using System.Security.Cryptography;
using System.Text;
using System.Text.Json;

namespace CampusErrand.Services;

/// <summary>
/// 腾讯 IM 服务，负责生成 UserSig 和调用服务端 REST API
/// </summary>
public class TencentIMService
{
    private readonly long _sdkAppId;
    private readonly string _secretKey;
    private readonly HttpClient _httpClient;
    private const string AdminAccount = "administrator";

    public TencentIMService(IConfiguration configuration, IHttpClientFactory httpClientFactory)
    {
        var config = configuration.GetSection("TencentIM");
        _sdkAppId = config.GetValue<long>("SDKAppId");
        _secretKey = config["SecretKey"]!;
        _httpClient = httpClientFactory.CreateClient();
    }

    public long SDKAppId => _sdkAppId;

    /// <summary>
    /// 生成 UserSig
    /// </summary>
    public string GenerateUserSig(string userId, int expireSeconds = 604800)
    {
        var now = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
        var obj = new Dictionary<string, object>
        {
            ["TLS.ver"] = "2.0",
            ["TLS.identifier"] = userId,
            ["TLS.sdkappid"] = _sdkAppId,
            ["TLS.expire"] = expireSeconds,
            ["TLS.time"] = now
        };

        var contentToSign = $"TLS.identifier:{userId}\nTLS.sdkappid:{_sdkAppId}\nTLS.time:{now}\nTLS.expire:{expireSeconds}\n";
        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(_secretKey));
        var sig = hmac.ComputeHash(Encoding.UTF8.GetBytes(contentToSign));
        obj["TLS.sig"] = Convert.ToBase64String(sig);

        var jsonBytes = Encoding.UTF8.GetBytes(JsonSerializer.Serialize(obj));

        using var output = new MemoryStream();
        using (var zlib = new System.IO.Compression.ZLibStream(output, System.IO.Compression.CompressionLevel.Optimal))
        {
            zlib.Write(jsonBytes, 0, jsonBytes.Length);
        }

        return Convert.ToBase64String(output.ToArray())
            .Replace('+', '*')
            .Replace('/', '-')
            .Replace('=', '_');
    }

    /// <summary>
    /// 通过服务端 REST API 拉取两个用户之间的漫游消息
    /// </summary>
    public async Task<JsonElement> GetRoamMessagesAsync(string fromUserId, string toUserId, int maxCnt = 100, long minTime = 0, long maxTime = 0)
    {
        var adminSig = GenerateUserSig(AdminAccount);
        var random = Random.Shared.Next(100000, 999999);
        var url = $"https://console.tim.qq.com/v4/openim/admin_getroammsg?sdkappid={_sdkAppId}&identifier={AdminAccount}&usersig={adminSig}&random={random}&contenttype=json";

        var body = new
        {
            Operator_Account = fromUserId,
            Peer_Account = toUserId,
            MaxCnt = maxCnt,
            MinTime = minTime,
            MaxTime = maxTime > 0 ? maxTime : DateTimeOffset.UtcNow.ToUnixTimeSeconds()
        };

        var content = new StringContent(JsonSerializer.Serialize(body), Encoding.UTF8, "application/json");
        var response = await _httpClient.PostAsync(url, content);
        var json = await response.Content.ReadAsStringAsync();
        Console.WriteLine($"[IM] 拉取漫游消息: {fromUserId} -> {toUserId}, 响应: {json}");
        return JsonSerializer.Deserialize<JsonElement>(json);
    }
}