// Package backup handles SQLite backups: on-demand, scheduled, and
// restore. It uses SQLite's own online backup (via VACUUM INTO), which is
// safe to run against a live WAL-mode database without blocking writers
// for more than the duration of the copy.
package backup

import (
	"context"
	"database/sql"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"sort"
	"time"
)

// Run performs a single backup of the database at db into dir, named with
// a timestamp, then prunes old backups beyond keep.
func Run(db *sql.DB, dir string, keep int) (string, error) {
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return "", err
	}
	name := fmt.Sprintf("vibeproxy-%s.db", time.Now().UTC().Format("20060102-150405"))
	path := filepath.Join(dir, name)

	if _, err := db.Exec(`VACUUM INTO ?`, path); err != nil {
		return "", fmt.Errorf("backup failed: %w", err)
	}
	if err := os.Chmod(path, 0o600); err != nil {
		return "", err
	}
	if keep > 0 {
		if err := prune(dir, keep); err != nil {
			return path, err
		}
	}
	return path, nil
}

func prune(dir string, keep int) error {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return err
	}
	var names []string
	for _, e := range entries {
		if !e.IsDir() {
			names = append(names, e.Name())
		}
	}
	sort.Strings(names) // timestamped names sort chronologically
	if len(names) <= keep {
		return nil
	}
	for _, n := range names[:len(names)-keep] {
		os.Remove(filepath.Join(dir, n))
	}
	return nil
}

// StartScheduledBackups runs Run on the given interval until ctx is done.
func StartScheduledBackups(ctx context.Context, db *sql.DB, log *slog.Logger, getDir func() string, getIntervalHours func() int, getKeep func() int, getEnabled func() bool) {
	ticker := time.NewTicker(1 * time.Hour)
	lastRun := time.Time{}
	go func() {
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				if !getEnabled() {
					continue
				}
				interval := time.Duration(getIntervalHours()) * time.Hour
				if interval <= 0 {
					interval = 24 * time.Hour
				}
				if time.Since(lastRun) < interval {
					continue
				}
				lastRun = time.Now()
				path, err := Run(db, getDir(), getKeep())
				if err != nil {
					log.Error("scheduled backup failed", "err", err)
				} else {
					log.Info("scheduled backup complete", "path", path)
				}
			}
		}
	}()
}

// Restore replaces the live database file at dbPath with backupPath. The
// caller must have closed all connections to dbPath before calling this
// and reopen afterward.
func Restore(backupPath, dbPath string) error {
	data, err := os.ReadFile(backupPath)
	if err != nil {
		return err
	}
	tmp := dbPath + ".restoring"
	if err := os.WriteFile(tmp, data, 0o600); err != nil {
		return err
	}
	// Remove any stale WAL/SHM files so SQLite doesn't try to replay a
	// journal that belongs to the old database.
	os.Remove(dbPath + "-wal")
	os.Remove(dbPath + "-shm")
	return os.Rename(tmp, dbPath)
}