using System.Collections.Concurrent;
using System.Security.Cryptography;
using System.Text;
using System.Xml.Linq;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace WebDrop.Api.Tests;

/// <summary>
/// 只实现备份用到的 S3 子集(PUT、HEAD、DELETE、ListObjectsV2),路径风格,数据放在内存里。
/// 检查 SigV4 的凭据字段和 x-amz-content-sha256 与正文是否一致;不重算签名本身(签名算法由真实服务兜底)。
/// </summary>
public sealed class FakeS3 : IAsyncDisposable
{
    private readonly WebApplication _app;
    /// <summary>键(不含存储桶)→ 内容</summary>
    public ConcurrentDictionary<string, byte[]> Files { get; } = new();
    public bool Down { get; set; }
    public string Url { get; private set; } = "";
    public const string AccessKey = "AKIATEST", SecretKey = "secret", Bucket = "bk";

    public FakeS3()
    {
        var builder = WebApplication.CreateSlimBuilder();
        builder.Configuration["urls"] = "http://127.0.0.1:0";
        builder.Logging.ClearProviders();
        _app = builder.Build();
        _app.Map("/{bucket}/{**key}", async (HttpContext ctx, string bucket, string? key) =>
        {
            if (Down) { ctx.Response.StatusCode = 503; return; }
            string auth = ctx.Request.Headers.Authorization.ToString();
            if (bucket != Bucket || !auth.StartsWith($"AWS4-HMAC-SHA256 Credential={AccessKey}/", StringComparison.Ordinal) || !auth.Contains("Signature=") || !ctx.Request.Headers.ContainsKey("x-amz-date"))
            { ctx.Response.StatusCode = 403; return; }
            key = Uri.UnescapeDataString(key ?? "");
            switch (ctx.Request.Method)
            {
                case "PUT":
                    {
                        using var ms = new MemoryStream();
                        await ctx.Request.Body.CopyToAsync(ms);
                        var body = ms.ToArray();
                        if (!string.Equals(ctx.Request.Headers["x-amz-content-sha256"], Convert.ToHexStringLower(SHA256.HashData(body)), StringComparison.Ordinal)) { ctx.Response.StatusCode = 400; return; }
                        Files[key] = body;
                        ctx.Response.StatusCode = 200;
                        break;
                    }
                case "HEAD": ctx.Response.StatusCode = Files.ContainsKey(key) ? 200 : 404; break;
                case "DELETE": Files.TryRemove(key, out _); ctx.Response.StatusCode = 204; break;
                case "GET":
                    {
                        string prefix = ctx.Request.Query["prefix"].ToString(), delimiter = ctx.Request.Query["delimiter"].ToString();
                        var keys = Files.Keys.Where(k => k.StartsWith(prefix, StringComparison.Ordinal)).Order(StringComparer.Ordinal).ToList();
                        XNamespace ns = "http://s3.amazonaws.com/doc/2006-03-01/";
                        var root = new XElement(ns + "ListBucketResult", new XElement(ns + "IsTruncated", "false"));
                        var folders = new SortedSet<string>(StringComparer.Ordinal);
                        foreach (var k in keys)
                        {
                            int cut = delimiter.Length == 0 ? -1 : k.IndexOf(delimiter, prefix.Length, StringComparison.Ordinal);
                            if (cut < 0) root.Add(new XElement(ns + "Contents", new XElement(ns + "Key", k)));
                            else folders.Add(k[..(cut + delimiter.Length)]);
                        }
                        foreach (var f in folders) root.Add(new XElement(ns + "CommonPrefixes", new XElement(ns + "Prefix", f)));
                        ctx.Response.StatusCode = 200;
                        ctx.Response.ContentType = "application/xml";
                        await ctx.Response.WriteAsync(root.ToString(), Encoding.UTF8);
                        break;
                    }
                default: ctx.Response.StatusCode = 405; break;
            }
        });
    }

    public async Task StartAsync()
    {
        await _app.StartAsync();
        Url = _app.Services.GetRequiredService<IServer>().Features.Get<IServerAddressesFeature>()!.Addresses.First().TrimEnd('/');
    }

    public async ValueTask DisposeAsync()
    {
        await _app.StopAsync();
        await _app.DisposeAsync();
    }
}