package backup

import (
	"fmt"
	"path/filepath"
	"regexp"
)

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

// RestoreApp restores an app from a restic snapshot.
// All apps get config + DB dump restored. Apps with HDD data also get user data restored.
func (m *Manager) RestoreApp(stackName, snapshotID string) error {
	if m.stackProvider == nil {
		return fmt.Errorf("stack provider not configured")
	}

	// Validate snapshot ID format
	if !snapshotIDRe.MatchString(snapshotID) {
		return fmt.Errorf("invalid snapshot ID: must be 8-64 lowercase hex characters")
	}

	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: stack=%s, snapshotID=%s", stackName, snapshotID)
	}

	// Prevent concurrent operations
	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()
	}()

	// Determine what to restore
	hddMounts := m.stackProvider.GetStackHDDMounts(stackName)
	hasHDD := len(hddMounts) > 0

	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: %s has %d HDD mount(s), hasHDD=%v", stackName, len(hddMounts), hasHDD)
	}

	// Build list of paths to restore from the snapshot
	var restorePaths []string

	// Always restore the stack's config dir (compose + app.yaml + .felhom.yml)
	composePath, ok := m.stackProvider.GetStackComposePath(stackName)
	if ok {
		stackDir := filepath.Dir(composePath)
		restorePaths = append(restorePaths, stackDir)
		if m.isDebug() {
			m.logger.Printf("[DEBUG] RestoreApp: will restore config dir: %s", stackDir)
		}
	}

	// Restore DB dump files for this stack (per-drive path)
	drivePath := m.GetAppDrivePath(stackName)
	dumpDir := AppDBDumpPath(drivePath, stackName)
	restorePaths = append(restorePaths, dumpDir)
	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: will restore DB dump dir: %s", dumpDir)
	}

	// Restore HDD data (always included for apps that have it — backup is mandatory)
	if hasHDD {
		restorePaths = append(restorePaths, hddMounts...)
		if m.isDebug() {
			m.logger.Printf("[DEBUG] RestoreApp: will restore HDD data: %v", hddMounts)
		}
	}

	if len(restorePaths) == 0 {
		return fmt.Errorf("no restorable paths found for %s", stackName)
	}

	// Use the app's primary restic repo
	repoPath := PrimaryResticRepoPath(drivePath)

	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: using repo=%s, %d restore path(s)", repoPath, len(restorePaths))
	}

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

	// Stop the app before restore
	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: step 1/4 — stopping app %s", stackName)
	}
	if err := m.stackProvider.StopStack(stackName); err != nil {
		m.logger.Printf("[WARN] RESTORE could not stop %s: %v (proceeding anyway)", stackName, err)
	}

	// Execute restore via restic
	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: step 2/4 — restoring data from snapshot %s", snapshotID)
	}
	if err := m.restic.RestoreAppData(repoPath, snapshotID, restorePaths); err != nil {
		m.logger.Printf("[ERROR] RESTORE failed for %s: %v", stackName, err)
		if m.isDebug() {
			m.logger.Printf("[DEBUG] RestoreApp: step 3/4 — restarting app %s after failure", stackName)
		}
		if startErr := m.stackProvider.StartStack(stackName); startErr != nil {
			m.logger.Printf("[WARN] RESTORE could not restart %s after failure: %v", stackName, startErr)
		}
		return err
	}

	// Restart the app
	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: step 3/4 — restarting app %s after successful restore", stackName)
	}
	if err := m.stackProvider.StartStack(stackName); err != nil {
		m.logger.Printf("[WARN] RESTORE could not restart %s after restore: %v", stackName, err)
	}

	restoreType := "config+DB"
	if hasHDD {
		restoreType = "full (config+DB+userdata)"
	}
	if m.isDebug() {
		m.logger.Printf("[DEBUG] RestoreApp: step 4/4 — restore completed, type=%s", restoreType)
	}
	m.logger.Printf("[INFO] RESTORE completed: stack=%s, snapshot=%s, type=%s", stackName, snapshotID, restoreType)
	return nil
}