// Sub-national region data: loaded ONCE at server boot from
// `public/regions.geo.json` (dev) or `dist/regions.geo.json` (prod — Vite copies
// `public/` → `dist/`). It builds two in-memory maps that power the
// sub-region-level territory model (v0.19):
//
//   - `regionIndex`     : region id → { name, parent } (parent = ISO_A3 country)
//   - `regionsByCountry`: ISO_A3 country → array of its region ids
//
// These are used to (a) expand a nation's ISO_A3 territory into its sub-region
// ids at game creation / load-time migration, and (b) hand the LLM a human
// name for each region id it may reference in a TurnResult.
//
// This is deliberately turf-free (plain `JSON.parse`): importing `@turf/*`
// would pull `@types/geojson` into the tsc program and break `WorldMap.tsx`
// (see AGENTS.md / the v0.17 changelog note on the geojson type gotcha).
//
// The server must still boot and the app still work when the geo file is
// missing or unreadable: the maps stay empty, `hasRegionData()` stays false,
// and the territory model gracefully degrades to whole-country ISO_A3 codes
// (the pre-v0.19 behavior). Nothing here ever throws.
import { existsSync, readFileSync } from 'node:fs';
import path from 'node:path';
import type { GameState } from '../shared/types';

/** A region's stable identity: display name + the parent country's ISO_A3. */
export interface RegionInfo {
  name: string;
  parent: string;
}

let regionIndex: Record<string, RegionInfo> = {};
let regionsByCountry: Record<string, string[]> = {};
let loaded = false;

/** True once the region geo has been loaded successfully. */
export function hasRegionData(): boolean {
  return loaded;
}

/**
 * (Re)build the in-memory region maps from the region geo. Idempotent: a second
 * call is a no-op. Tries `<root>/public/regions.geo.json` first (dev), then
 * `<root>/dist/regions.geo.json` (prod, where Vite copies `public/` → `dist/`).
 * If no candidate file is found, or it fails to parse, the maps stay empty and
 * `hasRegionData()` stays false (graceful fallback to ISO_A3) — never throws.
 */
export function loadRegions(root: string): void {
  if (loaded) return;
  const candidates = [
    path.join(root, 'public', 'regions.geo.json'),
    path.join(root, 'dist', 'regions.geo.json'),
  ];
  const file = candidates.find((c) => existsSync(c));
  if (!file) {
    console.warn(
      '[history] regions.geo.json not found (tried: ' + candidates.join(', ') +
        ') — falling back to whole-country (ISO_A3) territory',
    );
    return;
  }
  try {
    const geo = JSON.parse(readFileSync(file, 'utf8')) as {
      features?: Array<{
        id?: string | number;
        properties?: { name?: string; parent?: string };
      }>;
    };
    const index: Record<string, RegionInfo> = {};
    const byCountry: Record<string, string[]> = {};
    for (const f of geo.features ?? []) {
      const id = f.id == null ? '' : String(f.id);
      const parent = typeof f.properties?.parent === 'string' ? f.properties.parent : '';
      const name = typeof f.properties?.name === 'string' ? f.properties.name : '';
      if (!id || !parent) continue;
      index[id] = { name, parent };
      (byCountry[parent] ??= []).push(id);
    }
    regionIndex = index;
    regionsByCountry = byCountry;
    loaded = Object.keys(index).length > 0;
  } catch (e) {
    console.warn('[history] failed to load regions.geo.json (' + file + '):', e);
  }
}

/**
 * Expand a list of ISO_A3 country codes into the union of all their sub-region
 * ids (deduped, preserving first-seen order). When the region data is not
 * loaded, returns the input unchanged (graceful fallback to ISO_A3 territory).
 */
export function expandTerritory(countryCodes: string[]): string[] {
  if (!loaded) return countryCodes;
  const seen = new Set<string>();
  const out: string[] = [];
  for (const code of countryCodes) {
    for (const id of regionsByCountry[code] ?? []) {
      if (!seen.has(id)) {
        seen.add(id);
        out.push(id);
      }
    }
  }
  return out;
}

/**
 * A `{ [regionId]: "name (parent)" }` object for the given region ids, for the
 * LLM prompt. Unknown ids (not in the loaded index) are skipped. Empty when the
 * region data is not loaded.
 */
export function regionNamesFor(ids: Iterable<string>): Record<string, string> {
  const out: Record<string, string> = {};
  for (const id of ids) {
    const info = regionIndex[id];
    if (info) out[id] = `${info.name} (${info.parent})`;
  }
  return out;
}

/**
 * Human-readable label for a single region id: `id — name (parent)`, or just
 * the id when it is unknown (e.g. a region that predates the geo or a
 * synthetic id).
 */
export function regionLabel(id: string): string {
  const info = regionIndex[id];
  return info ? `${id} — ${info.name} (${info.parent})` : id;
}

/** A bare ISO_A3 country code: exactly three uppercase letters (no hyphen). */
const ISO_A3_RE = /^[A-Z]{3}$/;

/**
 * Migrate a loaded game's territory from whole-country ISO_A3 codes to
 * sub-region ids, for nations that still carry ISO_A3 entries (i.e. games
 * saved before v0.19). Each such nation's ISO_A3 codes are expanded to all
 * their sub-region ids; any entries that are already region ids (they contain
 * a hyphen, so they never match `ISO_A3_RE`) are kept. Idempotent and
 * no-op when the region data is not loaded or a nation has no ISO_A3 codes.
 * Mutates and returns the (fresh) state it is given.
 */
export function migrateTerritoryToRegions(state: GameState): GameState {
  if (!loaded) return state;
  for (const n of Object.values(state.nations)) {
    if (!n.territory.some((t) => ISO_A3_RE.test(t))) continue;
    const isoCodes = n.territory.filter((t) => ISO_A3_RE.test(t));
    const existingRegions = n.territory.filter((t) => !ISO_A3_RE.test(t));
    const merged = expandTerritory(isoCodes).concat(existingRegions);
    const seen = new Set<string>();
    const out: string[] = [];
    for (const id of merged) {
      if (!seen.has(id)) {
        seen.add(id);
        out.push(id);
      }
    }
    n.territory = out;
  }
  return state;
}

// --- Test-only seams ---------------------------------------------------------

/**
 * Test-only: reset the module state to "not loaded" (empty maps,
 * `hasRegionData()` false). Lets a test exercise the graceful-fallback path.
 */
export function _resetRegionsForTests(): void {
  regionIndex = {};
  regionsByCountry = {};
  loaded = false;
}

/**
 * Test-only: inject region maps directly (bypassing the file load) so a unit
 * test can drive `expandTerritory` / `regionNamesFor` / `regionLabel` /
 * `migrateTerritoryToRegions` against a small, deterministic fixture without
 * reading the 3.4 MB geo file. `loaded` becomes true iff `index` is non-empty.
 */
export function _setRegionsForTests(
  index: Record<string, RegionInfo>,
  byCountry: Record<string, string[]>,
): void {
  regionIndex = index;
  regionsByCountry = byCountry;
  loaded = Object.keys(index).length > 0;
}