export const BAR_DEPTH_MAX_PX = 7;
/** The side parallelogram's back edge lifts by `depth * this ratio`, giving a
 * subtle head-on perspective slope. */
export const BAR_DEPTH_PERSPECTIVE_RATIO = 0.45;

/**
 * Maximum side-face depth in px for a chart, clamped so depth never spills past
 * the gap between bars. `stepWidth` is d3-scaleBand's `step()` (bandwidth +
 * gap); `bandWidth` is a single bar's width. Returns 0 for gapless/dense charts.
 */
export function barDepthMaxDepth(stepWidth: number, bandWidth: number): number {
  const gap = Math.max(0, stepWidth - bandWidth);
  return Math.min(bandWidth * 0.22, Math.max(0, gap - 1), BAR_DEPTH_MAX_PX);
}

/**
 * Per-bar side-face depth + perspective rise.
 *
 * - `absOffset` ∈ [0, 1]: the bar's normalized distance from the chart's
 *   horizontal center. 0 = dead center (no depth); 1 = chart edge (full depth).
 * - `naturalHeight`: the bar's pixel height. Depth is capped by it so a short
 *   bar's side never reads wider than the bar is tall.
 * - `maxDepth`: from `barDepthMaxDepth`.
 */
export function barDepthAndRise(
  absOffset: number,
  naturalHeight: number,
  maxDepth: number
): { depth: number; perspectiveRise: number } {
  const offset = Math.min(1, Math.max(0, absOffset));
  const cappedMaxDepth = Math.min(maxDepth, Math.max(0, naturalHeight));
  const depth = offset * cappedMaxDepth;
  return { depth, perspectiveRise: depth * BAR_DEPTH_PERSPECTIVE_RATIO };
}