package db

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// Snapshot creates a consistent backup of the database at destPath using
// SQLite's VACUUM INTO statement.  VACUUM INTO acquires a read lock for the
// duration of the copy, which is safe while the server is running in WAL mode.
// The destination file is created by SQLite; the caller must ensure the parent
// directory exists.
func (db *DB) Snapshot(destPath string) error {
	// VACUUM INTO is not supported on in-memory databases.
	if strings.Contains(db.path, "mode=memory") {
		return fmt.Errorf("db: snapshot not supported on in-memory databases")
	}
	if _, err := db.sql.Exec("VACUUM INTO ?", destPath); err != nil {
		return fmt.Errorf("db: snapshot VACUUM INTO %q: %w", destPath, err)
	}
	return nil
}

// SnapshotDir creates a timestamped backup in dir and prunes backups older
// than retainDays days.  dir is created with mode 0750 if it does not exist.
// The backup filename format is mcias-20060102-150405.db.
func (db *DB) SnapshotDir(dir string, retainDays int) (string, error) {
	if err := os.MkdirAll(dir, 0750); err != nil {
		return "", fmt.Errorf("db: create backup dir %q: %w", dir, err)
	}

	ts := time.Now().UTC().Format("20060102-150405")
	dest := filepath.Join(dir, fmt.Sprintf("mcias-%s.db", ts))
	if err := db.Snapshot(dest); err != nil {
		return "", err
	}

	// Prune backups older than retainDays.
	if retainDays > 0 {
		cutoff := time.Now().UTC().AddDate(0, 0, -retainDays)
		entries, err := os.ReadDir(dir)
		if err != nil {
			// Non-fatal: the backup was written; log pruning failure separately.
			return dest, fmt.Errorf("db: list backup dir for pruning: %w", err)
		}
		for _, e := range entries {
			if e.IsDir() || !strings.HasSuffix(e.Name(), ".db") {
				continue
			}
			// Skip the file we just wrote.
			if e.Name() == filepath.Base(dest) {
				continue
			}
			info, err := e.Info()
			if err != nil {
				continue
			}
			if info.ModTime().Before(cutoff) {
				_ = os.Remove(filepath.Join(dir, e.Name()))
			}
		}
	}

	return dest, nil
}