import { oklch2oklab } from '~/converters';
import { GAMUT_EPSILON, MESSAGES, PRECISION } from '~/modules/constants';
import { invariant } from '~/modules/invariant';
import { isInGamut, oklabToLinearP3 } from '~/modules/linear-rgb';
import { round } from '~/modules/utils';
import { isNumberInRange, isString } from '~/modules/validators';
import parseCSS from '~/parse-css';

import { LCH } from '~/types';

/**
 * Get the maximum chroma for a given lightness and hue in the OkLCH color space.
 *
 * @param input - The input color string or LCH object.
 * @param precision - The number of decimal places for the result.
 * @returns The maximum chroma value within P3 gamut.
 */
export function getP3MaxChroma(input: string | LCH, precision = PRECISION): number {
  const { l, h } = isString(input) ? parseCSS(input, 'oklch') : input;

  invariant(isNumberInRange(l, 0, 1), MESSAGES.lightnessRange);
  invariant(isNumberInRange(h, 0, 360), MESSAGES.hueRange);

  // Binary search parameters
  const epsilon = GAMUT_EPSILON;
  let low = 0;
  let high = 0.5; // Increased max theoretical chroma

  while (high - low > epsilon) {
    const mid = (low + high) / 2;
    const { l: L, a, b } = oklch2oklab({ l, c: mid, h }, 16);

    const p3Color = oklabToLinearP3(L, a, b);

    if (isInGamut(p3Color)) {
      low = mid;
    } else {
      high = mid;
    }
  }

  return round(low, precision);
}

/**
 * Get an OkLCH color with maximum chroma in the P3 color space.
 *
 * @param input - The input color string or LCH object.
 * @returns The OkLCH color string with maximum chroma.
 */
export function getP3MaxColor(input: string | LCH): string {
  const lch = isString(input) ? parseCSS(input, 'oklch') : input;

  return `oklch(${round(lch.l, PRECISION, false)} ${getP3MaxChroma(lch)} ${round(lch.h, PRECISION, false)})`;
}