using System;
using System.Diagnostics;
using System.Drawing.Imaging;
using System.Linq;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;

   /// <summary>
   /// 加载Bing壁纸，单例，使用CreateInstance方法创建类的实例
   /// </summary>
   public sealed class BingWallpaperAPI
   {
       private static BingWallpaperAPI _instance = null;
       private static readonly object _padlock = new Object();
       /// <summary>
       /// 创建类的实例
       /// </summary>
       /// <param name="imgnums">壁纸的张数，可以是1-8之间的数</param>
       /// <returns></returns>
       public static BingWallpaperAPI CreateInstance(byte imgnums = 3)
       {
           if (_instance is null)
           {
               lock (_padlock)
               {
                   if (_instance is null) _instance = new BingWallpaperAPI(imgnums);
               }
           }
           return _instance;
       }
       private BingWallpaperAPI(byte imgnums)
       {
           if (imgnums > 8 || imgnums <= 0)
           {
               _imgnums = 3;
               Debug.WriteLine($"仅支持1-8张图片，你输入的{imgnums}被重置为3");
           }
           else { _imgnums = imgnums; }
           GetWallpaperLink();
       }
       /// <summary>内置索引</summary>
       private int _index = -1;
       /// <summary>
       /// 加载Bing壁纸的数量，默认为3
       /// </summary>
       private static byte _imgnums;
       private BingApiModel _bingApiModel;
       /// <summary>
       /// 加载壁纸的JSON格式文件，文件中包含了壁纸的下载地址等关键信息
       /// </summary>
       /// <exception cref="Exception"></exception>
       private void GetWallpaperLink()
       {
           HttpClient client = new HttpClient();
           for (int i = 0; i < 3; i++) //这个步骤会尝试3次
           {
               try
               {
                   var res = client.GetAsync($"https://cn.bing.com/HPImageArchive.aspx?format=js&idx=0&n={_imgnums}&mkt=zh-CN").Result;
                   //参数n:1-8 返回请求数量，目前最多一次获取8张
                   //参数format:js/xml
                   //参数idx:请求图片截止天数 0 今天;1 截止至昨天，类推（目前最多获取到7天前的图片）
                   //参数mkt:地区
                   var json = res.Content.ReadAsStringAsync().Result;
                   BingApiModel bingApiModel = new BingApiModel();
                   _bingApiModel = JsonSerializer.Deserialize<BingApiModel>(json);
                   ImageCount = _bingApiModel.images.Count();
                   if (ImageCount == _imgnums)
                   {
                       break;  //加载成功时直接终止循环
                   }
               }
               catch (Exception ex)
               {
                   if (i == 2) { throw ex; } else Console.WriteLine(ex.Message);
               }
           }
       }
       /// <summary>
       /// 根据JSON数据下载壁纸
       /// </summary>
       /// <param name="index">_bingApiModel索引</param>
       /// <returns></returns>
       /// <exception cref="Exception"></exception>
       private async Task<BingWallpaper> GetWallpaper(int index)
       {
           try
           {
               using (HttpClient client = new HttpClient())
               {
                   var element = _bingApiModel.images[index];
                   var res = await client.GetAsync("https://cn.bing.com" + element.url);
                   //这个URL中的第一个1920x1080改成UHD是4k
                   var imgStream = await res.Content.ReadAsStreamAsync();
                   return (new BingWallpaper()
                   {
                       Wallpaper = System.Drawing.Image.FromStream(imgStream),
                       Title = element.title,
                       Copyright = element.copyright,
                       CopyrightLink = element.copyrightlink,
                       EndDate = element.enddate,
                   });
               }
           }
           catch (Exception ex)
           {
               throw ex;
           }
       }
       /// <summary>
       /// 加载JSON数据包含的URL数量
       /// </summary>
       public int ImageCount { get;private set; }
       /// <summary>
       /// 下一张壁纸
       /// </summary>
       /// <returns></returns>        
       /// <exception cref="Exception"></exception>
       public async Task<BingWallpaper> Next()
       {
           if (ImageCount == 0)
           {
               return null;
           }
           _index++;
           if (_index >= ImageCount)   //重置索引
           {
               _index = 0;
           }
           return await GetWallpaper(_index);
       }
       /// <summary>
       /// 上一张壁纸
       /// </summary>
       /// <returns></returns>
       /// <exception cref="Exception"></exception>
       public async Task<BingWallpaper> Previous()
       {
           if (ImageCount == 0)
           {
               return null;
           }
           _index--;
           if (_index < 0)
           {
               _index = ImageCount - 1;    //重置索引
           }
           return await GetWallpaper(_index);
       }

       /// <summary>
       /// 保存当前的壁纸到本地
       /// </summary>
       /// <param name="path">保存的路径、含文件名（如c:\1.jpg），格式为JPEG</param>
       /// <returns>保存是否成功</returns>
       /// <exception cref="Exception"></exception>
       public async Task<bool> SaveCurrentWallpaper(string path)
       {
           try
           {
               var task = await Current();
               task.Wallpaper.Save(path, ImageFormat.Jpeg);
               return true;
           }
           catch (Exception ex)
           {
               throw ex;
           }
       }
       /// <summary>
       /// 当前壁纸
       /// </summary>
       /// <returns></returns>
       /// <exception cref="Exception"></exception>
       public async Task<BingWallpaper> Current()
       {
           if (ImageCount == 0)
           {
               return null;
           }
           if (_index == -1)
           {
               _index = 0;
           }
           return await GetWallpaper(_index);
       }
   }
   /// <summary>
   /// 用来保存壁纸信息的类模型
   /// </summary>
   public class BingWallpaper
   {
       /// <summary>壁纸</summary>
       public System.Drawing.Image Wallpaper { get; set; }
       /// <summary>标题</summary>
       public string Title { get; set; }
       /// <summary>版权</summary>
       public string Copyright { get; set; }
       /// <summary>版权链接</summary>
       public string CopyrightLink { get; set; }
       /// <summary>
       /// 壁纸所属日期
       /// </summary>
       public string EndDate { get; set; }
   }
   /// <summary>
   /// 用来解析JSON数据的类模型
   /// </summary>
   public class BingApiModel
   {
       /// <summary>
       /// 返回图片集合
       /// </summary>
       public Image[] images { get; set; }
   }
   public class Image
   {
       /// <summary>
       /// 每日壁纸的日期
       /// </summary>
       public string enddate { get; set; }
       /// <summary>
       /// 壁纸的地址
       /// </summary>
       public string url { get; set; }
       /// <summary>壁纸的简述、拍摄地址(摄影人)</summary>
       public string copyright { get; set; }
       /// <summary>壁纸相关搜索链接</summary>
       public string copyrightlink { get; set; }
       /// <summary>壁纸的标题</summary>
       public string title { get; set; }
   }