/**
 * Scatterplot-specific `RelativeData` transform. Scatter data is
 * `[number, number][]` — each series is a list of `[x, y]` tuples.
 * Relative is a values-axis concept, so this rewrites `y` to its
 * share of the series's total `y` (0–100) and leaves `x` raw — x is
 * coordinate space, not part of the cohort total.
 *
 * Pass to `<Widget.RelativeData transform={toRelativeScatterplotData} />`.
 *
 * The denominator is the sum of |y| across the series so mixed-sign
 * y values produce sane signed shares-of-magnitude. A series whose
 * total y-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, number][]` fall through
 * untouched.
 */
export const toRelativeScatterplotData = (input: unknown): unknown => {
  if (!Array.isArray(input)) return input
  return input.map((series: unknown): unknown => {
    if (!isXyTupleArray(series)) return series
    const total = series.reduce((acc, [, y]) => acc + Math.abs(y), 0)
    if (total <= 0) return series
    return series.map(([x, y]) => [x, (y / total) * 100] as [number, number])
  })
}

function isXyTupleArray(v: unknown): v is [number, number][] {
  if (!Array.isArray(v)) return false
  return v.every(
    (item) =>
      Array.isArray(item) &&
      item.length === 2 &&
      typeof item[0] === 'number' &&
      Number.isFinite(item[0]) &&
      typeof item[1] === 'number' &&
      Number.isFinite(item[1]),
  )
}