Task Management System

Implement a task-management service by processing a finite sequence of timestamped operations in order.

Every operation begins with an opcode. Timestamps are strictly increasing.

• ["ADD_USER", t, userId, quota] creates a user with a maximum number of active tasks.
• ["CREATE", t, taskId, userId, priority, dueAt, expiresAt] creates an active task. It fails if the task identifier already exists, the user does not exist, or the user's active-task quota is full.
• ["GET", t, taskId] returns [taskId, userId, priority, createdAt, dueAt, expiresAt, status], or an empty row for a missing or deleted task.
• ["UPDATE", t, taskId, priority, dueAt, expiresAt] updates an active task.
• ["DELETE", t, taskId] marks an existing non-deleted task as deleted.
• ["SEARCH", t, userId] returns that user's active task identifiers ordered by decreasing priority, then increasing creation timestamp, then identifier.
• ["SET_QUOTA", t, userId, quota] changes a user's quota. Lowering it does not remove existing tasks, but new tasks remain blocked until the active count is below the quota.
• ["COMPLETE", t, taskId] marks an active task completed.
• ["HISTORY", t, userId, view] returns identifiers in increasing creation order. view is COMPLETED, EXPIRED, UNFINISHED, or OVERDUE. Unfinished tasks are active; overdue tasks are active tasks with dueAt < t.

Before each operation at time t, every active task with expiresAt <= t becomes expired. Completion, deletion, and expiration free an active-task quota slot.