# App and Perf modules

## `src/app.rs` — GlintApp

Iced application entry point. Holds state and implements `update`/`view`.

### `GlintApp`

```rust
pub struct GlintApp {
    pub doc:        Document<'static>,
    pub vdom_roots: Vec<Element<'static>>,
    pub rhei:       RheiContext,
}
```

- `doc` — original Document (styles, variables, tracker)
- `vdom_roots` — result of the last evaluate_vdom (_incr)
- `rhei` — Rhai engine with cached ASTs

### `update(&mut self, message: Message) -> iced::Task<Message>`

Processing messages from Iced:

| Message | Action |
|---------|--------|
| `WindowScrolled(y)` | Set `__scroll_y`, call `on_variable_changed` |
| `ScrollableScrolled(id, y)` | Set `__scroll_{id}`, call `on_variable_changed` |
| `EventTriggered(script)` | `execute_action()`, then diff variables to find changed ones |
| `InputChanged(var, val)` | Set variable, call `on_variable_changed` |
| `ToggleChanged(var, val)` | Set `Bool`, call `on_variable_changed` |
| `SliderChanged(var, val)` | Set `Float`, call `on_variable_changed` |

After processing the message:
1. `tracker.take_dirty_set()` — get dirty elements
2. `evaluate_vdom_incr()` — recalculate VDOM
3. Save to `self.vdom_roots`

**Perf:** VDOM phase is measured with `PerfScope::new("vdom")`.

### `view(&self) -> iced::Element`

Build Iced widgets from `self.vdom_roots`:

1. Collect scroll_positions from `__scroll_*` variables
2. For each root: `render_element()` → push into column
3. Overlay global fixed/absolute/sticky layers
4. Return `container(layout).into()`

**Perf:** Render phase is measured with `PerfScope::new("render")`.
At the end `perf::print_frame()` — output to stderr.

---

## `src/perf.rs` — Performance Monitoring

Phase timing system (VDOM, Style, Render). Enabled with `--perf` flag.

### `PerfReport`

```rust
pub struct PerfReport {
    pub vdom_eval: f64,  // ms
    pub style: f64,      // ms
    pub render: f64,     // ms
    pub total: f64,      // ms
}
```

Stored in `thread_local!` `RefCell<PerfReport>`.

### `PerfScope`

Drop-guard: measures time from creation to destruction.

```rust
pub struct PerfScope {
    name: &'static str,
    start: Instant,
}
```

On `drop()`: adds elapsed ms to the corresponding `PerfReport` field.
Names: `"vdom"`, `"style"`, `"render"`.

### Functions

| Function | Description |
|----------|-------------|
| `set_enabled(bool)` | Enable/disable measurements |
| `is_enabled() -> bool` | Check state |
| `report_and_reset() -> Option<String>` | Collect report, check >16ms threshold |
| `reset()` | Reset PerfReport |
| `print_frame()` | Call report_and_reset + reset, print to stderr |

### Example output

```
[perf] VDOM: 6.63ms | Style: 0.26ms | Render: 7.19ms | Total: 14.08ms
[perf] VDOM: 13.26ms | Style: 0.52ms | Render: 7.18ms | Total: 20.95ms ⚠️ Frame budget exceeded! 20.95ms > 16ms
```

### Instrumentation points

| File | Phase | Location |
|------|-------|----------|
| `app.rs:update` | vdom | Around `evaluate_vdom_incr()` |
| `app.rs:view` | render | Entire `view()` function |
| `style.rs:compute_cached` | style | Inside `StyleSheet::compute_cached()` |