// Sizing rules for the HTML5 <video> element in the full-screen player.
// Extracted from VideoPlayer.svelte so the fit behaviour is unit-testable.

/**
 * Classes applied to the <video> element so it fits the player viewport.
 *
 * TRACES: UR-005
 *
 * `max-w-full max-h-full` only ever *shrinks* oversized media, so a source
 * smaller than the window (e.g. 480p on a 1080p display) rendered at its
 * intrinsic size - a small box in the middle of a black screen. Filling the
 * container and letting `object-contain` do the scaling fits the picture to
 * whichever axis constrains it, in both directions, preserving aspect ratio.
 */
export function videoFitClass(): string {
  return "w-full h-full object-contain";
}

export interface FittedSize {
  width: number;
  height: number;
}

/**
 * The rendered size of a video of the given intrinsic dimensions once it has
 * been fitted into the container - i.e. scaled (up or down) so that it touches
 * the container on its constraining axis, with the other axis letter/pillar
 * boxed. Mirrors what `object-fit: contain` on a full-size element does.
 */
export function fittedVideoSize(
  intrinsicWidth: number,
  intrinsicHeight: number,
  containerWidth: number,
  containerHeight: number,
): FittedSize {
  if (intrinsicWidth <= 0 || intrinsicHeight <= 0) {
    return { width: 0, height: 0 };
  }

  const scale = Math.min(
    containerWidth / intrinsicWidth,
    containerHeight / intrinsicHeight,
  );

  return {
    width: intrinsicWidth * scale,
    height: intrinsicHeight * scale,
  };
}