/**
 * Default data-side transform for `RelativeData`: rewrite each
 * `{ name, value }` datum's `value` to its share of the series total
 * expressed as 0–100 (matches v1's range). The companion percent
 * formatter divides by 100 so it can call `Intl.NumberFormat` with
 * `style: 'percent'`.
 *
 * Used by widgets whose series are arrays of `{ name, value }`
 * objects — bar, pie, timeseries, category. Widgets with a different
 * data shape pass their own transform via
 * `<RelativeData transform={...} />`; see `widgets-v2/histogram` and
 * `widgets-v2/scatterplot` for in-tree examples.
 *
 * The denominator is the sum of |value| across the series so mixed-sign
 * series (e.g. cashflow with inflows + outflows) 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. Series whose shape doesn't match
 * the named-value pattern fall through untouched.
 */

interface NamedValue {
  name: unknown
  value: number
  [k: string]: unknown
}

function isNamedValueArray(v: unknown): v is NamedValue[] {
  if (!Array.isArray(v)) return false
  return v.every(
    (item) =>
      item != null &&
      typeof item === 'object' &&
      'value' in item &&
      typeof (item as { value: unknown }).value === 'number',
  )
}

export const toRelativeData = (input: unknown): unknown => {
  if (!Array.isArray(input)) return input
  return input.map((series: unknown): unknown => {
    if (!isNamedValueArray(series)) return series
    const total = series.reduce((acc, d) => acc + Math.abs(d.value), 0)
    if (total <= 0) return series
    return series.map((d) => ({ ...d, value: (d.value / total) * 100 }))
  })
}

/**
 * Build a percent formatter using `Intl.NumberFormat`. The returned function
 * expects values in the 0–100 range (output of {@link toRelativeData}) and
 * divides by 100 internally before calling `style: 'percent'`.
 *
 * Locale: passed straight to `Intl.NumberFormat`. Falls back to the runtime
 * default when omitted.
 */
export function createPercentFormatter(
  locale?: string,
): (value: number) => string {
  const fmt = new Intl.NumberFormat(locale, {
    style: 'percent',
    minimumFractionDigits: 0,
    maximumFractionDigits: 2,
  })
  return (value: number) => {
    if (typeof value !== 'number' || !Number.isFinite(value))
      return String(value)
    return fmt.format(value / 100)
  }
}