import { readFile, writeFile } from "node:fs/promises";
import { fileURLToPath } from "node:url";
import path from "node:path";

const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
const tokenPath = path.join(root, "src/lib/tokens.json");
const outputPath = path.join(root, "src/styles/theme.generated.css");
const source = JSON.parse(await readFile(tokenPath, "utf8"));

const variableName = (key) =>
  `--${key
    .replace(/([a-z0-9])([A-Z])/g, "$1-$2")
    .replace(/([a-zA-Z])([0-9])/g, "$1-$2")
    .toLowerCase()}`;

function hexToHsl(hex) {
  const value = hex.replace("#", "");
  const [r, g, b] = [0, 2, 4].map((offset) => parseInt(value.slice(offset, offset + 2), 16) / 255);
  const max = Math.max(r, g, b);
  const min = Math.min(r, g, b);
  const lightness = (max + min) / 2;
  let hue = 0;
  let saturation = 0;

  if (max !== min) {
    const delta = max - min;
    saturation = lightness > 0.5 ? delta / (2 - max - min) : delta / (max + min);
    if (max === r) hue = (g - b) / delta + (g < b ? 6 : 0);
    if (max === g) hue = (b - r) / delta + 2;
    if (max === b) hue = (r - g) / delta + 4;
    hue /= 6;
  }

  return `${Math.round(hue * 360)} ${Math.round(saturation * 100)}% ${Math.round(lightness * 100)}%`;
}

function block(selector, colors) {
  const variables = Object.entries(colors)
    .map(([name, value]) => `  ${variableName(name)}: ${hexToHsl(value)};`)
    .join("\n");
  return `${selector} {\n${variables}\n}`;
}

const generated = `/* Generated by scripts/generate-theme.mjs from src/lib/tokens.json. */\n${block(":root, .dark", source.color.dark)}\n\n${block(".light", source.color.light)}\n`;
const check = process.argv.includes("--check");

if (check) {
  const current = await readFile(outputPath, "utf8").catch(() => "");
  if (current !== generated) {
    console.error("Generated theme is stale. Run npm run tokens:generate.");
    process.exit(1);
  }
} else {
  await writeFile(outputPath, generated);
}