fix: implement client-side caching for example diagrams (#150)

- Add client-side cache check in onFormSubmit to bypass API calls for example prompts
- Use findCachedResponse to match input against cached examples
- Directly set messages with cached tool response when example matches
- Hide regenerate button for cached example responses (toolCallId starts with 'cached-')
- Prevents unnecessary API calls when using example buttons

Co-authored-by: dayuan.jiang <jiangdy@amazon.co.jp>

app/api/chat/route.ts

@@ -195,20 +195,44 @@ async function handleChatRequest(req: Request): Promise<Response> {
     const isFirstMessage = messages.length === 1
     const isEmptyDiagram = !xml || xml.trim() === "" || isMinimalDiagram(xml)
 
+    // DEBUG: Log cache check conditions
+    console.log("[Cache DEBUG] messages.length:", messages.length)
+    console.log("[Cache DEBUG] isFirstMessage:", isFirstMessage)
+    console.log("[Cache DEBUG] xml length:", xml?.length || 0)
+    console.log("[Cache DEBUG] xml preview:", xml?.substring(0, 200))
+    console.log("[Cache DEBUG] isEmptyDiagram:", isEmptyDiagram)
+
     if (isFirstMessage && isEmptyDiagram) {
         const lastMessage = messages[0]
         const textPart = lastMessage.parts?.find((p: any) => p.type === "text")
         const filePart = lastMessage.parts?.find((p: any) => p.type === "file")
 
+        console.log("[Cache DEBUG] textPart?.text:", textPart?.text)
+        console.log("[Cache DEBUG] hasFilePart:", !!filePart)
+
         const cached = findCachedResponse(textPart?.text || "", !!filePart)
 
+        console.log("[Cache DEBUG] cached found:", !!cached)
+
         if (cached) {
             console.log(
                 "[Cache] Returning cached response for:",
                 textPart?.text,
             )
             return createCachedStreamResponse(cached.xml)
+        } else {
+            console.log("[Cache DEBUG] No cache match - checking why...")
+            console.log(
+                "[Cache DEBUG] Exact promptText:",
+                JSON.stringify(textPart?.text),
+            )
         }
+    } else {
+        console.log("[Cache DEBUG] Skipping cache check - conditions not met")
+        if (!isFirstMessage)
+            console.log("[Cache DEBUG] Reason: not first message")
+        if (!isEmptyDiagram)
+            console.log("[Cache DEBUG] Reason: diagram not empty")
     }
     // === CACHE CHECK END ===
 

components/chat-message-display.tsx

@@ -676,9 +676,14 @@ export function ChatMessageDisplay({
                                                     <Copy className="h-3.5 w-3.5" />
                                                 )}
                                             </button>
-                                            {/* Regenerate button - only on last assistant message */}
+                                            {/* Regenerate button - only on last assistant message, not for cached examples */}
                                             {onRegenerate &&
-                                                isLastAssistantMessage && (
+                                                isLastAssistantMessage &&
+                                                !message.parts?.some((p: any) =>
+                                                    p.toolCallId?.startsWith(
+                                                        "cached-",
+                                                    ),
+                                                ) && (
                                                     <button
                                                         type="button"
                                                         onClick={() =>

components/chat-panel.tsx

@@ -32,6 +32,7 @@ const STORAGE_SESSION_ID_KEY = "next-ai-draw-io-session-id"
 const STORAGE_DIAGRAM_XML_KEY = "next-ai-draw-io-diagram-xml"
 
 import { useDiagram } from "@/contexts/diagram-context"
+import { findCachedResponse } from "@/lib/cached-responses"
 import { formatXML } from "@/lib/utils"
 import { ChatMessageDisplay } from "./chat-message-display"
 
@@ -450,6 +451,42 @@ Please retry with an adjusted search pattern or use display_diagram if retries a
         e.preventDefault()
         const isProcessing = status === "streaming" || status === "submitted"
         if (input.trim() && !isProcessing) {
+            // Check if input matches a cached example (only when no messages yet)
+            if (messages.length === 0) {
+                const cached = findCachedResponse(
+                    input.trim(),
+                    files.length > 0,
+                )
+                if (cached) {
+                    // Add user message and fake assistant response to messages
+                    // The chat-message-display useEffect will handle displaying the diagram
+                    const toolCallId = `cached-${Date.now()}`
+                    setMessages([
+                        {
+                            id: `user-${Date.now()}`,
+                            role: "user" as const,
+                            parts: [{ type: "text" as const, text: input }],
+                        },
+                        {
+                            id: `assistant-${Date.now()}`,
+                            role: "assistant" as const,
+                            parts: [
+                                {
+                                    type: "tool-display_diagram" as const,
+                                    toolCallId,
+                                    state: "output-available" as const,
+                                    input: { xml: cached.xml },
+                                    output: "Successfully displayed the diagram.",
+                                },
+                            ],
+                        },
+                    ] as any)
+                    setInput("")
+                    setFiles([])
+                    return
+                }
+            }
+
             try {
                 let chartXml = await onFetchChart()
                 chartXml = formatXML(chartXml)