package database

import (
	domain "RenewCMS/internal/domain/update"
	"errors"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"gorm.io/gorm"
)

var errBackupExists = errors.New("a backup with this name already exists")

const (
	backupsToKeep       = 3
	backupFileExtension = ".db"
	backupFilePrefix    = "renewcms-"
	backupTimeLayout    = "20060102T150405.000000000Z"
)

type SQLiteBackup struct {
	db        *gorm.DB
	directory string
	now       func() time.Time
}

var _ domain.DatabaseBackup = &SQLiteBackup{}

func NewSQLiteBackup(db *gorm.DB, directory string, now func() time.Time) *SQLiteBackup {
	return &SQLiteBackup{db: db, directory: directory, now: now}
}

func (b *SQLiteBackup) Backup() (string, error) {
	if err := os.MkdirAll(b.directory, os.ModePerm); err != nil {
		return "", err
	}
	target := filepath.Join(b.directory, backupFilePrefix+b.now().UTC().Format(backupTimeLayout)+backupFileExtension)
	if _, err := os.Stat(target); err == nil {
		return "", errBackupExists
	}
	if err := b.db.Exec("VACUUM INTO ?", target).Error; err != nil {
		_ = os.Remove(target)
		return "", err
	}
	if err := b.prune(); err != nil {
		return "", err
	}
	return target, nil
}

type backupFile struct {
	path     string
	modified time.Time
}

func (b *SQLiteBackup) prune() error {
	entries, err := os.ReadDir(b.directory)
	if err != nil {
		return err
	}
	files := make([]backupFile, 0, len(entries))
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), backupFileExtension) {
			continue
		}
		info, err := entry.Info()
		if err != nil {
			return err
		}
		files = append(files, backupFile{path: filepath.Join(b.directory, entry.Name()), modified: info.ModTime()})
	}
	sort.Slice(files, func(i, j int) bool {
		if files[i].modified.Equal(files[j].modified) {
			return files[i].path > files[j].path
		}
		return files[i].modified.After(files[j].modified)
	})
	for _, stale := range files[min(backupsToKeep, len(files)):] {
		if err := os.Remove(stale.path); err != nil {
			return err
		}
	}
	return nil
}