Add method to intelligently insert/update.

The `upsert()` method can both create and update tasks. The method
checks for an `id` propery to determine whether to `INSERT` or `UPDATE`.

A successful operation returns a `ServiceResponse` object with the
inserted task `id`, which can be used to fetch updated information if
needed.

The `NewTask` type is exported for use in form actions, etc.

src/lib/server/services/tasks.ts

@@ -1,7 +1,7 @@
 import { type DB, db } from "$lib/server/db/db";
-import type { tasks, taskTypes } from "$lib/server/db/schema/tasks";
+import { tasks, type taskTypes } from "$lib/server/db/schema/tasks";
 import type { ServiceResponse } from "$lib/server/services/service.types";
-import type { InferSelectModel } from "drizzle-orm";
+import { eq, type InferSelectModel } from "drizzle-orm";
 import logger from "../logger";
 
 export type Task = InferSelectModel<typeof tasks> & {
@@ -12,6 +12,8 @@ export type TaskOrNull = InferSelectModel<typeof tasks> & {
   type: InferSelectModel<typeof taskTypes> | null;
 };
 
+export type NewTask = typeof tasks.$inferInsert;
+
 class TasksService {
   private db: DB;
   private caller: "internal" | "api";
@@ -90,6 +92,33 @@ class TasksService {
       })
     );
   }
+
+  public async upsert(taskData: NewTask): Promise<ServiceResponse<{ id: number }, "INTERNAL_ERROR" | "VALIDATION_ERROR">> {
+    try {
+      if (taskData.id) {
+        const updated = await this.db.update(tasks)
+          .set(taskData)
+          .where(eq(tasks.id, taskData.id))
+          .returning({ id: tasks.id });
+        if (updated.length === 0) {
+          return { status: "failure", code: "VALIDATION_ERROR", error: `Task with ID ${taskData.id} not found for update.` };
+        }
+        return { status: "ok", data: { id: updated[0].id } };
+      } else {
+        const created = await this.db.insert(tasks)
+          .values(taskData)
+          .returning({ id: tasks.id });
+        if (created.length === 0) {
+          throw new Error("Insert operation failed to return the new task.");
+        }
+        return { status: "ok", data: { id: created[0].id } };
+      }
+    }
+    catch (error) {
+      logger.error({ msg: "Error upserting task.", error });
+      return { status: "failure", error: "An internal server error occurred while saving the task.", code: "INTERNAL_ERROR" };
+    }
+  }
 }
 
 export default TasksService;