#!/usr/bin/env node
// Every path in this repo that a chapter names in backticks must exist.
//
// The book teaches out of `template/`: it says "open
// `template/server/index.js`", "the aliases are in `template/client/vite.config.js`",
// "your tables go in `template/server/db/schema.sql`". None of that is a markdown
// link, so `checkLinks.js` never looks at it — and none of it is code, so nothing
// else does either. Rename one template file and four chapters quietly point at
// nothing, which is the exact rot this repo exists to be immune to.
//
// This is the cheap half of "is the book still true", and it is honest about
// being only the half a machine can answer. Whether a paragraph has become wrong
// about a file that still exists is a reviewer's job (MODULE_SYSTEM.md §2.10).
//
// ── What counts as a claim about this repo ────────────────────────────────────
//
// An inline code span whose text begins with one of this repo's own top-level
// directories, `ANCHORS` below. That is what makes the check answerable: a
// chapter also quotes `server/index.js` loosely, and `sidecar/src/store.rs`,
// which lives in another repo entirely and cannot be resolved here. Anchoring on
// our own directory names means every token this check reads is a claim it can
// actually settle.
//
// **The anchors are stated, not derived from the tree**, and that is deliberate
// for the reason core's own build guard states it (MODULE_API.md §3.6): a list
// derived from what exists cannot fail when what exists changes. Rename
// `template/` and a derived anchor set would simply stop checking every
// `template/…` mention in the book, silently, at the moment they all became
// wrong. So the anchors are written down — and each one must exist, or this check
// fails. An anchor that has stopped matching is a check that has stopped
// checking, the same rule the identifier exemptions in core's CI follow.
//
// Fenced blocks are excluded (`lib/markdown.js`). A fence in this book is often a
// listing of the reader's own future tree, and their files are not ours.
//
// Usage: node scripts/checkChapterPaths.js        (from the repo root)

const fs = require('fs')
const path = require('path')

const { codeSpans } = require('./lib/markdown')

const ROOT = path.resolve(__dirname, '..')

// This repo's own top-level directories. See the note above on why this is a list
// and not a directory scan.
const ANCHORS = ['template/', 'book/', 'scripts/', 'ci/']

const SKIP_DIRS = new Set(['.git', 'node_modules', 'dist'])

/** Every markdown file in the repo, repo-relative, sorted. */
function markdownFiles(dir = ROOT, out = []) {
  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
    if (entry.isDirectory()) {
      if (SKIP_DIRS.has(entry.name)) continue
      markdownFiles(path.join(dir, entry.name), out)
    } else if (entry.name.toLowerCase().endsWith('.md')) {
      out.push(path.relative(ROOT, path.join(dir, entry.name)).split(path.sep).join('/'))
    }
  }
  return out.sort()
}

/**
 * The repo paths a document claims, from its inline code spans.
 *
 * A span is a claim when it starts with an anchor and names something a
 * filesystem could answer for. Three kinds are skipped, each because the answer
 * would be "no" for a reason that is not a mistake:
 *
 *   • a placeholder — `template/<id>/…`, `scripts/*.js` — which is a shape rather
 *     than a path;
 *   • a span with whitespace in it, which is a phrase or a command line
 *     (`npm ci --prefix template/server` is not a path and its first word is not
 *     an anchor either, but a span like `cd template/server && npm test` would
 *     slip through on its first token without this);
 *   • trailing prose punctuation, stripped rather than skipped, so `template/`
 *     ending a sentence still resolves.
 */
function claimedPaths(markdown) {
  const found = []
  for (const { text, line } of codeSpans(markdown)) {
    const token = text.trim()
    if (/\s/.test(token)) continue
    if (!ANCHORS.some((a) => token.startsWith(a))) continue
    if (/[<>*?]|\.\.\./.test(token)) continue
    // A path may legitimately end in `/` (a directory); anything else in this set
    // is the sentence around it, not part of the name.
    const cleaned = token.replace(/[.,;:)\]]+$/, '')
    if (cleaned) found.push({ path: cleaned, line })
  }
  return found
}

/** Everything wrong, as sentences. Empty means every claim resolves. */
function problems({ claims, exists }) {
  const out = []

  for (const anchor of ANCHORS) {
    const dir = anchor.replace(/\/$/, '')
    if (!exists(dir)) {
      out.push(
        `${anchor} is listed as an anchor and does not exist. ` +
        'Either restore it or update ANCHORS — an anchor that matches nothing is a ' +
        'check that has silently stopped checking.',
      )
    }
  }

  for (const { file, path: claimed, line } of claims) {
    if (!exists(claimed)) {
      out.push(`${file}:${line}: no such path — ${claimed}`)
    }
  }

  return out
}

module.exports = { ANCHORS, claimedPaths, problems, markdownFiles }

if (require.main !== module) return

const files = markdownFiles()
const claims = []
for (const file of files) {
  const text = fs.readFileSync(path.join(ROOT, file), 'utf8')
  for (const claim of claimedPaths(text)) claims.push({ file, ...claim })
}

const exists = (p) => fs.existsSync(path.join(ROOT, p))
const found = problems({ claims, exists })

if (found.length) {
  console.error(`\ncheckChapterPaths: ${found.length} problem(s):\n`)
  for (const p of found) console.error(`  - ${p}`)
  console.error('')
  process.exit(1)
}

console.log(
  `checkChapterPaths: ${claims.length} path(s) claimed across ${files.length} markdown file(s) — all present.`,
)