#!/usr/bin/env node
// Generate docs/INDEX.md from the front-matter and headings of every
// .md file under docs/. Pure Node 20 — no external dependencies.
//
// Usage: `npm run docs:index` (or `node scripts/generate-docs-index.mjs`).
//
// Idempotent: rewriting INDEX.md from the same inputs produces identical
// output (apart from the generation date in the header), so the script
// is safe to run repeatedly and in pre-commit hooks.

import { readdir, readFile, writeFile } from 'node:fs/promises';
import { join, relative, basename, sep } from 'node:path';
import { fileURLToPath } from 'node:url';

const SCRIPT_DIR = fileURLToPath(new URL('.', import.meta.url));
const REPO_ROOT = join(SCRIPT_DIR, '..');
const DOCS_DIR = join(REPO_ROOT, 'docs');
const INDEX_PATH = join(DOCS_DIR, 'INDEX.md');

// Paths (relative to repo root, forward-slashed) that the index should
// skip entirely. Templates and archived plans aren't useful in the live
// roster; sidecar files prefixed with `_` are personal Obsidian scratch.
const EXCLUDE_PATTERNS = [
  /^docs\/adr\/templates\//,
  /^docs\/adr\/README\.md$/,
  /\/_[^/]+\.md$/,
  /^docs\/INDEX\.md$/,
  /^docs\/old\//,
];

async function walk(dir) {
  const entries = await readdir(dir, { withFileTypes: true });
  const files = [];
  for (const e of entries) {
    const full = join(dir, e.name);
    if (e.isDirectory()) {
      files.push(...(await walk(full)));
    } else if (e.isFile() && e.name.endsWith('.md')) {
      files.push(full);
    }
  }
  return files;
}

// Minimal YAML front-matter parser. Front-matter in this repo is restricted
// to flat `key: value` pairs, so a hand-rolled parser is enough — and
// keeps the script dependency-free.
function parseFrontMatter(content) {
  if (!content.startsWith('---\n')) return { data: {}, body: content };
  const end = content.indexOf('\n---\n', 4);
  if (end === -1) return { data: {}, body: content };
  const block = content.slice(4, end);
  const data = {};
  for (const raw of block.split('\n')) {
    const line = raw.trim();
    if (!line || line.startsWith('#')) continue;
    const m = line.match(/^([A-Za-z][\w-]*)\s*:\s*(.*?)\s*$/);
    if (!m) continue;
    let val = m[2];
    if (
      (val.startsWith('"') && val.endsWith('"')) ||
      (val.startsWith("'") && val.endsWith("'"))
    ) {
      val = val.slice(1, -1);
    }
    data[m[1]] = val;
  }
  return { data, body: content.slice(end + 5) };
}

function extractFirstH1(text) {
  const m = text.match(/^#\s+(.+?)\s*$/m);
  return m ? m[1] : null;
}

// For Nygard-style ADRs the status lives under a `## Status` heading
// instead of YAML front-matter. Pull the first non-empty line after the
// heading so the index can still show it.
function extractStatusSection(text) {
  const m = text.match(/^##\s+Status\s*\n+([^\n#].*?)(?:\n|$)/m);
  return m ? m[1].trim() : null;
}

function isExcluded(relPath) {
  return EXCLUDE_PATTERNS.some((rx) => rx.test(relPath));
}

// Map a path under docs/ to one of the four named sections, or "Other".
// Folder-based first; root-level docs fall back to a name-prefix rule
// so legacy `scrum4me-*.md` files still surface under Specs until the
// docs-restructure migrates them into `docs/specs/`.
function categorize(relPath) {
  const parts = relPath.split('/');
  if (parts[0] !== 'docs') return 'Other';
  if (parts.length === 2) {
    return /^scrum4me-/.test(parts[1]) ? 'Specs' : 'Other';
  }
  const sub = parts[1];
  if (sub === 'adr') return 'ADRs';
  if (sub === 'specs') return 'Specs';
  if (sub === 'plans') return 'Plans';
  if (sub === 'patterns') return 'Patterns';
  return 'Other';
}

function adrNumber(filename) {
  const m = filename.match(/^(\d{4})-/);
  return m ? parseInt(m[1], 10) : null;
}

function escapePipe(s) {
  return String(s).replace(/\|/g, '\\|');
}

async function main() {
  const files = await walk(DOCS_DIR);
  const docs = [];

  for (const full of files) {
    const rel = relative(REPO_ROOT, full).split(sep).join('/');
    if (isExcluded(rel)) continue;

    const content = await readFile(full, 'utf8');
    const { data, body } = parseFrontMatter(content);
    if (data.archived === 'true') continue;

    const title =
      data.title || extractFirstH1(body) || basename(full, '.md');
    const status = data.status || extractStatusSection(body) || '';
    const date = data.date || data.last_updated || '';
    const linkPath = './' + rel.replace(/^docs\//, '');
    const category = categorize(rel);

    docs.push({
      rel,
      title,
      status,
      date,
      linkPath,
      category,
      basename: basename(full),
    });
  }

  const groups = { ADRs: [], Specs: [], Plans: [], Patterns: [], Other: [] };
  for (const d of docs) {
    if (groups[d.category]) groups[d.category].push(d);
  }

  groups.ADRs.sort((a, b) => {
    const na = adrNumber(a.basename) ?? 9999;
    const nb = adrNumber(b.basename) ?? 9999;
    if (na !== nb) return na - nb;
    return a.basename.localeCompare(b.basename);
  });
  for (const k of ['Specs', 'Plans', 'Patterns', 'Other']) {
    groups[k].sort((a, b) => a.rel.localeCompare(b.rel));
  }

  const lines = [];
  lines.push(
    '<!-- Generated by scripts/generate-docs-index.mjs. Do not edit by hand. Run `npm run docs:index`. -->'
  );
  lines.push('');
  lines.push('# Documentation Index');
  lines.push('');
  lines.push(
    `Auto-generated on ${new Date().toISOString().slice(0, 10)} from front-matter and headings.`
  );
  lines.push('');

  // --- ADRs ---
  lines.push('## Architecture Decision Records');
  lines.push('');
  if (groups.ADRs.length === 0) {
    lines.push('_No ADRs yet._');
    lines.push('');
  } else {
    lines.push('| # | Title | Status |');
    lines.push('|---|---|---|');
    for (const d of groups.ADRs) {
      const n = adrNumber(d.basename);
      const num = n !== null ? String(n).padStart(4, '0') : '—';
      lines.push(
        `| ${num} | [${escapePipe(d.title)}](${d.linkPath}) | ${escapePipe(d.status || '—')} |`
      );
    }
    lines.push('');
  }

  // --- Specs ---
  lines.push('## Specifications');
  lines.push('');
  if (groups.Specs.length === 0) {
    lines.push('_No specs yet._');
    lines.push('');
  } else {
    lines.push('| Title | Status | Updated |');
    lines.push('|---|---|---|');
    for (const d of groups.Specs) {
      lines.push(
        `| [${escapePipe(d.title)}](${d.linkPath}) | ${escapePipe(d.status || '—')} | ${escapePipe(d.date || '—')} |`
      );
    }
    lines.push('');
  }

  // --- Plans (with archive subsection) ---
  lines.push('## Plans');
  lines.push('');
  const plansActive = groups.Plans.filter((d) => !d.rel.includes('/archive/'));
  const plansArchive = groups.Plans.filter((d) => d.rel.includes('/archive/'));
  if (plansActive.length === 0) {
    lines.push('_No active plans._');
    lines.push('');
  } else {
    lines.push('| Title | Status | Updated |');
    lines.push('|---|---|---|');
    for (const d of plansActive) {
      lines.push(
        `| [${escapePipe(d.title)}](${d.linkPath}) | ${escapePipe(d.status || '—')} | ${escapePipe(d.date || '—')} |`
      );
    }
    lines.push('');
  }
  if (plansArchive.length > 0) {
    lines.push('### Archive');
    lines.push('');
    lines.push('| Title | Updated |');
    lines.push('|---|---|');
    for (const d of plansArchive) {
      lines.push(
        `| [${escapePipe(d.title)}](${d.linkPath}) | ${escapePipe(d.date || '—')} |`
      );
    }
    lines.push('');
  }

  // --- Patterns ---
  lines.push('## Patterns');
  lines.push('');
  if (groups.Patterns.length === 0) {
    lines.push('_No patterns yet._');
    lines.push('');
  } else {
    lines.push('| Title | Status | Updated |');
    lines.push('|---|---|---|');
    for (const d of groups.Patterns) {
      lines.push(
        `| [${escapePipe(d.title)}](${d.linkPath}) | ${escapePipe(d.status || '—')} | ${escapePipe(d.date || '—')} |`
      );
    }
    lines.push('');
  }

  // --- Other (catches design/, api/, runbooks/, etc. until they get
  //     dedicated sections after the docs-restructure) ---
  if (groups.Other.length > 0) {
    lines.push('## Other Docs');
    lines.push('');
    lines.push('| Title | Path | Status | Updated |');
    lines.push('|---|---|---|---|');
    for (const d of groups.Other) {
      lines.push(
        `| [${escapePipe(d.title)}](${d.linkPath}) | \`${d.rel.replace(/^docs\//, '')}\` | ${escapePipe(d.status || '—')} | ${escapePipe(d.date || '—')} |`
      );
    }
    lines.push('');
  }

  const out = lines.join('\n');
  await writeFile(INDEX_PATH, out, 'utf8');
  console.log(`Wrote ${relative(REPO_ROOT, INDEX_PATH)} (${docs.length} docs indexed)`);
}

main().catch((err) => {
  console.error(err);
  process.exit(1);
});