Migrations tweaks

src/invidious/database/migration.cr

@@ -0,0 +1,38 @@
+abstract class Invidious::Database::Migration
+  macro inherited
+    Migrator.migrations << self
+  end
+
+  @@version : Int64?
+
+  def self.version(version : Int32 | Int64)
+    @@version = version.to_i64
+  end
+
+  getter? completed = false
+
+  def initialize(@db : DB::Database)
+  end
+
+  abstract def up(conn : DB::Connection)
+
+  def migrate
+    # migrator already ignores completed migrations
+    # but this is an extra check to make sure a migration doesn't run twice
+    return if completed?
+
+    @db.transaction do |txn|
+      up(txn.connection)
+      track(txn.connection)
+      @completed = true
+    end
+  end
+
+  def version : Int64
+    @@version.not_nil!
+  end
+
+  private def track(conn : DB::Connection)
+    conn.exec("INSERT INTO #{Migrator::MIGRATIONS_TABLE} (version) VALUES ($1)", version)
+  end
+end