/**
 * Histogram-specific `RelativeData` transform. Histogram data is
 * `number[][]` — each series is a flat list of bin counts. This
 * rewrites each count to its share of the series total (0–100), so
 * pairing with `createPercentFormatter` renders the y-axis as
 * percentages.
 *
 * Pass to `<Widget.RelativeData transform={toRelativeHistogramData} />`.
 *
 * The denominator is the sum of |value| across the series so mixed-sign
 * inputs produce sane signed shares-of-magnitude. A series whose total
 * magnitude is zero (all-zero or empty input) is returned unchanged so
 * a stalled or empty data set doesn't show misleading 0% values. Inputs
 * whose shape isn't `number[][]` fall through untouched (same defensive
 * shape-check pattern as the default transform).
 */
export const toRelativeHistogramData = (input: unknown): unknown => {
  if (!Array.isArray(input)) return input
  return input.map((series: unknown): unknown => {
    if (!isFlatNumberArray(series)) return series
    const total = series.reduce((acc, v) => acc + Math.abs(v), 0)
    if (total <= 0) return series
    return series.map((v) => (v / total) * 100)
  })
}

function isFlatNumberArray(v: unknown): v is number[] {
  if (!Array.isArray(v)) return false
  return v.every((item) => typeof item === 'number' && Number.isFinite(item))
}