using System.IO.Compression;
using System.Text;
using Grpc.Core;
using Microsoft.Extensions.Options;
using ScrapperAPI.AgentGrpc;

namespace VoyagerAgent;

public sealed class AgentWorker : BackgroundService
{
    private readonly ILogger<AgentWorker> _logger;
    private readonly AgentClientOptions _opts;
    private readonly GrpcAgentClient _grpc;

    public AgentWorker(ILogger<AgentWorker> logger, IOptions<AgentClientOptions> opts, GrpcAgentClient grpc)
    {
        _logger = logger;
        _opts = opts.Value;
        _grpc = grpc;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        if (_opts.SessionIds.Length == 0)
        {
            _logger.LogWarning("No Agent:SessionIds configured. Agent will idle.");
        }

        var client = _grpc.CreateClient();

        await TryRegisterAsync(client, stoppingToken);

        using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(30) };
        http.DefaultRequestHeaders.UserAgent.ParseAdd("voyager-agent/1.0");

        while (!stoppingToken.IsCancellationRequested)
        {
            var didWork = false;

            foreach (var sessionId in _opts.SessionIds)
            {
                if (stoppingToken.IsCancellationRequested) break;

                try
                {
                    var lease = await client.LeaseWorkAsync(new LeaseWorkRequest
                    {
                        AgentId = _opts.AgentId,
                        SessionId = sessionId,
                        Capacity = _opts.Capacity
                    }, cancellationToken: stoppingToken);

                    if (lease.Items.Count == 0)
                        continue;

                    didWork = true;

                    foreach (var item in lease.Items)
                    {
                        if (stoppingToken.IsCancellationRequested) break;

                        try
                        {
                            var html = await http.GetStringAsync(item.Url, stoppingToken);
                            var compressed = GzipCompressUtf8(html, CompressionLevel.Fastest, out var origLen);

                            var submit = await client.SubmitResultAsync(new SubmitResultRequest
                            {
                                QueueId = item.QueueId,
                                AgentId = _opts.AgentId,
                                Success = true,
                                ContentEncoding = "gzip",
                                ContentBytes = Google.Protobuf.ByteString.CopyFrom(compressed),
                                OriginalLength = origLen,
                                CompressedLength = compressed.Length
                            }, cancellationToken: stoppingToken);

                            if (!submit.Ok)
                                _logger.LogWarning("SubmitResult not ok for queue {QueueId}: {Message}", item.QueueId, submit.Message);
                        }
                        catch (Exception ex)
                        {
                            _logger.LogError(ex, "Scrape failed for {Url}", item.Url);

                            try
                            {
                                await client.SubmitResultAsync(new SubmitResultRequest
                                {
                                    QueueId = item.QueueId,
                                    AgentId = _opts.AgentId,
                                    Success = false,
                                    Error = ex.Message
                                }, cancellationToken: stoppingToken);
                            }
                            catch (Exception inner)
                            {
                                _logger.LogError(inner, "Failed to submit failure status for queue {QueueId}", item.QueueId);
                            }
                        }
                    }
                }
                catch (RpcException rpc)
                {
                    _logger.LogWarning("gRPC error: {Status} {Detail}", rpc.StatusCode, rpc.Status.Detail);
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "Unhandled error while leasing work.");
                }
            }

            // heartbeat (best-effort)
            try
            {
                await client.HeartbeatAsync(new HeartbeatRequest { AgentId = _opts.AgentId }, cancellationToken: stoppingToken);
            }
            catch { /* ignore */ }

            if (!didWork)
                await Task.Delay(_opts.PollDelayMs, stoppingToken);
        }
    }

    private async Task TryRegisterAsync(AgentService.AgentServiceClient client, CancellationToken ct)
    {
        try
        {
            await client.RegisterAgentAsync(new RegisterAgentRequest
            {
                AgentId = _opts.AgentId,
                DisplayName = _opts.DisplayName ?? string.Empty
            }, cancellationToken: ct);

            _logger.LogInformation("Agent registered as {AgentId}", _opts.AgentId);
        }
        catch (RpcException rpc)
        {
            _logger.LogWarning("RegisterAgent failed: {Status} {Detail}", rpc.StatusCode, rpc.Status.Detail);
        }
    }

    private static byte[] GzipCompressUtf8(string content, CompressionLevel level, out int originalLength)
    {
        var bytes = Encoding.UTF8.GetBytes(content);
        originalLength = bytes.Length;

        using var ms = new MemoryStream();
        using (var gzip = new GZipStream(ms, level, leaveOpen: true))
        {
            gzip.Write(bytes, 0, bytes.Length);
        }
        return ms.ToArray();
    }
}