/**
 * KenEvent 信封 → 前端 `ServerFrame` 的映射。
 *
 * 应用层（transcript reducer、typing registry、通知面板）消费的是 `RoomEvent` /
 * `UserEvent` 联合类型，而 KenEvent 只发 RocketMQ 的 `{topic, tag, properties,
 * body}`。这一层是唯一的翻译点：新增事件时只改这里，页面代码不动。
 *
 * 约定（来自 `docs/events.json` 与 KenApi 的发布点）：
 * - `body` 对 chat 消息类事件就是 `MessageDto` 本体，`seq` 也在里面
 *   （所以 `message_published` 的游标可直接用 `body.seq`）。
 * - `properties` 里的资源 id 全是字符串（RocketMQ 用户属性）。
 * - 详情永远以 REST 为准，这里只负责"告诉页面什么变了"。
 */
import type { MessageDto } from '@app/services/api'

import { CHAT_TOPIC, type KenEventEnvelope, NOTIFY_TOPIC, prop } from './kenEvent'
import type { RoomEvent, ServerFrame, UserEvent, WsNotification, WsReactionSummary } from './protocol'

function record(value: unknown): Record<string, unknown> | null {
  return typeof value === 'object' && value !== null ? (value as Record<string, unknown>) : null
}

function str(value: unknown): string | null {
  return typeof value === 'string' && value.length > 0 ? value : null
}

function num(value: unknown): number | undefined {
  return typeof value === 'number' && Number.isFinite(value) ? value : undefined
}

function messageOf(envelope: KenEventEnvelope): MessageDto | null {
  const body = record(envelope.body)
  if (!body) return null
  return typeof body.id === 'string' && typeof body.room_id === 'string' ? (body as unknown as MessageDto) : null
}

function reactionsOf(envelope: KenEventEnvelope): WsReactionSummary[] {
  const body = record(envelope.body)
  const raw = body?.reactions
  if (!Array.isArray(raw)) return []
  return raw.flatMap((entry) => {
    const item = record(entry)
    const emoji = str(item?.emoji)
    const count = num(item?.count)
    return emoji && count !== undefined ? [{ emoji, count }] : []
  })
}

function deletedIds(envelope: KenEventEnvelope): string[] {
  const body = record(envelope.body)
  const candidates = [body?.message_ids, body?.ids, body?.messages]
  for (const candidate of candidates) {
    if (Array.isArray(candidate)) {
      const ids = candidate.map((item) => str(item) ?? str(record(item)?.id)).filter(Boolean)
      if (ids.length > 0) return ids as string[]
    }
  }
  const single = prop(envelope, 'message_id') ?? str(body?.id)
  return single ? [single] : []
}

function roomEvent(envelope: KenEventEnvelope): RoomEvent | null {
  const roomId = prop(envelope, 'room_id')
  const message = messageOf(envelope)
  const messageId = prop(envelope, 'message_id') ?? str(record(envelope.body)?.id)
  const userId = envelope.user_id != null ? String(envelope.user_id) : prop(envelope, 'user_id')
  const seq = num(record(envelope.body)?.seq) ?? 0

  switch (envelope.tag) {
    case 'message-create':
    case 'message-update': {
      if (!roomId || !message) return null
      return {
        kind: envelope.tag === 'message-create' ? 'message_published' : 'message_edited',
        room_id: roomId,
        seq,
        message,
      }
    }
    case 'message-delete':
    case 'messages-delete': {
      if (!roomId) return null
      const ids = deletedIds(envelope)
      if (ids.length === 0) return null
      return envelope.tag === 'messages-delete' && ids.length > 1
        ? { kind: 'messages_deleted', room_id: roomId, seq, message_ids: ids }
        : { kind: 'message_deleted', room_id: roomId, seq, message_id: ids[0] }
    }
    case 'pin-create':
    case 'pin-delete': {
      if (!roomId || !messageId) return null
      return {
        kind: 'message_pinned',
        room_id: roomId,
        seq,
        message_id: messageId,
        pinned: envelope.tag === 'pin-create',
      }
    }
    case 'reaction-update': {
      if (!roomId || !messageId) return null
      return {
        kind: 'reaction_updated',
        room_id: roomId,
        message_id: messageId,
        reactions: reactionsOf(envelope),
      }
    }
    case 'room-update':
      return roomId ? { kind: 'room_updated', room_id: roomId } : null
    case 'member-create':
      return roomId && userId ? { kind: 'member_joined', room_id: roomId, user_id: userId } : null
    case 'member-delete':
      return roomId && userId ? { kind: 'member_left', room_id: roomId, user_id: userId } : null
    case 'thread-update': {
      const threadId = prop(envelope, 'thread_id')
      return roomId && threadId ? { kind: 'thread_updated', room_id: roomId, thread_id: threadId } : null
    }
    case 'voice-presence':
      return roomId ? { kind: 'voice_presence', room_id: roomId } : null
    case 'voice-hand':
      return roomId ? { kind: 'voice_hands', room_id: roomId } : null
    case 'voice-layout':
      return roomId ? { kind: 'voice_layout', room_id: roomId } : null
    case 'voice-moderate':
      return roomId && userId
        ? {
            kind: 'voice_moderation',
            room_id: roomId,
            user_id: userId,
            action: str(record(envelope.body)?.action) ?? 'update',
          }
        : null
    default:
      return null
  }
}

function userEvent(envelope: KenEventEnvelope): UserEvent | null {
  const roomId = prop(envelope, 'room_id')
  const messageId = prop(envelope, 'message_id') ?? str(record(envelope.body)?.id)

  if (envelope.topic === NOTIFY_TOPIC && envelope.tag === 'notification-create') {
    const body = record(envelope.body)
    if (!body || typeof body.id !== 'string') return null
    return { kind: 'notification', notification: body as unknown as WsNotification }
  }

  if (envelope.topic !== CHAT_TOPIC) return null

  switch (envelope.tag) {
    case 'mention-create':
      return roomId && messageId
        ? {
            kind: 'mention',
            room_id: roomId,
            message_id: messageId,
            everyone: record(envelope.body)?.everyone === true ? true : undefined,
          }
        : null
    case 'reminder-create':
      return roomId && messageId ? { kind: 'reminder', room_id: roomId, message_id: messageId } : null
    case 'membership-create':
      return roomId ? { kind: 'room_added', room_id: roomId } : null
    case 'read_state-update': {
      const body = record(envelope.body)
      const lastRead = str(body?.last_read_message_id)
      const lastSeq = num(body?.last_read_seq) ?? 0
      return roomId
        ? {
            kind: 'read_marker',
            room_id: roomId,
            last_read_message_id: lastRead,
            last_read_seq: lastSeq,
          }
        : null
    }
    case 'presence-update': {
      const status = str(record(envelope.body)?.status)
      return status ? { kind: 'presence', status: status as never } : null
    }
    default:
      return null
  }
}

/** 单个信封 → 页面帧；无法映射（未消费的事件）返回 null，由调用方静默忽略。 */
export function toServerFrame(envelope: KenEventEnvelope): ServerFrame | null {
  const event = userEvent(envelope)
  if (event) return { type: 'user_event', event }

  const room = roomEvent(envelope)
  if (!room) return null
  if ('room_id' in room) return { type: 'event', room_id: room.room_id, event: room }
  return null
}

/** 从消息类帧里取房间游标，供 `lastKnownSeq` 使用。 */
export function frameSeq(frame: ServerFrame): { roomId: string; seq: number } | null {
  if (frame.type !== 'event' || !frame.event) return null
  if ('seq' in frame.event && typeof frame.event.seq === 'number') {
    return { roomId: frame.room_id, seq: frame.event.seq }
  }
  return null
}