import api from "./api"

export interface MessageResponse {
  id: string
  role: "user" | "assistant"
  content: string
  created_at: string
  plots?: string[] // base64 encoded plots
  steps?: string[] // reasoning steps
}

export interface ChatEvent {
  type: string
  name?: string
  node?: string
  data?: any
}

export interface StreamCallbacks {
  onMessageUpdate: (messages: MessageResponse[]) => void
  onDone?: () => void
  onError?: (error: string) => void
}

export const ChatService = {
  /**
   * Parse a raw SSE chunk into one or more ChatEvent objects.
   * Handles partial lines by returning the processed events and any remaining buffer.
   */
  parseSSEBuffer(buffer: string): { events: ChatEvent[], remaining: string } {
    const events: ChatEvent[] = []
    const lines = buffer.split("\n")
    
    // The last element might be a partial line if it doesn't end with \n
    const remaining = buffer.endsWith("\n") ? "" : lines.pop() || ""
    
    for (const line of lines) {
      if (line.startsWith("data: ")) {
        const dataStr = line.slice(6).trim()
        if (!dataStr) continue
        
        try {
          const event = JSON.parse(dataStr)
          events.push(event)
        } catch (err) {
          console.error("Failed to parse SSE event JSON:", err, dataStr)
        }
      }
    }
    
    return { events, remaining }
  },

  /**
   * Legacy method for backward compatibility in tests
   */
  parseSSEChunk(chunk: string): ChatEvent[] {
    return this.parseSSEBuffer(chunk).events
  },

  /**
   * Update a list of messages based on a new ChatEvent.
   * This is a pure function designed for use with React state updates.
   */
  updateMessagesWithEvent(messages: MessageResponse[], event: ChatEvent): MessageResponse[] {
    const { type, name, node, data } = event
    
    // 1. Handle incremental LLM chunks for terminal nodes
    if (type === "on_chat_model_stream" && (node === "summarizer" || node === "researcher" || node === "clarification")) {
      const chunk = data?.chunk?.content || ""
      if (!chunk) return messages
      
      const newMessages = [...messages]
      const lastMsgIndex = newMessages.length - 1
      const lastMsg = { ...newMessages[lastMsgIndex] }
      
      if (lastMsg && lastMsg.role === "assistant") {
        lastMsg.content = (lastMsg.content || "") + chunk
        newMessages[lastMsgIndex] = lastMsg
      }
      return newMessages
    }

    // 2. Handle final node outputs
    if (type === "on_chain_end") {
      const newMessages = [...messages]
      const lastMsgIndex = newMessages.length - 1
      const lastMsg = { ...newMessages[lastMsgIndex] }

      if (!lastMsg || lastMsg.role !== "assistant") return messages

      // Terminal nodes final text
      if (name === "summarizer" || name === "researcher" || name === "clarification") {
        const messages_list = data?.output?.messages
        const msg = messages_list ? messages_list[messages_list.length - 1]?.content : null
        
        if (msg) {
          lastMsg.content = msg
          newMessages[lastMsgIndex] = lastMsg
          return newMessages
        }
      }

      // Plots from executor
      if (name === "executor" && data?.encoded_plots) {
        lastMsg.plots = [...(lastMsg.plots || []), ...data.encoded_plots]
        // Filter out the 'active' step and replace with 'complete'
        const filteredSteps = (lastMsg.steps || []).filter(s => s !== "Performing data analysis...");
        lastMsg.steps = [...filteredSteps, "Data analysis and visualization complete."]
        newMessages[lastMsgIndex] = lastMsg
        return newMessages
      }

      // Status for intermediate nodes (completion)
      const statusMap: Record<string, string> = {
        "query_analyzer": "Query analysis complete.",
        "planner": "Strategic plan generated.",
        "coder": "Analysis code generated."
      }

      if (name && statusMap[name]) {
        // Find and replace the active status if it exists
        const activeStatus = name === "query_analyzer" ? "Analyzing query..." : 
                           name === "planner" ? "Generating strategic plan..." : 
                           name === "coder" ? "Writing analysis code..." : null;
        
        let filteredSteps = lastMsg.steps || [];
        if (activeStatus) {
          filteredSteps = filteredSteps.filter(s => s !== activeStatus);
        }
        
        lastMsg.steps = [...filteredSteps, statusMap[name]]
        newMessages[lastMsgIndex] = lastMsg
        return newMessages
      }
    }

    // 3. Handle node start events for progress feedback
    if (type === "on_chain_start") {
      const startStatusMap: Record<string, string> = {
        "query_analyzer": "Analyzing query...",
        "planner": "Generating strategic plan...",
        "coder": "Writing analysis code...",
        "executor": "Performing data analysis..."
      }

      if (name && startStatusMap[name]) {
        const newMessages = [...messages]
        const lastMsgIndex = newMessages.length - 1
        const lastMsg = { ...newMessages[lastMsgIndex] }

        if (lastMsg && lastMsg.role === "assistant") {
          // Avoid duplicate start messages
          if (!(lastMsg.steps || []).includes(startStatusMap[name])) {
            lastMsg.steps = [...(lastMsg.steps || []), startStatusMap[name]]
            newMessages[lastMsgIndex] = lastMsg
            return newMessages
          }
        }
      }
    }
    
    return messages
  },

  /**
   * Stream agent execution events via SSE.
   * Uses fetch + ReadableStream because backend uses POST.
   */
  async streamChat(
    message: string, 
    threadId: string, 
    currentMessages: MessageResponse[],
    callbacks: StreamCallbacks
  ) {
    const { onMessageUpdate, onDone, onError } = callbacks
    
    // Add user message and a placeholder assistant message
    let activeMessages: MessageResponse[] = [
      ...currentMessages,
      { 
        id: `user-${Date.now()}`, 
        role: "user", 
        content: message, 
        created_at: new Date().toISOString() 
      },
      { 
        id: `assistant-${Date.now()}`, 
        role: "assistant", 
        content: "", 
        created_at: new Date().toISOString(),
        plots: []
      }
    ]
    onMessageUpdate(activeMessages)

    let buffer = ""
    try {
      const API_URL = import.meta.env.VITE_API_URL || ""
      const response = await fetch(`${API_URL}/api/v1/chat/stream`, {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          message,
          thread_id: threadId
        }),
        credentials: "include"
      })

      if (!response.ok) {
        throw new Error(`Streaming failed: ${response.statusText}`)
      }

      const reader = response.body?.getReader()
      if (!reader) throw new Error("No readable stream in response body")

      const decoder = new TextDecoder()
      
      while (true) {
        const { done, value } = await reader.read()
        if (done) break

        buffer += decoder.decode(value, { stream: true })
        const { events, remaining } = this.parseSSEBuffer(buffer)
        buffer = remaining

        for (const event of events) {
          if (event.type === "done") {
            if (onDone) onDone()
            continue
          }
          if (event.type === "error") {
            if (onError) onError(event.data?.message || "Unknown error")
            continue
          }

          activeMessages = this.updateMessagesWithEvent(activeMessages, event)
          onMessageUpdate(activeMessages)
        }
      }
    } catch (err: any) {
      console.error("Streaming error:", err)
      if (onError) onError(err.message || "Connection failed")
    }
  },

  async listConversations() {
    const response = await api.get("/conversations")
    return response.data
  },

  async createConversation(name: string = "New Conversation") {
    const response = await api.post("/conversations", { name })
    return response.data
  },

  async getMessages(conversationId: string) {
    const response = await api.get(`/conversations/${conversationId}/messages`)
    return response.data
  }
}