import 'dart:async';
import 'dart:ui' as ui;

import 'package:flutter/foundation.dart';
import 'package:flutter/painting.dart';
import 'package:flutter_map/flutter_map.dart';
import 'package:http/http.dart' as http;

/// ESRI World Imagery 底图地址（国内网络可能不可达）
const String kEsriWorldImageryUrl =
    'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}';

/// 网络超时时长（瓦片加载）
const Duration _kTileTimeout = Duration(seconds: 8);

/// ─────────────────────────────────────────────────────────
/// 容错网络瓦片图
/// ─────────────────────────────────────────────────────────
///
/// 加载失败（超时 / 断网 / 404 等）时返回 1×1 透明 PNG，
/// 避免 SocketException 刷屏并保证地图其余部分正常渲染。
class ResilientNetworkImage extends ImageProvider<ResilientNetworkImage> {
  const ResilientNetworkImage(this.url);

  final String url;

  @override
  Future<ResilientNetworkImage> obtainKey(ImageConfiguration configuration) =>
      SynchronousFuture<ResilientNetworkImage>(this);

  @override
  ImageStreamCompleter loadImage(
    ResilientNetworkImage key,
    ImageDecoderCallback decode,
  ) {
    return MultiFrameImageStreamCompleter(
      codec: _loadAsync(decode),
      scale: 1.0,
      debugLabel: 'ResilientNetworkImage(${url.split('/').last})',
    );
  }

  Future<ui.Codec> _loadAsync(ImageDecoderCallback decode) async {
    try {
      final client = http.Client();
      final response = await client
          .get(Uri.parse(url))
          .timeout(_kTileTimeout);

      if (response.statusCode == 200 && response.bodyBytes.isNotEmpty) {
        final buffer = await ui.ImmutableBuffer.fromUint8List(
          response.bodyBytes,
        );
        return decode(buffer);
      }
    } catch (_) {
      // 超时 / 网络异常 / 解码失败 → 走下面的透明兜底
    }
    // 1×1 透明 PNG，避免 Flutter 框架抛出 MissingImageException
    return decode(
      await ui.ImmutableBuffer.fromUint8List(_transparentPng),
    );
  }

  @override
  bool operator ==(Object other) =>
      other is ResilientNetworkImage && other.url == url;

  @override
  int get hashCode => url.hashCode;
}

/// ─────────────────────────────────────────────────────────
/// 容错 TileProvider —— 直接在 TileLayer.tileProvider 中使用
/// ─────────────────────────────────────────────────────────
///
/// ```dart
/// TileLayer(
///   urlTemplate: kEsriWorldImageryUrl,
///   tileProvider: ResilientTileProvider(),
///   minZoom: 0,
///   maxZoom: 19,
/// )
/// ```
class ResilientTileProvider extends TileProvider {
  @override
  ImageProvider<Object> getImage(TileCoordinates coordinates, TileLayer options) {
    final url = getTileUrl(coordinates, options);
    return ResilientNetworkImage(url);
  }
}

/// 1×1 透明 PNG 字节（兜底用）
final Uint8List _transparentPng = Uint8List.fromList(<int>[
  0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, // PNG signature
  0x00, 0x00, 0x00, 0x0D, 0x49, 0x48, 0x44, 0x52, // IHDR chunk
  0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, // 1×1
  0x08, 0x06, 0x00, 0x00, 0x00, 0x1F, 0x15, 0xC4, // RGBA 8bit
  0x89, 0x00, 0x00, 0x00, 0x0A, 0x49, 0x44, 0x41, // IDAT chunk
  0x54, 0x78, 0x9C, 0x62, 0x00, 0x00, 0x00, 0x02,
  0x00, 0x01, 0xE5, 0x27, 0xDE, 0xFC, 0x00, 0x00, // compressed data
  0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, // IEND chunk
  0x60, 0x82,
]);