Add error in case a task was added to a bucket which has its limit already exceeded

docs/content/doc/usage/errors.md

@@ -134,3 +134,4 @@ This document describes the different errors Vikunja can return.
 | 10001 | 404 | The bucket does not exist. | 
 | 10002 | 400 | The bucket does not belong to that list. | 
 | 10003 | 412 | You cannot remove the last bucket on a list. | 
+| 10004 | 412 | You cannot add the task to this bucket as it already exceeded the limit of tasks it can hold. | 

pkg/models/error.go

@@ -1334,3 +1334,32 @@ func (err ErrCannotRemoveLastBucket) HTTPError() web.HTTPError {
 		Message:  "You cannot remove the last bucket on this list.",
 	}
 }
+
+// ErrBucketLimitExceeded represents an error where a task is being created or moved to a bucket which has its limit already exceeded.
+type ErrBucketLimitExceeded struct {
+	BucketID int64
+	Limit    int64
+	TaskID   int64 // may be 0
+}
+
+// IsErrBucketLimitExceeded checks if an error is ErrBucketLimitExceeded.
+func IsErrBucketLimitExceeded(err error) bool {
+	_, ok := err.(ErrBucketLimitExceeded)
+	return ok
+}
+
+func (err ErrBucketLimitExceeded) Error() string {
+	return fmt.Sprintf("Cannot add a task to this bucket because it would exceed the limit [BucketID: %d, Limit: %d, TaskID: %d]", err.BucketID, err.Limit, err.TaskID)
+}
+
+// ErrCodeBucketLimitExceeded holds the unique world-error code of this error
+const ErrCodeBucketLimitExceeded = 10004
+
+// HTTPError holds the http error description
+func (err ErrBucketLimitExceeded) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusPreconditionFailed,
+		Code:     ErrCodeBucketLimitExceeded,
+		Message:  "You cannot add the task to this bucket as it already exceeded the limit of tasks it can hold.",
+	}
+}

pkg/models/tasks.go

@@ -608,12 +608,37 @@ func createTask(s *xorm.Session, t *Task, a web.Auth, updateAssignees bool) (err
 	}
 
 	// Get the default bucket and move the task there
+	var bucket *Bucket
 	if t.BucketID == 0 {
-		defaultBucket, err := getDefaultBucket(s, t.ListID)
+		bucket, err = getDefaultBucket(s, t.ListID)
 		if err != nil {
 			return err
 		}
-		t.BucketID = defaultBucket.ID
+		t.BucketID = bucket.ID
+	} else {
+		// We need the bucket to check if it has more tasks than the limit allows
+		bucket, err = getBucketByID(s, t.BucketID)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Check the limit
+	if bucket.Limit > 0 {
+		type currentTasks struct {
+			count int64
+		}
+		taskCount := &currentTasks{}
+		_, err = s.
+			Table("tasks").
+			Where("bucket_id = ?", bucket.ID).
+			Count(taskCount)
+		if err != nil {
+			return err
+		}
+		if taskCount.count >= bucket.Limit {
+			return ErrBucketLimitExceeded{TaskID: t.ID, BucketID: bucket.ID, Limit: bucket.Limit}
+		}
 	}
 
 	// Get the index for this task