task-guards.ts

import type { Task, TaskPriority } from '@/types/task';

const STATUSES = new Set(['todo', 'in_progress', 'done', 'archived']);
const PRIORITIES = new Set<number>([1, 2, 3]);

/**
 * Runtime validation for data crossing the WebSocket boundary. The socket
 * payload is untrusted at runtime (the `Task` type is only a compile-time
 * contract), so we verify shape before letting it into React state — a
 * malformed event can't silently corrupt the board (e.g. `NaN` sort keys).
 */
export function isTask(value: unknown): value is Task {
  if (typeof value !== 'object' || value === null) return false;
  const t = value as Record<string, unknown>;
  return (
    typeof t.id === 'string' &&
    typeof t.title === 'string' &&
    typeof t.status === 'string' &&
    STATUSES.has(t.status) &&
    typeof t.priority === 'number' &&
    PRIORITIES.has(t.priority as TaskPriority) &&
    Array.isArray(t.tags) &&
    t.tags.every((tag) => typeof tag === 'string') &&
    typeof t.createdAt === 'string' &&
    typeof t.updatedAt === 'string'
  );
}