package worker

import (
	"context"
	"fmt"
	"strings"
	"time"

	"github.com/jfraeys/fetch_ml/internal/logging"
	"github.com/jfraeys/fetch_ml/internal/queue"
	"github.com/jfraeys/fetch_ml/internal/resources"
)

// Start starts the worker's main processing loop.
func (w *Worker) Start() {
	w.logger.Info("worker started",
		"worker_id", w.id,
		"max_concurrent", w.config.MaxWorkers,
		"poll_interval", w.config.PollInterval)

	go w.heartbeat()
	if w.config != nil && w.config.PrewarmEnabled {
		go w.prewarmNextLoop()
		go w.prewarmImageGCLoop()
	}

	for {
		switch {
		case w.ctx.Err() != nil:
			w.logger.Info("shutdown signal received, waiting for tasks")
			w.waitForTasks()
			return
		default:
		}
		if w.runningCount() >= w.config.MaxWorkers {
			time.Sleep(50 * time.Millisecond)
			continue
		}

		queueStart := time.Now()
		blockTimeout := time.Duration(w.config.PollInterval) * time.Second
		task, err := w.queue.GetNextTaskWithLeaseBlocking(
			w.config.WorkerID,
			w.config.TaskLeaseDuration,
			blockTimeout,
		)
		queueLatency := time.Since(queueStart)
		if err != nil {
			if err == context.DeadlineExceeded {
				continue
			}
			w.logger.Error("error fetching task",
				"worker_id", w.id,
				"error", err)
			continue
		}

		if task == nil {
			if queueLatency > 200*time.Millisecond {
				w.logger.Debug("queue poll latency",
					"latency_ms", queueLatency.Milliseconds())
			}
			continue
		}

		if depth, derr := w.queue.QueueDepth(); derr == nil {
			if queueLatency > 100*time.Millisecond || depth > 0 {
				w.logger.Debug("queue fetch metrics",
					"latency_ms", queueLatency.Milliseconds(),
					"remaining_depth", depth)
			}
		} else if queueLatency > 100*time.Millisecond {
			w.logger.Debug("queue fetch metrics",
				"latency_ms", queueLatency.Milliseconds(),
				"depth_error", derr)
		}

		// Reserve a running slot *before* starting the goroutine so we don't drain
		// the entire queue while max_workers is 1.
		w.reserveRunningSlot(task.ID)
		go w.executeTaskWithLease(task)
	}
}

func (w *Worker) reserveRunningSlot(taskID string) {
	w.runningMu.Lock()
	defer w.runningMu.Unlock()
	if w.running == nil {
		w.running = make(map[string]context.CancelFunc)
	}
	// Track a cancel func for future shutdown handling; currently best-effort.
	_, cancel := context.WithCancel(w.ctx)
	w.running[taskID] = cancel
}

func (w *Worker) releaseRunningSlot(taskID string) {
	w.runningMu.Lock()
	defer w.runningMu.Unlock()
	if w.running == nil {
		return
	}
	if cancel, ok := w.running[taskID]; ok {
		cancel()
		delete(w.running, taskID)
	}
}

func (w *Worker) prewarmImageGCLoop() {
	if w.config == nil || !w.config.PrewarmEnabled {
		return
	}
	if w.envPool == nil {
		return
	}
	if w.config.LocalMode {
		return
	}
	if strings.TrimSpace(w.config.PodmanImage) == "" {
		return
	}

	lastSeen := ""
	ticker := time.NewTicker(5 * time.Minute)
	defer ticker.Stop()

	runGC := func() {
		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
		defer cancel()
		_ = w.envPool.PruneImages(ctx, 24*time.Hour)
	}

	for {
		select {
		case <-w.ctx.Done():
			return
		case <-ticker.C:
			if w.queue != nil {
				v, err := w.queue.PrewarmGCRequestValue()
				if err == nil && v != "" && v != lastSeen {
					lastSeen = v
					runGC()
					continue
				}
			}
			runGC()
		}
	}
}

func (w *Worker) heartbeat() {
	ticker := time.NewTicker(30 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-w.ctx.Done():
			return
		case <-ticker.C:
			if err := w.queue.Heartbeat(w.id); err != nil {
				w.logger.Warn("heartbeat failed",
					"worker_id", w.id,
					"error", err)
			}
		}
	}
}

func (w *Worker) waitForTasks() {
	timeout := time.After(5 * time.Minute)
	ticker := time.NewTicker(1 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-timeout:
			w.logger.Warn("shutdown timeout, force stopping",
				"running_tasks", len(w.running))
			return
		case <-ticker.C:
			count := w.runningCount()
			if count == 0 {
				w.logger.Info("all tasks completed, shutting down")
				return
			}
			w.logger.Debug("waiting for tasks to complete",
				"remaining", count)
		}
	}
}

func (w *Worker) runningCount() int {
	w.runningMu.RLock()
	defer w.runningMu.RUnlock()
	return len(w.running)
}

// GetMetrics returns current worker metrics.
func (w *Worker) GetMetrics() map[string]any {
	stats := w.metrics.GetStats()
	stats["worker_id"] = w.id
	stats["max_workers"] = w.config.MaxWorkers
	return stats
}

// Stop gracefully shuts down the worker.
func (w *Worker) Stop() {
	w.cancel()
	w.waitForTasks()

	// FIXED: Check error return values
	if err := w.server.Close(); err != nil {
		w.logger.Warn("error closing server connection", "error", err)
	}
	if err := w.queue.Close(); err != nil {
		w.logger.Warn("error closing queue connection", "error", err)
	}
	if w.metricsSrv != nil {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := w.metricsSrv.Shutdown(ctx); err != nil {
			w.logger.Warn("metrics exporter shutdown error", "error", err)
		}
	}
	w.logger.Info("worker stopped", "worker_id", w.id)
}

// Execute task with lease management and retry.
func (w *Worker) executeTaskWithLease(task *queue.Task) {
	defer w.releaseRunningSlot(task.ID)

	// Track task for graceful shutdown
	w.gracefulWait.Add(1)
	w.activeTasks.Store(task.ID, task)
	defer w.gracefulWait.Done()
	defer w.activeTasks.Delete(task.ID)

	// Create task-specific context with timeout
	taskCtx := logging.EnsureTrace(w.ctx)               // add trace + span if missing
	taskCtx = logging.CtxWithJob(taskCtx, task.JobName) // add job metadata
	taskCtx = logging.CtxWithTask(taskCtx, task.ID)     // add task metadata

	taskCtx, taskCancel := context.WithTimeout(taskCtx, 24*time.Hour)
	defer taskCancel()

	logger := w.logger.Job(taskCtx, task.JobName, task.ID)
	logger.Info("starting task",
		"worker_id", w.id,
		"datasets", task.Datasets,
		"priority", task.Priority)

	// Record task start
	w.metrics.RecordTaskStart()
	defer w.metrics.RecordTaskCompletion()

	// Check for context cancellation
	select {
	case <-taskCtx.Done():
		logger.Info("task cancelled before execution")
		return
	default:
	}

	// Jupyter tasks are executed directly by the worker (no experiment/provenance pipeline).
	if isJupyterTask(task) {
		out, err := w.runJupyterTask(taskCtx, task)
		endTime := time.Now()
		task.EndedAt = &endTime
		if err != nil {
			logger.Error("jupyter task failed", "error", err)
			task.Status = "failed"
			task.Error = err.Error()
			_ = w.queue.UpdateTaskWithMetrics(task, "final")
			w.metrics.RecordTaskFailure()
			_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
			return
		}
		if len(out) > 0 {
			task.Output = string(out)
		}
		task.Status = "completed"
		_ = w.queue.UpdateTaskWithMetrics(task, "final")
		_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
		return
	}

	// Parse datasets from task arguments
	task.Datasets = resolveDatasets(task)

	if err := w.validateTaskForExecution(taskCtx, task); err != nil {
		logger.Error("task validation failed", "error", err)
		task.Status = "failed"
		task.Error = fmt.Sprintf("Validation failed: %v", err)
		endTime := time.Now()
		task.EndedAt = &endTime
		if updateErr := w.queue.UpdateTaskWithMetrics(task, "final"); updateErr != nil {
			logger.Error("failed to update task status after validation failure", "error", updateErr)
		}
		w.metrics.RecordTaskFailure()
		_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
		return
	}

	if err := w.enforceTaskProvenance(taskCtx, task); err != nil {
		logger.Error("provenance validation failed", "error", err)
		task.Status = "failed"
		task.Error = fmt.Sprintf("Provenance validation failed: %v", err)
		endTime := time.Now()
		task.EndedAt = &endTime
		if updateErr := w.queue.UpdateTaskWithMetrics(task, "final"); updateErr != nil {
			logger.Error(
				"failed to update task status after provenance validation failure",
				"error", updateErr)
		}
		w.metrics.RecordTaskFailure()
		_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
		return
	}

	lease, err := w.resources.Acquire(taskCtx, task)
	if err != nil {
		logger.Error("resource acquisition failed", "error", err)
		task.Status = "failed"
		task.Error = fmt.Sprintf("Resource acquisition failed: %v", err)
		endTime := time.Now()
		task.EndedAt = &endTime
		if updateErr := w.queue.UpdateTaskWithMetrics(task, "final"); updateErr != nil {
			logger.Error(
				"failed to update task status after resource acquisition failure",
				"error", updateErr)
		}
		w.metrics.RecordTaskFailure()
		_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
		return
	}
	defer lease.Release()

	// Start heartbeat goroutine
	heartbeatCtx, cancelHeartbeat := context.WithCancel(context.Background())
	defer cancelHeartbeat()

	go w.heartbeatLoop(heartbeatCtx, task.ID)

	// Update task status and record attempt start
	task.Status = "running"
	now := time.Now()
	task.StartedAt = &now
	task.WorkerID = w.id

	// Record this attempt in the task history
	attempt := queue.Attempt{
		Attempt:   task.RetryCount + 1, // 1-indexed attempt number
		StartedAt: now,
		WorkerID:  w.id,
		Status:    "running",
	}
	task.Attempts = append(task.Attempts, attempt)

	// Phase 1 provenance capture: best-effort metadata enrichment before persisting the running state.
	w.recordTaskProvenance(taskCtx, task)

	if err := w.queue.UpdateTaskWithMetrics(task, "start"); err != nil {
		logger.Error("failed to update task status", "error", err)
		w.metrics.RecordTaskFailure()
		return
	}

	if w.config.AutoFetchData && len(task.Datasets) > 0 {
		if err := w.fetchDatasets(taskCtx, task); err != nil {
			logger.Error("data fetch failed", "error", err)
			task.Status = "failed"
			task.Error = fmt.Sprintf("Data fetch failed: %v", err)
			endTime := time.Now()
			task.EndedAt = &endTime
			err := w.queue.UpdateTask(task)
			if err != nil {
				logger.Error("failed to update task status after data fetch failure", "error", err)
			}
			w.metrics.RecordTaskFailure()
			return
		}
	}
	if err := w.verifyDatasetSpecs(taskCtx, task); err != nil {
		logger.Error("dataset checksum verification failed", "error", err)
		task.Status = "failed"
		task.Error = fmt.Sprintf("Dataset checksum verification failed: %v", err)
		endTime := time.Now()
		task.EndedAt = &endTime
		if updateErr := w.queue.UpdateTaskWithMetrics(task, "final"); updateErr != nil {
			logger.Error(
				"failed to update task after dataset checksum verification failure",
				"error", updateErr)
		}
		w.metrics.RecordTaskFailure()
		return
	}
	if err := w.verifySnapshot(taskCtx, task); err != nil {
		logger.Error("snapshot checksum verification failed", "error", err)
		task.Status = "failed"
		task.Error = fmt.Sprintf("Snapshot checksum verification failed: %v", err)
		endTime := time.Now()
		task.EndedAt = &endTime
		if updateErr := w.queue.UpdateTaskWithMetrics(task, "final"); updateErr != nil {
			logger.Error(
				"failed to update task after snapshot checksum verification failure",
				"error", updateErr)
		}
		w.metrics.RecordTaskFailure()
		return
	}

	// Execute job with panic recovery
	var execErr error
	func() {
		defer func() {
			if r := recover(); r != nil {
				execErr = fmt.Errorf("panic during execution: %v", r)
			}
		}()
		cudaVisible := resources.FormatCUDAVisibleDevices(lease)
		execErr = w.runJob(taskCtx, task, cudaVisible)
	}()

	// Finalize task and record attempt completion
	endTime := time.Now()
	task.EndedAt = &endTime

	// Update the last attempt with completion info
	if len(task.Attempts) > 0 {
		lastIdx := len(task.Attempts) - 1
		task.Attempts[lastIdx].EndedAt = &endTime
	}

	if execErr != nil {
		task.Error = execErr.Error()

		// Update last attempt with failure info
		if len(task.Attempts) > 0 {
			lastIdx := len(task.Attempts) - 1
			task.Attempts[lastIdx].Status = "failed"
			task.Attempts[lastIdx].Error = execErr.Error()
			task.Attempts[lastIdx].FailureClass = queue.ClassifyFailure(0, nil, execErr.Error())
			// TODO: Capture exit code and signal from actual execution
		}

		// Check if transient error (network, timeout, etc)
		if isTransientError(execErr) && task.RetryCount < task.MaxRetries {
			w.logger.Warn("task failed with transient error, will retry",
				"task_id", task.ID,
				"error", execErr,
				"retry_count", task.RetryCount)
			_ = w.queue.RetryTask(task)
		} else {
			task.Status = "failed"
			_ = w.queue.UpdateTaskWithMetrics(task, "final")
		}
	} else {
		task.Status = "completed"
		// Update last attempt with success
		if len(task.Attempts) > 0 {
			lastIdx := len(task.Attempts) - 1
			task.Attempts[lastIdx].Status = "completed"
		}
		_ = w.queue.UpdateTaskWithMetrics(task, "final")
	}

	// Release lease
	_ = w.queue.ReleaseLease(task.ID, w.config.WorkerID)
}

// Heartbeat loop to renew lease.
func (w *Worker) heartbeatLoop(ctx context.Context, taskID string) {
	ticker := time.NewTicker(w.config.HeartbeatInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if err := w.queue.RenewLease(taskID, w.config.WorkerID, w.config.TaskLeaseDuration); err != nil {
				w.logger.Error("failed to renew lease", "task_id", taskID, "error", err)
				return
			}
			// Also update worker heartbeat
			_ = w.queue.Heartbeat(w.config.WorkerID)
		}
	}
}

// Shutdown gracefully shuts down the worker.
func (w *Worker) Shutdown() error {
	w.logger.Info("starting graceful shutdown", "active_tasks", w.countActiveTasks())

	// Wait for active tasks with timeout
	done := make(chan struct{})
	go func() {
		w.gracefulWait.Wait()
		close(done)
	}()

	timeout := time.After(w.config.GracefulTimeout)
	select {
	case <-done:
		w.logger.Info("all tasks completed, shutdown successful")
	case <-timeout:
		w.logger.Warn("graceful shutdown timeout, releasing active leases")
		w.releaseAllLeases()
	}

	return w.queue.Close()
}

// Release all active leases.
func (w *Worker) releaseAllLeases() {
	w.activeTasks.Range(func(key, _ interface{}) bool {
		taskID := key.(string)
		if err := w.queue.ReleaseLease(taskID, w.config.WorkerID); err != nil {
			w.logger.Error("failed to release lease", "task_id", taskID, "error", err)
		}
		return true
	})
}

// Helper functions.
func (w *Worker) countActiveTasks() int {
	count := 0
	w.activeTasks.Range(func(_, _ interface{}) bool {
		count++
		return true
	})
	return count
}

func isTransientError(err error) bool {
	if err == nil {
		return false
	}
	// Check if error is transient (network, timeout, resource unavailable, etc)
	errStr := err.Error()
	transientIndicators := []string{
		"connection refused",
		"timeout",
		"temporary failure",
		"resource temporarily unavailable",
		"no such host",
		"network unreachable",
	}
	for _, indicator := range transientIndicators {
		if strings.Contains(strings.ToLower(errStr), indicator) {
			return true
		}
	}
	return false
}