"use client";

import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
import { useCallback, useEffect, useRef, useState } from "react";
import {
  buildDisplayMessages,
  createPendingStateOnError,
  createPendingStateOnSend,
  type MentorChatMessage,
  type MentorPendingState,
  shouldBlockSend,
} from "@/lib/mentor-chat-utils";

const DELETE_CONFIRM_MESSAGE =
  "Delete this chat? Your saved AI memories will not be affected.";

type ChatSessionData = {
  session: { id: string; title: string };
  messages: MentorChatMessage[];
};

type SendChatResponse = {
  memorySuggestions?: unknown[];
  memoryAction?: {
    type: string;
    intent?: string;
    status?: string;
    error?: string;
  };
};

export function useMentorChat(sessionId: string | null) {
  const queryClient = useQueryClient();
  const bottomRef = useRef<HTMLDivElement>(null);
  const [input, setInput] = useState("");
  const [pendingState, setPendingState] = useState<MentorPendingState | null>(null);
  const [deleteError, setDeleteError] = useState<string | null>(null);

  const { data: chatData } = useQuery<ChatSessionData>({
    queryKey: ["chat-session", sessionId],
    queryFn: async () => {
      const res = await fetch(`/api/ai/chat/sessions/${sessionId}`);
      if (!res.ok) throw new Error("Failed to load chat");
      return res.json();
    },
    enabled: !!sessionId,
  });

  const serverMessages = chatData?.messages ?? [];
  const displayMessages = buildDisplayMessages(serverMessages, pendingState);

  useEffect(() => {
    bottomRef.current?.scrollIntoView({ behavior: "smooth" });
  }, [displayMessages.length, pendingState]);

  const send = useMutation({
    mutationFn: async (content: string) => {
      const res = await fetch(`/api/ai/chat/sessions/${sessionId}`, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ content }),
      });
      if (!res.ok) {
        const body = await res.json().catch(() => ({}));
        throw new Error(body.error ?? "Send failed");
      }
      return res.json() as Promise<SendChatResponse>;
    },
    onMutate: (content) => {
      setInput("");
      setPendingState(createPendingStateOnSend(content));
    },
    onSuccess: (data) => {
      setPendingState(null);
      queryClient.invalidateQueries({ queryKey: ["chat-session", sessionId] });
      queryClient.invalidateQueries({ queryKey: ["chat-sessions"] });
      queryClient.invalidateQueries({ queryKey: ["ai-memory-suggestions"] });
      queryClient.invalidateQueries({ queryKey: ["ai-knows"] });
      if (
        data.memoryAction?.type === "memory_created" ||
        data.memoryAction?.type === "memory_suggestion_accepted"
      ) {
        queryClient.invalidateQueries({ queryKey: ["ai-memory"] });
      }
    },
    onError: (_err, content) => {
      setPendingState(createPendingStateOnError(content));
    },
  });

  const archive = useMutation({
    mutationFn: async () => {
      const res = await fetch(`/api/ai/chat/sessions/${sessionId}`, { method: "DELETE" });
      if (!res.ok) {
        const body = await res.json().catch(() => ({}));
        throw new Error(body.error ?? "Delete failed");
      }
      return res.json();
    },
    onMutate: () => {
      setDeleteError(null);
    },
    onSuccess: () => {
      setPendingState(null);
      setInput("");
      queryClient.invalidateQueries({ queryKey: ["chat-sessions"] });
    },
    onError: (err: Error) => {
      setDeleteError(err.message || "Could not delete chat. Please try again.");
    },
  });

  const sendMessage = useCallback(
    (content: string) => {
      if (!sessionId || shouldBlockSend(send.isPending, content)) return;
      send.mutate(content.trim());
    },
    [sessionId, send]
  );

  const retry = useCallback(() => {
    const content = pendingState?.lastFailedContent;
    if (!content || send.isPending) return;
    setPendingState(null);
    send.mutate(content);
  }, [pendingState?.lastFailedContent, send]);

  const deleteChat = useCallback(() => {
    if (!sessionId || archive.isPending) return;
    if (!confirm(DELETE_CONFIRM_MESSAGE)) return;
    archive.mutate();
  }, [sessionId, archive]);

  const handleKeyDown = useCallback(
    (e: React.KeyboardEvent<HTMLInputElement>) => {
      if (e.key === "Enter" && input.trim()) {
        e.preventDefault();
        sendMessage(input);
      }
    },
    [input, sendMessage]
  );

  return {
    input,
    setInput,
    displayMessages,
    sendMessage,
    retry,
    deleteChat,
    handleKeyDown,
    bottomRef,
    isSendPending: send.isPending,
    isDeletePending: archive.isPending,
    canRetry: !!pendingState?.lastFailedContent,
    deleteError,
    archiveSuccess: archive.isSuccess,
    resetArchiveSuccess: archive.reset,
  };
}

export async function createChatSession(title?: string): Promise<{ id: string }> {
  const res = await fetch("/api/ai/chat/sessions", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(title ? { title } : {}),
  });
  if (!res.ok) throw new Error("Failed to create session");
  return res.json();
}

export async function fetchChatSessions(): Promise<{ sessions: { id: string; title: string }[] }> {
  const res = await fetch("/api/ai/chat/sessions");
  if (!res.ok) throw new Error("Failed to load sessions");
  return res.json();
}