From 850e4a27d8577f9e4135f8c9c96e2064fa13903d Mon Sep 17 00:00:00 2001
From: Sebastiaan de Schaetzen <sebastiaan.de.schaetzen@gmail.com>
Date: Mon, 24 Mar 2025 06:27:05 +0100
Subject: [PATCH] Backup databases before migrating

---
 database.go |  7 ++++---
 migrator.go | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/database.go b/database.go
index a075054..4122f0e 100644
--- a/database.go
+++ b/database.go
@@ -8,8 +8,9 @@ import (
 
 // Db holds a connection to a SQLite database.
 type Db struct {
-	Db   *sqlite.Conn
-	lock sync.Mutex
+	Db     *sqlite.Conn
+	source string
+	lock   sync.Mutex
 }
 
 // OpenDb opens a new connection to a SQLite database.
@@ -21,7 +22,7 @@ func OpenDb(databaseSource string) (*Db, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Db{Db: conn}, nil
+	return &Db{Db: conn, source: databaseSource}, nil
 }
 
 // Close closes the database.
diff --git a/migrator.go b/migrator.go
index 68bc011..7c4b258 100644
--- a/migrator.go
+++ b/migrator.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io/fs"
 	"log"
+	"os"
 	"path"
 	"strconv"
 	"strings"
@@ -40,6 +41,20 @@ func (d *Db) MigrateDb(filesystem ReadDirFileFS, directory string) error {
 	}
 	log.Printf("Current version is %d, max migration version is %d", currentVersion, latestVersion)
 
+	// Create a backup if we're not on the latest version
+	if currentVersion != latestVersion && d.source != ":memory:" {
+		target := d.source + ".backup." + strconv.Itoa(currentVersion)
+		log.Printf("Creating backup of database to %s", target)
+		data, err := d.Db.Serialize("main")
+		if err != nil {
+			return fmt.Errorf("error serializing database: %v", err)
+		}
+		err = os.WriteFile(target, data, 0644)
+		if err != nil {
+			return fmt.Errorf("error writing backup: %v", err)
+		}
+	}
+
 	// If we are no up-to-date, bring the db up-to-date
 	for currentVersion != latestVersion {
 		targetVersion := currentVersion + 1