tools/eu4_clausewitz/src/overlay.mjs

// Vanilla + mod load semantics for EU4's directory-level overlay model.
//
// There is no `replace_path` entry in this mod's descriptor.mod (confirmed
// by direct inspection), so every directory here is loaded as a file-level
// overlay: vanilla's files load first, then the mod's files load on top,
// per the rules in the table below (measured against the real vanilla +
// Ab_Integro install, not assumed from EU4 documentation in general).
//
//   common/country_tags/   merge: every file loads, tags accumulate. Each
//                           file is itself a table of TAG = "path" pointers
//                           (not one-tag-per-file), so the merge unit is tag
//                           *entries inside files*, not whole files.
//   common/countries/      same-filename whole-file replace
//   history/provinces/     match by leading numeric ID, replace
//   history/countries/     match by leading 3-letter TAG, replace
//   common/cultures/       same filename replaces; different filename is
//                           spec'd to "append" — see the dedicated note on
//                           CULTURES_MODE below, this collapses to the same
//                           file-selection algorithm as `replace`.
//   (default)               same-filename replace
//
// This module never parses game *data* beyond what's needed to resolve
// country_tags pointers (which are themselves TAG = "path" pairs, so
// resolving them requires tokenizing+parsing those specific files — every
// other directory here is selected by filename alone).

import { readdir } from 'node:fs/promises';
import { join } from 'node:path';
import { tokenize } from './lexer.mjs';
import { parse } from './ast.mjs';
import { readGameText } from './codec.mjs';

const PROVINCE_ID_RE = /^(\d+)/;
const COUNTRY_TAG_RE = /^([A-Z]{3})\b/;

/**
 * @param {string} filename
 * @returns {string|null}
 */
export function extractProvinceId(filename) {
  const m = PROVINCE_ID_RE.exec(filename);
  return m ? m[1] : null;
}

/**
 * @param {string} filename
 * @returns {string|null}
 */
export function extractCountryTag(filename) {
  const m = COUNTRY_TAG_RE.exec(filename);
  return m ? m[1] : null;
}

// Static directory -> mode table. Anything not listed here defaults to
// 'replace', which is exactly what makes overlay.dir()/loadDir() work for
// any directory with zero registration: they consult this same table with
// the same fallback, nothing needs to be declared up front.
const MODE_TABLE = new Map([
  ['common/country_tags', 'merge'],
  ['history/provinces', 'province-id'],
  ['history/countries', 'country-tag'],
  ['common/cultures', 'cultures'],
]);

/**
 * @param {string} relPath - forward-slash-normalized relative path, e.g. "history/provinces"
 * @returns {'merge'|'province-id'|'country-tag'|'cultures'|'replace'}
 */
export function modeFor(relPath) {
  const normalized = relPath.replace(/\\/g, '/').replace(/\/+$/, '');
  return MODE_TABLE.get(normalized) ?? 'replace';
}

async function listFiles(dir) {
  let entries;
  try {
    entries = await readdir(dir, { withFileTypes: true });
  } catch {
    return [];
  }
  return entries
    .filter((e) => e.isFile() && e.name.toLowerCase().endsWith('.txt'))
    .map((e) => e.name);
}

// Shared by 'replace' and 'cultures' modes: key by filename, mod entries
// overlay vanilla entries on the same filename, everything else (unique to
// either side) just accumulates. This is deliberately the SAME algorithm
// for both modes — see the header note on 'cultures' above. A file unique
// to the mod under this algorithm keeps its own filename as its key, which
// is indistinguishable at the file-selection level from a true "append";
// the append/replace distinction only becomes meaningful one layer up, once
// something merges parsed culture *entries* across files sharing a
// namespace, which is out of scope for this function's job of picking
// which file wins for a given key.
function replaceByFilename(vanillaFiles, modFiles, gameDir, modDir, relPath) {
  const entries = new Map();
  const ambiguities = [];

  for (const name of vanillaFiles) {
    entries.set(name, { path: join(gameDir, name), layer: 'vanilla' });
  }
  for (const name of modFiles) {
    entries.set(name, { path: join(modDir, name), layer: 'mod' });
  }

  return { entries, ambiguities };
}

// Shared by 'province-id' and 'country-tag' modes: key by a prefix
// extracted from the filename. Mod wins over vanilla on the same key
// (normal overlay). Two different filenames resolving to the SAME key
// within the same layer (mod-vs-mod, or vanilla-vs-vanilla) is an
// ambiguity: EU4 loads both and which one wins depends on filesystem
// order, so this is reported rather than silently resolved. Confirmed real
// cases: history/countries/ has CMP - Rewa Kantha.txt + CMP - RewaKantha.txt,
// and SOF - Segu.txt + SOF - Sofala.txt, both within the mod layer.
function replaceByExtractedKey(vanillaFiles, modFiles, gameDir, modDir, relPath, extractKey) {
  const entries = new Map();
  const ambiguities = [];
  // Track, per layer, every filename seen for a given key so within-layer
  // collisions can be reported with all competing paths.
  const seenPerLayer = new Map(); // key -> { vanilla: string[], mod: string[] }

  function note(key, layer, filename) {
    let rec = seenPerLayer.get(key);
    if (!rec) {
      rec = { vanilla: [], mod: [] };
      seenPerLayer.set(key, rec);
    }
    rec[layer].push(filename);
  }

  for (const name of vanillaFiles) {
    const key = extractKey(name);
    if (key === null) continue;
    note(key, 'vanilla', name);
    if (!entries.has(key)) {
      entries.set(key, { path: join(gameDir, name), layer: 'vanilla' });
    }
  }
  for (const name of modFiles) {
    const key = extractKey(name);
    if (key === null) continue;
    note(key, 'mod', name);
    const existing = entries.get(key);
    if (!existing || existing.layer === 'vanilla') {
      // First mod claim for this key, or overlaying a vanilla entry: normal
      // overlay, mod wins.
      entries.set(key, { path: join(modDir, name), layer: 'mod' });
    }
    // Else: a different mod filename already claimed this key — leave the
    // first mod claim active (deterministic single winner for callers that
    // just want ONE node), the ambiguity itself is reported below from
    // seenPerLayer so nothing is silently dropped from view.
  }

  for (const [key, rec] of seenPerLayer) {
    if (rec.vanilla.length > 1) {
      ambiguities.push({
        dir: relPath,
        key,
        layer: 'vanilla',
        paths: rec.vanilla.map((n) => join(gameDir, n)),
      });
    }
    if (rec.mod.length > 1) {
      ambiguities.push({
        dir: relPath,
        key,
        layer: 'mod',
        paths: rec.mod.map((n) => join(modDir, n)),
      });
    }
  }

  return { entries, ambiguities };
}

// country_tags is a genuine special case: the files themselves are not
// game-data records, they are TAG = "relative/path" pointer tables. The
// merge unit is tag *entries*, and "loading" a tag means resolving its
// pointer against common/ and reading THAT file's text — which is why this
// mode alone needs to tokenize+parse eagerly (every other mode only reads
// bytes for whichever winning file a caller actually asks for, deferred to
// index.mjs; this one has to look inside every tags file just to know what
// keys exist at all).
async function loadCountryTagsMerge(gameDir, modDir, relPath, gameRoot, modRoot) {
  const entries = new Map();
  const ambiguities = [];

  async function ingest(dir, root, layer, filenames) {
    for (const name of filenames) {
      const path = join(dir, name);
      const { text } = await readGameText(path);
      const tokens = tokenize(text);
      const tree = parse(tokens);
      for (const item of tree.items) {
        if (item.kind !== 'pair' || item.value.type !== 'scalar' || !item.value.token) continue;
        const tag = item.keyToken.value;
        const pointer = item.value.token.value; // e.g. "countries/Rebels.txt"
        const resolvedPath = join(root, 'common', ...pointer.split(/[\\/]/));
        const existing = entries.get(tag);
        if (existing && existing.layer === layer) {
          ambiguities.push({
            dir: relPath,
            key: tag,
            layer,
            paths: [existing.path, resolvedPath],
          });
          continue;
        }
        entries.set(tag, { path: resolvedPath, layer });
      }
    }
  }

  const vanillaFiles = await listFiles(gameDir);
  const modFiles = await listFiles(modDir);
  await ingest(gameDir, gameRoot, 'vanilla', vanillaFiles);
  await ingest(modDir, modRoot, 'mod', modFiles); // mod entries overlay vanilla on same tag, by insertion after

  return { entries, ambiguities };
}

/**
 * Resolve which files win for one directory, across vanilla + mod, per the
 * table above. Does NOT read file contents (except for 'merge' mode, which
 * must look inside country_tags files to find their tag keys at all) —
 * callers that need text/bom/encoding should read the winning `path` via
 * codec.mjs themselves; index.mjs does this when building Nodes.
 *
 * @param {{ gameRoot: string, modRoot: string, relPath: string }} spec
 * @returns {Promise<{ entries: Map<string, {path:string, layer:'vanilla'|'mod'}>, ambiguities: Array }>}
 */
export async function loadDir({ gameRoot, modRoot, relPath }) {
  const normalized = relPath.replace(/\\/g, '/').replace(/\/+$/, '');
  const gameDir = join(gameRoot, normalized);
  const modDir = join(modRoot, normalized);
  const mode = modeFor(normalized);

  if (mode === 'merge') {
    return loadCountryTagsMerge(gameDir, modDir, normalized, gameRoot, modRoot);
  }

  const vanillaFiles = await listFiles(gameDir);
  const modFiles = await listFiles(modDir);

  if (mode === 'province-id') {
    return replaceByExtractedKey(vanillaFiles, modFiles, gameDir, modDir, normalized, extractProvinceId);
  }
  if (mode === 'country-tag') {
    return replaceByExtractedKey(vanillaFiles, modFiles, gameDir, modDir, normalized, extractCountryTag);
  }
  // 'replace' and 'cultures' share the same file-selection algorithm — see
  // the note on replaceByFilename above for why.
  return replaceByFilename(vanillaFiles, modFiles, gameDir, modDir, normalized);
}

/**
 * Zero-config accessor: resolves any directory's overlay without it being
 * registered anywhere. Internally this is exactly `loadDir` consulting the
 * same MODE_TABLE-with-'replace'-fallback that every other path uses.
 *
 * @param {string} relPath
 * @param {{ gameRoot: string, modRoot: string }} roots
 */
export function dir(relPath, roots) {
  return loadDir({ gameRoot: roots.gameRoot, modRoot: roots.modRoot, relPath });
}

/**
 * A collection over a resolved directory: identical API for every
 * directory, parsing files lazily (on first access to a given key) via the
 * injected `parseFn` so this module never needs to import node.mjs (keeping
 * the dependency direction one-way: index.mjs wires node construction in).
 *
 * @param {Map<string, {path:string, layer:'vanilla'|'mod'}>} entries
 * @param {(entry: {path:string, layer:'vanilla'|'mod'}) => Promise<any>} parseFn
 */
export function makeCollection(entries, parseFn) {
  const cache = new Map();

  async function resolve(key) {
    if (cache.has(key)) return cache.get(key);
    const entry = entries.get(key);
    if (!entry) throw new Error(`collection.get(): no entry for key "${key}"`);
    const node = await parseFn(entry);
    cache.set(key, node);
    return node;
  }

  return {
    get(key) {
      return resolve(key);
    },
    async all() {
      const out = [];
      for (const key of entries.keys()) out.push(await resolve(key));
      return out;
    },
    async where(predicate) {
      const nodes = await this.all();
      if (typeof predicate === 'function') return nodes.filter(predicate);
      return nodes.filter((node) => Object.entries(predicate).every(([k, v]) => node.get(k) === v));
    },
  };
}