frontend/src/components/SessionChat.tsx

/**
 * Per-session chat component.
 *
 * Each session renders its own SessionChat. The hook (useAgentChat) always
 * runs — processing events — but only the active session renders visible
 * UI (MessageList + ChatInput).
 */
import { useCallback, useEffect, useState } from 'react';
import { useAgentChat } from '@/hooks/useAgentChat';
import { useAgentStore } from '@/store/agentStore';
import { useSessionStore } from '@/store/sessionStore';
import MessageList from '@/components/Chat/MessageList';
import ChatInput from '@/components/Chat/ChatInput';
import { apiFetch } from '@/utils/api';
import { logger } from '@/utils/logger';

interface SessionChatProps {
  sessionId: string;
  isActive: boolean;
  onSessionDead: (sessionId: string) => void;
}

export default function SessionChat({ sessionId, isActive, onSessionDead }: SessionChatProps) {
  const { isConnected, isProcessing, activityStatus, updateSession } = useAgentStore();
  const { updateSessionTitle } = useSessionStore();

  const [wasCancelled, setWasCancelled] = useState(false);

  const { messages, sendMessage, stop, status, undoLastTurn, approveTools } = useAgentChat({
    sessionId,
    isActive,
    onReady: () => logger.log(`Session ${sessionId} ready`),
    onError: (error) => logger.error(`Session ${sessionId} error:`, error),
    onSessionDead,
  });

  // When this session becomes active, restore its per-session state to the
  // global flat fields. The per-session state map is kept up-to-date by
  // side-channel callbacks even while the session is in the background.
  useEffect(() => {
    if (isActive) {
      useAgentStore.getState().switchActiveSession(sessionId);
      useAgentStore.getState().setConnected(true);
    }
  }, [isActive, sessionId]);

  // Re-sync state when the browser tab regains focus (Chrome throttles
  // timers in background tabs which can stall the AI SDK's update flushing).
  // Fires for ALL sessions so background sessions also recover after sleep.
  useEffect(() => {
    const onVisible = () => {
      if (document.visibilityState === 'visible' && isActive) {
        useAgentStore.getState().switchActiveSession(sessionId);
      }
    };
    document.addEventListener('visibilitychange', onVisible);
    return () => document.removeEventListener('visibilitychange', onVisible);
  }, [isActive, sessionId]);

  // Wrap stop to track cancellation
  const handleStop = useCallback(() => {
    stop();
    setWasCancelled(true);
  }, [stop]);

  // SDK status is the ground truth — if it's streaming/submitted, agent is busy
  const sdkBusy = status === 'streaming' || status === 'submitted';
  const busy = isProcessing || sdkBusy;

  const handleSendMessage = useCallback(
    async (text: string) => {
      if (!text.trim() || busy) return;

      setWasCancelled(false);
      updateSession(sessionId, { isProcessing: true });
      sendMessage({ text: text.trim(), metadata: { createdAt: new Date().toISOString() } });

      // Auto-title the session from the first user message
      const isFirstMessage = messages.filter((m) => m.role === 'user').length <= 1;
      if (isFirstMessage) {
        apiFetch('/api/title', {
          method: 'POST',
          body: JSON.stringify({ session_id: sessionId, text: text.trim() }),
        })
          .then((res) => res.json())
          .then((data) => {
            if (data.title) updateSessionTitle(sessionId, data.title);
          })
          .catch(() => {
            const raw = text.trim();
            updateSessionTitle(sessionId, raw.length > 40 ? raw.slice(0, 40) + '\u2026' : raw);
          });
      }
    },
    [sessionId, sendMessage, messages, updateSessionTitle, busy, updateSession],
  );

  // Don't render UI for background sessions — hooks still run
  if (!isActive) return null;

  return (
    <>
      <MessageList
        messages={messages}
        isProcessing={busy}
        approveTools={approveTools}
        onUndoLastTurn={undoLastTurn}
      />
      <ChatInput
        onSend={handleSendMessage}
        onStop={handleStop}
        isProcessing={busy}
        disabled={!isConnected || activityStatus.type === 'waiting-approval'}
        placeholder={
          activityStatus.type === 'waiting-approval'
            ? 'Approve or reject pending tools first...'
            : wasCancelled
              ? 'What should the agent do instead?'
              : undefined
        }
      />
    </>
  );
}