// Design-system registry. Scans <projectRoot>/design-systems/* for DESIGN.md
// files. Title comes from the first H1. Category comes from a
// `> Category: <name>` blockquote line beneath the H1. Summary is the first
// paragraph between the H1 and the next heading (Category line stripped).

import { readdir, readFile, stat } from 'node:fs/promises';
import path from 'node:path';

export async function listDesignSystems(root) {
  const out = [];
  let entries = [];
  try {
    entries = await readdir(root, { withFileTypes: true });
  } catch {
    return out;
  }
  for (const entry of entries) {
    if (!entry.isDirectory()) continue;
    const designPath = path.join(root, entry.name, 'DESIGN.md');
    try {
      const stats = await stat(designPath);
      if (!stats.isFile()) continue;
      const raw = await readFile(designPath, 'utf8');
      const titleMatch = /^#\s+(.+?)\s*$/m.exec(raw);
      const title = cleanTitle(titleMatch?.[1] ?? entry.name);
      out.push({
        id: entry.name,
        title,
        category: extractCategory(raw) ?? 'Uncategorized',
        summary: summarize(raw),
        swatches: extractSwatches(raw),
        body: raw,
      });
    } catch {
      // Skip.
    }
  }
  return out;
}

export async function readDesignSystem(root, id) {
  const file = path.join(root, id, 'DESIGN.md');
  try {
    return await readFile(file, 'utf8');
  } catch {
    return null;
  }
}

function summarize(raw) {
  const lines = raw.split(/\r?\n/);
  const firstH1 = lines.findIndex((l) => /^#\s+/.test(l));
  if (firstH1 === -1) return '';
  const afterH1 = lines.slice(firstH1 + 1);
  const nextHeading = afterH1.findIndex((l) => /^#{1,6}\s+/.test(l));
  const window = (nextHeading === -1 ? afterH1 : afterH1.slice(0, nextHeading))
    .join('\n')
    // Drop the Category metadata line — it's surfaced separately.
    .replace(/^>\s*Category:.*$/gim, '')
    .replace(/^>\s*/gm, '')
    .trim();
  return window.split(/\n\n/)[0]?.slice(0, 240) ?? '';
}

function extractCategory(raw) {
  const m = /^>\s*Category:\s*(.+?)\s*$/im.exec(raw);
  return m?.[1];
}

// Strip boilerplate like "Design System Inspired by Cohere" → "Cohere" so
// the picker dropdown reads cleanly. Hand-authored titles that don't match
// the pattern (e.g. "Neutral Modern") pass through unchanged.
function cleanTitle(raw) {
  return raw
    .replace(/^Design System (Inspired by|for)\s+/i, '')
    .trim();
}

/**
 * Pull 4 representative colors from a DESIGN.md so the picker can render
 * a tiny swatch row next to each system. Order: [bg, support, fg, accent].
 *
 * The shape is deliberately compact — one accent + one background + one
 * fg + one supporting tone — so the row reads like a brand mark even at
 * thumbnail scale. Picked greedily by token-name hints (matches the
 * heuristics in design-system-preview.js so the strip and the showcase
 * agree on which colors the system "is").
 *
 * @param {string} raw  Markdown body of DESIGN.md
 * @returns {string[]}  Up to 4 hex strings; [] if extraction fails.
 */
function extractSwatches(raw) {
  const colors = [];
  const seen = new Set();
  function push(name, value) {
    const cleanName = name.replace(/[*_`]+/g, '').replace(/\s+/g, ' ').trim().toLowerCase();
    const v = normalizeHex(value);
    if (!v || cleanName.length > 60) return;
    const key = `${cleanName}|${v}`;
    if (seen.has(key)) return;
    seen.add(key);
    colors.push({ name: cleanName, value: v });
  }
  // Form A: "- **Background:** `#FAFAFA`"
  const reA = /^[\s>*-]*\**\s*([A-Za-z][A-Za-z0-9 /&()+_-]{1,40}?)\s*\**\s*[:：]\s*`?(#[0-9a-fA-F]{3,8})/gm;
  let m;
  while ((m = reA.exec(raw)) !== null) push(m[1], m[2]);
  // Form B: "**Stripe Purple** (`#533afd`)"
  const reB = /\*\*([A-Za-z][A-Za-z0-9 /&()+_-]{1,40}?)\*\*\s*\(?\s*`?(#[0-9a-fA-F]{3,8})/g;
  while ((m = reB.exec(raw)) !== null) push(m[1], m[2]);
  if (colors.length === 0) return [];

  function pick(hints) {
    for (const h of hints) {
      const found = colors.find((c) => c.name.includes(h));
      if (found) return found.value;
    }
    return null;
  }
  function isNeutral(hex) {
    if (!/^#[0-9a-f]{6}$/.test(hex)) return false;
    const r = parseInt(hex.slice(1, 3), 16);
    const g = parseInt(hex.slice(3, 5), 16);
    const b = parseInt(hex.slice(5, 7), 16);
    return Math.max(r, g, b) - Math.min(r, g, b) < 10;
  }

  const bg =
    pick(['page background', 'background', 'canvas', 'paper', 'surface'])
    ?? '#ffffff';
  const fg =
    pick(['heading', 'foreground', 'ink', 'fg', 'text', 'navy', 'graphite'])
    ?? '#111111';
  const accent =
    pick(['primary brand', 'brand primary', 'accent', 'brand', 'primary'])
    ?? colors.find((c) => !isNeutral(c.value))?.value
    ?? colors[0]?.value
    ?? '#888888';
  const support =
    pick(['border', 'divider', 'rule', 'muted', 'secondary', 'subtle'])
    ?? colors.find(
      (c) => isNeutral(c.value) && c.value !== bg && c.value !== fg,
    )?.value
    ?? '#cccccc';

  return [bg, support, fg, accent];
}

function normalizeHex(raw) {
  if (typeof raw !== 'string') return null;
  const m = /^#([0-9a-fA-F]{3,8})$/.exec(raw.trim());
  if (!m) return null;
  let hex = m[1];
  if (hex.length === 3) hex = hex.split('').map((c) => c + c).join('');
  if (hex.length === 4) hex = hex.split('').map((c) => c + c).join('').slice(0, 8);
  return '#' + hex.toLowerCase();
}