package backup

import (
	"context"
	"fmt"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
	"gitea.dooplex.hu/admin/felhom-controller/internal/system"
)

// CrossDriveRunner handles per-app backup to secondary storage.
type CrossDriveRunner struct {
	sett          *settings.Settings
	stackProvider StackDataProvider
	logger        *log.Logger
	mu            sync.Mutex
	running       map[string]bool // per-app running state
}

// NewCrossDriveRunner creates a new CrossDriveRunner.
func NewCrossDriveRunner(sett *settings.Settings, provider StackDataProvider, logger *log.Logger) *CrossDriveRunner {
	return &CrossDriveRunner{
		sett:          sett,
		stackProvider: provider,
		logger:        logger,
		running:       make(map[string]bool),
	}
}

// RunAppBackup runs cross-drive backup for a single app.
func (r *CrossDriveRunner) RunAppBackup(ctx context.Context, stackName string) error {
	cfg := r.sett.GetCrossDriveConfig(stackName)
	if cfg == nil || !cfg.Enabled {
		return fmt.Errorf("cross-drive backup not configured or disabled for %s", stackName)
	}

	// Prevent concurrent runs for the same app
	r.mu.Lock()
	if r.running[stackName] {
		r.mu.Unlock()
		return fmt.Errorf("cross-drive backup already running for %s", stackName)
	}
	r.running[stackName] = true
	r.mu.Unlock()
	defer func() {
		r.mu.Lock()
		r.running[stackName] = false
		r.mu.Unlock()
	}()

	// Mark as running in settings
	_ = r.sett.UpdateCrossDriveStatus(stackName, func(c *settings.CrossDriveBackup) {
		c.LastStatus = "running"
	})

	start := time.Now()
	r.logger.Printf("[INFO] Cross-drive backup starting: %s → %s (method: %s)",
		stackName, cfg.DestinationPath, cfg.Method)

	if err := r.ValidateDestination(cfg.DestinationPath); err != nil {
		r.updateStatus(stackName, "error", err.Error(), time.Since(start), "")
		return fmt.Errorf("destination validation failed: %w", err)
	}

	// Resolve HDD mounts for this app
	mounts := r.stackProvider.GetStackHDDMounts(stackName)
	if len(mounts) == 0 {
		r.updateStatus(stackName, "error", "no HDD data paths found for this app", time.Since(start), "")
		return fmt.Errorf("no HDD data paths found for %s", stackName)
	}

	// Safety: destination must not overlap with any source
	for _, m := range mounts {
		if system.PathsOverlap(cfg.DestinationPath, m) {
			msg := fmt.Sprintf("destination %s overlaps with source %s — aborted", cfg.DestinationPath, m)
			r.updateStatus(stackName, "error", msg, time.Since(start), "")
			return fmt.Errorf("%s", msg)
		}
	}

	var runErr error
	switch cfg.Method {
	case "rsync":
		runErr = r.runRsyncBackup(ctx, stackName, cfg.DestinationPath, mounts)
	case "restic":
		runErr = r.runResticBackup(ctx, stackName, cfg.DestinationPath, mounts)
	default:
		runErr = fmt.Errorf("unknown backup method: %s", cfg.Method)
	}

	duration := time.Since(start)

	if runErr != nil {
		r.logger.Printf("[ERROR] Cross-drive backup failed: %s: %v", stackName, runErr)
		r.updateStatus(stackName, "error", runErr.Error(), duration, "")
		return runErr
	}

	// Calculate backup size
	var sizeHuman string
	if cfg.Method == "rsync" {
		destDir := filepath.Join(cfg.DestinationPath, "backups", "rsync", stackName)
		if sz, err := dirSizeBytes(destDir); err == nil {
			sizeHuman = humanizeBytes(sz)
		}
	}

	r.logger.Printf("[INFO] Cross-drive backup completed: %s (%s)", stackName, duration.Round(time.Second))
	r.updateStatus(stackName, "ok", "", duration, sizeHuman)
	return nil
}

// RunAllScheduled runs cross-drive backups for all apps matching the schedule.
// Runs sequentially (disk I/O bound).
func (r *CrossDriveRunner) RunAllScheduled(ctx context.Context, schedule string) error {
	configs := r.sett.GetAllCrossDriveConfigs()
	if len(configs) == 0 {
		return nil
	}

	var errs []string
	for stackName, cfg := range configs {
		if !cfg.Enabled {
			continue
		}
		if cfg.Schedule != schedule {
			continue
		}

		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		if err := r.RunAppBackup(ctx, stackName); err != nil {
			errs = append(errs, fmt.Sprintf("%s: %v", stackName, err))
		}
	}

	if len(errs) > 0 {
		return fmt.Errorf("cross-drive backup errors: %s", strings.Join(errs, "; "))
	}
	return nil
}

// IsRunning returns true if the given app's backup is currently running.
func (r *CrossDriveRunner) IsRunning(stackName string) bool {
	r.mu.Lock()
	defer r.mu.Unlock()
	return r.running[stackName]
}

// ValidateDestination checks that the destination path exists, is writable,
// and has sufficient free space (at least 100MB).
// A non-mount-point destination (e.g. a folder on the system drive) is allowed
// with a logged warning — consistent with the web UI's CheckBackupDestination.
func (r *CrossDriveRunner) ValidateDestination(path string) error {
	if path == "" {
		return fmt.Errorf("destination path is empty")
	}
	if _, err := os.Stat(path); os.IsNotExist(err) {
		return fmt.Errorf("destination %s does not exist", path)
	}
	if !system.IsMountPoint(path) {
		r.logger.Printf("[WARN] Destination %s is not a separate mount point (system drive) — backup will proceed but data is not protected against drive failure", path)
	}
	if !system.IsWritable(path) {
		return fmt.Errorf("destination %s is not writable", path)
	}
	di := system.GetDiskUsage(path)
	if di != nil && di.AvailGB < 0.1 {
		return fmt.Errorf("destination %s has insufficient free space (%.1f GB)", path, di.AvailGB)
	}
	return nil
}

// --- rsync ---

func (r *CrossDriveRunner) runRsyncBackup(ctx context.Context, stackName, destBase string, mounts []string) error {
	destDir := filepath.Join(destBase, "backups", "rsync", stackName)
	if err := os.MkdirAll(destDir, 0755); err != nil {
		return fmt.Errorf("creating rsync dest dir: %w", err)
	}

	for _, srcMount := range mounts {
		// Preserve directory structure: strip the storage path prefix to get relative subpath
		// e.g., /mnt/hdd_placeholder/storage/immich/ → storage/immich/
		rel := srcMount
		// Find the topmost non-root segment of the mount path (after the mount point itself)
		// Use a simple approach: keep everything from the first significant segment after /mnt/...
		parts := strings.SplitN(strings.TrimPrefix(srcMount, "/"), "/", 3)
		if len(parts) >= 3 {
			rel = parts[2] // e.g., "storage/immich"
		} else {
			rel = filepath.Base(srcMount)
		}

		dstPath := filepath.Join(destDir, rel)
		if err := os.MkdirAll(dstPath, 0755); err != nil {
			return fmt.Errorf("creating rsync destination: %w", err)
		}

		// Ensure trailing slash on source for rsync semantics (copy contents, not the dir itself)
		src := strings.TrimRight(srcMount, "/") + "/"
		dst := strings.TrimRight(dstPath, "/") + "/"

		cmd := exec.CommandContext(ctx, "rsync", "-a", "--delete", src, dst)
		r.logger.Printf("[DEBUG] rsync: %s → %s", src, dst)
		if out, err := cmd.CombinedOutput(); err != nil {
			return fmt.Errorf("rsync failed for %s: %v (%s)", srcMount, err, strings.TrimSpace(string(out)))
		}
	}
	return nil
}

// --- restic ---

func (r *CrossDriveRunner) runResticBackup(ctx context.Context, stackName, destBase string, mounts []string) error {
	repoPath := filepath.Join(destBase, "backups", "restic")

	// Get or create the cross-drive restic password
	password, err := r.sett.GetOrCreateCrossDrivePassword()
	if err != nil {
		return fmt.Errorf("getting restic password: %w", err)
	}

	// H6: Write password to temp file with safe cleanup order (close before deferred remove).
	pwFile, err := os.CreateTemp("", "felhom-crossdrive-pw-*")
	if err != nil {
		return fmt.Errorf("creating password file: %w", err)
	}
	pwPath := pwFile.Name()
	if _, err := pwFile.WriteString(password); err != nil {
		pwFile.Close()
		os.Remove(pwPath)
		return fmt.Errorf("writing password file: %w", err)
	}
	pwFile.Close()
	defer os.Remove(pwPath)

	// Ensure repo is initialized
	if err := r.ensureResticRepo(ctx, repoPath, pwPath); err != nil {
		return err
	}

	// Run restic backup
	args := []string{
		"backup", "--repo", repoPath,
		"--password-file", pwPath,
		"--tag", stackName,
		"--tag", "cross-drive",
	}
	args = append(args, mounts...)

	cmd := exec.CommandContext(ctx, "restic", args...)
	r.logger.Printf("[DEBUG] restic backup: %v", args)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("restic backup failed: %v (%s)", err, strings.TrimSpace(string(out)))
	}

	// H5: Prune old snapshots to prevent unbounded accumulation.
	return r.pruneResticRepo(ctx, repoPath, pwPath)
}

// pruneResticRepo forgets old snapshots in a cross-drive restic repo, keeping recent ones.
func (r *CrossDriveRunner) pruneResticRepo(ctx context.Context, repoPath, pwPath string) error {
	args := []string{
		"forget", "--repo", repoPath,
		"--password-file", pwPath,
		"--keep-daily", "7",
		"--keep-weekly", "4",
		"--prune",
	}
	cmd := exec.CommandContext(ctx, "restic", args...)
	r.logger.Printf("[DEBUG] restic forget (prune): %s", repoPath)
	if out, err := cmd.CombinedOutput(); err != nil {
		// Non-fatal: log warning but don't fail the backup
		r.logger.Printf("[WARN] restic forget failed for %s: %v (%s)", repoPath, err, strings.TrimSpace(string(out)))
	}
	return nil
}

func (r *CrossDriveRunner) ensureResticRepo(ctx context.Context, repoPath, pwFile string) error {
	// Check if repo config exists
	if _, err := os.Stat(filepath.Join(repoPath, "config")); err == nil {
		return nil // already initialized
	}

	if err := os.MkdirAll(repoPath, 0755); err != nil {
		return fmt.Errorf("creating restic repo dir: %w", err)
	}

	cmd := exec.CommandContext(ctx, "restic", "init", "--repo", repoPath, "--password-file", pwFile)
	r.logger.Printf("[INFO] Initializing cross-drive restic repo at %s", repoPath)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("restic init failed: %v (%s)", err, strings.TrimSpace(string(out)))
	}
	return nil
}

// --- helpers ---

func (r *CrossDriveRunner) updateStatus(stackName, status, errMsg string, duration time.Duration, sizeHuman string) {
	_ = r.sett.UpdateCrossDriveStatus(stackName, func(c *settings.CrossDriveBackup) {
		c.LastRun = time.Now().UTC().Format(time.RFC3339)
		c.LastStatus = status
		c.LastError = errMsg
		c.LastDuration = duration.Round(time.Second).String()
		if sizeHuman != "" {
			c.LastSizeHuman = sizeHuman
		}
	})
}

// dirSizeBytes returns the total byte size of all files under path.
// H7: Walk errors are now propagated instead of silently swallowed.
func dirSizeBytes(path string) (int64, error) {
	var total int64
	err := filepath.Walk(path, func(_ string, info os.FileInfo, err error) error {
		if err != nil {
			return err // propagate permission/IO errors
		}
		if !info.IsDir() {
			total += info.Size()
		}
		return nil
	})
	return total, err
}