/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule SectionList
 * @flow
 * @format
 */
'use strict';

const MetroListView = require('MetroListView');
const Platform = require('Platform');
const React = require('React');
const VirtualizedSectionList = require('VirtualizedSectionList');

import type {ViewToken} from 'ViewabilityHelper';
import type {Props as VirtualizedSectionListProps} from 'VirtualizedSectionList';

type Item = any;

type SectionBase<SectionItemT> = {
  /**
   * The data for rendering items in this section.
   */
  data: $ReadOnlyArray<SectionItemT>,
  /**
   * Optional key to keep track of section re-ordering. If you don't plan on re-ordering sections,
   * the array index will be used by default.
   */
  key?: string,

  // Optional props will override list-wide props just for this section.
  renderItem?: ?(info: {
    item: SectionItemT,
    index: number,
    section: SectionBase<SectionItemT>,
    separators: {
      highlight: () => void,
      unhighlight: () => void,
      updateProps: (select: 'leading' | 'trailing', newProps: Object) => void,
    },
  }) => ?React.Element<any>,
  ItemSeparatorComponent?: ?ReactClass<any>,
  keyExtractor?: (item: SectionItemT) => string,

  // TODO: support more optional/override props
  // onViewableItemsChanged?: ...
};

type RequiredProps<SectionT: SectionBase<any>> = {
  /**
   * The actual data to render, akin to the `data` prop in [`<FlatList>`](/react-native/docs/flatlist.html).
   *
   * General shape:
   *
   *     sections: $ReadOnlyArray<{
   *       data: $ReadOnlyArray<SectionItem>,
   *       renderItem?: ({item: SectionItem, ...}) => ?React.Element<*>,
   *       ItemSeparatorComponent?: ?ReactClass<{highlighted: boolean, ...}>,
   *     }>
   */
  sections: $ReadOnlyArray<SectionT>,
};

type OptionalProps<SectionT: SectionBase<any>> = {
  /**
   * Default renderer for every item in every section. Can be over-ridden on a per-section basis.
   */
  renderItem: (info: {
    item: Item,
    index: number,
    section: SectionT,
    separators: {
      highlight: () => void,
      unhighlight: () => void,
      updateProps: (select: 'leading' | 'trailing', newProps: Object) => void,
    },
  }) => ?React.Element<any>,
  /**
   * Rendered in between each item, but not at the top or bottom. By default, `highlighted`,
   * `section`, and `[leading/trailing][Item/Separator]` props are provided. `renderItem` provides
   * `separators.highlight`/`unhighlight` which will update the `highlighted` prop, but you can also
   * add custom props with `separators.updateProps`.
   */
  ItemSeparatorComponent?: ?ReactClass<any>,
  /**
   * Rendered at the very beginning of the list. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListHeaderComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Rendered when the list is empty. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListEmptyComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Rendered at the very end of the list. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListFooterComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Rendered at the top and bottom of each section (note this is different from
   * `ItemSeparatorComponent` which is only rendered between items). These are intended to separate
   * sections from the headers above and below and typically have the same highlight response as
   * `ItemSeparatorComponent`. Also receives `highlighted`, `[leading/trailing][Item/Separator]`,
   * and any custom props from `separators.updateProps`.
   */
  SectionSeparatorComponent?: ?ReactClass<any>,
  /**
   * A marker property for telling the list to re-render (since it implements `PureComponent`). If
   * any of your `renderItem`, Header, Footer, etc. functions depend on anything outside of the
   * `data` prop, stick it here and treat it immutably.
   */
  extraData?: any,
  /**
   * How many items to render in the initial batch. This should be enough to fill the screen but not
   * much more. Note these items will never be unmounted as part of the windowed rendering in order
   * to improve perceived performance of scroll-to-top actions.
   */
  initialNumToRender: number,
  /**
   * Reverses the direction of scroll. Uses scale transforms of -1.
   */
  inverted?: ?boolean,
  /**
   * Used to extract a unique key for a given item at the specified index. Key is used for caching
   * and as the react key to track item re-ordering. The default extractor checks item.key, then
   * falls back to using the index, like react does. Note that this sets keys for each item, but 
   * each overall section still needs its own key.
   */
  keyExtractor: (item: Item, index: number) => string,
  /**
   * Called once when the scroll position gets within `onEndReachedThreshold` of the rendered
   * content.
   */
  onEndReached?: ?(info: {distanceFromEnd: number}) => void,
  /**
   * How far from the end (in units of visible length of the list) the bottom edge of the
   * list must be from the end of the content to trigger the `onEndReached` callback.
   * Thus a value of 0.5 will trigger `onEndReached` when the end of the content is
   * within half the visible length of the list.
   */
  onEndReachedThreshold?: ?number,
  /**
   * If provided, a standard RefreshControl will be added for "Pull to Refresh" functionality. Make
   * sure to also set the `refreshing` prop correctly.
   */
  onRefresh?: ?() => void,
  /**
   * Called when the viewability of rows changes, as defined by the
   * `viewabilityConfig` prop.
   */
  onViewableItemsChanged?: ?(info: {
    viewableItems: Array<ViewToken>,
    changed: Array<ViewToken>,
  }) => void,
  /**
   * Set this true while waiting for new data from a refresh.
   */
  refreshing?: ?boolean,
  /**
   * Note: may have bugs (missing content) in some circumstances - use at your own risk.
   *
   * This may improve scroll performance for large lists.
   */
  removeClippedSubviews?: boolean,
  /**
   * Rendered at the top of each section. These stick to the top of the `ScrollView` by default on
   * iOS. See `stickySectionHeadersEnabled`.
   */
  renderSectionHeader?: ?(info: {section: SectionT}) => ?React.Element<any>,
  /**
   * Rendered at the bottom of each section.
   */
  renderSectionFooter?: ?(info: {section: SectionT}) => ?React.Element<any>,
  /**
   * Makes section headers stick to the top of the screen until the next one pushes it off. Only
   * enabled by default on iOS because that is the platform standard there.
   */
  stickySectionHeadersEnabled?: boolean,

  legacyImplementation?: ?boolean,
};

type Props<SectionT> = RequiredProps<SectionT> &
  OptionalProps<SectionT> &
  VirtualizedSectionListProps<SectionT>;

const defaultProps = {
  ...VirtualizedSectionList.defaultProps,
  stickySectionHeadersEnabled: Platform.OS === 'ios',
};

type DefaultProps = typeof defaultProps;

/**
 * A performant interface for rendering sectioned lists, supporting the most handy features:
 *
 *  - Fully cross-platform.
 *  - Configurable viewability callbacks.
 *  - List header support.
 *  - List footer support.
 *  - Item separator support.
 *  - Section header support.
 *  - Section separator support.
 *  - Heterogeneous data and item rendering support.
 *  - Pull to Refresh.
 *  - Scroll loading.
 *
 * If you don't need section support and want a simpler interface, use
 * [`<FlatList>`](/react-native/docs/flatlist.html).
 *
 * Simple Examples:
 *
 *     <SectionList
 *       renderItem={({item}) => <ListItem title={item.title} />}
 *       renderSectionHeader={({section}) => <H1 title={section.title} />}
 *       sections={[ // homogenous rendering between sections
 *         {data: [...], title: ...},
 *         {data: [...], title: ...},
 *         {data: [...], title: ...},
 *       ]}
 *     />
 *
 *     <SectionList
 *       sections={[ // heterogeneous rendering between sections
 *         {data: [...], title: ..., renderItem: ...},
 *         {data: [...], title: ..., renderItem: ...},
 *         {data: [...], title: ..., renderItem: ...},
 *       ]}
 *     />
 *
 * This is a convenience wrapper around [`<VirtualizedList>`](docs/virtualizedlist.html),
 * and thus inherits its props (as well as those of `ScrollView`) that aren't explicitly listed
 * here, along with the following caveats:
 *
 * - Internal state is not preserved when content scrolls out of the render window. Make sure all
 *   your data is captured in the item data or external stores like Flux, Redux, or Relay.
 * - This is a `PureComponent` which means that it will not re-render if `props` remain shallow-
 *   equal. Make sure that everything your `renderItem` function depends on is passed as a prop
 *   (e.g. `extraData`) that is not `===` after updates, otherwise your UI may not update on
 *   changes. This includes the `data` prop and parent component state.
 * - In order to constrain memory and enable smooth scrolling, content is rendered asynchronously
 *   offscreen. This means it's possible to scroll faster than the fill rate and momentarily see
 *   blank content. This is a tradeoff that can be adjusted to suit the needs of each application,
 *   and we are working on improving it behind the scenes.
 * - By default, the list looks for a `key` prop on each item and uses that for the React key.
 *   Alternatively, you can provide a custom `keyExtractor` prop.
 *
 */
class SectionList<SectionT: SectionBase<any>> extends React.PureComponent<
  DefaultProps,
  Props<SectionT>,
  void,
> {
  props: Props<SectionT>;
  static defaultProps: DefaultProps = defaultProps;

  /**
   * Scrolls to the item at the specified `sectionIndex` and `itemIndex` (within the section)
   * positioned in the viewable area such that `viewPosition` 0 places it at the top (and may be
   * covered by a sticky header), 1 at the bottom, and 0.5 centered in the middle. `viewOffset` is a
   * fixed number of pixels to offset the final target position, e.g. to compensate for sticky
   * headers.
   *
   * Note: cannot scroll to locations outside the render window without specifying the
   * `getItemLayout` prop.
   */
  scrollToLocation(params: {
    animated?: ?boolean,
    itemIndex: number,
    sectionIndex: number,
    viewOffset?: number,
    viewPosition?: number,
  }) {
    this._wrapperListRef.scrollToLocation(params);
  }

  /**
   * Tells the list an interaction has occured, which should trigger viewability calculations, e.g.
   * if `waitForInteractions` is true and the user has not scrolled. This is typically called by
   * taps on items or by navigation actions.
   */
  recordInteraction() {
    const listRef = this._wrapperListRef && this._wrapperListRef.getListRef();
    listRef && listRef.recordInteraction();
  }

  /**
   * Displays the scroll indicators momentarily.
   *
   * @platform ios
   */
  flashScrollIndicators() {
    const listRef = this._wrapperListRef && this._wrapperListRef.getListRef();
    listRef && listRef.flashScrollIndicators();
  }

  /**
   * Provides a handle to the underlying scroll responder.
   */
  getScrollResponder() {
    const listRef = this._wrapperListRef && this._wrapperListRef.getListRef();
    if (listRef) {
      return listRef.getScrollResponder();
    }
  }

  getScrollableNode() {
    const listRef = this._wrapperListRef && this._wrapperListRef.getListRef();
    if (listRef) {
      return listRef.getScrollableNode();
    }
  }

  render() {
    const List = this.props.legacyImplementation
      ? MetroListView
      : VirtualizedSectionList;
    return <List {...this.props} ref={this._captureRef} />;
  }

  _wrapperListRef: MetroListView | VirtualizedSectionList<any>;
  _captureRef = ref => {
    this._wrapperListRef = ref;
  };
}

module.exports = SectionList;