import type { PowerlineBlockName } from "../types.js";
import type { PowerlinePreset } from "./types.js";

const BLOCK_NAMES: PowerlineBlockName[] = ["header", "directory", "git", "runtime", "meter"];

type PaletteRamp = readonly [string, string, string, string, string];

export function createRampPreset(backgrounds: PaletteRamp): PowerlinePreset {
  return {
    lead: backgrounds[0],
    blocks: Object.fromEntries(
      BLOCK_NAMES.map((block, index) => {
        const background = backgrounds[index];
        return [block, { fg: contrastColor(background), bg: background }];
      }),
    ) as Record<PowerlineBlockName, { fg: string; bg: string }>,
    extensionSeparator: backgrounds[2],
  };
}

function contrastColor(hex: string): string {
  const background = relativeLuminance(hex);
  const dark = relativeLuminance("#090c0c");
  const light = relativeLuminance("#f0f0f0");
  return contrastRatio(background, dark) >= contrastRatio(background, light) ? "#090c0c" : "#f0f0f0";
}

function contrastRatio(left: number, right: number): number {
  return (Math.max(left, right) + 0.05) / (Math.min(left, right) + 0.05);
}

function relativeLuminance(hex: string): number {
  const normalized = hex.slice(1);
  const channels = [0, 2, 4].map((offset) => {
    const value = Number.parseInt(normalized.slice(offset, offset + 2), 16) / 255;
    return value <= 0.04045 ? value / 12.92 : ((value + 0.055) / 1.055) ** 2.4;
  });
  return 0.2126 * (channels[0] ?? 0) + 0.7152 * (channels[1] ?? 0) + 0.0722 * (channels[2] ?? 0);
}