Refactor position move logic

backend/helpers/positionMove.js

@@ -0,0 +1,63 @@
+const isMissingPositionColumn = (error) =>
+  error &&
+  error.code === "ER_BAD_FIELD_ERROR" &&
+  String(error.sqlMessage || "").includes("position");
+
+const moveByPosition = async ({
+  db,
+  table,
+  id,
+  direction,
+  selectQuery,
+  missingColumnMessage,
+  notFoundMessage,
+}) => {
+  if (direction !== "up" && direction !== "down") {
+    return { status: 400, body: { error: "Ungueltige Richtung" } };
+  }
+
+  let rows;
+
+  try {
+    await db.query(
+      `UPDATE ${table} SET position = id WHERE position IS NULL`
+    );
+
+    ;[rows] = await db.query(selectQuery);
+  } catch (error) {
+    if (isMissingPositionColumn(error)) {
+      return { status: 400, body: { error: missingColumnMessage } };
+    }
+
+    throw error;
+  }
+
+  const index = rows.findIndex((row) => row.id == id);
+
+  if (index === -1) {
+    return { status: 404, body: { error: notFoundMessage } };
+  }
+
+  const swapIndex = direction === "up" ? index - 1 : index + 1;
+
+  if (swapIndex < 0 || swapIndex >= rows.length) {
+    return { status: 200, body: { success: true } };
+  }
+
+  const moved = rows.splice(index, 1)[0];
+  rows.splice(swapIndex, 0, moved);
+
+  for (let i = 0; i < rows.length; i++) {
+    await db.query(
+      `UPDATE ${table} SET position = ? WHERE id = ?`,
+      [i + 1, rows[i].id]
+    );
+  }
+
+  return { status: 200, body: { success: true } };
+};
+
+module.exports = {
+  moveByPosition,
+  isMissingPositionColumn,
+};