feat: add storage monitor to track localStorage usage

CLAUDE.md

@@ -15,4 +15,7 @@ Instructions for Claude Code when working on this project.
 
 ## Current Status
 
-refer `docs/dev-plan.md` for the current status.
+**Completed**: Phases 0-8 (All core functionality including storage monitoring)
+**Next**: Phase 9 - Export/Import
+
+See `docs/dev-plan.md` for complete roadmap and technical details.

docs/dev-plan.md

@@ -156,16 +156,17 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 
 ---
 
-### **Phase 8: Storage Monitoring**
+### **Phase 8: Storage Monitoring** ✅ **COMPLETE**
 **Goal**: Show storage usage and limits
 
-- [ ] Calculate total localStorage usage
-- [ ] Display as progress bar or text (e.g., "2.3 MB / ~5 MB")
-- [ ] Show individual snippet sizes in list
-- [ ] Add warning indicator when approaching 80% capacity
-- [ ] Display draft vs published size differences
-
-**Deliverable**: User can see storage consumption
+**Deliverables**:
+- Storage usage calculation using Blob API for accurate byte counting
+- Progress bar display showing usage vs 5MB limit (e.g., "2.3 MB / 5 MB")
+- Visual warning states: green (normal), orange (90%+ warning), red (95%+ critical)
+- Storage monitor positioned at bottom of snippet panel below metadata
+- Automatic updates after every save operation
+- Alert dialog when localStorage quota is exceeded
+- Flexbox layout ensuring monitor stays at panel bottom with scrollable snippet list
 
 ---
 
@@ -304,15 +305,15 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 
 ## Current Status
 
-**Completed**: Phases 0-7 (Storage, UI, editor, rendering, persistence, CRUD, organization, draft/published workflow)
-**Active**: Phase 8 - Storage Monitoring
+**Completed**: Phases 0-8 (Storage, UI, editor, rendering, persistence, CRUD, organization, draft/published workflow, storage monitoring)
+**Next**: Phase 9 - Export/Import
 **See**: `CLAUDE.md` for concise current state summary
 
 ---
 
 ## Implemented Features
 
-### Core Capabilities (Phases 0-7)
+### Core Capabilities (Phases 0-8)
 - Three-panel resizable layout with memory and persistence
 - Monaco Editor v0.47.0 with Vega-Lite v5 schema validation
 - Live Vega-Lite rendering with debounced updates and error display
@@ -324,6 +325,7 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 - Draft/Published workflow with version control
 - Status indicator lights (green/yellow) showing draft state
 - Context-aware Publish/Revert buttons with color coding
+- Storage monitoring with visual progress bar and warning states
 - Retro Windows 2000 aesthetic throughout
 
 ### Technical Implementation
@@ -335,3 +337,5 @@ Astrolabe is a focused tool for managing, editing, and previewing Vega-Lite visu
 - **AMD Resolution**: Temporary `window.define` disabling for Vega library loading
 - **Panel Memory**: localStorage persistence for sizes and visibility across sessions
 - **Data Model**: Phase 0 schema with `spec` (published) and `draftSpec` (working) fields
+- **Storage Calculation**: Blob API for accurate byte counting of snippet data
+- **Flexbox Layout**: Scrollable snippet list with fixed metadata and storage monitor at bottom

index.html

@@ -94,6 +94,15 @@
                             <button class="meta-btn delete-btn" id="delete-btn">Delete</button>
                         </div>
                     </div>
+                    <div class="storage-monitor" id="storage-monitor">
+                        <div class="storage-info">
+                            <span class="storage-label">Storage:</span>
+                            <span class="storage-text" id="storage-text">0 KB / 5 MB</span>
+                        </div>
+                        <div class="storage-bar">
+                            <div class="storage-fill" id="storage-fill"></div>
+                        </div>
+                    </div>
                 </div>
             </div>
 

src/js/app.js

@@ -12,6 +12,9 @@ document.addEventListener('DOMContentLoaded', function () {
 
     renderSnippetList();
 
+    // Update storage monitor
+    updateStorageMonitor();
+
     // Auto-select first snippet on page load
     const firstSnippet = SnippetStorage.listSnippets()[0];
     if (firstSnippet) {

src/js/snippet-manager.js

@@ -1,5 +1,9 @@
 // Snippet management and localStorage functionality
 
+// Storage limits (5MB in bytes)
+const STORAGE_LIMIT_BYTES = 5 * 1024 * 1024;
+const WARNING_THRESHOLD = 0.9; // 90% = 4.5MB
+
 // Generate unique ID using Date.now() + random numbers
 function generateSnippetId() {
     return Date.now() + Math.random() * 1000;
@@ -39,10 +43,11 @@ const SnippetStorage = {
     saveSnippets(snippets) {
         try {
             localStorage.setItem(this.STORAGE_KEY, JSON.stringify(snippets));
+            updateStorageMonitor();
             return true;
         } catch (error) {
             console.error('Failed to save snippets to localStorage:', error);
-            // TODO: Handle quota exceeded, show user error
+            alert('Failed to save: Storage quota may be exceeded. Consider deleting old snippets.');
             return false;
         }
     },
@@ -798,3 +803,46 @@ function revertDraft() {
     }
 }
 
+// Calculate storage usage in bytes
+function calculateStorageUsage() {
+    const snippetsData = localStorage.getItem(SnippetStorage.STORAGE_KEY);
+    if (!snippetsData) return 0;
+
+    // Calculate size in bytes
+    return new Blob([snippetsData]).size;
+}
+
+// Format bytes to human-readable size
+function formatBytes(bytes) {
+    if (bytes < 1024) return `${bytes} B`;
+    if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
+    return `${(bytes / (1024 * 1024)).toFixed(2)} MB`;
+}
+
+// Update storage monitor display
+function updateStorageMonitor() {
+    const usedBytes = calculateStorageUsage();
+    const percentage = (usedBytes / STORAGE_LIMIT_BYTES) * 100;
+
+    const storageText = document.getElementById('storage-text');
+    const storageFill = document.getElementById('storage-fill');
+
+    if (storageText) {
+        storageText.textContent = `${formatBytes(usedBytes)} / 5 MB`;
+    }
+
+    if (storageFill) {
+        storageFill.style.width = `${Math.min(percentage, 100)}%`;
+
+        // Remove all state classes
+        storageFill.classList.remove('warning', 'critical');
+
+        // Add warning/critical classes based on usage
+        if (percentage >= 95) {
+            storageFill.classList.add('critical');
+        } else if (percentage >= 90) {
+            storageFill.classList.add('warning');
+        }
+    }
+}
+

src/styles.css

@@ -332,9 +332,11 @@ body {
 .panel-content {
     flex: 1;
     padding: 8px;
-    overflow: auto;
+    overflow: hidden;
     background: #ffffff;
     border: 1px inset #c0c0c0;
+    display: flex;
+    flex-direction: column;
 }
 
 /* Panel sizing */
@@ -392,6 +394,10 @@ body {
 
 .snippet-list {
     list-style: none;
+    flex: 1;
+    overflow-y: auto;
+    overflow-x: hidden;
+    margin-bottom: 8px;
 }
 
 .snippet-item {
@@ -477,13 +483,14 @@ body {
 /* Snippet meta section */
 .snippet-meta {
     margin-top: 12px;
-    padding: 8px;
+    padding: 8px 8px 16px 8px;
     border-top: 1px solid #808080;
     background: #f0f0f0;
     border: 1px inset #c0c0c0;
     margin-left: -8px;
     margin-right: -8px;
-    margin-bottom: -8px;
+    margin-bottom: 0;
+    flex-shrink: 0;
 }
 
 .meta-header {
@@ -599,3 +606,51 @@ body {
 .ghost-card .snippet-date {
     color: #808080;
 }
+
+/* Storage monitor */
+.storage-monitor {
+    padding: 8px;
+    background: #f0f0f0;
+    border-top: 1px solid #808080;
+    margin: 0 -8px -8px -8px;
+    flex-shrink: 0;
+}
+
+.storage-info {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    margin-bottom: 4px;
+    font-size: 10px;
+}
+
+.storage-label {
+    font-weight: bold;
+    color: #000000;
+}
+
+.storage-text {
+    color: #606060;
+}
+
+.storage-bar {
+    width: 100%;
+    height: 12px;
+    background: #ffffff;
+    border: 1px inset #c0c0c0;
+    position: relative;
+}
+
+.storage-fill {
+    height: 100%;
+    background: #00aa00;
+    transition: width 0.3s ease, background-color 0.3s ease;
+}
+
+.storage-fill.warning {
+    background: #ff8800;
+}
+
+.storage-fill.critical {
+    background: #ff0000;
+}