add fetching message history

database.go

@@ -57,7 +57,7 @@ func DbInit(ctx context.Context) {
 		CREATE TABLE IF NOT EXISTS messages (
 			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
 			sender_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-			receiver_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+			receiver_id UUID NOT NULL REFERENCES user_connections(id) ON DELETE CASCADE,
 			created_at TIMESTAMP NOT NULL DEFAULT NOW(),
 			content TEXT NOT NULL,
 			is_group_message BOOLEAN DEFAULT FALSE
@@ -217,12 +217,47 @@ func DbConnectionUpdateState(ctx context.Context, conn *Connection) error {
 }
 
 func DbMessageSave(ctx context.Context, message *Message) error {
+	if message.Id != (uuid.UUID{}) {
+		_, err := dbConn.Exec(ctx, `
+			INSERT INTO messages (id, sender_id, receiver_id, created_at, content, is_group_message) VALUES ($1, $2, $3, $4, $5, $6)
+		`, message.Id, message.Sender, message.Receiver, message.CreatedAt, message.Content, message.IsGroupMessage)
+		return err
+	}
 	return dbConn.QueryRow(ctx, `
 		INSERT INTO messages (sender_id, receiver_id, created_at, content, is_group_message) VALUES ($1, $2, $3, $4, $5)
 		RETURNING id
 	`, message.Sender, message.Receiver, message.CreatedAt, message.Content, message.IsGroupMessage).Scan(&message.Id)
 }
 
+func DbConnectionGetMessagesBefore(ctx context.Context, before time.Time, connection uuid.UUID, cap uint32) ([]*Message, error) {
+	rows, err := dbConn.Query(ctx, `
+		SELECT id, sender_id, receiver_id, created_at, content, is_group_message
+		FROM (
+			SELECT id, sender_id, receiver_id, created_at, content, is_group_message
+			FROM messages
+			WHERE receiver_id = $1
+			  AND created_at < $2
+			ORDER BY created_at DESC
+			LIMIT $3
+		) sub
+		ORDER BY created_at ASC
+	`, connection, before, cap)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	messages := make([]*Message, 0, cap)
+	for rows.Next() {
+		msg := &Message{}
+		if err = rows.Scan(&msg.Id, &msg.Sender, &msg.Receiver, &msg.CreatedAt, &msg.Content, &msg.IsGroupMessage); err != nil {
+			return nil, err
+		}
+		messages = append(messages, msg)
+	}
+	return messages, rows.Err()
+}
+
 func DbGroupSave(ctx context.Context, group *Group) error {
 	err := dbConn.QueryRow(ctx, `
 		INSERT INTO chat_groups (name, creator_id, owner_id, enable_client_colors, color_red, color_green, color_blue, created_at)