/**
 * Display size for a Giphy / Tenor link-preview GIF. The card used to force
 * every GIF into a full-width × 200px band with `object-fit: cover`, so square
 * and portrait GIFs lost most of their height and small ones were blown up.
 * Fit the GIF inside `maxWidth × maxHeight` keeping its aspect ratio, and
 * enlarge a small GIF at most `maxUpscale`× so it stays sharp.
 */

/** The GIF card's width (UrlPreview is 25rem); a phone shrinks it further via CSS. */
export const GIF_PREVIEW_MAX_WIDTH = 400;
export const GIF_PREVIEW_MAX_HEIGHT = 320;
export const GIF_PREVIEW_MAX_UPSCALE = 2;

export type GifPreviewBox = { width: number; height: number };

// og:image:width / og:image:height are numbers from Synapse, but some sites
// publish them as strings; anything else (missing, 0, NaN) means "unknown".
const dimension = (value: unknown): number | undefined => {
  const n = typeof value === 'string' ? Number(value) : value;
  return typeof n === 'number' && Number.isFinite(n) && n > 0 ? n : undefined;
};

/** The box to render the GIF in, or `undefined` when its size isn't known. */
export const gifPreviewBox = (
  rawWidth: unknown,
  rawHeight: unknown,
  maxWidth = GIF_PREVIEW_MAX_WIDTH,
  maxHeight = GIF_PREVIEW_MAX_HEIGHT,
  maxUpscale = GIF_PREVIEW_MAX_UPSCALE,
): GifPreviewBox | undefined => {
  const width = dimension(rawWidth);
  const height = dimension(rawHeight);
  if (!width || !height) return undefined;
  const scale = Math.min(maxWidth / width, maxHeight / height, maxUpscale);
  return {
    width: Math.max(1, Math.round(width * scale)),
    height: Math.max(1, Math.round(height * scale)),
  };
};