feat: add task scheduling logic

backend/src/assignment-scheduler.service.ts

@@ -1,24 +1,50 @@
 import { Injectable } from '@nestjs/common';
 import { Cron, CronExpression } from '@nestjs/schedule';
+import { dbGetTaskGroupUsers } from './db/functions/task-group';
 import {
-  dbGetTaskGroupUsers,
-  dbGetTaskGroupsToCreateForCurrentInterval,
-} from './db/functions/task-group';
-import { dbGetAssignmentsForTaskGroup } from './db/functions/assignment-task-group';
+  dbCreateTaskGroupAssignment,
+  dbGetAssignmentsForTaskGroup,
+  dbGetTaskGroupsToAssignForCurrentInterval,
+} from './db/functions/assignment-task-group';
+import { randomFromArray } from './utils/array';
 
 @Injectable()
 export class AssignmentSchedulerService {
   @Cron(CronExpression.EVERY_5_SECONDS)
   async handleCron() {
+    console.debug('CRON job running');
     const taskGroupsToCreateAssignmentsFor =
-      await dbGetTaskGroupsToCreateForCurrentInterval();
+      await dbGetTaskGroupsToAssignForCurrentInterval();
+    console.debug({ taskGroupsToCreateAssignmentsFor });
     for (const { taskGroupId } of taskGroupsToCreateAssignmentsFor) {
-      const users = await dbGetTaskGroupUsers(taskGroupId);
-      const assignments = await dbGetAssignmentsForTaskGroup(
+      const userIds = await dbGetTaskGroupUsers(taskGroupId);
+      if (userIds.length === 0) {
+        continue;
+      }
+      const lastAssignments = await dbGetAssignmentsForTaskGroup(
         taskGroupId,
-        users.length,
+        userIds.length,
       );
-      console.log({ assignments });
+      const firstTimeAssignmentUsers = userIds.filter(
+        ({ userId }) =>
+          !lastAssignments.some((assignment) => assignment.userId === userId),
+      );
+
+      console.debug({ userIds });
+      console.debug({ firstTimeAssignmentUsers });
+      console.debug({ lastAssignments, taskGroupId });
+
+      let nextResponsibleUserId: number;
+      if (firstTimeAssignmentUsers.length === 0) {
+        nextResponsibleUserId =
+          lastAssignments[lastAssignments.length - 1].userId;
+      } else {
+        nextResponsibleUserId = randomFromArray(
+          firstTimeAssignmentUsers,
+        ).userId;
+      }
+
+      await dbCreateTaskGroupAssignment(taskGroupId, nextResponsibleUserId);
     }
   }
 }

backend/src/db/functions/assignment-task-group.ts

@@ -1,6 +1,6 @@
-import { desc, eq } from 'drizzle-orm';
+import { count, desc, eq, or, sql } from 'drizzle-orm';
 import { db } from '..';
-import { taskGroupAssignmentTable } from '../schema';
+import { taskGroupAssignmentTable, taskGroupTable } from '../schema';
 
 export async function dbGetAssignmentsForTaskGroup(
   taskGroupId: number,
@@ -16,3 +16,36 @@ export async function dbGetAssignmentsForTaskGroup(
   }
   return await result.limit(limit);
 }
+
+export async function dbCreateTaskGroupAssignment(
+  taskGroupId: number,
+  userId: number,
+) {
+  await db.insert(taskGroupAssignmentTable).values({ taskGroupId, userId });
+}
+
+export async function dbGetTaskGroupsToAssignForCurrentInterval() {
+  try {
+    const taskGroupIdsToCreateAssignmentsFor = await db
+      .select({
+        taskGroupId: taskGroupTable.id,
+      })
+      .from(taskGroupTable)
+      .leftJoin(
+        taskGroupAssignmentTable,
+        eq(taskGroupTable.id, taskGroupAssignmentTable.taskGroupId),
+      )
+      .groupBy(taskGroupTable.id)
+      .having(
+        or(
+          eq(count(taskGroupAssignmentTable.id), 0),
+          sql`MAX(${taskGroupAssignmentTable.createdAt}) < (NOW() - ${taskGroupTable.interval})`,
+        ),
+      );
+
+    return taskGroupIdsToCreateAssignmentsFor;
+  } catch (error) {
+    console.error({ error });
+    throw error;
+  }
+}

backend/src/db/functions/task-group.ts

@@ -1,12 +1,7 @@
-import { eq, sql } from 'drizzle-orm';
+import { eq } from 'drizzle-orm';
 import { CreateTaskGroup } from 'src/task-group.controller';
 import { db } from '..';
-import {
-  taskGroupAssignmentTable,
-  taskGroupTable,
-  taskGroupUserTable,
-  userTable,
-} from '../schema';
+import { taskGroupTable, taskGroupUserTable, userTable } from '../schema';
 
 export async function dbGetTaskGroups() {
   return await db.select().from(taskGroupTable);
@@ -44,28 +39,6 @@ export async function dbCreateTaskGroup({
   }
 }
 
-export async function dbGetTaskGroupsToCreateForCurrentInterval() {
-  try {
-    const taskGroupIdsToCreateAssignmentsFor = await db
-      .select({
-        taskGroupId: taskGroupTable.id,
-      })
-      .from(taskGroupTable)
-      .innerJoin(
-        taskGroupAssignmentTable,
-        eq(taskGroupTable.id, taskGroupAssignmentTable.taskGroupId),
-      )
-      .groupBy(taskGroupTable.id)
-      .having(
-        sql`MAX(${taskGroupAssignmentTable.createdAt}) < (NOW() - ${taskGroupTable.interval})`,
-      );
-    return taskGroupIdsToCreateAssignmentsFor;
-  } catch (error) {
-    console.error({ error });
-    throw error;
-  }
-}
-
 export async function dbGetTaskGroupUsers(taskGroupId: number) {
   try {
     const taskGroupUsers = await db

backend/src/utils/array.ts

@@ -0,0 +1,11 @@
+/**
+ * Returns a random value from an array of data.
+ *
+ * @param array - An array of data from which to select a random value.
+ * @returns A random value from the array.
+ */
+export function randomFromArray<TItem>(array: readonly TItem[]) {
+  const randomIndex = Math.floor(Math.random() * array.length);
+  const randomValue = array[randomIndex];
+  return randomValue;
+}