move sort plugin to data plugins

- Introduced a new sort plugin that allows sorting of entities based on a specified field.
- Added API endpoints for reordering items and recalculating sort order.
- Implemented tests to ensure correct functionality of sorting and reordering features.

app/src/plugins/data/sort.plugin.spec.ts

@@ -0,0 +1,858 @@
+import { describe, test, expect, beforeAll, afterAll } from "bun:test";
+import { sort } from "./sort.plugin";
+import { em, entity, text, number } from "bknd";
+import { createApp } from "core/test/utils";
+import { disableConsoleLog, enableConsoleLog } from "core/utils/test";
+
+beforeAll(() => disableConsoleLog());
+afterAll(enableConsoleLog);
+
+describe("sort plugin", () => {
+   test("should add sort field to configured entities", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const taskEntity = app.em.entity("tasks");
+      expect(taskEntity).toBeDefined();
+      expect(taskEntity?.fields.map((f) => f.name)).toContain("position");
+      expect(taskEntity?.field("position")?.type).toBe("number");
+   });
+
+   test("should auto-assign sort values on insert (starting from 0)", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // insert first item
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      expect(task1.position).toBe(0);
+
+      // insert second item
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      expect(task2.position).toBe(1);
+
+      // insert third item
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+      expect(task3.position).toBe(2);
+   });
+
+   test("should preserve manually set sort values on insert", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // insert with explicit position
+      const { data: task } = await mutator.insertOne({ title: "Task 1", position: 10 });
+      expect(task.position).toBe(10);
+   });
+
+   test("should reorder items via API endpoint", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks at positions 0, 1, 2
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+
+      // move task3 (position 2) to position 0
+      const res = await app.server.request("/api/sort/tasks/reorder", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({ id: task3.id, position: 0 }),
+      });
+
+      expect(res.status).toBe(200);
+
+      // verify positions
+      const repo = app.em.repo("tasks");
+      const { data: updatedTask1 } = await repo.findOne({ id: task1.id });
+      const { data: updatedTask2 } = await repo.findOne({ id: task2.id });
+      const { data: updatedTask3 } = await repo.findOne({ id: task3.id });
+
+      expect(updatedTask3.position).toBe(0); // moved to position 0
+      expect(updatedTask1.position).toBe(1); // shifted down
+      expect(updatedTask2.position).toBe(2); // shifted down
+   });
+
+   test("should automatically reorder when updating sort field directly", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks at positions 0, 1, 2, 3
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+      const { data: task4 } = await mutator.insertOne({ title: "Task 4" });
+
+      // move task4 (position 3) to position 1 by updating directly
+      await mutator.updateOne(task4.id, { position: 1 });
+
+      // verify positions
+      const repo = app.em.repo("tasks");
+      const { data: updatedTask1 } = await repo.findOne({ id: task1.id });
+      const { data: updatedTask2 } = await repo.findOne({ id: task2.id });
+      const { data: updatedTask3 } = await repo.findOne({ id: task3.id });
+      const { data: updatedTask4 } = await repo.findOne({ id: task4.id });
+
+      expect(updatedTask1.position).toBe(0); // unchanged
+      expect(updatedTask2.position).toBe(2); // shifted down
+      expect(updatedTask3.position).toBe(3); // shifted down
+      expect(updatedTask4.position).toBe(1); // moved to position 1
+   });
+
+   test("should automatically reorder when moving items up", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks at positions 0, 1, 2, 3
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+      const { data: task4 } = await mutator.insertOne({ title: "Task 4" });
+
+      // move task1 (position 0) to position 2 by updating directly
+      await mutator.updateOne(task1.id, { position: 2 });
+
+      // verify positions
+      const repo = app.em.repo("tasks");
+      const { data: updatedTask1 } = await repo.findOne({ id: task1.id });
+      const { data: updatedTask2 } = await repo.findOne({ id: task2.id });
+      const { data: updatedTask3 } = await repo.findOne({ id: task3.id });
+      const { data: updatedTask4 } = await repo.findOne({ id: task4.id });
+
+      expect(updatedTask1.position).toBe(2); // moved to position 2
+      expect(updatedTask2.position).toBe(0); // shifted up
+      expect(updatedTask3.position).toBe(1); // shifted up
+      expect(updatedTask4.position).toBe(3); // unchanged
+   });
+
+   test("should support scoped sorting", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+                  project_id: number(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                        scope: "project_id",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks in project 1
+      const { data: p1t1 } = await mutator.insertOne({
+         title: "P1 Task 1",
+         project_id: 1,
+      });
+      const { data: p1t2 } = await mutator.insertOne({
+         title: "P1 Task 2",
+         project_id: 1,
+      });
+
+      // create tasks in project 2
+      const { data: p2t1 } = await mutator.insertOne({
+         title: "P2 Task 1",
+         project_id: 2,
+      });
+      const { data: p2t2 } = await mutator.insertOne({
+         title: "P2 Task 2",
+         project_id: 2,
+      });
+
+      // positions should be scoped per project
+      expect(p1t1.position).toBe(0);
+      expect(p1t2.position).toBe(1);
+      expect(p2t1.position).toBe(0); // resets for new scope
+      expect(p2t2.position).toBe(1);
+   });
+
+   test("should reorder only within scope", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+                  project_id: number(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                        scope: "project_id",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks in project 1
+      const { data: p1t1 } = await mutator.insertOne({
+         title: "P1 Task 1",
+         project_id: 1,
+      });
+      const { data: p1t2 } = await mutator.insertOne({
+         title: "P1 Task 2",
+         project_id: 1,
+      });
+      const { data: p1t3 } = await mutator.insertOne({
+         title: "P1 Task 3",
+         project_id: 1,
+      });
+
+      // create tasks in project 2
+      const { data: p2t1 } = await mutator.insertOne({
+         title: "P2 Task 1",
+         project_id: 2,
+      });
+      const { data: p2t2 } = await mutator.insertOne({
+         title: "P2 Task 2",
+         project_id: 2,
+      });
+
+      // move p1t3 to position 0 (should only affect project 1)
+      await app.server.request("/api/sort/tasks/reorder", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({ id: p1t3.id, position: 0 }),
+      });
+
+      // verify project 1 tasks
+      const repo = app.em.repo("tasks");
+      const { data: updatedP1t1 } = await repo.findOne({ id: p1t1.id });
+      const { data: updatedP1t2 } = await repo.findOne({ id: p1t2.id });
+      const { data: updatedP1t3 } = await repo.findOne({ id: p1t3.id });
+
+      expect(updatedP1t3.position).toBe(0); // moved to position 0
+      expect(updatedP1t1.position).toBe(1); // shifted
+      expect(updatedP1t2.position).toBe(2); // shifted
+
+      // verify project 2 tasks are unchanged
+      const { data: updatedP2t1 } = await repo.findOne({ id: p2t1.id });
+      const { data: updatedP2t2 } = await repo.findOne({ id: p2t2.id });
+
+      expect(updatedP2t1.position).toBe(0); // unchanged
+      expect(updatedP2t2.position).toBe(1); // unchanged
+   });
+
+   test("should recalculate all positions", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks with irregular positions
+      await mutator.insertOne({ title: "Task 1", position: 5 });
+      await mutator.insertOne({ title: "Task 2", position: 10 });
+      await mutator.insertOne({ title: "Task 3", position: 15 });
+      await mutator.insertOne({ title: "Task 4", position: 100 });
+
+      // recalculate
+      const res = await app.server.request("/api/sort/tasks/recalculate", {
+         method: "POST",
+         body: JSON.stringify({}),
+         headers: {
+            "Content-Type": "application/json",
+         },
+      });
+
+      expect(res.status).toBe(200);
+
+      // verify positions are now 0, 1, 2, 3
+      const { data: tasks } = await app.em.repo("tasks").findMany({
+         orderBy: [{ position: "asc" }],
+      });
+
+      expect(tasks.length).toBe(4);
+      expect(tasks[0].position).toBe(0);
+      expect(tasks[1].position).toBe(1);
+      expect(tasks[2].position).toBe(2);
+      expect(tasks[3].position).toBe(3);
+   });
+
+   test("should recalculate positions within scope only", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+                  project_id: number(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                        scope: "project_id",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks in project 1 with irregular positions
+      await mutator.insertOne({ title: "P1 Task 1", project_id: 1, position: 5 });
+      await mutator.insertOne({ title: "P1 Task 2", project_id: 1, position: 15 });
+
+      // create tasks in project 2 with irregular positions
+      await mutator.insertOne({ title: "P2 Task 1", project_id: 2, position: 10 });
+      await mutator.insertOne({ title: "P2 Task 2", project_id: 2, position: 20 });
+
+      // recalculate only project 1
+      const res = await app.server.request("/api/sort/tasks/recalculate", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({ scope: 1 }),
+      });
+
+      expect(res.status).toBe(200);
+
+      // verify project 1 tasks are recalculated
+      const { data: p1Tasks } = await app.em.repo("tasks").findMany({
+         where: { project_id: 1 },
+         orderBy: [{ position: "asc" }],
+      });
+
+      expect(p1Tasks.length).toBe(2);
+      expect(p1Tasks[0].position).toBe(0);
+      expect(p1Tasks[1].position).toBe(1);
+
+      // verify project 2 tasks are unchanged
+      const { data: p2Tasks } = await app.em.repo("tasks").findMany({
+         where: { project_id: 2 },
+         orderBy: [{ position: "asc" }],
+      });
+
+      expect(p2Tasks.length).toBe(2);
+      expect(p2Tasks[0].position).toBe(10); // unchanged
+      expect(p2Tasks[1].position).toBe(20); // unchanged
+   });
+
+   test("should handle moving items to the end", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks at positions 0, 1, 2, 3
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+      const { data: task4 } = await mutator.insertOne({ title: "Task 4" });
+
+      // move task1 to the end (position 3)
+      await app.server.request("/api/sort/tasks/reorder", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({ id: task1.id, position: 3 }),
+      });
+
+      // verify positions
+      const repo = app.em.repo("tasks");
+      const { data: updatedTask1 } = await repo.findOne({ id: task1.id });
+      const { data: updatedTask2 } = await repo.findOne({ id: task2.id });
+      const { data: updatedTask3 } = await repo.findOne({ id: task3.id });
+      const { data: updatedTask4 } = await repo.findOne({ id: task4.id });
+
+      expect(updatedTask1.position).toBe(3); // moved to end
+      expect(updatedTask2.position).toBe(0); // shifted up
+      expect(updatedTask3.position).toBe(1); // shifted up
+      expect(updatedTask4.position).toBe(2); // shifted up
+   });
+
+   test("should return 400 for invalid item id", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const res = await app.server.request("/api/sort/tasks/reorder", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({ id: 999999, position: 0 }),
+      });
+
+      expect(res.status).toBe(400);
+   });
+
+   test("should handle multiple entities with different configurations", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+               categories: entity("categories", {
+                  name: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                     categories: {
+                        field: "order",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      // verify both entities have their sort fields
+      const taskEntity = app.em.entity("tasks");
+      const categoryEntity = app.em.entity("categories");
+
+      expect(taskEntity?.fields.map((f) => f.name)).toContain("position");
+      expect(categoryEntity?.fields.map((f) => f.name)).toContain("order");
+
+      // create items in both entities
+      const { data: task } = await app.em.mutator("tasks").insertOne({ title: "Task 1" });
+      const { data: category } = await app.em.mutator("categories").insertOne({ name: "Cat 1" });
+
+      expect(task.position).toBe(0);
+      expect(category.order).toBe(0);
+
+      // verify both endpoints exist
+      const taskRes = await app.server.request("/api/sort/tasks/recalculate", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({}),
+      });
+      const catRes = await app.server.request("/api/sort/categories/recalculate", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({}),
+      });
+
+      expect(taskRes.status).toBe(200);
+      expect(catRes.status).toBe(200);
+   });
+
+   test("should not trigger reorder when updating other fields", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+      const { data: task3 } = await mutator.insertOne({ title: "Task 3" });
+
+      // update title only (should not trigger reordering)
+      await mutator.updateOne(task2.id, { title: "Task 2 Updated" });
+
+      // verify positions are unchanged
+      const repo = app.em.repo("tasks");
+      const { data: updatedTask1 } = await repo.findOne({ id: task1.id });
+      const { data: updatedTask2 } = await repo.findOne({ id: task2.id });
+      const { data: updatedTask3 } = await repo.findOne({ id: task3.id });
+
+      expect(updatedTask1.position).toBe(0);
+      expect(updatedTask2.position).toBe(1);
+      expect(updatedTask2.title).toBe("Task 2 Updated");
+      expect(updatedTask3.position).toBe(2);
+   });
+
+   test("should handle null sort values", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create task with null position (bypass listener by using kysely directly)
+      await app.connection.kysely
+         .insertInto("tasks")
+         .values({ title: "Task with null", position: null })
+         .execute();
+
+      // create normal task
+      await mutator.insertOne({ title: "Task 2" });
+
+      // update the null task to have a position
+      const nullTask = await app.connection.kysely
+         .selectFrom("tasks")
+         .selectAll()
+         .where("title", "=", "Task with null")
+         .executeTakeFirst();
+
+      await mutator.updateOne(nullTask!.id, { position: 0 });
+
+      // verify both tasks have proper positions
+      const { data: tasks } = await app.em.repo("tasks").findMany({
+         sort: { by: "position", dir: "asc" },
+      });
+
+      expect(tasks.length).toBe(2);
+      expect(tasks[0].position).toBe(0);
+      expect(tasks[1].position).toBe(1);
+   });
+
+   test("should not create duplicates when moving to an occupied position", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create two tasks at positions 0 and 1
+      const { data: task1 } = await mutator.insertOne({ title: "Task 1" });
+      const { data: task2 } = await mutator.insertOne({ title: "Task 2" });
+
+      expect(task1.position).toBe(0);
+      expect(task2.position).toBe(1);
+
+      // move task2 (at position 1) to position 0
+      await mutator.updateOne(task2.id, { position: 0 });
+
+      // verify no duplicates
+      const { data: tasks } = await app.em.repo("tasks").findMany({
+         sort: { by: "position", dir: "asc" },
+      });
+
+      expect(tasks.length).toBe(2);
+      expect(tasks[0].id).toBe(task2.id);
+      expect(tasks[0].position).toBe(0);
+      expect(tasks[1].id).toBe(task1.id);
+      expect(tasks[1].position).toBe(1);
+
+      // verify no tasks have the same position
+      const positions = tasks.map((t) => t.position);
+      const uniquePositions = new Set(positions);
+      expect(uniquePositions.size).toBe(positions.length);
+   });
+
+   test("should preserve order when recalculating", async () => {
+      const app = createApp({
+         config: {
+            data: em({
+               tasks: entity("tasks", {
+                  title: text(),
+               }),
+            }).toJSON(),
+         },
+         options: {
+            plugins: [
+               sort({
+                  entities: {
+                     tasks: {
+                        field: "position",
+                     },
+                  },
+               }),
+            ],
+         },
+      });
+      await app.build();
+
+      const mutator = app.em.mutator("tasks");
+
+      // create tasks with specific positions
+      const { data: taskA } = await mutator.insertOne({ title: "Task A", position: 5 });
+      const { data: taskB } = await mutator.insertOne({ title: "Task B", position: 3 });
+      const { data: taskC } = await mutator.insertOne({ title: "Task C", position: 10 });
+
+      // recalculate
+      await app.server.request("/api/sort/tasks/recalculate", {
+         method: "POST",
+         headers: {
+            "Content-Type": "application/json",
+         },
+         body: JSON.stringify({}),
+      });
+
+      // verify order is preserved (B, A, C based on original positions)
+      const { data: tasks } = await app.em.repo("tasks").findMany({
+         sort: { by: "position", dir: "asc" },
+      });
+
+      expect(tasks[0].id).toBe(taskB.id); // was at 3, now at 0
+      expect(tasks[0].position).toBe(0);
+      expect(tasks[1].id).toBe(taskA.id); // was at 5, now at 1
+      expect(tasks[1].position).toBe(1);
+      expect(tasks[2].id).toBe(taskC.id); // was at 10, now at 2
+      expect(tasks[2].position).toBe(2);
+   });
+});

app/src/plugins/data/sort.plugin.ts

@@ -0,0 +1,423 @@
+import { Exception, type App, type AppPlugin, DatabaseEvents, em, entity, number } from "bknd";
+import { invariant, HttpStatus, jsc, s, $console } from "bknd/utils";
+import { Hono } from "hono";
+import { sql } from "kysely";
+
+const DEFAULT_BATCH_SIZE = 1000;
+
+export type SortPluginOptions = {
+   /**
+    * The base path for the API endpoints.
+    * @default "/api/sort"
+    */
+   apiBasePath?: string;
+
+   /**
+    * Configuration for entities that should have sorting enabled.
+    * Key is the entity name, value is the configuration.
+    */
+   entities: Record<
+      string,
+      {
+         /**
+          * The name of the sort property (must be a number field).
+          */
+         field: string;
+
+         /**
+          * Optional scope field name. If provided, sorting will only happen within the same scope.
+          * For example, if scope is "category_id", items will only be sorted within items
+          * that have the same category_id value.
+          */
+         scope?: string;
+      }
+   >;
+
+   /**
+    * The batch size for recalculating sort order.
+    * @default 1000
+    */
+   recalculateBatchSize?: number;
+};
+
+class SortError extends Exception {
+   override name = "SortError";
+   override code = HttpStatus.BAD_REQUEST;
+}
+
+export function sort({
+   apiBasePath = "/api/sort",
+   entities,
+   recalculateBatchSize = DEFAULT_BATCH_SIZE,
+}: SortPluginOptions): AppPlugin {
+   return (app: App) => {
+      return {
+         name: "sort",
+         schema: () => {
+            return em(
+               Object.fromEntries(
+                  Object.entries(entities).map(([entityName, config]) => [
+                     entityName,
+                     entity(entityName, {
+                        [config.field]: number({ default_value: 0 }),
+                     }),
+                  ]),
+               ),
+               ({ index }, schema) => {
+                  for (const [entityName, config] of Object.entries(entities)) {
+                     const indexed = app.em.getIndexedFields(entityName);
+                     if (!indexed.some((f) => f.name === config.field)) {
+                        index(schema[entityName]!).on([config.field]);
+                     }
+                  }
+               },
+            );
+         },
+         onBuilt: async () => {
+            invariant(
+               entities && Object.keys(entities).length > 0,
+               "At least one entity must be configured",
+            );
+
+            // validate entities exist and have the configured fields
+            for (const [entityName, config] of Object.entries(entities)) {
+               const entity = app.em.entity(entityName);
+               invariant(entity, `Entity "${entityName}" not found in schema`);
+
+               const sortFieldSchema = entity.field(config.field)!;
+               invariant(
+                  sortFieldSchema,
+                  `Sort field "${config.field}" not found in entity "${entityName}"`,
+               );
+               invariant(
+                  sortFieldSchema.type === "number",
+                  `Sort field "${config.field}" in entity "${entityName}" must be a number field`,
+               );
+
+               if (config.scope) {
+                  const scopeFieldSchema = entity.field(config.scope);
+                  invariant(
+                     scopeFieldSchema,
+                     `Scope field "${config.scope}" not found in entity "${entityName}"`,
+                  );
+               }
+            }
+
+            const hono = new Hono();
+
+            // register recalculate endpoints for each entity
+            for (const [entityName, config] of Object.entries(entities)) {
+               hono.post(
+                  `/${entityName}/recalculate`,
+                  jsc(
+                     "json",
+                     s
+                        .object({
+                           scope: s.any().optional(),
+                        })
+                        .optional(),
+                  ),
+                  async (c) => {
+                     const body = c.req.valid("json");
+                     const scope = body?.scope;
+
+                     await recalculateSortOrder(
+                        app,
+                        entityName,
+                        config,
+                        recalculateBatchSize,
+                        scope,
+                     );
+
+                     return c.json({ success: true, message: "Sort order recalculated" });
+                  },
+               );
+
+               hono.post(
+                  `/${entityName}/reorder`,
+                  jsc(
+                     "json",
+                     s.object({
+                        id: s.any(),
+                        position: s.number(),
+                     }),
+                  ),
+                  async (c) => {
+                     const { id, position } = c.req.valid("json");
+
+                     await reorderItem(app, entityName, config, id, position);
+
+                     return c.json({ success: true, message: "Item reordered" });
+                  },
+               );
+            }
+
+            app.server.route(apiBasePath, hono);
+
+            // register listeners for automatic reordering
+            registerListeners(app, entities);
+         },
+      };
+   };
+}
+
+async function reorderItem(
+   app: App,
+   entityName: string,
+   config: SortPluginOptions["entities"][string],
+   id: any,
+   newPosition: number,
+) {
+   const { field: sortField, scope: scopeField } = config;
+   const em = app.em.fork();
+   const kysely = em.connection.kysely;
+
+   // get the item
+   const { data: item } = await em.repo(entityName).findOne({ id });
+   if (!item) {
+      throw new SortError(`Item with id "${id}" not found in entity "${entityName}"`);
+   }
+
+   const oldPosition = item[sortField] as number | null | undefined;
+   const scopeValue = scopeField ? item[scopeField] : undefined;
+
+   // update the item with new position (using forked em, so no listeners are triggered)
+   await em.mutator(entityName).updateOne(id, { [sortField]: newPosition });
+
+   // shift other items using kysely
+   if (oldPosition !== undefined && oldPosition !== null && oldPosition !== newPosition) {
+      if (newPosition < oldPosition) {
+         // moving up: increment items between newPosition and oldPosition
+         let query = kysely
+            .updateTable(entityName)
+            .set({ [sortField]: sql`${sql.ref(sortField)} + 1` } as any)
+            .where(sortField as any, ">=", newPosition)
+            .where(sortField as any, "<", oldPosition)
+            .where("id", "!=", id);
+
+         if (scopeField && scopeValue !== undefined) {
+            query = query.where(scopeField as any, "=", scopeValue);
+         }
+
+         await query.execute();
+      } else {
+         // moving down: decrement items between oldPosition and newPosition
+         let query = kysely
+            .updateTable(entityName)
+            .set({ [sortField]: sql`${sql.ref(sortField)} - 1` } as any)
+            .where(sortField as any, ">", oldPosition)
+            .where(sortField as any, "<=", newPosition)
+            .where("id", "!=", id);
+
+         if (scopeField && scopeValue !== undefined) {
+            query = query.where(scopeField as any, "=", scopeValue);
+         }
+
+         await query.execute();
+      }
+   } else if (oldPosition === undefined || oldPosition === null) {
+      // new item, shift everything at or after this position
+      let query = kysely
+         .updateTable(entityName)
+         .set({ [sortField]: sql`${sql.ref(sortField)} + 1` } as any)
+         .where(sortField as any, ">=", newPosition)
+         .where("id", "!=", id);
+
+      if (scopeField && scopeValue !== undefined) {
+         query = query.where(scopeField as any, "=", scopeValue);
+      }
+
+      await query.execute();
+   }
+}
+
+async function recalculateSortOrder(
+   app: App,
+   entityName: string,
+   config: SortPluginOptions["entities"][string],
+   batchSize: number,
+   scope?: any,
+) {
+   const { field: sortField, scope: scopeField } = config;
+   const db = app.connection.kysely;
+
+   const { count } = (await db
+      .selectFrom(entityName)
+      .select((eb) => eb.fn.count<number>("id").as("count"))
+      .$if(Boolean(scopeField && scope !== undefined), (eb) =>
+         eb.where(scopeField as any, "=", scope),
+      )
+      .$castTo<{ count: number }>()
+      .executeTakeFirst()) ?? { count: 0 };
+
+   const batches = Math.ceil(count / batchSize);
+   for (let i = 0; i < batches; i++) {
+      // get all items in scope, ordered by current sort value
+      const items = await db
+         .selectFrom(entityName)
+         .select(["id", sortField])
+         .$if(Boolean(scopeField && scope !== undefined), (eb) =>
+            eb.where(scopeField as any, "=", scope),
+         )
+         .orderBy(sortField, "asc")
+         .limit(batchSize)
+         .offset(i * batchSize)
+         .execute();
+
+      const newQbs = items.map((item, index) =>
+         db
+            .updateTable(entityName)
+            .set({ [sortField]: index })
+            .where("id", "=", item.id),
+      );
+
+      await app.connection.executeQueries(...newQbs);
+      $console.log(
+         `[Sort Plugin] Recalculated sort order for ${items.length} items in entity "${entityName}"${scopeField && scope !== undefined ? ` (scope: ${scope})` : ""} [batch ${i + 1}/${batches}]`,
+      );
+   }
+}
+
+function registerListeners(app: App, entities: SortPluginOptions["entities"]) {
+   const kysely = app.connection.kysely;
+
+   // handle insert events
+   app.emgr.onEvent(
+      DatabaseEvents.MutatorInsertBefore,
+      async (e) => {
+         const entityName = e.params.entity.name;
+         const config = entities[entityName];
+         if (!config) return e.params.data;
+
+         const { field: sortField, scope: scopeField } = config;
+         const data = e.params.data;
+         const scopeValue = scopeField ? data[scopeField] : undefined;
+
+         // if no position provided, set to max + 1
+         if (data[sortField] === undefined || data[sortField] === null) {
+            const query = kysely
+               .selectFrom(entityName)
+               .select((eb) => [eb.fn.max<number>(eb.ref(sortField)).as("max")])
+               // add scope filter if needed
+               .$if(Boolean(scopeField && scopeValue), (eb) =>
+                  eb.where(scopeField as any, "=", scopeValue as any),
+               );
+
+            const result = await query.executeTakeFirst();
+            const max = result?.max ?? -1;
+
+            return {
+               ...data,
+               [sortField]: max + 1,
+            };
+         }
+
+         // if position is provided, shift other items at or after that position
+         const newPosition = data[sortField] as number;
+
+         let shiftQuery = kysely
+            .updateTable(entityName)
+            .set({ [sortField]: sql`${sql.ref(sortField)} + 1` } as any)
+            .where(sortField as any, ">=", newPosition);
+
+         if (scopeField && scopeValue !== undefined) {
+            shiftQuery = shiftQuery.where(scopeField as any, "=", scopeValue);
+         }
+
+         await shiftQuery.execute();
+
+         return data;
+      },
+      {
+         mode: "sync",
+         id: "bknd-sort-insert",
+      },
+   );
+
+   // handle update events
+   app.emgr.onEvent(
+      DatabaseEvents.MutatorUpdateBefore,
+      async (e) => {
+         const entityName = e.params.entity.name;
+         const config = entities[entityName];
+         if (!config) return e.params.data;
+
+         const { field: sortField, scope: scopeField } = config;
+         const data = e.params.data;
+
+         // only handle if sort field is being updated
+         if (!(sortField in data)) return e.params.data;
+
+         const newPosition = data[sortField] as number;
+         const id = e.params.entityId;
+
+         // get the current item to know its old position and scope
+         const item = await kysely
+            .selectFrom(entityName)
+            .selectAll()
+            .where("id" as any, "=", id)
+            .executeTakeFirst();
+
+         if (!item) return data;
+
+         const oldPosition = item[sortField] as number | null | undefined;
+         const scopeValue = scopeField ? item[scopeField] : undefined;
+
+         // if oldPosition is null or undefined, treat as inserting at newPosition
+         if (oldPosition === null || oldPosition === undefined) {
+            // shift items at or after the new position
+            let query = kysely
+               .updateTable(entityName)
+               .set({ [sortField]: sql`${sql.ref(sortField)} + 1` } as any)
+               .where(sortField as any, ">=", newPosition)
+               .where("id" as any, "!=", id);
+
+            if (scopeField && scopeValue !== undefined) {
+               query = query.where(scopeField as any, "=", scopeValue);
+            }
+
+            await query.execute();
+            return data;
+         }
+
+         // shift other items using kysely
+         if (oldPosition !== newPosition) {
+            if (newPosition < oldPosition) {
+               // moving up: increment items between newPosition and oldPosition
+               let query = kysely
+                  .updateTable(entityName)
+                  .set({ [sortField]: sql`${sql.ref(sortField)} + 1` } as any)
+                  .where(sortField as any, ">=", newPosition)
+                  .where(sortField as any, "<", oldPosition)
+                  .where("id" as any, "!=", id);
+
+               if (scopeField && scopeValue !== undefined) {
+                  query = query.where(scopeField as any, "=", scopeValue);
+               }
+
+               await query.execute();
+            } else {
+               // moving down: decrement items between oldPosition and newPosition
+               let query = kysely
+                  .updateTable(entityName)
+                  .set({ [sortField]: sql`${sql.ref(sortField)} - 1` } as any)
+                  .where(sortField as any, ">", oldPosition)
+                  .where(sortField as any, "<=", newPosition)
+                  .where("id" as any, "!=", id);
+
+               if (scopeField && scopeValue !== undefined) {
+                  query = query.where(scopeField as any, "=", scopeValue);
+               }
+
+               await query.execute();
+            }
+         }
+
+         return data;
+      },
+      {
+         mode: "sync",
+         id: "bknd-sort-update",
+      },
+   );
+}

app/src/plugins/index.ts

@@ -9,3 +9,4 @@ export { syncTypes, type SyncTypesOptions } from "./dev/sync-types.plugin";
 export { syncSecrets, type SyncSecretsOptions } from "./dev/sync-secrets.plugin";
 export { timestamps, type TimestampsPluginOptions } from "./data/timestamps.plugin";
 export { emailOTP, type EmailOTPPluginOptions } from "./auth/email-otp.plugin";
+export { sort, type SortPluginOptions } from "./data/sort.plugin";