using ClaudeDo.Data;
using ClaudeDo.Data.Models;
using ClaudeDo.Data.Repositories;
using ClaudeDo.Worker.Config;
using ClaudeDo.Worker.Runner;
using Microsoft.EntityFrameworkCore;

namespace ClaudeDo.Worker.Services;

public sealed class QueueSlotState
{
    public required string TaskId { get; init; }
    public required DateTime StartedAt { get; init; }
    public required CancellationTokenSource Cts { get; init; }
}

public sealed class QueueService : BackgroundService
{
    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
    private readonly TaskRunner _runner;
    private readonly WorkerConfig _cfg;
    private readonly ILogger<QueueService> _logger;

    private readonly object _lock = new();
    private volatile QueueSlotState? _queueSlot;
    private volatile QueueSlotState? _overrideSlot;

    private readonly SemaphoreSlim _wakeSignal = new(0, 1);

    public QueueService(
        IDbContextFactory<ClaudeDoDbContext> dbFactory,
        TaskRunner runner,
        WorkerConfig cfg,
        ILogger<QueueService> logger)
    {
        _dbFactory = dbFactory;
        _runner = runner;
        _cfg = cfg;
        _logger = logger;
    }

    public IReadOnlyList<(string slot, string taskId, DateTime startedAt)> GetActive()
    {
        var list = new List<(string, string, DateTime)>();
        var q = _queueSlot;
        if (q is not null) list.Add(("queue", q.TaskId, q.StartedAt));
        var o = _overrideSlot;
        if (o is not null) list.Add(("override", o.TaskId, o.StartedAt));
        return list;
    }

    public void WakeQueue()
    {
        // Release if not already signalled.
        try { _wakeSignal.Release(); }
        catch (SemaphoreFullException) { /* already signalled */ }
    }

    public async Task RunNow(string taskId)
    {
        using (var context = _dbFactory.CreateDbContext())
        {
            var taskRepo = new TaskRepository(context);
            var exists = await taskRepo.GetByIdAsync(taskId);
            if (exists is null)
                throw new KeyNotFoundException($"Task '{taskId}' not found.");
        }

        lock (_lock)
        {
            if (_queueSlot?.TaskId == taskId)
                throw new InvalidOperationException("task is already running in queue slot");
            if (_overrideSlot is not null)
                throw new InvalidOperationException("override slot busy");

            var cts = new CancellationTokenSource();
            _overrideSlot = new QueueSlotState { TaskId = taskId, StartedAt = DateTime.UtcNow, Cts = cts };

            _ = RunInSlotAsync(taskId, "override", cts.Token).ContinueWith(t =>
            {
                if (t.IsFaulted)
                    _logger.LogError(t.Exception, "RunInSlotAsync failed for task {TaskId}", taskId);
                lock (_lock) { _overrideSlot = null; }
                cts.Dispose();
            }, TaskScheduler.Default);
        }
    }

    public async Task<string> ContinueTask(string taskId, string followUpPrompt)
    {
        using var context = _dbFactory.CreateDbContext();
        var taskRepo = new TaskRepository(context);
        var task = await taskRepo.GetByIdAsync(taskId)
            ?? throw new KeyNotFoundException($"Task '{taskId}' not found.");

        if (task.Status == Data.Models.TaskStatus.Running)
            throw new InvalidOperationException("task is already running");

        lock (_lock)
        {
            if (_queueSlot?.TaskId == taskId)
                throw new InvalidOperationException("task is already running in queue slot");
            if (_overrideSlot is not null)
                throw new InvalidOperationException("override slot busy");

            var cts = new CancellationTokenSource();
            _overrideSlot = new QueueSlotState { TaskId = taskId, StartedAt = DateTime.UtcNow, Cts = cts };

            _ = RunContinueInSlotAsync(taskId, followUpPrompt, cts.Token).ContinueWith(t =>
            {
                if (t.IsFaulted)
                    _logger.LogError(t.Exception, "RunContinueInSlotAsync failed for task {TaskId}", taskId);
                lock (_lock) { _overrideSlot = null; }
                cts.Dispose();
            }, TaskScheduler.Default);
        }

        return taskId;
    }

    public bool CancelTask(string taskId)
    {
        lock (_lock)
        {
            if (_queueSlot is not null && _queueSlot.TaskId == taskId)
            {
                _queueSlot.Cts.Cancel();
                return true;
            }
            if (_overrideSlot is not null && _overrideSlot.TaskId == taskId)
            {
                _overrideSlot.Cts.Cancel();
                return true;
            }
        }
        return false;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("QueueService started");

        using var timer = new PeriodicTimer(TimeSpan.FromMilliseconds(_cfg.QueueBackstopIntervalMs));

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                // Wait for wake signal or backstop timer.
                var wakeTask = _wakeSignal.WaitAsync(stoppingToken);
                var timerTask = timer.WaitForNextTickAsync(stoppingToken).AsTask();

                await Task.WhenAny(wakeTask, timerTask);

                // Drain wake signal if it fired.
                if (wakeTask.IsCompletedSuccessfully)
                {
                    // Good — signal consumed.
                }

                if (_queueSlot is not null) continue;

                TaskEntity? task;
                using (var context = _dbFactory.CreateDbContext())
                {
                    var taskRepo = new TaskRepository(context);
                    task = await taskRepo.GetNextQueuedAgentTaskAsync(DateTime.UtcNow, stoppingToken);
                }
                if (task is null) continue;

                lock (_lock)
                {
                    if (_queueSlot is not null) continue;

                    var cts = CancellationTokenSource.CreateLinkedTokenSource(stoppingToken);
                    _queueSlot = new QueueSlotState { TaskId = task.Id, StartedAt = DateTime.UtcNow, Cts = cts };

                    _ = RunInSlotAsync(task.Id, "queue", cts.Token).ContinueWith(t =>
                    {
                        if (t.IsFaulted)
                            _logger.LogError(t.Exception, "RunInSlotAsync failed for task {TaskId} in queue slot", task.Id);
                        lock (_lock) { _queueSlot = null; }
                        cts.Dispose();
                        WakeQueue(); // Check for next task immediately.
                    }, TaskScheduler.Default);
                }
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                break;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "QueueService loop error");
            }
        }

        _logger.LogInformation("QueueService stopping");
    }

    private async Task RunInSlotAsync(string taskId, string slot, CancellationToken ct)
    {
        try
        {
            _logger.LogInformation("Starting task {TaskId} in {Slot} slot", taskId, slot);

            TaskEntity task;
            using (var context = _dbFactory.CreateDbContext())
            {
                var taskRepo = new TaskRepository(context);
                task = await taskRepo.GetByIdAsync(taskId, ct)
                    ?? throw new KeyNotFoundException($"Task '{taskId}' not found.");
            }

            await _runner.RunAsync(task, slot, ct);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Slot runner error for task {TaskId}", taskId);
        }
    }

    private async Task RunContinueInSlotAsync(string taskId, string followUpPrompt, CancellationToken ct)
    {
        try
        {
            _logger.LogInformation("Continuing task {TaskId} in override slot", taskId);
            await _runner.ContinueAsync(taskId, followUpPrompt, "override", ct);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Continue runner error for task {TaskId}", taskId);
        }
    }
}