/**
 * 系统消息的种类与投影 —— 纯逻辑,零 IO(编码规范 §5.3;语义出处 OS 2.1 / 06)。
 *
 * 「消息是**信息**,不产生责任」—— 与任务、审批(责任要素)分明。
 * 三类内容:通知(承载触发器的邮件和消息、公告、提醒与告警)+ 跨任务征答(他人任务发来的卡)
 * + 死信与回执的人侧呈现。
 */

export const MESSAGE_KINDS = ['notice', 'elicitation', 'dead-letter', 'unowned', 'receipt'] as const;
export type MessageKind = (typeof MESSAGE_KINDS)[number];

export const MESSAGE_KIND_LABEL: Readonly<Record<MessageKind, string>> = {
  notice: '通知',
  elicitation: '跨任务征答',
  'dead-letter': '死信',
  unowned: '无主入站',
  receipt: '回执',
};

export type SystemMessage = {
  readonly id: string;
  readonly kind: MessageKind;
  /** 收件人:员工;跨任务卡按岗位解析出人后落到具体员工 */
  readonly staffId: string;
  /** 岗位收件(无主兜底按默认认领岗位投递) */
  readonly positionId?: string;
  readonly title: string;
  readonly body: string;
  readonly at: string;
  readonly readAt?: string;
  /** 跨任务征答:卡本体与来源任务 —— 就地作答,不开放任务对话流 */
  readonly card?: {
    readonly cardId: string;
    readonly sourceTaskId: string;
    readonly payload: Record<string, unknown>;
    readonly answeredAt?: string;
    /** 驳回重答:新卡实例,附驳回理由与原答引用;原卡闭合 —— 只增不改 */
    readonly supersededBy?: string;
    readonly rejectedReason?: string;
  };
  readonly eventRef?: string;
};

/**
 * 跨人卡是**一次性的解答请求**,不是责任转移 ——
 * 作答权限只及卡面与决策包,不开放任务对话流(OS 2.1)。
 */
export function canAnswer(message: SystemMessage, staffId: string): boolean {
  if (message.kind !== 'elicitation') return false;
  if (message.staffId !== staffId) return false;
  if (message.card === undefined) return false;
  // 已作答或已被驳回重答闭合的卡不得再答 —— 每次请求与回答都是独立消息
  return message.card.answeredAt === undefined && message.card.supersededBy === undefined;
}

/** 未读计数:消息不产生责任,只做信息提示 */
export function unreadCount(messages: readonly SystemMessage[]): number {
  return messages.filter((m) => m.readAt === undefined).length;
}

/** 待答计数:跨任务征答里还没作答的 */
export function pendingAnswerCount(messages: readonly SystemMessage[]): number {
  return messages.filter((m) => m.kind === 'elicitation' && m.card?.answeredAt === undefined && m.card?.supersededBy === undefined)
    .length;
}