// Copyright (c) 2026 Dominic Masters
//
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT

// extends UIElement (not Label) deliberately: only a UIElement/SCRIPTED
// instance's render()/update() override actually gets dispatched by the
// engine (the native Label/Rectangle callback tables never consult a
// subclass's override -- they're not scripted types themselves). So this
// composes a child Label instead of subclassing one, same as Button.
//
// Overrides render() rather than update(): update()/uiUpdate() only run
// on the one fixed-timestep tick per real frame that actually crosses a
// DUSK_TIME_STEP boundary (see Time.renderDelta's doc), but an FPS
// counter needs to sample every real frame -- which is exactly what
// render() does.
class FpsCounter extends UIElement {
  init() {
    this.label = new Label();
    this.add(this.label);

    this._average = 0;
  }

  render() {
    const delta = Time.renderDelta;
    if(delta > 0) {
      const fps = 1 / delta;
      this._average = this._average === 0
        ? fps
        : this._average + (fps - this._average) * FpsCounter.SMOOTHING;
    }

    this.label.text = 'FPS: ' + Math.round(this._average);
    this.renderChildren();
  }
}

// Exponential-moving-average weight per sample -- lower is smoother/
// slower to react, higher tracks instantaneous frame time more closely.
FpsCounter.SMOOTHING = 0.1;

module.exports = FpsCounter;