package backup

import (
	"fmt"
	"regexp"
)

// snapshotIDRe validates restic snapshot IDs: 8-64 lowercase hex characters.
var snapshotIDRe = regexp.MustCompile(`^[0-9a-f]{8,64}$`)

// RestoreApp restores an app's HDD data from a restic snapshot.
func (m *Manager) RestoreApp(stackName, snapshotID string) error {
	// Validate app has backup enabled
	if !m.settings.IsAppBackupEnabled(stackName) {
		return fmt.Errorf("backup not enabled for %s", stackName)
	}

	// Resolve HDD paths for this app
	if m.stackProvider == nil {
		return fmt.Errorf("stack provider not configured")
	}
	hddMounts := m.stackProvider.GetStackHDDMounts(stackName)
	if len(hddMounts) == 0 {
		return fmt.Errorf("no HDD data paths found for %s", stackName)
	}

	// H4: Validate snapshot ID format by regex instead of listing all snapshots (list caps at 100).
	// restic restore will return a clear error if the snapshot ID doesn't exist.
	if !snapshotIDRe.MatchString(snapshotID) {
		return fmt.Errorf("invalid snapshot ID: must be 8-64 lowercase hex characters")
	}

	// Use the running flag to prevent concurrent backup/restore
	m.mu.Lock()
	if m.running {
		m.mu.Unlock()
		return fmt.Errorf("backup or restore already in progress")
	}
	m.running = true
	m.mu.Unlock()

	defer func() {
		m.mu.Lock()
		m.running = false
		m.mu.Unlock()
	}()

	m.logger.Printf("[WARN] RESTORE starting: stack=%s, snapshot=%s, paths=%v", stackName, snapshotID, hddMounts)

	// Stop the app before restore to avoid data corruption
	if err := m.stackProvider.StopStack(stackName); err != nil {
		m.logger.Printf("[WARN] RESTORE could not stop %s before restore: %v (proceeding anyway)", stackName, err)
	}

	// Execute restore
	if err := m.restic.RestoreAppData(snapshotID, hddMounts); err != nil {
		m.logger.Printf("[ERROR] RESTORE failed for %s: %v", stackName, err)
		// Try to restart the app even on failure
		if startErr := m.stackProvider.StartStack(stackName); startErr != nil {
			m.logger.Printf("[WARN] RESTORE could not restart %s after failed restore: %v", stackName, startErr)
		}
		return err
	}

	// Restart the app after successful restore
	if err := m.stackProvider.StartStack(stackName); err != nil {
		m.logger.Printf("[WARN] RESTORE could not restart %s after restore: %v", stackName, err)
	}

	m.logger.Printf("[INFO] RESTORE completed: stack=%s, snapshot=%s", stackName, snapshotID)
	return nil
}