feat: add task status transition utility

nexus-frontend/src/utils/transitions.ts

@@ -0,0 +1,40 @@
+import type { TaskStatus } from '../types/task';
+
+/**
+ * Defines the valid status transitions for tasks.
+ * State machine: TODO → IN_PROGRESS → IN_REVIEW → DONE
+ */
+const TRANSITION_MAP: Readonly<Record<TaskStatus, readonly TaskStatus[]>> = {
+  TODO: ['IN_PROGRESS'],
+  IN_PROGRESS: ['IN_REVIEW'],
+  IN_REVIEW: ['DONE'],
+  DONE: [],
+};
+
+/**
+ * Returns the list of valid next statuses for a given current status.
+ * Returns an empty array if no transitions are available (terminal state).
+ */
+export function getValidTransitions(currentStatus: TaskStatus): TaskStatus[] {
+  return [...(TRANSITION_MAP[currentStatus] ?? [])];
+}
+
+/**
+ * Checks whether transitioning from one status to another is valid.
+ */
+export function isValidTransition(
+  from: TaskStatus,
+  to: TaskStatus
+): boolean {
+  return TRANSITION_MAP[from]?.includes(to) ?? false;
+}
+
+/**
+ * Human-readable labels for task statuses.
+ */
+export const STATUS_LABELS: Record<TaskStatus, string> = {
+  TODO: 'To Do',
+  IN_PROGRESS: 'In Progress',
+  IN_REVIEW: 'In Review',
+  DONE: 'Done',
+};