using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Text.Encodings.Web;
using Admin.NET.Core;
using Admin.NET.Core.Service;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Admin.NET.Plugin.AiDOP.DataPlatform.Inbound;

/// <summary>
/// 插件侧入站验签：签名串含原始 body 摘要 + Idempotency-Key。不改框架 Core。
/// </summary>
public sealed class InboundSignatureHandler : AuthenticationHandler<InboundSignatureOptions>
{
    private readonly SysOpenAccessService _openAccess;
    private readonly SysCacheService _cache;

    public InboundSignatureHandler(
        IOptionsMonitor<InboundSignatureOptions> options,
        ILoggerFactory logger,
        UrlEncoder encoder,
        SysOpenAccessService openAccess,
        SysCacheService cache)
        : base(options, logger, encoder)
    {
        _openAccess = openAccess;
        _cache = cache;
    }

    protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        var accessKey = Header(InboundSignatureDefaults.AccessKeyHeader);
        var timestampStr = Header(InboundSignatureDefaults.TimestampHeader);
        var nonce = Header(InboundSignatureDefaults.NonceHeader);
        var signature = Header(InboundSignatureDefaults.SignatureHeader);
        var idempotencyKey = Header(InboundSignatureDefaults.IdempotencyKeyHeader);
        var contentShaHeader = Header(InboundSignatureDefaults.ContentSha256Header);

        if (string.IsNullOrWhiteSpace(idempotencyKey))
            return Fail(InboundSignatureDefaults.MissingIdempotencyKey);
        if (string.IsNullOrWhiteSpace(accessKey))
            return Fail("missing X-Access-Key");
        if (string.IsNullOrWhiteSpace(timestampStr))
            return Fail("missing X-Timestamp");
        if (string.IsNullOrWhiteSpace(nonce))
            return Fail("missing X-Nonce");
        if (string.IsNullOrWhiteSpace(signature))
            return Fail("missing X-Signature");
        if (string.IsNullOrWhiteSpace(contentShaHeader))
            return Fail("missing X-Content-SHA256");

        if (!long.TryParse(timestampStr, out var unixSec))
            return Fail("invalid X-Timestamp");

        var nowUnix = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
        if (Math.Abs(nowUnix - unixSec) > Options.AllowedDateDrift.TotalSeconds)
            return Fail("timestamp outside allowed window");

        Request.EnableBuffering();
        using var ms = new MemoryStream();
        await Request.Body.CopyToAsync(ms);
        Request.Body.Position = 0;
        var bodyBytes = ms.ToArray();
        var contentSha256 = Convert.ToHexString(SHA256.HashData(bodyBytes)).ToLowerInvariant();
        if (!string.Equals(contentSha256, contentShaHeader.Trim(), StringComparison.OrdinalIgnoreCase))
            return Fail(InboundSignatureDefaults.ContentDigestMismatch);

        SysOpenAccess openAccess;
        try
        {
            openAccess = await _openAccess.GetByKey(accessKey);
        }
        catch (Exception ex)
        {
            Logger.LogWarning(ex, "InboundSignature GetByKey failed");
            return Fail("unknown AccessKey");
        }

        if (openAccess == null || string.IsNullOrWhiteSpace(openAccess.AccessSecret))
            return Fail("unknown AccessKey");

        var path = Request.Path.Value ?? string.Empty;
        // 接收 POST 与方案 §5.2 一致（POST&path&...）；schema/receipts 等 GET 用实际方法名。
        var method = (Request.Method ?? "POST").Trim().ToUpperInvariant();
        var message = $"{method}&{path}&{accessKey}&{timestampStr}&{nonce}&{contentSha256}&{idempotencyKey}";
        var expected = Sign(openAccess.AccessSecret, message);
        var expectedBytes = Encoding.UTF8.GetBytes(expected);
        var actualBytes = Encoding.UTF8.GetBytes(signature);
        if (expectedBytes.Length != actualBytes.Length
            || !CryptographicOperations.FixedTimeEquals(expectedBytes, actualBytes))
            return Fail("invalid signature");

        var nonceKey = $"AIDOP_INBOUND_NONCE:{accessKey}:{nonce}";
        if (_cache.ExistKey(nonceKey))
            return Fail("nonce replay");
        _cache.Set(nonceKey, 1, Options.AllowedDateDrift * 2);

        var identity = new ClaimsIdentity(InboundSignatureDefaults.AuthenticationScheme);
        identity.AddClaim(new Claim(ClaimConst.TenantId, openAccess.BindTenantId.ToString()));
        identity.AddClaim(new Claim(ClaimConst.UserId, openAccess.BindUserId.ToString()));
        identity.AddClaim(new Claim(InboundSignatureDefaults.AccessKeyClaim, accessKey));
        var ticket = new AuthenticationTicket(
            new ClaimsPrincipal(identity),
            InboundSignatureDefaults.AuthenticationScheme);
        return AuthenticateResult.Success(ticket);
    }

    protected override async Task HandleChallengeAsync(AuthenticationProperties properties)
    {
        var result = await HandleAuthenticateOnceSafeAsync();
        var message = result.Failure?.Message
                      ?? Context.Items[InboundSignatureDefaults.FailMessageItemKey] as string
                      ?? "unauthorized";
        var status = IsBadRequest(message) ? 400 : 401;
        if (Context.Response.HasStarted)
            return;
        Context.Response.StatusCode = status;
        Context.Response.ContentType = "application/json; charset=utf-8";
        await Context.Response.WriteAsync($"{{\"code\":{status},\"message\":{System.Text.Json.JsonSerializer.Serialize(message)},\"data\":null}}");
    }

    private AuthenticateResult Fail(string message)
    {
        Context.Items[InboundSignatureDefaults.FailMessageItemKey] = message;
        return AuthenticateResult.Fail(message);
    }

    private string Header(string name) => Request.Headers[name].FirstOrDefault();

    private static bool IsBadRequest(string message) =>
        string.Equals(message, InboundSignatureDefaults.MissingIdempotencyKey, StringComparison.OrdinalIgnoreCase)
        || string.Equals(message, InboundSignatureDefaults.ContentDigestMismatch, StringComparison.OrdinalIgnoreCase);

    private static string Sign(string secret, string message)
    {
        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
        return Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(message)));
    }
}