using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using System;
using System.IO;
using System.Threading.Tasks;

namespace Nirvana.Common.Middleware
{
    /// <summary>
    /// 默认图片中间件,使用方法app.UseDefaultImage(defaultImagePath: Configuration.GetSection("defaultImagePath").Value);
    /// </summary>
    public class DefaultImageMiddleware
    {
        private readonly RequestDelegate _next;
        public static string DefaultImagePath { get; set; }

        public DefaultImageMiddleware(RequestDelegate next)
        {
            this._next = next;
        }
        public async Task InvokeAsync(HttpContext context)
        {
            await _next(context);
            if (context.Response.StatusCode == 404)
            {
                var contentType = context.Request.Headers["accept"].ToString().ToLower();
                if (contentType.StartsWith("image"))
                {
                    await SetDefaultImageAsync(context);
                }
            }
        }
        /// <summary>
        /// 设置默认图片
        /// </summary>
        /// <param name="context"></param>
        private async Task SetDefaultImageAsync(HttpContext context)
        {
            try
            {
                string path = Path.Combine(Directory.GetCurrentDirectory(), DefaultImagePath);
                FileStream fs = System.IO.File.OpenRead(path);
                byte[] bytes = new byte[fs.Length];
                await fs.ReadAsync(bytes, 0, bytes.Length);
                //this header is use for browser cache, format like: "Mon, 15 May 2017 07:03:37 GMT".
                //context.Response.Headers.Append("Last-Modified", $"{File.GetLastWriteTimeUtc(path).ToString("ddd, dd MMM yyyy HH:mm:ss")} GMT");
                await context.Response.Body.WriteAsync(bytes, 0, bytes.Length);
            }
            catch (Exception ex)
            {

                await context.Response.WriteAsync(ex.Message);
            }
        }
    }
    /// <summary>
    /// 默认图片中间件扩展
    /// </summary>
    public static class DefaultImageMiddlewareExtensions
    {
        public static IApplicationBuilder UseDefaultImage(this IApplicationBuilder app, string defaultImagePath)
        {
            DefaultImageMiddleware.DefaultImagePath = defaultImagePath;
            app.UseMiddleware<DefaultImageMiddleware>();
            return app;
        }
    }
}