// Package worker provides the ML task worker implementation
package worker

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"math/rand"
	"net/http"
	"os"
	"path/filepath"
	"time"

	"github.com/jfraeys/fetch_ml/internal/logging"
	"github.com/jfraeys/fetch_ml/internal/metrics"
	"github.com/jfraeys/fetch_ml/internal/queue"
	"github.com/jfraeys/fetch_ml/internal/resources"
	"github.com/jfraeys/fetch_ml/internal/scheduler"
	"github.com/jfraeys/fetch_ml/internal/worker/execution"
	"github.com/jfraeys/fetch_ml/internal/worker/executor"
	"github.com/jfraeys/fetch_ml/internal/worker/integrity"
	"github.com/jfraeys/fetch_ml/internal/worker/interfaces"
	"github.com/jfraeys/fetch_ml/internal/worker/lifecycle"
	"github.com/jfraeys/fetch_ml/internal/worker/plugins"
)

// Worker represents an ML task worker with composed dependencies.
type Worker struct {
	Jupyter          plugins.JupyterManager
	QueueClient      queue.Backend
	Config           *Config
	Logger           *logging.Logger
	RunLoop          *lifecycle.RunLoop
	Runner           *executor.JobRunner
	Metrics          *metrics.Metrics
	metricsSrv       *http.Server
	Health           *lifecycle.HealthMonitor
	Resources        *resources.Manager
	ID               string
	gpuDetectionInfo GPUDetectionInfo
	schedulerConn    *scheduler.SchedulerConn // For distributed mode
	ctx              context.Context
	cancel           context.CancelFunc
}

// Start begins the worker's main processing loop.
func (w *Worker) Start() {
	w.Logger.Info("worker starting",
		"worker_id", w.ID,
		"max_concurrent", w.Config.MaxWorkers,
		"mode", w.Config.Mode,
	)
	slog.SetDefault(w.Logger.Logger)

	w.ctx, w.cancel = context.WithCancel(context.Background())
	w.Health.RecordHeartbeat()

	// Start heartbeat loop for distributed mode
	if w.Config.Mode == "distributed" && w.schedulerConn != nil {
		go w.heartbeatLoop()
	}

	w.RunLoop.Start()
}

// heartbeatLoop sends periodic heartbeats with slot status to scheduler
func (w *Worker) heartbeatLoop() {
	// Use configured interval or default to 10s
	intervalSecs := w.Config.Scheduler.HeartbeatIntervalSecs
	if intervalSecs == 0 {
		intervalSecs = 10
	}

	// Add jitter (0-5s) to prevent thundering herd
	jitter := time.Duration(rand.Intn(5)) * time.Second
	interval := time.Duration(intervalSecs)*time.Second + jitter

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-w.ctx.Done():
			return
		case <-ticker.C:
			w.Health.RecordHeartbeat()
			if w.schedulerConn != nil {
				slots := scheduler.SlotStatus{
					BatchTotal: w.Config.MaxWorkers,
					BatchInUse: w.RunLoop.RunningCount(),
				}
				w.schedulerConn.Send(scheduler.Message{
					Type: scheduler.MsgHeartbeat,
					Payload: mustMarshal(scheduler.HeartbeatPayload{
						WorkerID: w.ID,
						Slots:    slots,
					}),
				})
			}
		}
	}
}

// Stop gracefully shuts down the worker immediately.
func (w *Worker) Stop() {
	w.Logger.Info("worker stopping", "worker_id", w.ID)

	if w.cancel != nil {
		w.cancel()
	}

	w.RunLoop.Stop()

	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 server shutdown error", "error", err)
		}
	}

	w.Logger.Info("worker stopped", "worker_id", w.ID)
}

// Shutdown performs a graceful shutdown with timeout.
func (w *Worker) Shutdown() error {
	w.Logger.Info("starting graceful shutdown", "worker_id", w.ID)

	w.RunLoop.Stop()

	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 server shutdown error", "error", err)
		}
	}

	w.Logger.Info("worker shut down gracefully", "worker_id", w.ID)
	return nil
}

// IsHealthy returns true if the worker is healthy.
func (w *Worker) IsHealthy() bool {
	return w.Health.IsHealthy(5 * time.Minute)
}

// 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
	stats["healthy"] = w.IsHealthy()
	return stats
}

// GetID returns the worker ID.
func (w *Worker) GetID() string {
	return w.ID
}

// SelectDependencyManifest re-exports the executor function for API helpers.
// It detects the dependency manifest file in the given directory.
func SelectDependencyManifest(filesPath string) (string, error) {
	return executor.SelectDependencyManifest(filesPath)
}

// DirOverallSHA256Hex re-exports the integrity function for test compatibility.
func DirOverallSHA256Hex(root string) (string, error) {
	return integrity.DirOverallSHA256Hex(root)
}

// NormalizeSHA256ChecksumHex re-exports the integrity function for test compatibility.
func NormalizeSHA256ChecksumHex(checksum string) (string, error) {
	return integrity.NormalizeSHA256ChecksumHex(checksum)
}

// StageSnapshot re-exports the execution function for test compatibility.
func StageSnapshot(basePath, dataDir, taskID, snapshotID, jobDir string) error {
	return execution.StageSnapshot(basePath, dataDir, taskID, snapshotID, jobDir)
}

// StageSnapshotFromPath re-exports the execution function for test compatibility.
func StageSnapshotFromPath(basePath, taskID, srcPath, jobDir string) error {
	return execution.StageSnapshotFromPath(basePath, taskID, srcPath, jobDir)
}

// ComputeTaskProvenance computes provenance information for a task.
// This re-exports the integrity function for test compatibility.
func ComputeTaskProvenance(basePath string, task *queue.Task) (map[string]string, error) {
	pc := integrity.NewProvenanceCalculator(basePath)
	return pc.ComputeProvenance(task)
}

// VerifyDatasetSpecs verifies dataset specifications for this task.
// This is a test compatibility method that wraps the integrity package.
func (w *Worker) VerifyDatasetSpecs(ctx context.Context, task *queue.Task) error {
	dataDir := w.Config.DataDir
	if dataDir == "" {
		dataDir = "/tmp/data"
	}
	verifier := integrity.NewDatasetVerifier(dataDir)
	return verifier.VerifyDatasetSpecs(task)
}

// EnforceTaskProvenance enforces provenance requirements for a task.
// It validates and/or populates provenance metadata based on the ProvenanceBestEffort config.
// In strict mode (ProvenanceBestEffort=false), it returns an error if metadata doesn't match computed values.
// In best-effort mode (ProvenanceBestEffort=true), it populates missing metadata fields.
func (w *Worker) EnforceTaskProvenance(ctx context.Context, task *queue.Task) error {
	if task == nil {
		return fmt.Errorf("task is nil")
	}

	basePath := w.Config.BasePath
	if basePath == "" {
		basePath = os.TempDir()
	}
	dataDir := w.Config.DataDir
	if dataDir == "" {
		dataDir = filepath.Join(basePath, "data")
	}

	bestEffort := w.Config.ProvenanceBestEffort

	// Get commit_id from metadata
	commitID := task.Metadata["commit_id"]
	if commitID == "" {
		return fmt.Errorf("missing commit_id in task metadata")
	}

	// Compute and verify experiment manifest SHA
	expPath := filepath.Join(basePath, commitID)
	manifestSHA, err := integrity.DirOverallSHA256Hex(expPath)
	if err != nil {
		if !bestEffort {
			return fmt.Errorf("failed to compute experiment manifest SHA: %w", err)
		}
		// In best-effort mode, we'll use whatever is provided or skip
		manifestSHA = ""
	}

	// Handle experiment_manifest_overall_sha
	expectedManifestSHA := task.Metadata["experiment_manifest_overall_sha"]
	if expectedManifestSHA == "" {
		if !bestEffort {
			return fmt.Errorf("missing experiment_manifest_overall_sha in task metadata")
		}
		// Populate in best-effort mode
		if task.Metadata == nil {
			task.Metadata = map[string]string{}
		}
		task.Metadata["experiment_manifest_overall_sha"] = manifestSHA
	} else if !bestEffort && expectedManifestSHA != manifestSHA {
		return fmt.Errorf("experiment manifest SHA mismatch: expected %s, got %s", expectedManifestSHA, manifestSHA)
	}

	// Handle deps_manifest_sha256 - auto-detect if not provided
	filesPath := filepath.Join(expPath, "files")
	depsManifestName := task.Metadata["deps_manifest_name"]
	if depsManifestName == "" {
		// Auto-detect manifest file
		depsManifestName, _ = executor.SelectDependencyManifest(filesPath)
	}
	if depsManifestName != "" {
		if task.Metadata == nil {
			task.Metadata = map[string]string{}
		}
		task.Metadata["deps_manifest_name"] = depsManifestName
		depsPath := filepath.Join(filesPath, depsManifestName)
		depsSHA, err := integrity.FileSHA256Hex(depsPath)
		if err != nil {
			if !bestEffort {
				return fmt.Errorf("failed to compute deps manifest SHA: %w", err)
			}
			depsSHA = ""
		}

		expectedDepsSHA := task.Metadata["deps_manifest_sha256"]
		if expectedDepsSHA == "" {
			if !bestEffort {
				return fmt.Errorf("missing deps_manifest_sha256 in task metadata")
			}
			task.Metadata["deps_manifest_sha256"] = depsSHA
		} else if !bestEffort && expectedDepsSHA != depsSHA {
			return fmt.Errorf("deps manifest SHA mismatch: expected %s, got %s", expectedDepsSHA, depsSHA)
		}
	}

	// Handle snapshot_sha256 if SnapshotID is set
	if task.SnapshotID != "" {
		snapPath := filepath.Join(dataDir, "snapshots", task.SnapshotID)
		snapSHA, err := integrity.DirOverallSHA256Hex(snapPath)
		if err != nil {
			if !bestEffort {
				return fmt.Errorf("failed to compute snapshot SHA: %w", err)
			}
			snapSHA = ""
		}

		expectedSnapSHA, _ := integrity.NormalizeSHA256ChecksumHex(task.Metadata["snapshot_sha256"])
		if expectedSnapSHA == "" {
			if !bestEffort {
				return fmt.Errorf("missing snapshot_sha256 in task metadata")
			}
			if task.Metadata == nil {
				task.Metadata = map[string]string{}
			}
			task.Metadata["snapshot_sha256"] = snapSHA
		} else if !bestEffort && expectedSnapSHA != snapSHA {
			return fmt.Errorf("snapshot SHA mismatch: expected %s, got %s", expectedSnapSHA, snapSHA)
		}
	}

	return nil
}

// VerifySnapshot verifies snapshot integrity for this task.
// It computes the SHA256 of the snapshot directory and compares with task metadata.
func (w *Worker) VerifySnapshot(ctx context.Context, task *queue.Task) error {
	if task.SnapshotID == "" {
		return nil // No snapshot to verify
	}

	dataDir := w.Config.DataDir
	if dataDir == "" {
		dataDir = os.TempDir() + "/data"
	}

	// Get expected checksum from metadata
	expectedChecksum, ok := task.Metadata["snapshot_sha256"]
	if !ok || expectedChecksum == "" {
		return fmt.Errorf("missing snapshot_sha256 in task metadata")
	}

	// Normalize the checksum (remove sha256: prefix if present)
	expectedChecksum, err := integrity.NormalizeSHA256ChecksumHex(expectedChecksum)
	if err != nil {
		return fmt.Errorf("invalid snapshot_sha256 format: %w", err)
	}

	// Compute actual checksum of snapshot directory
	snapshotDir := filepath.Join(dataDir, "snapshots", task.SnapshotID)
	actualChecksum, err := integrity.DirOverallSHA256Hex(snapshotDir)
	if err != nil {
		return fmt.Errorf("failed to compute snapshot hash: %w", err)
	}

	// Compare checksums
	if actualChecksum != expectedChecksum {
		return fmt.Errorf("snapshot checksum mismatch: expected %s, got %s", expectedChecksum, actualChecksum)
	}

	return nil
}

// GetJupyterManager returns the Jupyter manager for plugin use
// This implements the plugins.TaskRunner interface
func (w *Worker) GetJupyterManager() plugins.JupyterManager {
	return w.Jupyter
}

// PrewarmNextOnce prewarms the next task in queue.
// It fetches the next task, verifies its snapshot, and stages it to the prewarm directory.
// Returns true if prewarming was performed, false if disabled or queue empty.
func (w *Worker) PrewarmNextOnce(ctx context.Context) (bool, error) {
	// Check if prewarming is enabled
	if !w.Config.PrewarmEnabled {
		return false, nil
	}

	// Get base path and data directory
	basePath := w.Config.BasePath
	if basePath == "" {
		basePath = "/tmp"
	}
	dataDir := w.Config.DataDir
	if dataDir == "" {
		dataDir = filepath.Join(basePath, "data")
	}

	// Create prewarm directory
	prewarmDir := filepath.Join(basePath, ".prewarm", "snapshots")
	if err := os.MkdirAll(prewarmDir, 0o750); err != nil {
		return false, fmt.Errorf("failed to create prewarm directory: %w", err)
	}

	// Try to get next task from queue client if available (peek, don't lease)
	if w.QueueClient != nil {
		task, err := w.QueueClient.PeekNextTask()
		if err != nil {
			// Queue empty - check if we have existing prewarm state
			// Return false but preserve any existing state (don't delete)
			state, _ := w.QueueClient.GetWorkerPrewarmState(w.ID)
			if state != nil {
				// We have existing state, return true to indicate prewarm is active
				return true, nil
			}
			return false, nil
		}
		if task != nil && task.SnapshotID != "" {
			// Resolve snapshot path using SHA from metadata if available
			snapshotSHA := task.Metadata["snapshot_sha256"]
			if snapshotSHA != "" {
				snapshotSHA, _ = integrity.NormalizeSHA256ChecksumHex(snapshotSHA)
			}

			var srcDir string
			if snapshotSHA != "" {
				// Check if snapshot exists in SHA cache directory
				shaDir := filepath.Join(dataDir, "snapshots", "sha256", snapshotSHA)
				if info, err := os.Stat(shaDir); err == nil && info.IsDir() {
					srcDir = shaDir
				}
			}

			// Fall back to direct snapshot path if SHA directory doesn't exist
			if srcDir == "" {
				srcDir = filepath.Join(dataDir, "snapshots", task.SnapshotID)
			}

			dstDir := filepath.Join(prewarmDir, task.ID)
			if err := execution.CopyDir(srcDir, dstDir); err != nil {
				return false, fmt.Errorf("failed to stage snapshot: %w", err)
			}

			// Store prewarm state in queue backend
			if w.QueueClient != nil {
				now := time.Now().UTC().Format(time.RFC3339)
				state := queue.PrewarmState{
					WorkerID:   w.ID,
					TaskID:     task.ID,
					SnapshotID: task.SnapshotID,
					StartedAt:  now,
					UpdatedAt:  now,
					Phase:      "staged",
				}
				_ = w.QueueClient.SetWorkerPrewarmState(state)
			}

			return true, nil
		}
	}

	// If we have a runLoop but no queue client, use runLoop (for backward compatibility)
	if w.RunLoop != nil {
		return true, nil
	}

	return false, nil
}

// RunJob runs a job task.
// It uses the JobRunner to execute the job and write the run manifest.
func (w *Worker) RunJob(ctx context.Context, task *queue.Task, outputDir string) error {
	if w.Runner == nil {
		return fmt.Errorf("job runner not configured")
	}

	basePath := w.Config.BasePath
	if basePath == "" {
		basePath = "/tmp"
	}

	// Determine execution mode
	mode := executor.ModeAuto
	if w.Config.LocalMode {
		mode = executor.ModeLocal
	}

	// Create minimal GPU environment (empty for now)
	gpuEnv := interfaces.ExecutionEnv{}

	// Run the job
	return w.Runner.Run(ctx, task, basePath, mode, w.Config.LocalMode, gpuEnv)
}

func mustMarshal(v any) []byte {
	b, _ := json.Marshal(v)
	return b
}