feat(web): chat UI with conversations and WebSocket streaming (#84)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/web/src/app/(dashboard)/chat/page.tsx

@@ -1,8 +1,179 @@
+'use client';
+
+import { useCallback, useEffect, useRef, useState } from 'react';
+import { api } from '@/lib/api';
+import { getSocket } from '@/lib/socket';
+import type { Conversation, Message } from '@/lib/types';
+import { ConversationList } from '@/components/chat/conversation-list';
+import { MessageBubble } from '@/components/chat/message-bubble';
+import { ChatInput } from '@/components/chat/chat-input';
+import { StreamingMessage } from '@/components/chat/streaming-message';
+
 export default function ChatPage(): React.ReactElement {
+  const [conversations, setConversations] = useState<Conversation[]>([]);
+  const [activeId, setActiveId] = useState<string | null>(null);
+  const [messages, setMessages] = useState<Message[]>([]);
+  const [streamingText, setStreamingText] = useState('');
+  const [isStreaming, setIsStreaming] = useState(false);
+  const messagesEndRef = useRef<HTMLDivElement>(null);
+
+  // Load conversations on mount
+  useEffect(() => {
+    api<Conversation[]>('/api/conversations')
+      .then(setConversations)
+      .catch(() => {});
+  }, []);
+
+  // Load messages when active conversation changes
+  useEffect(() => {
+    if (!activeId) {
+      setMessages([]);
+      return;
+    }
+    api<Message[]>(`/api/conversations/${activeId}/messages`)
+      .then(setMessages)
+      .catch(() => {});
+  }, [activeId]);
+
+  // Auto-scroll to bottom
+  useEffect(() => {
+    messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' });
+  }, [messages, streamingText]);
+
+  // Socket.io setup
+  useEffect(() => {
+    const socket = getSocket();
+    socket.connect();
+
+    socket.on('agent:text', (data: { conversationId: string; text: string }) => {
+      setStreamingText((prev) => prev + data.text);
+    });
+
+    socket.on('agent:start', () => {
+      setIsStreaming(true);
+      setStreamingText('');
+    });
+
+    socket.on('agent:end', (data: { conversationId: string }) => {
+      setIsStreaming(false);
+      setStreamingText('');
+      // Reload messages to get the final persisted version
+      api<Message[]>(`/api/conversations/${data.conversationId}/messages`)
+        .then(setMessages)
+        .catch(() => {});
+    });
+
+    socket.on('error', (data: { error: string }) => {
+      setIsStreaming(false);
+      setStreamingText('');
+      setMessages((prev) => [
+        ...prev,
+        {
+          id: `error-${Date.now()}`,
+          conversationId: '',
+          role: 'system',
+          content: `Error: ${data.error}`,
+          createdAt: new Date().toISOString(),
+        },
+      ]);
+    });
+
+    return () => {
+      socket.off('agent:text');
+      socket.off('agent:start');
+      socket.off('agent:end');
+      socket.off('error');
+      socket.disconnect();
+    };
+  }, []);
+
+  const handleNewConversation = useCallback(async () => {
+    const conv = await api<Conversation>('/api/conversations', {
+      method: 'POST',
+      body: { title: 'New conversation' },
+    });
+    setConversations((prev) => [conv, ...prev]);
+    setActiveId(conv.id);
+    setMessages([]);
+  }, []);
+
+  const handleSend = useCallback(
+    async (content: string) => {
+      let convId = activeId;
+
+      // Auto-create conversation if none selected
+      if (!convId) {
+        const conv = await api<Conversation>('/api/conversations', {
+          method: 'POST',
+          body: { title: content.slice(0, 50) },
+        });
+        setConversations((prev) => [conv, ...prev]);
+        setActiveId(conv.id);
+        convId = conv.id;
+      }
+
+      // Optimistic user message
+      const userMsg: Message = {
+        id: `temp-${Date.now()}`,
+        conversationId: convId,
+        role: 'user',
+        content,
+        createdAt: new Date().toISOString(),
+      };
+      setMessages((prev) => [...prev, userMsg]);
+
+      // Persist user message
+      await api<Message>(`/api/conversations/${convId}/messages`, {
+        method: 'POST',
+        body: { role: 'user', content },
+      });
+
+      // Send to WebSocket for streaming response
+      const socket = getSocket();
+      socket.emit('message', { conversationId: convId, content });
+    },
+    [activeId],
+  );
+
   return (
-    <div>
-      <h1 className="text-2xl font-semibold">Chat</h1>
-      <p className="mt-2 text-text-secondary">Conversations will appear here.</p>
+    <div className="-m-6 flex h-[calc(100vh-3.5rem)]">
+      <ConversationList
+        conversations={conversations}
+        activeId={activeId}
+        onSelect={setActiveId}
+        onNew={handleNewConversation}
+      />
+
+      <div className="flex flex-1 flex-col">
+        {activeId ? (
+          <>
+            <div className="flex-1 space-y-4 overflow-y-auto p-6">
+              {messages.map((msg) => (
+                <MessageBubble key={msg.id} message={msg} />
+              ))}
+              {isStreaming && <StreamingMessage text={streamingText} />}
+              <div ref={messagesEndRef} />
+            </div>
+            <ChatInput onSend={handleSend} disabled={isStreaming} />
+          </>
+        ) : (
+          <div className="flex flex-1 items-center justify-center">
+            <div className="text-center">
+              <h2 className="text-lg font-medium text-text-secondary">Welcome to Mosaic Chat</h2>
+              <p className="mt-1 text-sm text-text-muted">
+                Select a conversation or start a new one
+              </p>
+              <button
+                type="button"
+                onClick={handleNewConversation}
+                className="mt-4 rounded-lg bg-blue-600 px-4 py-2 text-sm font-medium text-white transition-colors hover:bg-blue-700"
+              >
+                Start new conversation
+              </button>
+            </div>
+          </div>
+        )}
+      </div>
     </div>
   );
 }