// Package snapshotter provides functionality for creating periodic and on-demand
// snapshots of the routing table state.
package snapshotter

import (
	"compress/gzip"
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"runtime"
	"sync"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/routingtable"
)

const (
	snapshotInterval = 10 * time.Minute
	snapshotFilename = "routewatch-snapshot.json.gz"
	tempFileSuffix   = ".tmp"
)

// Snapshotter handles periodic and on-demand snapshots of the routing table
type Snapshotter struct {
	rt           *routingtable.RoutingTable
	stateDir     string
	logger       *slog.Logger
	ctx          context.Context
	cancel       context.CancelFunc
	mu           sync.Mutex // Ensures only one snapshot runs at a time
	wg           sync.WaitGroup
	lastSnapshot time.Time
}

// New creates a new Snapshotter instance
func New(rt *routingtable.RoutingTable, logger *slog.Logger) (*Snapshotter, error) {
	stateDir, err := getStateDirectory()
	if err != nil {
		return nil, fmt.Errorf("failed to determine state directory: %w", err)
	}

	// Ensure state directory exists
	const stateDirPerms = 0750
	if err := os.MkdirAll(stateDir, stateDirPerms); err != nil {
		return nil, fmt.Errorf("failed to create state directory: %w", err)
	}

	s := &Snapshotter{
		rt:       rt,
		stateDir: stateDir,
		logger:   logger,
	}

	return s, nil
}

// Start begins the periodic snapshot process
func (s *Snapshotter) Start(ctx context.Context) {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.ctx != nil {
		// Already started
		return
	}

	ctx, cancel := context.WithCancel(ctx)
	s.ctx = ctx
	s.cancel = cancel

	// Start periodic snapshot goroutine
	s.wg.Add(1)
	go s.periodicSnapshot()
}

// getStateDirectory returns the appropriate state directory based on the OS
func getStateDirectory() (string, error) {
	switch runtime.GOOS {
	case "darwin":
		// macOS: Use ~/Library/Application Support/routewatch
		home, err := os.UserHomeDir()
		if err != nil {
			return "", err
		}

		return filepath.Join(home, "Library", "Application Support", "routewatch"), nil
	case "linux", "freebsd", "openbsd", "netbsd":
		// Unix-like: Use /var/lib/routewatch if running as root, otherwise use XDG_STATE_HOME
		if os.Geteuid() == 0 {
			return "/var/lib/routewatch", nil
		}
		// Check XDG_STATE_HOME first
		if xdgState := os.Getenv("XDG_STATE_HOME"); xdgState != "" {
			return filepath.Join(xdgState, "routewatch"), nil
		}
		// Fall back to ~/.local/state/routewatch
		home, err := os.UserHomeDir()
		if err != nil {
			return "", err
		}

		return filepath.Join(home, ".local", "state", "routewatch"), nil
	default:
		return "", fmt.Errorf("unsupported operating system: %s", runtime.GOOS)
	}
}

// periodicSnapshot runs periodic snapshots
func (s *Snapshotter) periodicSnapshot() {
	defer s.wg.Done()

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

	// Wait for the first interval before taking any snapshots
	for {
		select {
		case <-s.ctx.Done():
			return
		case <-ticker.C:
			if err := s.TakeSnapshot(); err != nil {
				s.logger.Error("Failed to take periodic snapshot", "error", err)
			}
		}
	}
}

// TakeSnapshot creates a snapshot of the current routing table state
func (s *Snapshotter) TakeSnapshot() error {
	// Ensure only one snapshot runs at a time
	s.mu.Lock()
	defer s.mu.Unlock()

	start := time.Now()
	s.logger.Info("Starting routing table snapshot")

	// Get a copy of all routes while holding read lock
	s.rt.RLock()
	routes := s.rt.GetAllRoutesUnsafe() // We'll need to add this method
	stats := s.rt.GetDetailedStats()
	s.rt.RUnlock()

	// Create snapshot data structure
	snapshot := struct {
		Timestamp time.Time                  `json:"timestamp"`
		Stats     routingtable.DetailedStats `json:"stats"`
		Routes    []*routingtable.Route      `json:"routes"`
	}{
		Timestamp: time.Now().UTC(),
		Stats:     stats,
		Routes:    routes,
	}

	// Serialize to JSON
	jsonData, err := json.Marshal(snapshot)
	if err != nil {
		return fmt.Errorf("failed to marshal snapshot: %w", err)
	}

	// Write compressed data to temporary file
	tempPath := filepath.Join(s.stateDir, snapshotFilename+tempFileSuffix)
	finalPath := filepath.Join(s.stateDir, snapshotFilename)

	// Clean the paths to avoid any path traversal issues
	tempPath = filepath.Clean(tempPath)
	finalPath = filepath.Clean(finalPath)

	tempFile, err := os.Create(tempPath)
	if err != nil {
		return fmt.Errorf("failed to create temporary file: %w", err)
	}
	defer func() {
		_ = tempFile.Close()
		// Clean up temp file if it still exists
		_ = os.Remove(tempPath)
	}()

	// Create gzip writer
	gzipWriter := gzip.NewWriter(tempFile)
	gzipWriter.Comment = fmt.Sprintf("RouteWatch snapshot taken at %s", snapshot.Timestamp.Format(time.RFC3339))

	// Write compressed data
	if _, err := gzipWriter.Write(jsonData); err != nil {
		return fmt.Errorf("failed to write compressed data: %w", err)
	}

	// Close gzip writer to flush all data
	if err := gzipWriter.Close(); err != nil {
		return fmt.Errorf("failed to close gzip writer: %w", err)
	}

	// Sync to disk
	if err := tempFile.Sync(); err != nil {
		return fmt.Errorf("failed to sync temporary file: %w", err)
	}

	// Close temp file before rename
	if err := tempFile.Close(); err != nil {
		return fmt.Errorf("failed to close temporary file: %w", err)
	}

	// Atomically rename temp file to final location
	if err := os.Rename(tempPath, finalPath); err != nil {
		return fmt.Errorf("failed to rename temporary file: %w", err)
	}

	duration := time.Since(start)
	s.lastSnapshot = time.Now()

	s.logger.Info("Routing table snapshot completed",
		"duration", duration,
		"routes", len(routes),
		"ipv4_routes", stats.IPv4Routes,
		"ipv6_routes", stats.IPv6Routes,
		"size_bytes", len(jsonData),
		"path", finalPath,
	)

	return nil
}

// Shutdown performs a final snapshot and cleans up resources
func (s *Snapshotter) Shutdown() error {
	s.logger.Info("Shutting down snapshotter")

	// Cancel context to stop periodic snapshots
	if s.cancel != nil {
		s.cancel()
	}

	// Wait for periodic snapshot goroutine to finish
	s.wg.Wait()

	// Take final snapshot
	if err := s.TakeSnapshot(); err != nil {
		return fmt.Errorf("failed to take final snapshot: %w", err)
	}

	return nil
}

// GetLastSnapshotTime returns the time of the last successful snapshot
func (s *Snapshotter) GetLastSnapshotTime() time.Time {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.lastSnapshot
}

// GetSnapshotPath returns the path to the snapshot file
func (s *Snapshotter) GetSnapshotPath() string {
	return filepath.Join(s.stateDir, snapshotFilename)
}