import React from 'react';
import { Platform, Keyboard } from 'react-native';
import { I18nManager } from 'react-native';
import type {
  OnPageScrollEventData,
  OnPageScrollStateChangedEventData,
  OnPageSelectedEventData,
} from './PagerViewNativeComponent';
import type * as ReactNative from 'react-native';

import type { NativeProps as PagerViewProps } from './PagerViewNativeComponent';
import { childrenWithOverriddenStyle } from './utils';
import PagerViewView, {
  Commands as PagerViewCommands,
} from './PagerViewNativeComponent';

/**
 * 新的 ViewPager 组件继承 PagerView 的功能
 */

export class ViewPager extends React.Component<PagerViewProps> {
  private isScrolling = false;
  pagerView: React.ElementRef<typeof PagerViewView> | null = null;

  private _onPageScroll = (
    e: ReactNative.NativeSyntheticEvent<OnPageScrollEventData>
  ) => {
    if (this.props.onPageScroll) {
      this.props.onPageScroll(e);
    }

    // Not implemented on iOS yet
    // @ts-ignore
    if (Platform.OS === 'android' || Platform.OS === 'harmony') {
      if (this.props.keyboardDismissMode === 'on-drag') {
        Keyboard.dismiss();
      }
    }
  };

  private _onPageScrollStateChanged = (
    e: ReactNative.NativeSyntheticEvent<OnPageScrollStateChangedEventData>
  ) => {
    if (this.props.onPageScrollStateChanged) {
      this.props.onPageScrollStateChanged(e);
    }
    this.isScrolling = e.nativeEvent.pageScrollState === 'dragging';
  };

  private _previousPagePosition: number | null = null;

  private _onPageSelected = (
    e: ReactNative.NativeSyntheticEvent<OnPageSelectedEventData>
  ) => {
    const currentPagePosition = e.nativeEvent.position;
    if (this._previousPagePosition !== currentPagePosition) {
      if (this.props.onPageSelected) {
        const initialPage = (e.currentTarget as any).currentProps.initialPage || 0;
        if (this._previousPagePosition === null && e.nativeEvent.position == initialPage) return
        this.props.onPageSelected(e);
      }
    }
    this._previousPagePosition = currentPagePosition;
  };

  /**
   * A helper function to scroll to a specific page in the PagerView.
   * The transition between pages will be animated.
   */
  public setPage = (selectedPage: number) => {
    if (this.pagerView) {
      PagerViewCommands.setPage(this.pagerView, selectedPage);
    }
  };

  /**
   * A helper function to scroll to a specific page in the PagerView.
   * The transition between pages will *not* be animated.
   */
  public setPageWithoutAnimation = (selectedPage: number) => {
    if (this.pagerView) {
      PagerViewCommands.setPageWithoutAnimation(this.pagerView, selectedPage);
    }
  };

  /**
   * A helper function to enable/disable scroll imperatively
   * The recommended way is using the scrollEnabled prop, however, there might be a case where a
   * imperative solution is more useful (e.g. for not blocking an animation)
   */
  public setScrollEnabled = (scrollEnabled: boolean) => {
    if (this.pagerView) {
      PagerViewCommands.setScrollEnabledImperatively(
        this.pagerView,
        scrollEnabled
      );
    }
  };

  private _onMoveShouldSetResponderCapture = () => {
    return this.isScrolling;
  };

  private get deducedLayoutDirection() {
    if (
      !this.props.layoutDirection ||
      //@ts-ignore fix it
      this.props.layoutDirection === 'locale'
    ) {
      return I18nManager.isRTL ? 'rtl' : 'ltr';
    } else {
      return this.props.layoutDirection;
    }
  }

  render() {
    return (
      <PagerViewView
        {...this.props}
        ref={(ref) => {
          this.pagerView = ref;
        }}
        style={this.props.style}
        layoutDirection={this.deducedLayoutDirection}
        onPageScroll={this._onPageScroll}
        onPageScrollStateChanged={this._onPageScrollStateChanged}
        onPageSelected={this._onPageSelected}
        onMoveShouldSetResponderCapture={this._onMoveShouldSetResponderCapture}
        children={childrenWithOverriddenStyle(this.props.children)}
      />
    );
  }
}