import type { ThemeCssVarMap, ThemeStyleConfig, ThemeStylePresetId } from './types';
import { THEME_STYLE_PRESETS } from './presets';

function mergeLayer(base: ThemeCssVarMap | undefined, over: ThemeCssVarMap | undefined): ThemeCssVarMap {
  return { ...base, ...over };
}

/**
 * Tailwind v4 `rounded-*` utilities are backed by `--radius-*` scale variables.
 * When semantic `radius` is present, emit the derived scale too.
 */
function withTailwindRadiusScale(vars: ThemeCssVarMap): Array<[string, string]> {
  const entries = Object.entries(vars);
  const radius = vars.radius;
  if (!radius) return entries;

  const r = String(radius).trim();
  if (!r) return entries;

  const scale: Array<[string, string]> = [
    ['radius-xs', `calc(${r} - 6px)`],
    ['radius-sm', `calc(${r} - 4px)`],
    ['radius-md', `calc(${r} - 2px)`],
    ['radius-lg', r],
    ['radius-xl', `calc(${r} + 4px)`],
    ['radius-2xl', `calc(${r} + 8px)`],
    ['radius-3xl', `calc(${r} + 12px)`],
    ['radius-4xl', `calc(${r} + 16px)`],
  ];

  return [...entries, ...scale];
}

/**
 * Build a stylesheet fragment: preset → vars.light / vars.dark.
 * Inject this after globals (later rule wins).
 */
export function buildThemeStyleSheet(style?: ThemeStyleConfig): string {
  if (!style) return '';

  const presetId: ThemeStylePresetId = style.preset ?? 'default';
  const preset = THEME_STYLE_PRESETS[presetId] ?? THEME_STYLE_PRESETS.default;

  const light = mergeLayer(preset.light, style.vars?.light);
  const dark = mergeLayer(preset.dark, style.vars?.dark);

  const blocks: string[] = [];

  if (Object.keys(light).length > 0) {
    const body = withTailwindRadiusScale(light)
      .map(([k, v]) => `  --${k}: ${v};`)
      .join('\n');
    blocks.push(`:root {\n${body}\n}`);
  }

  if (Object.keys(dark).length > 0) {
    const body = withTailwindRadiusScale(dark)
      .map(([k, v]) => `  --${k}: ${v};`)
      .join('\n');
    blocks.push(`.dark {\n${body}\n}`);
  }

  return blocks.join('\n\n');
}