/**
 * Chart palette.
 *
 * Categorical slots are assigned in fixed order and never cycled — a series keeps its
 * hue when a filter removes its neighbours. Both modes are separately stepped for their
 * own surface, not an automatic flip of the light values.
 *
 * Validated against this app's card surfaces (light `#ffffff`, dark `#0f1729`) with the
 * dataviz six-check validator, six slots, adjacent pairlist:
 *   light — CVD ΔE 9.1, normal-vision ΔE 19.6, contrast WARN on aqua/yellow/magenta
 *   dark  — CVD ΔE 8.4, normal-vision ΔE 19.3, contrast all ≥ 3:1
 * The light-mode contrast WARN obliges *relief*: every chart using these slots ships a
 * legend with visible text labels and a table view of the same numbers.
 */

export interface ChartPalette {
  /** Categorical slots, in fixed assignment order. */
  categorical: readonly string[];
  /** Single hue for magnitude — one colour for every bar in a one-series chart. */
  sequential: string;
  /** Recessive chrome. */
  grid: string;
  axis: string;
  /** Text tokens — labels never wear the data colour. */
  textMuted: string;
  /** Surface, for the 2px gaps and rings that separate marks. */
  surface: string;
  tooltipBg: string;
  tooltipBorder: string;
}

const LIGHT: ChartPalette = {
  categorical: ['#2a78d6', '#eb6834', '#1baf7a', '#eda100', '#e87ba4', '#008300'],
  sequential: '#2a78d6',
  grid: '#e1e0d9',
  axis: '#c3c2b7',
  textMuted: '#898781',
  surface: '#ffffff',
  tooltipBg: '#ffffff',
  tooltipBorder: 'rgba(11,11,11,0.10)',
};

const DARK: ChartPalette = {
  categorical: ['#3987e5', '#d95926', '#199e70', '#c98500', '#d55181', '#008300'],
  sequential: '#3987e5',
  grid: '#2c2c2a',
  axis: '#383835',
  textMuted: '#898781',
  surface: '#0f1729',
  tooltipBg: '#0f1729',
  tooltipBorder: 'rgba(255,255,255,0.10)',
};

export function getChartPalette(isDark: boolean): ChartPalette {
  return isDark ? DARK : LIGHT;
}

/**
 * Colour for a categorical member, keyed by its position in a **stable** ordering of the
 * whole domain — never by its rank in the current filtered view, so filtering does not
 * repaint the survivors. Past the last slot everything folds into one neutral bucket
 * rather than inventing a hue no CVD check would pass.
 */
export function categoricalColor(palette: ChartPalette, index: number): string {
  return palette.categorical[index] ?? palette.textMuted;
}