From 3695587b48ab896506937ac9819d526b1659dd10 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Mon, 26 Feb 2024 11:40:12 +0100
Subject: [PATCH] Add DB migration infrastructure

---
 db.go      | 52 ++++++++++++++++++++++++++++++++++++++++++++++------
 schema.sql |  2 --

diff --git a/db.go b/db.go
index fff905e1975a1828bee34ab92f4c70f640354155..f1dbab190c309899e6d590b034659e2fda2f8369 100644
--- a/db.go
+++ b/db.go
@@ -13,6 +13,10 @@
 //go:embed schema.sql
 var schema string
 
+var migrations = []string{
+	"", // migration #0 is reserved for schema initialization
+}
+
 var errNoDBRows = sql.ErrNoRows
 
 type DB struct {
@@ -35,15 +39,13 @@ 	return db, nil
 }
 
 func (db *DB) init(ctx context.Context) error {
-	var n int
-	if err := db.db.QueryRowContext(ctx, "SELECT COUNT(*) FROM sqlite_schema").Scan(&n); err != nil {
+	version, err := db.upgrade(ctx)
+	if err != nil {
 		return err
-	} else if n != 0 {
-		return nil
 	}
 
-	if _, err := db.db.ExecContext(ctx, schema); err != nil {
-		return err
+	if version > 0 {
+		return nil
 	}
 
 	// TODO: drop this
@@ -52,6 +54,44 @@ 	if err := defaultUser.SetPassword("root"); err != nil {
 		return err
 	}
 	return db.StoreUser(ctx, &defaultUser)
+}
+
+func (db *DB) upgrade(ctx context.Context) (version int, err error) {
+	if err := db.db.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
+		return 0, fmt.Errorf("failed to query schema version: %v", err)
+	}
+
+	if version == len(migrations) {
+		return version, nil
+	} else if version > len(migrations) {
+		return version, fmt.Errorf("sinwon (version %d) older than schema (version %d)", len(migrations), version)
+	}
+
+	tx, err := db.db.Begin()
+	if err != nil {
+		return version, err
+	}
+	defer tx.Rollback()
+
+	if version == 0 {
+		if _, err := tx.Exec(schema); err != nil {
+			return version, fmt.Errorf("failed to initialize schema: %v", err)
+		}
+	} else {
+		for i := version; i < len(migrations); i++ {
+			if _, err := tx.Exec(migrations[i]); err != nil {
+				return version, fmt.Errorf("failed to execute migration #%v: %v", i, err)
+			}
+		}
+	}
+
+	// For some reason prepared statements don't work here
+	_, err = tx.Exec(fmt.Sprintf("PRAGMA user_version = %d", len(migrations)))
+	if err != nil {
+		return version, fmt.Errorf("failed to bump schema version: %v", err)
+	}
+
+	return version, tx.Commit()
 }
 
 func (db *DB) Close() error {
diff --git a/schema.sql b/schema.sql
index 7bfcd417e5110f27559ee62a04fe02f73c3c51e8..86a892f57152029daf1ab4dfde6ae56971ba85fe 100644
--- a/schema.sql
+++ b/schema.sql
@@ -1,5 +1,3 @@
-PRAGMA user_version = 1;
-
 CREATE TABLE User (
 	id INTEGER PRIMARY KEY,
 	username TEXT NOT NULL UNIQUE,

-- 
2.48.1