/**
 * Language persistence for pi-mcp-market.
 *
 * Stores the user's language preference to
 * `<agentDir>/pi-mcp-market/language.json`.
 *
 * Auto-detection order:
 * 1. Saved language config file (explicit user choice persists)
 * 2. PI_MCP_MARKET_LANG env var override (for scripting)
 * 3. LANG env var — if starts with "zh", picks "zh", else "en"
 * 4. Default: "zh"
 */
import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { join } from "node:path";
import { getAgentDir } from "./config.ts";
import type { Lang } from "./i18n.ts";

interface LanguageConfig {
  language: Lang;
}

function getLanguageConfigPath(): string {
  return join(getAgentDir(), "pi-mcp-market", "language.json");
}

/** Detect language without I/O — pure env + fallback. */
export function detectLanguage(): Lang {
  const fromEnv = process.env.PI_MCP_MARKET_LANG;
  if (fromEnv === "zh" || fromEnv === "en") return fromEnv;
  const systemLang = process.env.LANG ?? "";
  if (systemLang.startsWith("zh")) return "zh";
  return "en";
}

/** Load persisted language; on missing/corrupt → auto-detect. */
export function loadLanguage(): Lang {
  const path = getLanguageConfigPath();
  if (!existsSync(path)) return detectLanguage();
  try {
    const raw = readFileSync(path, "utf8");
    const parsed = JSON.parse(raw) as LanguageConfig;
    if (parsed.language === "zh" || parsed.language === "en") return parsed.language;
    return detectLanguage();
  } catch {
    return detectLanguage();
  }
}

/** Persist a language choice so it survives restarts. */
export function saveLanguage(lang: Lang): void {
  const path = getLanguageConfigPath();
  const dir = join(getAgentDir(), "pi-mcp-market");
  if (!existsSync(dir)) {
    mkdirSync(dir, { recursive: true });
  } else {
    // dir already exists
  }
  writeFileSync(path, JSON.stringify({ language: lang } as LanguageConfig, null, 2) + "\n", "utf8");
}