From ffeb8938097bc0308cb0450f8fdcad51bce871bc Mon Sep 17 00:00:00 2001
From: Oleh Omelchenko <ptrvtch@protonmail.com>
Date: Mon, 13 Oct 2025 01:28:58 +0300
Subject: [PATCH] Implement Vega-Lite rendering with error handling and dynamic
 library loading

---
 docs/dev-plan.md | 23 ++++++++----
 index.html       | 92 +++++++++++++++++++++++++++++++++++++++++-------
 src/styles.css   |  6 ++--
 3 files changed, 99 insertions(+), 22 deletions(-)

diff --git a/docs/dev-plan.md b/docs/dev-plan.md
index b51facc..050e6df 100644
--- a/docs/dev-plan.md
+++ b/docs/dev-plan.md
@@ -105,17 +105,26 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 
 ---
 
-### **Phase 4: Vega-Lite Rendering**
+### **Phase 4: Vega-Lite Rendering** ✅ **COMPLETE**
 **Goal**: Live preview of visualizations
 
-- [ ] Load Vega-Embed from CDN
-- [ ] Create render function that takes spec from editor
-- [ ] Add debounced auto-render on editor change
-- [ ] Display rendered chart in right panel
-- [ ] Handle rendering errors gracefully (show in preview panel)
+- [x] Load Vega-Embed from CDN
+- [x] Create render function that takes spec from editor
+- [x] Add debounced auto-render on editor change
+- [x] Display rendered chart in right panel
+- [x] Handle rendering errors gracefully (show in preview panel)
 
 **Deliverable**: Editor → live chart pipeline working with auto-refresh
 
+**Key Achievements**:
+- Successfully resolved AMD loader conflicts with Monaco Editor
+- Implemented UMD build loading with temporary AMD disable/restore
+- Added 1.5s debounced rendering for smooth editing experience
+- Created comprehensive error handling with user-friendly messages
+- Established working editor → JSON parsing → Vega-Lite rendering pipeline
+- Sample bar chart loads and renders immediately on page load
+- Live preview updates automatically as user edits JSON specification
+
 ---
 
 ### **Phase 5: Data Model + LocalStorage**
@@ -275,5 +284,5 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 
 ---
 
-**Current Phase**: Phase 4 - Vega-Lite Rendering
+**Current Phase**: Phase 5 - Data Model + LocalStorage
 **Status**: Ready to begin implementation
\ No newline at end of file
diff --git a/index.html b/index.html
index d7151ec..a194268 100644
--- a/index.html
+++ b/index.html
@@ -83,14 +83,7 @@
                     Preview
                 </div>
                 <div class="panel-content">
-                    <div class="preview-placeholder">
-                        <div class="placeholder">
-                            Vega-Lite visualization will render here
-                        </div>
-                        <div style="margin-top: 8px; font-size: 12px; color: #adb5bd;">
-                            Live preview • Auto-refresh • Error display
-                        </div>
-                    </div>
+                    <div id="vega-preview" style="height: 100%; width: 100%; overflow: auto;"></div>
                 </div>
             </div>
         </div>
@@ -98,6 +91,7 @@
 
     <script>
         let editor; // Global editor instance
+        let renderTimeout; // For debouncing
 
         // Sample Vega-Lite specification
         const sampleSpec = {
@@ -122,6 +116,74 @@
             }
         };
 
+        // Render function that takes spec from editor
+        async function renderVisualization() {
+            const previewContainer = document.getElementById('vega-preview');
+
+            try {
+                // Get current content from editor
+                const specText = editor.getValue();
+                const spec = JSON.parse(specText);
+
+                // Render with Vega-Embed (use global variable)
+                await window.vegaEmbed('#vega-preview', spec, {
+                    actions: false, // Hide action menu for cleaner look
+                    renderer: 'svg' // Use SVG for better quality
+                });
+
+            } catch (error) {
+                // Handle rendering errors gracefully
+                previewContainer.innerHTML = `
+                    <div style="padding: 20px; color: #d32f2f; font-size: 12px; font-family: monospace;">
+                        <strong>Rendering Error:</strong><br>
+                        ${error.message}
+                        <br><br>
+                        <em>Check your JSON syntax and Vega-Lite specification.</em>
+                    </div>
+                `;
+            }
+        }
+
+        // Debounced render function
+        function debouncedRender() {
+            clearTimeout(renderTimeout);
+            renderTimeout = setTimeout(renderVisualization, 1500); // 500ms delay
+        }
+
+        // Load Vega libraries dynamically with UMD builds
+        function loadVegaLibraries() {
+            return new Promise((resolve, reject) => {
+                // Temporarily disable AMD define to avoid conflicts
+                const originalDefine = window.define;
+                window.define = undefined;
+
+                // Load Vega
+                const vegaScript = document.createElement('script');
+                vegaScript.src = 'https://unpkg.com/vega@5/build/vega.min.js';
+                vegaScript.onload = () => {
+                    // Load Vega-Lite
+                    const vegaLiteScript = document.createElement('script');
+                    vegaLiteScript.src = 'https://unpkg.com/vega-lite@5/build/vega-lite.min.js';
+                    vegaLiteScript.onload = () => {
+                        // Load Vega-Embed
+                        const vegaEmbedScript = document.createElement('script');
+                        vegaEmbedScript.src = 'https://unpkg.com/vega-embed@6/build/vega-embed.min.js';
+                        vegaEmbedScript.onload = () => {
+                            // Restore AMD define
+                            window.define = originalDefine;
+                            resolve();
+                        };
+                        vegaEmbedScript.onerror = reject;
+                        document.head.appendChild(vegaEmbedScript);
+                    };
+                    vegaLiteScript.onerror = reject;
+                    document.head.appendChild(vegaLiteScript);
+                };
+                vegaScript.onerror = reject;
+                document.head.appendChild(vegaScript);
+            });
+        }
+
         document.addEventListener('DOMContentLoaded', function () {
             // Initialize Monaco Editor
             require.config({ paths: { vs: 'https://cdnjs.cloudflare.com/ajax/libs/monaco-editor/0.47.0/min/vs' } });
@@ -131,9 +193,7 @@
                 try {
                     const response = await fetch('https://vega.github.io/schema/vega-lite/v5.json');
                     vegaLiteSchema = await response.json();
-                    console.log('Vega-Lite schema loaded successfully');
                 } catch (error) {
-                    console.error('Failed to load Vega-Lite schema:', error);
                     vegaLiteSchema = null;
                 }
 
@@ -149,6 +209,9 @@
                     });
                 }
 
+                // Load Vega libraries before creating editor
+                await loadVegaLibraries();
+
                 // Create the editor with improved configuration
                 editor = monaco.editor.create(document.getElementById('monaco-editor'), {
                     value: JSON.stringify(sampleSpec, null, 2),
@@ -163,7 +226,13 @@
                     formatOnType: true
                 });
 
-                console.log('Monaco Editor initialized with enhanced Vega-Lite schema support');
+                // Add debounced auto-render on editor change
+                editor.onDidChangeModelContent(() => {
+                    debouncedRender();
+                });
+
+                // Initial render
+                renderVisualization();
             });
 
             // Basic toggle functionality
@@ -202,7 +271,6 @@
             const headerLinks = document.querySelectorAll('.header-link');
             headerLinks.forEach(link => {
                 link.addEventListener('click', function () {
-                    console.log('Header link clicked:', this.textContent);
                     // TODO: Implement actual functionality in future phases
                 });
             });
diff --git a/src/styles.css b/src/styles.css
index 724ea81..c5b0f3e 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -108,15 +108,15 @@ body {
 
 /* Panel sizing */
 .snippet-panel {
-    flex: 0 0 25%;
+    flex: 0 0 20%;
 }
 
 .editor-panel {
-    flex: 0 0 50%;
+    flex: 0 0 30%;
 }
 
 .preview-panel {
-    flex: 0 0 25%;
+    flex: 0 0 50%;
 }
 
 /* Toggle buttons */