Adding the least between current and previous next_run_start_at to merge conflict when scheduler updates

Signed-off-by: Yobannys Cabrera Gonzalez <ycabrera@webstaurantstore.com>

.changeset/dry-yaks-type.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-tasks': patch
+---
+
+Fixed bug in backend TaskWorker, 'next_run_start_at' will be always the least between schedule changes.

packages/backend-tasks/src/tasks/TaskWorker.test.ts

@@ -332,4 +332,41 @@ describe('TaskWorker', () => {
       expect(fn1.mock.calls.length).toBeGreaterThan(before);
     },
   );
+
+  it.each(databases.eachSupportedId())(
+    'next_run_start_at is always the min between schedule changes, %p',
+    async databaseId => {
+      const knex = await databases.init(databaseId);
+      await migrateBackendTasks(knex);
+
+      const fn = jest.fn(
+        async () => new Promise<void>(resolve => setTimeout(resolve, 50)),
+      );
+      const settings: TaskSettingsV2 = {
+        version: 2,
+        cadence: '*/15 * * * *',
+        initialDelayDuration: 'PT2M',
+        timeoutAfterDuration: 'PT1M',
+      };
+
+      const worker = new TaskWorker('task99', fn, knex, logger);
+      await worker.persistTask(settings);
+
+      const settings2 = {
+        ...settings,
+        cadence: '*/2 * * * *',
+        initialDelayDuration: 'PT1M',
+      };
+      await worker.persistTask(settings2);
+
+      const row2 = (await knex<DbTasksRow>(DB_TASKS_TABLE))[0];
+
+      const settings3 = { ...settings };
+      await worker.persistTask(settings3);
+
+      const row3 = (await knex<DbTasksRow>(DB_TASKS_TABLE))[0];
+
+      expect(row3.next_run_start_at).toBe(row2.next_run_start_at);
+    },
+  );
 });

packages/backend-tasks/src/tasks/TaskWorker.ts

@@ -190,6 +190,11 @@ export class TaskWorker {
 
     this.logger.debug(`task: ${this.taskId} configured to run at: ${startAt}`);
 
+    const start_at_previuos = this.knex(DB_TASKS_TABLE)
+      .where('id', '=', this.taskId)
+      .select('next_run_start_at')
+      .first();
+
     // It's OK if the task already exists; if it does, just replace its
     // settings with the new value and start the loop as usual.
     await this.knex<DbTasksRow>(DB_TASKS_TABLE)
@@ -199,7 +204,15 @@ export class TaskWorker {
         next_run_start_at: startAt,
       })
       .onConflict('id')
-      .merge(['settings_json', 'next_run_start_at']);
+      .merge({
+        settings_json: JSON.stringify(settings),
+        next_run_start_at: this.knex.raw('CASE WHEN ? < ? THEN ? ELSE ? END', [
+          start_at_previuos,
+          startAt,
+          start_at_previuos,
+          startAt,
+        ]),
+      });
   }
 
   /**