package appstate

import (
	"archive/zip"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"github.com/glebarez/sqlite"
	"gorm.io/gorm"
	"gorm.io/gorm/logger"
)

type backupPeriod struct {
	name      string
	retention int
	key       func(time.Time) string
	date      func(time.Time) string
}

var backupPeriods = []backupPeriod{
	{
		name:      "daily",
		retention: 7,
		key: func(t time.Time) string {
			return t.Format("2006-01-02")
		},
		date: func(t time.Time) string {
			return t.Format("2006-01-02")
		},
	},
	{
		name:      "weekly",
		retention: 4,
		key: func(t time.Time) string {
			y, w := t.ISOWeek()
			return fmt.Sprintf("%04d-W%02d", y, w)
		},
		date: func(t time.Time) string {
			return t.Format("2006-01-02")
		},
	},
	{
		name:      "monthly",
		retention: 12,
		key: func(t time.Time) string {
			return t.Format("2006-01")
		},
		date: func(t time.Time) string {
			return t.Format("2006-01-02")
		},
	},
	{
		name:      "yearly",
		retention: 10,
		key: func(t time.Time) string {
			return t.Format("2006")
		},
		date: func(t time.Time) string {
			return t.Format("2006-01-02")
		},
	},
}

const (
	envBackupDisable = "QFS_BACKUP_DISABLE"
	envBackupDir     = "QFS_BACKUP_DIR"
)

var backupNow = time.Now

// EnsureRotatingLocalBackup creates or refreshes daily/weekly/monthly/yearly backups
// for the local database and config. It keeps a limited number per period.
func EnsureRotatingLocalBackup(dbPath, configPath string) ([]string, error) {
	if isBackupDisabled() {
		return nil, nil
	}
	if dbPath == "" {
		return nil, nil
	}

	if _, err := os.Stat(dbPath); err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("stat db: %w", err)
	}

	root := resolveBackupRoot(dbPath)
	if err := validateBackupRoot(root); err != nil {
		return nil, err
	}
	now := backupNow()

	created := make([]string, 0)
	for _, period := range backupPeriods {
		newFiles, err := ensurePeriodBackup(root, period, now, dbPath, configPath)
		if err != nil {
			return created, err
		}
		if len(newFiles) > 0 {
			created = append(created, newFiles...)
		}
	}

	return created, nil
}

func resolveBackupRoot(dbPath string) string {
	if fromEnv := strings.TrimSpace(os.Getenv(envBackupDir)); fromEnv != "" {
		return filepath.Clean(fromEnv)
	}
	return filepath.Join(filepath.Dir(dbPath), "backups")
}

func validateBackupRoot(root string) error {
	absRoot, err := filepath.Abs(root)
	if err != nil {
		return fmt.Errorf("resolve backup root: %w", err)
	}

	if gitRoot, ok := findGitWorktreeRoot(absRoot); ok {
		return fmt.Errorf("backup root must stay outside git worktree: %s is inside %s", absRoot, gitRoot)
	}

	return nil
}

func findGitWorktreeRoot(path string) (string, bool) {
	current := filepath.Clean(path)
	info, err := os.Stat(current)
	if err == nil && !info.IsDir() {
		current = filepath.Dir(current)
	}

	for {
		gitPath := filepath.Join(current, ".git")
		if _, err := os.Stat(gitPath); err == nil {
			return current, true
		}

		parent := filepath.Dir(current)
		if parent == current {
			return "", false
		}
		current = parent
	}
}

func isBackupDisabled() bool {
	val := strings.ToLower(strings.TrimSpace(os.Getenv(envBackupDisable)))
	return val == "1" || val == "true" || val == "yes"
}

func ensurePeriodBackup(root string, period backupPeriod, now time.Time, dbPath, configPath string) ([]string, error) {
	key := period.key(now)
	periodDir := filepath.Join(root, period.name)
	if err := os.MkdirAll(periodDir, 0755); err != nil {
		return nil, fmt.Errorf("create %s backup dir: %w", period.name, err)
	}

	if hasBackupForKey(periodDir, key) {
		return nil, nil
	}

	archiveName := fmt.Sprintf("qfs-backp-%s.zip", period.date(now))
	archivePath := filepath.Join(periodDir, archiveName)

	if err := createBackupArchive(archivePath, dbPath, configPath); err != nil {
		return nil, fmt.Errorf("create %s backup archive: %w", period.name, err)
	}

	if err := writePeriodMarker(periodDir, key); err != nil {
		return []string{archivePath}, err
	}

	if err := pruneOldBackups(periodDir, period.retention); err != nil {
		return []string{archivePath}, err
	}

	return []string{archivePath}, nil
}

func hasBackupForKey(periodDir, key string) bool {
	marker := periodMarker{Key: ""}
	data, err := os.ReadFile(periodMarkerPath(periodDir))
	if err != nil {
		return false
	}
	if err := json.Unmarshal(data, &marker); err != nil {
		return false
	}
	return marker.Key == key
}

type periodMarker struct {
	Key string `json:"key"`
}

func periodMarkerPath(periodDir string) string {
	return filepath.Join(periodDir, ".period.json")
}

func writePeriodMarker(periodDir, key string) error {
	data, err := json.MarshalIndent(periodMarker{Key: key}, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(periodMarkerPath(periodDir), data, 0644)
}

func pruneOldBackups(periodDir string, keep int) error {
	entries, err := os.ReadDir(periodDir)
	if err != nil {
		return fmt.Errorf("read backups dir: %w", err)
	}

	files := make([]os.DirEntry, 0, len(entries))
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		if strings.HasSuffix(entry.Name(), ".zip") {
			files = append(files, entry)
		}
	}

	if len(files) <= keep {
		return nil
	}

	sort.Slice(files, func(i, j int) bool {
		infoI, errI := files[i].Info()
		infoJ, errJ := files[j].Info()
		if errI != nil || errJ != nil {
			return files[i].Name() < files[j].Name()
		}
		return infoI.ModTime().Before(infoJ.ModTime())
	})

	for i := 0; i < len(files)-keep; i++ {
		path := filepath.Join(periodDir, files[i].Name())
		if err := os.Remove(path); err != nil {
			return fmt.Errorf("remove old backup %s: %w", path, err)
		}
	}

	return nil
}

func createBackupArchive(destPath, dbPath, configPath string) error {
	snapshotPath, cleanup, err := createSQLiteSnapshot(dbPath)
	if err != nil {
		return err
	}
	defer cleanup()

	file, err := os.Create(destPath)
	if err != nil {
		return err
	}
	defer file.Close()

	zipWriter := zip.NewWriter(file)
	if err := addZipFileAs(zipWriter, snapshotPath, filepath.Base(dbPath)); err != nil {
		_ = zipWriter.Close()
		return err
	}

	if strings.TrimSpace(configPath) != "" {
		_ = addZipOptionalFile(zipWriter, configPath)
	}

	if err := zipWriter.Close(); err != nil {
		return err
	}
	return file.Sync()
}

func createSQLiteSnapshot(dbPath string) (string, func(), error) {
	tempFile, err := os.CreateTemp("", "qfs-backup-*.db")
	if err != nil {
		return "", func() {}, err
	}
	tempPath := tempFile.Name()
	if err := tempFile.Close(); err != nil {
		_ = os.Remove(tempPath)
		return "", func() {}, err
	}
	if err := os.Remove(tempPath); err != nil && !os.IsNotExist(err) {
		return "", func() {}, err
	}

	cleanup := func() {
		_ = os.Remove(tempPath)
	}

	db, err := gorm.Open(sqlite.Open(dbPath), &gorm.Config{
		Logger: logger.Default.LogMode(logger.Silent),
	})
	if err != nil {
		cleanup()
		return "", func() {}, err
	}

	sqlDB, err := db.DB()
	if err != nil {
		cleanup()
		return "", func() {}, err
	}
	defer sqlDB.Close()

	if err := db.Exec("PRAGMA busy_timeout = 5000").Error; err != nil {
		cleanup()
		return "", func() {}, fmt.Errorf("configure sqlite busy_timeout: %w", err)
	}

	literalPath := strings.ReplaceAll(tempPath, "'", "''")
	if err := vacuumIntoWithRetry(db, literalPath); err != nil {
		cleanup()
		return "", func() {}, err
	}

	return tempPath, cleanup, nil
}

func vacuumIntoWithRetry(db *gorm.DB, literalPath string) error {
	var lastErr error
	for attempt := 0; attempt < 3; attempt++ {
		if err := db.Exec("VACUUM INTO '" + literalPath + "'").Error; err != nil {
			lastErr = err
			if !isSQLiteBusyError(err) {
				return fmt.Errorf("create sqlite snapshot: %w", err)
			}
			time.Sleep(time.Duration(attempt+1) * 250 * time.Millisecond)
			continue
		}
		return nil
	}
	return fmt.Errorf("create sqlite snapshot after retries: %w", lastErr)
}

func isSQLiteBusyError(err error) bool {
	if err == nil {
		return false
	}
	lower := strings.ToLower(err.Error())
	return strings.Contains(lower, "database is locked") || strings.Contains(lower, "database is busy")
}

func addZipOptionalFile(writer *zip.Writer, path string) error {
	if _, err := os.Stat(path); err != nil {
		return nil
	}
	return addZipFile(writer, path)
}

func addZipFile(writer *zip.Writer, path string) error {
	return addZipFileAs(writer, path, filepath.Base(path))
}

func addZipFileAs(writer *zip.Writer, path string, archiveName string) error {
	in, err := os.Open(path)
	if err != nil {
		return err
	}
	defer in.Close()

	info, err := in.Stat()
	if err != nil {
		return err
	}

	header, err := zip.FileInfoHeader(info)
	if err != nil {
		return err
	}
	header.Name = archiveName
	header.Method = zip.Deflate

	out, err := writer.CreateHeader(header)
	if err != nil {
		return err
	}

	_, err = io.Copy(out, in)
	return err
}