import type { Palette } from './palette';
import type { AnsiSource } from './ansi-source';
import { UI, contrast, ensureContrast, luminance, mix, parseHex } from './contrast';

// An `AnsiSource` (16 ANSI slots + primary bg/fg) has no notion of "three background depths" or "an
// accent" — Omarchy 4's `colors.toml` is a richer, hand-curated shape that a sixteen-slot terminal scheme
// was never designed to fill. This derives one anyway, by role rather than by guessing a fixed value:
//
//   - accent is whichever blue-ish slot actually stands out from the background (every official palette
//     picks blue too — this just guards against a scheme that reused the background for it).
//   - the three depths are the background pushed a fixed distance toward black or white, in the direction
//     each mode's surfaces already move (dark themes rise lighter, light themes recede darker — see the
//     ratios comment below, calibrated against Nord and Rosé Pine's real colors.toml).
//   - the three foreground weights are the foreground pulled toward the background by a fixed fraction,
//     standing in for "faint", "muted" and "strong" text.
//
// None of this has to be exact. `mapPalette`'s `ensureContrast` re-checks every text/surface pair
// afterward and nudges anything that fails — the approximation only has to be plausible, not correct.

function pickAccent(a: AnsiSource): string {
  const candidates = [a.blue, a.brightBlue, a.cyan, a.brightCyan];
  const best = candidates.reduce((hi, c) => (contrast(c, a.background) > contrast(hi, a.background) ? c : hi));
  // `--ring` is this colour laid directly on `--background` (see `map.ts`), and it's in the contract's
  // PAIRS check same as the official themes — so guarantee it the way `ensureContrast` guarantees text,
  // rather than only guarding against a background-coloured accent.
  return ensureContrast(best, a.background, UI);
}

export function deriveOmarchyPalette(a: AnsiSource): Palette {
  const dark = luminance(parseHex(a.background)) < 0.5;
  const mode: Palette['mode'] = dark ? 'dark' : 'light';

  const darkerBackground = dark ? mix(a.background, '#000000', 0.45) : mix(a.background, '#000000', 0.1);
  const darkBackground = dark ? mix(a.background, '#000000', 0.22) : mix(a.background, '#000000', 0.06);
  const lighterBackground = dark ? mix(a.background, '#ffffff', 0.07) : mix(a.background, '#000000', 0.035);

  // Faintest → strongest, all pulled toward the background rather than toward a fixed grey, so a warm
  // palette's dim text stays warm instead of turning neutral.
  const darkForeground = mix(a.foreground, a.background, 0.55);
  const lightForeground = mix(a.foreground, a.background, 0.3);

  const accent = pickAccent(a);
  const muted = contrast(a.brightBlack, a.background) >= 1.15 ? a.brightBlack : mix(a.foreground, a.background, 0.6);

  return {
    mode,
    accent,
    // Unused by `mapPalette` today (grep confirms `p.selection` has no reader) — kept only because the
    // `Palette` type requires it.
    selection: mix(a.background, a.foreground, 0.2),
    muted,
    background: a.background,
    darkBackground,
    darkerBackground,
    lighterBackground,
    foreground: a.foreground,
    darkForeground,
    lightForeground,
    brightForeground: a.foreground,
    red: a.red,
    yellow: a.yellow,
    green: a.green,
    cyan: a.cyan,
    blue: a.blue,
    magenta: a.magenta,
    // Standard ANSI has no orange slot. Mixing red and yellow reads better as "busy" than falling back to
    // plain yellow the way `loadPalette` does for the 3 official themes that omit it.
    orange: mix(a.red, a.yellow, 0.5),
    brightRed: a.brightRed,
    brightYellow: a.brightYellow,
    brightGreen: a.brightGreen,
    brightCyan: a.brightCyan,
    brightBlue: a.brightBlue,
    brightMagenta: a.brightMagenta,
  };
}