import { useEffect, useRef, useState, useCallback } from 'react';
import type { Message, WsFrame, PendingChange } from '@/api/types';

interface State {
  messages: Message[];
  connected: boolean;
  error: string | null;
}

function applyFrame(state: State, frame: WsFrame): State {
  switch (frame.type) {
    case 'snapshot': {
      return { ...state, messages: frame.messages };
    }
    case 'message_started': {
      const exists = state.messages.some((m) => m.id === frame.message_id);
      if (exists) return state;
      const newMsg: Message = {
        id: frame.message_id,
        session_id: '',
        chat_id: frame.chat_id,
        role: frame.role,
        content: '',
        kind: 'message',
        tool_calls: null,
        tool_results: null,
        status: frame.role === 'system' ? 'complete' : 'streaming',
        tokens_used: null,
        ctx_used: null,
        ctx_max: null,
        started_at: null,
        finished_at: null,
        created_at: new Date().toISOString(),
        metadata: null,
      };
      return { ...state, messages: [...state.messages, newMsg] };
    }
    case 'delta': {
      const next = state.messages.map((m) =>
        m.id === frame.message_id ? { ...m, content: m.content + frame.content } : m,
      );
      return { ...state, messages: next };
    }
    case 'tool_call': {
      const next = state.messages.map((m) =>
        m.id === frame.message_id
          ? { ...m, tool_calls: [...(m.tool_calls ?? []), frame.tool_call] }
          : m,
      );
      return { ...state, messages: next };
    }
    case 'tool_result': {
      const exists = state.messages.some((m) => m.id === frame.tool_message_id);
      if (exists) {
        const next = state.messages.map((m) =>
          m.id === frame.tool_message_id
            ? {
                ...m,
                role: 'tool' as const,
                tool_results: {
                  tool_call_id: frame.tool_call_id,
                  output: frame.output,
                  truncated: frame.truncated,
                  ...(frame.error ? { error: frame.error } : {}),
                },
                status: 'complete' as const,
              }
            : m,
        );
        return { ...state, messages: next };
      }
      const newMsg: Message = {
        id: frame.tool_message_id,
        session_id: '',
        chat_id: frame.chat_id,
        role: 'tool',
        content: '',
        kind: 'message',
        tool_calls: null,
        tool_results: {
          tool_call_id: frame.tool_call_id,
          output: frame.output,
          truncated: frame.truncated,
          ...(frame.error ? { error: frame.error } : {}),
        },
        status: 'complete',
        tokens_used: null,
        ctx_used: null,
        ctx_max: null,
        started_at: null,
        finished_at: null,
        created_at: new Date().toISOString(),
        metadata: null,
      };
      return { ...state, messages: [...state.messages, newMsg] };
    }
    case 'message_complete': {
      const next = state.messages.map((m) =>
        m.id === frame.message_id
          ? {
              ...m,
              status: 'complete' as const,
              ...(frame.tokens_used !== undefined ? { tokens_used: frame.tokens_used } : {}),
              ...(frame.ctx_used !== undefined ? { ctx_used: frame.ctx_used } : {}),
              ...(frame.ctx_max !== undefined ? { ctx_max: frame.ctx_max } : {}),
              ...(frame.started_at !== undefined ? { started_at: frame.started_at } : {}),
              ...(frame.finished_at !== undefined ? { finished_at: frame.finished_at } : {}),
              ...(frame.metadata !== undefined ? { metadata: frame.metadata } : {}),
            }
          : m,
      );
      return { ...state, messages: next };
    }
    case 'error': {
      const next = frame.message_id
        ? state.messages.map((m) =>
            m.id === frame.message_id ? { ...m, status: 'failed' as const } : m,
          )
        : state.messages;
      return { ...state, messages: next, error: frame.error };
    }
    case 'pending_change_added':
    case 'pending_change_updated':
      // These are handled by the pending changes listener, not the message state
      return state;
  }
}

const RECONNECT_INITIAL_MS = 1000;
const RECONNECT_MAX_MS = 30_000;

interface SessionStreamResult {
  messages: Message[];
  connected: boolean;
  error: string | null;
  isStreaming: boolean;
  /** Listeners for pending change frames */
  onPendingChange: (cb: (change: PendingChange) => void) => () => void;
}

export function useSessionStream(sessionId: string | undefined): SessionStreamResult {
  const [state, setState] = useState<State>({ messages: [], connected: false, error: null });
  const wsRef = useRef<WebSocket | null>(null);
  const pendingListenersRef = useRef<Set<(change: PendingChange) => void>>(new Set());

  useEffect(() => {
    if (!sessionId) return;

    setState({ messages: [], connected: false, error: null });

    let unmounted = false;
    let reconnectTimer: ReturnType<typeof setTimeout> | null = null;
    let reconnectDelay = RECONNECT_INITIAL_MS;

    const connect = () => {
      if (unmounted) return;
      const proto = window.location.protocol === 'https:' ? 'wss' : 'ws';
      const url = `${proto}://${window.location.host}/api/ws/sessions/${sessionId}`;
      const ws = new WebSocket(url);
      wsRef.current = ws;

      ws.onopen = () => {
        reconnectDelay = RECONNECT_INITIAL_MS;
        setState((s) => ({ ...s, connected: true, error: null }));
      };

      ws.onmessage = (ev) => {
        let frame: WsFrame;
        try {
          frame = JSON.parse(typeof ev.data === 'string' ? ev.data : '') as WsFrame;
        } catch {
          return;
        }

        // Notify pending change listeners
        if (frame.type === 'pending_change_added' || frame.type === 'pending_change_updated') {
          for (const cb of pendingListenersRef.current) {
            cb(frame.change);
          }
        }

        setState((s) => applyFrame(s, frame));
      };

      ws.onerror = () => {
        try {
          ws.close();
        } catch {}
      };

      ws.onclose = () => {
        if (unmounted) return;
        setState((s) => ({ ...s, connected: false }));
        const delay = reconnectDelay;
        reconnectDelay = Math.min(reconnectDelay * 2, RECONNECT_MAX_MS);
        reconnectTimer = setTimeout(connect, delay);
      };
    };

    connect();

    return () => {
      unmounted = true;
      if (reconnectTimer) clearTimeout(reconnectTimer);
      const ws = wsRef.current;
      wsRef.current = null;
      if (ws)
        try {
          ws.close();
        } catch {}
    };
  }, [sessionId]);

  const isStreaming = state.messages.some((m) => m.status === 'streaming');

  const onPendingChange = useCallback((cb: (change: PendingChange) => void) => {
    pendingListenersRef.current.add(cb);
    return () => {
      pendingListenersRef.current.delete(cb);
    };
  }, []);

  return {
    messages: state.messages,
    connected: state.connected,
    error: state.error,
    isStreaming,
    onPendingChange,
  };
}