Reward with negative cost can no longer be created, fixes #11855 (#11870)

* Minor refactoring in scoreTask.js

* Reward value validation added (should be >= 0)

migrations/tasks/rewards-flip-negative-costs.js

@@ -0,0 +1,54 @@
+// @migrationName = 'RewardsMigrationFlipNegativeCostsValues';
+// @authorName = 'hamboomger';
+// @authorUuid = '80b61b73-2278-4947-b713-a10112cfe7f5';
+
+/*
+ * For each reward with negative cost, make it positive
+ * by assigning it an absolute value of itself
+ */
+
+import { Task } from '../../website/server/models/task';
+
+async function flipNegativeCostsValues () {
+  const query = {
+    type: 'reward',
+    value: { $lt: 0 },
+  };
+
+  const fields = {
+    _id: 1,
+    value: 1,
+  };
+
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    // eslint-disable-next-line no-await-in-loop
+    const rewards = await Task
+      .find(query)
+      .limit(250)
+      .sort({ _id: 1 })
+      .select(fields)
+      .lean()
+      .exec();
+
+    if (rewards.length === 0) {
+      break;
+    }
+
+    const promises = rewards.map(reward => {
+      const positiveValue = Math.abs(reward.value);
+      return Task.update({ _id: reward._id }, { $set: { value: positiveValue } }).exec();
+    });
+
+    // eslint-disable-next-line no-await-in-loop
+    await Promise.all(promises);
+
+    query._id = {
+      $gt: rewards[rewards.length - 1]._id,
+    };
+  }
+
+  console.log('All rewards with negative values were updated, migration finished');
+}
+
+export default flipNegativeCostsValues;