import { formatChatDayLabel, toLocalDayKey } from '@/lib/formatters'

interface DisplayableChatMessage {
  id: string
  senderId: string
  createdAt: string
}

export interface ChatDateSeparatorItem {
  kind: 'date'
  key: string
  label: string
}

export interface ChatMessageDisplayItem<TMessage extends DisplayableChatMessage = DisplayableChatMessage> {
  kind: 'message'
  key: string
  message: TMessage
  showSenderName: boolean
  showAvatar: boolean
  isClusterStart: boolean
  isClusterEnd: boolean
}

export type ChatDisplayItem<TMessage extends DisplayableChatMessage = DisplayableChatMessage> =
  | ChatDateSeparatorItem
  | ChatMessageDisplayItem<TMessage>

const SAME_SENDER_GAP_MS = 5 * 60 * 1000

const getTime = (value: string) => {
  const time = new Date(value).getTime()

  return Number.isFinite(time) ? time : 0
}

/**
 * Builds Telegram-like display rows: day separators + clustered messages.
 * Name on first of consecutive same-sender run; avatar on last of that run.
 */
export const groupMessagesForDisplay = <TMessage extends DisplayableChatMessage>(
  messages: TMessage[],
  options?: { showSenderNames?: boolean; now?: Date }
): ChatDisplayItem<TMessage>[] => {
  const showSenderNames = options?.showSenderNames ?? false
  const now = options?.now ?? new Date()
  const items: ChatDisplayItem<TMessage>[] = []
  let lastDayKey: string | null = null

  messages.forEach((message, index) => {
    const dayKey = toLocalDayKey(message.createdAt) ?? message.id

    if (dayKey !== lastDayKey) {
      items.push({
        kind: 'date',
        key: `date-${dayKey}`,
        label: formatChatDayLabel(message.createdAt, now),
      })
      lastDayKey = dayKey
    }

    const previousSameSender =
      index > 0 &&
      messages[index - 1].senderId === message.senderId &&
      toLocalDayKey(messages[index - 1].createdAt) === toLocalDayKey(message.createdAt) &&
      getTime(message.createdAt) - getTime(messages[index - 1].createdAt) <= SAME_SENDER_GAP_MS
    const nextSameSender =
      index < messages.length - 1 &&
      messages[index + 1].senderId === message.senderId &&
      toLocalDayKey(messages[index + 1].createdAt) === toLocalDayKey(message.createdAt) &&
      getTime(messages[index + 1].createdAt) - getTime(message.createdAt) <= SAME_SENDER_GAP_MS

    const isClusterStart = !previousSameSender
    const isClusterEnd = !nextSameSender

    items.push({
      kind: 'message',
      key: message.id,
      message,
      showSenderName: showSenderNames && isClusterStart,
      showAvatar: showSenderNames && isClusterEnd,
      isClusterStart,
      isClusterEnd,
    })
  })

  return items
}