// Game variants offered on New Game, and the Stage 15 gating of that choice by the
// languages the sign-in service supports. Kept out of the .svelte screen so the
// gating is unit-testable (the project's node-env Vitest layer).

import type { MessageKey } from './i18n/index.svelte';
import type { Variant } from './model';

// VariantOption is a selectable game variant with its i18n label key.
export interface VariantOption {
  id: Variant;
  label: MessageKey;
}

// ALL_VARIANTS lists every variant in display order.
export const ALL_VARIANTS: VariantOption[] = [
  { id: 'english', label: 'new.english' },
  { id: 'russian_scrabble', label: 'new.russian' },
  { id: 'erudit', label: 'new.erudit' },
];

// VARIANT_LANGUAGE maps each variant to its game language. en -> English;
// ru -> Russian + Эрудит.
export const VARIANT_LANGUAGE: Record<Variant, 'en' | 'ru'> = { english: 'en', russian_scrabble: 'ru', erudit: 'ru' };

// availableVariants gates ALL_VARIANTS by the session's supported languages. An empty
// or absent set is ungated (a web/legacy session without a declared set), returning
// every variant.
export function availableVariants(supportedLanguages: string[] | undefined): VariantOption[] {
  const langs = supportedLanguages ?? [];
  if (langs.length === 0) return ALL_VARIANTS;
  return ALL_VARIANTS.filter((v) => langs.includes(VARIANT_LANGUAGE[v.id]));
}