import type { AiConversation, AiMessage } from '~/types/ai'

export function useAiChat() {
  const client = useSupabaseClient()
  const user = useSupabaseUser()

  const conversations = ref<AiConversation[]>([])
  const currentConversation = ref<AiConversation | null>(null)
  const messages = ref<AiMessage[]>([])
  const streamingContent = ref('')
  const isStreaming = ref(false)
  const loading = ref(false)

  async function fetchConversations() {
    if (!user.value) return
    const { data } = await client
      .from('ai_conversations')
      .select('*')
      .order('updated_at', { ascending: false })
    conversations.value = (data as AiConversation[]) ?? []
  }

  async function createConversation(title: string = '새 대화') {
    if (!user.value) return null
    const { data, error } = await client
      .from('ai_conversations')
      .insert({ user_id: user.value.id, title })
      .select()
      .single()
    if (error) return null
    const conv = data as AiConversation
    conversations.value.unshift(conv)
    return conv
  }

  async function selectConversation(conv: AiConversation) {
    currentConversation.value = conv
    await fetchMessages(conv.id)
  }

  async function fetchMessages(conversationId: string) {
    const { data } = await client
      .from('ai_messages')
      .select('*')
      .eq('conversation_id', conversationId)
      .order('created_at', { ascending: true })
    messages.value = (data as AiMessage[]) ?? []
  }

  async function deleteConversation(id: string) {
    await client.from('ai_conversations').delete().eq('id', id)
    conversations.value = conversations.value.filter(c => c.id !== id)
    if (currentConversation.value?.id === id) {
      currentConversation.value = null
      messages.value = []
    }
  }

  async function sendMessage(content: string) {
    if (!currentConversation.value || isStreaming.value) return

    // Save user message to DB
    const { data: userMsg } = await client
      .from('ai_messages')
      .insert({
        conversation_id: currentConversation.value.id,
        role: 'user',
        content
      })
      .select()
      .single()

    if (userMsg) messages.value.push(userMsg as AiMessage)

    // Start streaming
    isStreaming.value = true
    streamingContent.value = ''

    try {
      const response = await fetch('/api/ai/chat', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          conversationId: currentConversation.value.id,
          messages: messages.value.map(m => ({ role: m.role, content: m.content }))
        })
      })

      if (!response.ok) throw new Error('API 오류')

      const reader = response.body!.getReader()
      const decoder = new TextDecoder()

      while (true) {
        const { done, value } = await reader.read()
        if (done) break
        streamingContent.value += decoder.decode(value, { stream: true })
      }

      // Save assistant message to DB
      const finalContent = streamingContent.value
      const { data: assistantMsg } = await client
        .from('ai_messages')
        .insert({
          conversation_id: currentConversation.value.id,
          role: 'assistant',
          content: finalContent
        })
        .select()
        .single()

      if (assistantMsg) messages.value.push(assistantMsg as AiMessage)

      // Update conversation title if it's the first message
      if (messages.value.length === 2) {
        const title = content.slice(0, 30) + (content.length > 30 ? '...' : '')
        await client
          .from('ai_conversations')
          .update({ title })
          .eq('id', currentConversation.value.id)
        const conv = conversations.value.find(c => c.id === currentConversation.value!.id)
        if (conv) conv.title = title
      }
    } catch (e) {
      console.error('Streaming error:', e)
    } finally {
      isStreaming.value = false
      streamingContent.value = ''
    }
  }

  return {
    conversations: readonly(conversations),
    currentConversation: readonly(currentConversation),
    messages: readonly(messages),
    streamingContent: readonly(streamingContent),
    isStreaming: readonly(isStreaming),
    loading: readonly(loading),
    fetchConversations,
    createConversation,
    selectConversation,
    deleteConversation,
    sendMessage
  }
}