicate request since the cursor hasn't been updated.
          // Do not overwrite the data.abortController
          action.abortController?.abort();

          return data;
        case 'update':
          // We're already loading, and an update happened at the same time (e.g. selectedKey changed).
          // Update data but don't abort previous load.
          return {
            ...data,
            ...action.updater?.(data)
          };
        default:
          throw new Error(`Invalid action "${action.type}" in state "${data.state}"`);
      }
    default:
      throw new Error(`Invalid state "${data.state}"`);
  }
}

/**
 * Manages state for an immutable async loaded list data structure, and provides convenience methods to
 * update the data over time. Manages loading and error states, pagination, and sorting.
 */
export function useAsyncList<T, C = string>(options: AsyncListOptions<T, C>): AsyncListData<T> {
  const {
    load,
    sort,
    initialSelectedKeys,
    initialSortDescriptor,
    getKey = (item: any) => item.id || item.key,
    initialFilterText = ''
  } = options;

  let [data, dispatch] = useReducer<AsyncListState<T, C>, [Action<T, C>]>(reducer, {
    state: 'idle',
    error: undefined,
    items: [],
    selectedKeys: initialSelectedKeys === 'all' ? 'all' : new Set(initialSelectedKeys),
    sortDescriptor: initialSortDescriptor,
    filterText: initialFilterText
  });

  const dispatchFetch = async (action: Action<T, C>, fn: AsyncListLoadFunction<T, C>) => {
    let abortController = new AbortController();
    try {
      dispatch({...action, abortController});
      let previousFilterText = action.filterText ?? data.filterText;

      let response = await fn({
        items: data.items.slice(),
        selectedKeys: data.selectedKeys,
        sortDescriptor: action.sortDescriptor ?? data.sortDescriptor,
        signal: abortController.signal,
        cursor: action.type === 'loadingMore' ? data.cursor : undefined,
        filterText: previousFilterText,
        loadingState: data.state
      });

      let filterText = response.filterText ?? previousFilterText;
      dispatch({type: 'success', ...response, abortController});

      // Fetch a new filtered list if filterText is updated via `load` response func rather than list.setFilterText
      // Only do this if not aborted (e.g. user triggers another filter action before load completes)
      if (filterText && (filterText !== previousFilterText) && !abortController.signal.aborted) {
        dispatchFetch({type: 'filtering', filterText}, load);
      }
    } catch (e) {
      dispatch({type: 'error', error: e as Error, abortController});
    }
  };

  let didDispatchInitialFetch = useRef(false);
  useEffect(() => {
    if (!didDispatchInitialFetch.current) {
      dispatchFetch({type: 'loading'}, load);
      didDispatchInitialFetch.current = true;
    }
  // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return {
    items: data.items,
    selectedKeys: data.selectedKeys,
    sortDescriptor: data.sortDescriptor,
    isLoading: data.state === 'loading' || data.state === 'loadingMore' || data.state === 'sorting' || data.state === 'filtering',
    loadingState: data.state,
    error: data.error,
    filterText: data.filterText,
    getItem(key: Key) {
      return data.items.find(item => getKey(item) === key);
    },
    reload() {
      dispatchFetch({type: 'loading'}, load);
    },
    loadMore() {
      // Ignore if already loading more or if performing server side filtering.
      if (data.state === 'loading' || data.state === 'loadingMore' || data.state === 'filtering' || data.cursor == null) {
        return;
      }

      dispatchFetch({type: 'loadingMore'}, load);
    },
    sort(sortDescriptor: SortDescriptor) {
      dispatchFetch({type: 'sorting', sortDescriptor}, (sort || load) as AsyncListLoadFunction<T, C>);
    },
    ...createListActions({...options, getKey, cursor: data.cursor}, fn => {
      dispatch({type: 'update', updater: fn});
    }),
    setFilterText(filterText: string) {
      dispatchFetch({type: 'filtering', filterText}, load);
    }
  };
}