import 'package:cs_resources/generated/assets.dart';
import 'package:flutter/material.dart';
import 'package:cs_resources/constants/color_constants.dart';
import 'my_load_image.dart';
import 'my_text_view.dart';

///四种视图状态
enum LoadState { State_Success, State_Error, State_Loading, State_Empty }

///根据不同状态来展示不同的视图
class LoadStateLayout extends StatefulWidget {
  final LoadState state; //页面状态
  final Widget? successWidget; //成功视图
  final List<Widget>? successSliverWidget; //成功的滚动视图（Sliver的布局）
  final VoidCallback? errorRetry; //错误事件处理
  final Color? themeColor;
  String? errorMessage;

  LoadStateLayout({
    Key? key,
    this.state = LoadState.State_Loading, //默认为加载状态
    this.successWidget, //成功的布局 （二选一）
    this.successSliverWidget, //成功的滚动布局（二选一）
    this.errorMessage, //错误的信息展示
    this.errorRetry, //错误重试的事件
    this.themeColor, //主题颜色，Loading,文本颜色
  }) : super(key: key);

  @override
  _LoadStateLayoutState createState() => _LoadStateLayoutState();
}

class _LoadStateLayoutState extends State<LoadStateLayout> {
  @override
  Widget build(BuildContext context) {
    if (widget.successSliverWidget != null) {
      //如果有 successSliverWidget 就使用 Slivers 的方式布局
      return CustomScrollView(
        slivers: _buildSlivers(),
      );
    } else {
      //如果没有有 successSliverWidget 就使用默认布局的方式布局
      return SizedBox(
        width: double.infinity,
        height: double.infinity,
        child: _buildWidget,
      );
    }
  }

  //Slivers的布局
  List<Widget> _buildSlivers() {
    return _buildListWidget;
  }

  ///根据不同状态来显示不同的视图 (默认布局)
  Widget get _buildWidget {
    switch (widget.state) {
      case LoadState.State_Success:
        return widget.successWidget ?? const SizedBox();
      case LoadState.State_Error:
        return _errorView;
      case LoadState.State_Loading:
        return _loadingView;
      case LoadState.State_Empty:
        return _emptyView;
      default:
        return _loadingView;
    }
  }

  ///根据不同状态来显示不同的视图 (CustomScrollView)
  List<Widget> get _buildListWidget {
    switch (widget.state) {
      case LoadState.State_Success:
        return widget.successSliverWidget != null
            ? widget.successSliverWidget!
            : widget.successWidget != null
                ? [widget.successWidget!]
                : [const SizedBox()];
      case LoadState.State_Error:
        return [widget.successSliverWidget != null ? _warpStateLayout(_errorView) : _errorView];
      case LoadState.State_Loading:
        return [widget.successSliverWidget != null ? _warpStateLayout(_loadingView) : _loadingView];
      case LoadState.State_Empty:
        return [widget.successSliverWidget != null ? _warpStateLayout(_emptyView) : _emptyView];
      default:
        return [widget.successSliverWidget != null ? _warpStateLayout(_loadingView) : _loadingView];
    }
  }

  //如果父布局是 CustomScrollView 则使用 SliverFillViewport 包裹状态布局
  Widget _warpStateLayout(Widget widget) {
    return SliverFillViewport(
      delegate: SliverChildBuilderDelegate(
        (context, index) {
          return widget;
        },
        childCount: 1,
      ),
    );
  }

  // ===================================== 真正的状态布局 ↓ =====================================

  ///加载中视图
  Widget get _loadingView {
    return Container(
      width: double.infinity,
      height: double.infinity,
      alignment: Alignment.center,
      child: Column(
        mainAxisSize: MainAxisSize.max,
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          CircularProgressIndicator(
            strokeWidth: 3,
            valueColor: AlwaysStoppedAnimation(widget.themeColor ?? const Color(0XFFD6E9F1)),
          ),
          MyTextView(
            'Loading...',
            marginTop: 15,
            fontSize: 14,
            textColor: widget.themeColor ?? const Color(0XFFD6E9F1),
          )
        ],
      ),
    );
  }

  ///错误视图
  Widget get _errorView {
    return Container(
        width: double.infinity,
        height: double.infinity,
        alignment: Alignment.center,
        padding: const EdgeInsets.only(bottom: 10),
        child: GestureDetector(
            onTap: widget.errorRetry,
            child: Column(
              mainAxisSize: MainAxisSize.max,
              crossAxisAlignment: CrossAxisAlignment.center,
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                const MyAssetImage(Assets.baseServicePageLoadError, width: 141, height: 117.5, fit: BoxFit.contain),
                MyTextView(
                  widget.errorMessage ?? 'Data loading failed! Please refresh and try again',
                  marginTop: 18,
                  fontSize: 14,
                  textColor: widget.themeColor ?? const Color(0XFFD6E9F1),
                ),
              ],
            )));
  }

  ///数据为空的视图
  Widget get _emptyView {
    return Container(
      width: double.infinity,
      height: double.infinity,
      alignment: Alignment.center,
      padding: const EdgeInsets.only(bottom: 10),
      child: Column(
        mainAxisSize: MainAxisSize.max,
        crossAxisAlignment: CrossAxisAlignment.center,
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          const MyAssetImage(Assets.baseServicePageNoData, width: 123.5, height: 115.5, fit: BoxFit.contain),
          MyTextView(
            'There is currently no content available',
            marginTop: 18,
            fontSize: 14,
            textColor: widget.themeColor ?? const Color(0XFFD6E9F1),
          ),
        ],
      ),
    );
  }
}