Frontend Development — Megahub IDE

Tech Stack

• Vite — build tool and dev server
• Blockly 12.3.1 — visual programming editor; custom blocks in /frontend/src/components/blockly/ — see blockly skill for block authoring, Lua generators, and BLOCKS.md generation
• Vanilla JS — no framework (intentionally lightweight for ESP32 flash size)
• Web Bluetooth API — browser BLE, Chrome/Edge/Opera only
• Prism.js — Lua syntax highlighting in the preview panel
• Web Components — all sidebar panels are custom elements with Shadow DOM

Build Modes

Mode	Description
dev	Hot reload, localStorage for persistence, no BLE
bt	Production BLE mode, deployed to GitHub Pages
web	WiFi/HTTP mode, served from firmware WebServer

Mode is available at runtime as import.meta.env.VITE_MODE.

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File Structure

frontend/
  index.html                  Main entry point (HTML skeleton)
  src/
    index.js                  App controller, event wiring, all Application.* methods
    bleclient.js              BLE protocol client (fragmentation, streaming, events)
    theme.css                 CSS design tokens (all --vscode-* variables)
    styles.css                Global styles, layout grid, all UI component CSS
    components/
      blockly/                Blockly editor + custom block definitions
      files/                  Project manager dialog (list/create/delete/autostart)
      logger/                 Terminal-style log output (max 50 entries)
      luapreview/             Syntax-highlighted Lua code preview
      portstatus/             Real-time LEGO port status cards
      ui/                     show_value block output display
      btdevicelist/           Bluetooth Classic device list + discovery
      sidebar-toggle/         Mobile sidebar toggle button

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VS Code Dark Theme System

All design tokens are CSS custom properties defined in theme.css. Always use these — never hardcode colors or sizes.

Key Color Tokens

--vscode-bg-primary: #1e1e1e      /* Main background */
--vscode-bg-secondary: #252526    /* Panels, cards, sidebar */
--vscode-bg-elevated: #2d2d30     /* Hover states */
--vscode-bg-input: #3c3c3c        /* Form inputs */

--vscode-text-primary: #cccccc    /* Main text */
--vscode-text-secondary: #858585  /* Muted text, breadcrumb items */
--vscode-text-tertiary: #6a6a6a   /* Very muted (separators) */
--vscode-text-bright: #ffffff     /* Headings, active labels */

--vscode-accent-blue: #007acc     /* Focus borders */
--vscode-accent-blue-dark: #0078d4 /* Primary buttons, status bar */
--vscode-accent-blue-hover: #1177bb
--vscode-accent-teal: #4ec9b0     /* Success, connected state */
--vscode-accent-yellow: #dcdcaa   /* Warning, connecting state */

--color-success: #4ec9b0
--color-error: #f48771
--color-error-bg: #5a1d1d
--color-warning: #dcdcaa

--vscode-border-light: #3c3c3c
--vscode-border-medium: #3e3e42

Key Spacing / Sizing Tokens

--spacing-xs: 0.25rem   --spacing-sm: 0.5rem
--spacing-md: 0.75rem   --spacing-lg: 1rem
--spacing-xl: 1.25rem   --spacing-2xl: 1.5rem

--transition-fast: 0.15s ease
--transition-medium: 0.3s ease

--header-height: 3rem
--z-modal: 1100   --z-tooltip: 2000

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Application Mode System

Three modes, switched via Application.setMode(mode):

Mode	View shown
btconnect	Welcome screen + connect button
management	Project list (files component)
editor	Blockly editor + sidebar controls

Visibility Mechanism

dynamicvisibility class (all modes):

// setMode() sets display:block/none on elements with class dynamicvisibility
// Elements also have class visible-{mode} to declare when they appear
// e.g. class="dynamicvisibility visible-editor visible-management"

⚠ setMode() always sets display: block — do NOT use dynamicvisibility for elements that need display: flex or display: grid.

body.dataset.mode (CSS-based, for flex/grid elements):

// setMode() also sets document.body.dataset.mode = mode
// Use CSS selectors: body[data-mode="editor"] .my-element { display: flex }
// Used by: header breadcrumb, back button

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Layout Grid

┌──────────────────────────────────────┐  ← header (3rem)
│ [←] Megahub IDE / project  [toggle] │
├──────────────────┬───────────────────┤  ← 1fr
│                  │ sidebar buttons   │
│  Blockly /       │ ─────────────────│
│  Files /         │ accordion panels  │
│  Welcome         │  lua / ports /   │
│                  │  ui / btdevices  │
├──────────────────┴───────────────────┤  ← footer (8–12rem)
│  Logger (terminal output)            │
├──────────────────────────────────────┤  ← statusbar (20px)
│ ● Connected to Megahub IDE           │
└──────────────────────────────────────┘

Desktop (≥1512px): 75/25 content/sidebar split. Mobile: sidebar is a slide-in overlay.

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Existing UI Patterns (use these, don't reinvent)

Notifications (Toast)

showNotification('success' | 'error' | 'warning' | 'info', title, message, durationMs)
// duration 0 = no auto-dismiss
// Returns the notification element (for manual dismissal)

Confirmation Dialog

const confirmed = await showConfirmDialog(title, message, {
  confirmText: 'Delete',   // default: 'Confirm'
  cancelText: 'Cancel',
  destructive: true        // red confirm button (default: true)
});

Top Progress Bar

Progress.show()   // indeterminate shimmer sweep
Progress.hide()
// Used for: project list load, file open, file save

BLE Connection Modal

ConnectionModal.show()              // resets all steps to pending
ConnectionModal.setStep(stepId)     // marks previous steps done, current active
ConnectionModal.setAllDone()        // all checkmarks
ConnectionModal.setError(stepId, message)  // marks step red, shows error text
ConnectionModal.hide()
// stepIds: 'requesting' | 'connecting' | 'services' | 'notifications' | 'mtu' | 'ready'

VS Code Status Bar

StatusBar.setConnecting()
StatusBar.setConnected(deviceName)
StatusBar.setDisconnected()
StatusBar.setMessage(text)   // right-side info text
StatusBar.clearMessage()

Sidebar Icon Buttons

.sidebar-icon-btn                   /* base */
.sidebar-icon-btn-primary           /* blue background (Execute) */
.sidebar-icon-btn-danger            /* red background (Stop) */
.sidebar-icon-btn-save              /* neutral, turns blue on hover */
.sidebar-icon-btn-toggle            /* teal when aria-pressed="true" */
.sidebar-icon-btn.btn-loading       /* spins the SVG icon */

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BLE Client Architecture (bleclient.js)

Connection Flow

connect(onProgress?)
  → navigator.bluetooth.requestDevice()  [requires user gesture]
  → _setupGattConnection(onProgress?)
      → gatt.connect()
      → getPrimaryService()
      → getCharacteristic() × 4
      → startNotifications() × 3
      → sleep(200)  ← CRITICAL: BLE stack propagation delay
      → waitForMTU(2000)
      → testControlChannel()
  → emits onProgress callbacks at each step

Message Protocol

• 5-byte fragment header: type, messageId, fragmentNum(2), flags
• MTU: default 23 bytes, negotiated up to 517 bytes
• Fragmentation: automatic for all requests/responses
• Streaming protocol: for large file uploads (chunks + ACK window)

Event System

bleClient.addEventListener(APP_EVENT_TYPE_*, callback)
bleClient.removeAllEventListeners()
// Event types: LOG, PORTSTATUS, COMMAND, BTCLASSICDEVICES

File Upload

await bleClient.uploadFileStreaming(projectId, filename, content, onProgress?)
// Sliding window: 8 chunks in flight, waits for ACK before advancing

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Animation Principles

All animations must be purposeful — each one communicates meaning:

Use case	Animation	Timing
State transitions	CSS transition	var(--transition-fast) = 0.15s ease
Indeterminate loading	Shimmer sweep (progress bar)	1.4s linear infinite
Spinner (waiting)	Rotate 360°	0.8s linear infinite
Step completion	Scale 0→1 + opacity	0.15s ease-out (one-shot)
Status dot state change	Color transition	0.3s ease
Connecting pulse	Opacity 1→0.3→1	1s ease-in-out infinite

Always wrap looping animations in:

@media (prefers-reduced-motion: reduce) {
  /* replace animation with instant state */
}

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Component Pattern (Web Components)

All sidebar panels are custom elements with Shadow DOM:

class MyComponent extends HTMLElement {
  connectedCallback() {
    const shadow = this.attachShadow({ mode: 'open' });
    const sheet = new CSSStyleSheet();
    sheet.replaceSync(styleSheet);   // import from style.css
    shadow.adoptedStyleSheets = [sheet];
    shadow.innerHTML = template;     // import from component.html
  }
}
customElements.define('custom-my-component', MyComponent);

Accordion behavior: dispatch accordion-expand / accordion-collapse custom events. Parent (initSidebarAccordion() in index.js) collapses all others on expand.

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Important Constraints

• Bundle size: Keep JS small — it's embedded in 4MB ESP32 flash
• No framework: No React/Vue/Angular — intentional
• Shadow DOM: Component styles are isolated; theme.css variables are inherited through the shadow boundary
• Web Bluetooth: User gesture required for requestDevice() — never call without a click handler
• Supported browsers: Chrome, Edge, Opera only — Firefox/Safari don't support Web Bluetooth