/**
 * scripts/build-region-keys.mjs — build the deterministic region-key manifest.
 *
 * Region ownership flips from whole-country (ISO_A3) to individual sub-region
 * granularity, but the LLM and the persisted `Nation.territory` list need a
 * *stable, human-readable, globally unique* identifier per sub-region. Raw
 * feature ids (`FR-57`) are opaque to the model, so we mint a readable key of
 * the form:
 *
 *     <name-slug>-<4char>        e.g.  brittany-xk2a, western-alun
 *
 * where:
 *   - <name-slug> = properties.name → NFKD → strip combining marks → lowercase
 *     → a tiny fold table for the handful of letters NFKD does NOT decompose
 *     (ə ø ð đ œ ł, the only non-folding letters present in this dataset)
 *     → every non-alphanumeric run collapsed to a single '-' → leading/trailing
 *     '-' trimmed.
 *   - <4char>     = a deterministic 4-letter lowercase code derived from the
 *     feature's stable id (FNV-1a 32-bit → 4 base-26 chars). It is stable
 *     (same id → same code on every run) because the key is persisted in
 *     SQLite and shown to the LLM. Within any name-slug group (e.g. the six
 *     regions all named "Western") the 4-char codes are made distinct by
 *     re-deriving with a deterministic salt on collision, which guarantees the
 *     full key is unique across all 1,800 regions.
 *
 * Output: `public/region-keys.json` — a `{ [stableFeatureId]: regionKey }`
 * object, e.g. `{ "FR-57": "brittany-xk2a" }`, in file (stable) order. The map
 * is looked up by the client (`WorldMap`) and the server (`map`/`presets`/
 * `engine`) to join a sub-region's stable id to its readable key.
 *
 * Builtins only — deliberately NO `@turf`/geojson import (importing one pulls
 * `@types/geojson` into the tsc program and breaks `WorldMap.tsx`; see the
 * v0.17 changelog note). Reads the geo file with plain `JSON.parse`.
 *
 * Idempotent: a re-run rewrites a byte-identical file (no timestamps, no
 * randomness, stable feature order, deterministic hash).
 *
 * Usage: `node scripts/build-region-keys.mjs`  (or `npm run build:region-keys`).
 */
import { readFileSync, writeFileSync } from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';

const here = path.dirname(fileURLToPath(import.meta.url));
const root = path.resolve(here, '..');

/**
 * Letters present in the dataset that NFKD does NOT decompose, and their
 * single/multi-letter ASCII equivalents, so their slugs aren't hyphen-soup.
 * Kept deliberately tiny + deterministic (only the six that actually occur).
 */
const FOLD = {
  'ə': 'a', // schwa
  'ø': 'o', // o-stroke
  'ð': 'd', // eth
  'đ': 'dj', // d-stroke
  'œ': 'oe', // oe ligature
  'ł': 'l', // l-stroke
};

/**
 * Readable slug from a region name. NFKD decomposes + we strip the combining
 * marks, lowercase, fold the non-decomposing letters, collapse every other
 * non-alphanumeric run to one hyphen, and trim leading/trailing hyphens.
 */
function slug(name) {
  let s = name.normalize('NFKD').replace(/[\u0300-\u036f]/g, '');
  s = s.toLowerCase();
  s = [...s].map((ch) => FOLD[ch] ?? ch).join('');
  s = s.replace(/[^a-z0-9]+/g, '-');
  s = s.replace(/^-+|-+$/g, '');
  return s;
}

/** FNV-1a 32-bit — a tiny, stable, pure string hash. */
function fnv1a32(str) {
  let h = 0x811c9dc5;
  for (let i = 0; i < str.length; i++) {
    h ^= str.charCodeAt(i);
    h = (h * 0x01000193) >>> 0;
  }
  return h >>> 0;
}

/** Spread a 32-bit hash across four lowercase letters (base 26 per byte). */
function code4(h) {
  let out = '';
  for (let i = 0; i < 4; i++) {
    out += String.fromCharCode(97 + ((((h >>> (i * 8)) & 0xff) % 26)));
  }
  return out;
}

/** The 4-char code for an id, deterministically salted on within-group collision. */
function codeFor(id, used) {
  let code = code4(fnv1a32(id));
  let attempt = 0;
  while (used.has(code)) {
    attempt += 1;
    code = code4(fnv1a32(`${id}#${attempt}`));
  }
  return code;
}

// --- load the region geo (plain parse; no geojson types) ---
const geoFile = path.join(root, 'public', 'regions.geo.json');
const geo = JSON.parse(readFileSync(geoFile, 'utf8'));
const features = Array.isArray(geo?.features) ? geo.features : [];

if (features.length !== 1800) {
  throw new Error(`expected 1,800 regions, got ${features.length} — regions.geo.json changed; re-verify the region-key contract`);
}

// Group features by their (computed) name-slug, preserving file order, so the
// within-slug 4-char uniqueness resolution below is deterministic.
const groups = new Map(); // slug -> array of { id }
for (const f of features) {
  const id = f.id == null ? '' : String(f.id);
  const name = f.properties?.name;
  if (!id || typeof name !== 'string') {
    throw new Error(`region with id ${JSON.stringify(id)} has no usable name`);
  }
  const s = slug(name);
  if (!groups.has(s)) groups.set(s, []);
  groups.get(s).push({ id });
}

// Assign keys, resolving 4-char collisions within each slug group.
const manifest = {};
for (const [s, ids] of groups) {
  const used = new Set();
  for (const { id } of ids) {
    manifest[id] = `${s}-${codeFor(id, used)}`;
    used.add(manifest[id].slice(-4));
  }
}

// --- hard assertions (the test re-checks these against the committed file) ---
const keys = Object.values(manifest);
if (new Set(keys).size !== keys.length) {
  throw new Error(`region-key collision: ${keys.length} keys but only ${new Set(keys).size} unique`);
}
const KEY_RE = /^[a-z0-9]+(?:-[a-z0-9]+)*-[a-z]{4}$/;
for (const k of keys) {
  if (!KEY_RE.test(k) || !k.includes('-')) {
    throw new Error(`malformed region key: ${JSON.stringify(k)}`);
  }
}

// --- write idempotently (stable order = insertion order = file order) ---
const out = JSON.stringify(manifest, null, 2) + '\n';
writeFileSync(path.join(root, 'public', 'region-keys.json'), out);

const western = Object.entries(manifest)
  .filter(([, k]) => k.startsWith('western-'))
  .sort((a, b) => a[0] < b[0] ? -1 : 1);
console.log(`[build-region-keys] wrote public/region-keys.json — ${keys.length} unique region keys (1,800 expected)`);
console.log(`  western group: ${western.map(([id, k]) => `${id}=${k}`).join(', ')}`);