Add inspect subcommand: read-only stats for v2 map files

Reads the map JSON, optionally loads --atlas-dir paths for name
resolution, and prints the inspector report to stdout. Missing
file, bad JSON, and missing --atlas-dir paths all produce
labelled stderr errors with exit 1.

src/cli.js

@@ -33,6 +33,7 @@ function run(argv, { out, err }) {
     encode: require('./commands/encode'),
     decode: require('./commands/decode'),
     build: require('./commands/build'),
+    inspect: require('./commands/inspect'),
   };
   const handler = handlers[head];
   if (!handler) {

src/commands/inspect.js

@@ -0,0 +1,77 @@
+'use strict';
+
+const fs = require('node:fs');
+const { loadAtlasDirs } = require('../atlas-loader');
+const { inspectMap } = require('../inspector');
+
+const USAGE = 'usage: sporel-mapper inspect <map.json> [--atlas-dir <path> ...]\n';
+
+function parseArgs(args) {
+  const positional = [];
+  const atlasDirs = [];
+  let i = 0;
+  while (i < args.length) {
+    const a = args[i];
+    if (a === '--atlas-dir') {
+      if (i + 1 >= args.length) {
+        throw new Error(`--atlas-dir requires a path`);
+      }
+      atlasDirs.push(args[i + 1]);
+      i += 2;
+    } else {
+      positional.push(a);
+      i += 1;
+    }
+  }
+  return { positional, atlasDirs };
+}
+
+function run(args, { out, err }) {
+  let parsed;
+  try {
+    parsed = parseArgs(args);
+  } catch (e) {
+    err.write(`error: ${e.message}\n${USAGE}`);
+    return 1;
+  }
+  if (parsed.positional.length !== 1) {
+    err.write(USAGE);
+    return 1;
+  }
+  const [mapPath] = parsed.positional;
+
+  let raw;
+  try {
+    raw = fs.readFileSync(mapPath, 'utf8');
+  } catch (e) {
+    err.write(`error: cannot read ${mapPath}: ${e.message}\n`);
+    return 1;
+  }
+
+  let map;
+  try {
+    map = JSON.parse(raw);
+  } catch (e) {
+    err.write(`error: ${mapPath} is not valid JSON: ${e.message}\n`);
+    return 1;
+  }
+
+  let registry = {};
+  if (parsed.atlasDirs.length > 0) {
+    try {
+      const result = loadAtlasDirs(parsed.atlasDirs);
+      registry = result.registry;
+      for (const w of result.warnings) {
+        err.write(`warning: ${w}\n`);
+      }
+    } catch (e) {
+      err.write(`error: ${e.message}\n`);
+      return 1;
+    }
+  }
+
+  out.write(inspectMap(map, registry));
+  return 0;
+}
+
+module.exports = { run };

tests/inspect.test.js

@@ -0,0 +1,53 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+const { run } = require('../src/cli');
+
+class Sink {
+  constructor() { this.chunks = []; }
+  write(s) { this.chunks.push(s); }
+  get text() { return this.chunks.join(''); }
+}
+
+const FIX_MAP = path.join(__dirname, 'fixtures', 'maps', 'inspect_sample.map.json');
+const FIX_ATLAS = path.join(__dirname, 'fixtures', 'atlases');
+
+test('inspect: prints report to stdout, exit 0', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['inspect', FIX_MAP], { out, err });
+  assert.equal(code, 0, err.text);
+  assert.match(out.text, /Map: inspect_sample/);
+  assert.match(out.text, /Roof: 4 cells flagged/);
+});
+
+test('inspect: --atlas-dir enables name resolution', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['inspect', FIX_MAP, '--atlas-dir', FIX_ATLAS], { out, err });
+  assert.equal(code, 0);
+  assert.match(out.text, /atlas_a:grass/);
+});
+
+test('inspect: missing positional arg prints usage, exit 1', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['inspect'], { out, err });
+  assert.equal(code, 1);
+  assert.match(err.text, /usage: sporel-mapper inspect/);
+});
+
+test('inspect: missing map file prints error, exit 1', () => {
+  const out = new Sink(); const err = new Sink();
+  const code = run(['inspect', '/no/such/map.json'], { out, err });
+  assert.equal(code, 1);
+  assert.match(err.text, /error: cannot read/);
+});
+
+test('inspect: invalid JSON prints error, exit 1', () => {
+  const out = new Sink(); const err = new Sink();
+  // Use a non-JSON file as bogus input
+  const reallyNotJson = path.join(__dirname, '..', 'src', 'cli.js');
+  const code = run(['inspect', reallyNotJson], { out, err });
+  assert.equal(code, 1);
+  assert.match(err.text, /error/i);
+});