import { readFileSync, writeFileSync, renameSync, existsSync, mkdirSync, copyFileSync } from 'fs';
import { resolve } from 'path';
import type { UnitsData } from '$lib/types';

// Path is relative to project root (where the server runs from)
const DATA_DIR = resolve('data');
const DEFAULTS_DIR = resolve('defaults');
const UNITS_PATH = resolve(DATA_DIR, 'units.json');
const CONFIG_PATH = resolve(DATA_DIR, 'config.json');
const DEFAULT_UNITS_PATH = resolve(DEFAULTS_DIR, 'units.json');
const DEFAULT_CONFIG_PATH = resolve(DEFAULTS_DIR, 'config.json');

export interface AppConfig {
  adminPath: string;
  /** Label shown next to the YOLO mode toggle. Defaults to "YOLO mode". */
  yoloLabel?: string;
  /** Description shown inline after the label. Defaults to "(cross-group conversions)". */
  yoloDescription?: string;
  /**
   * Controls when the YOLO mode toggle is visible to users.
   * 'auto'  — show only when more than one group is present (default)
   * 'never' — always hidden
   */
  yoloVisibility?: 'auto' | 'never';
}

/** Ensure data/ directory exists and seed missing files from defaults/. */
function ensureDataDir(): void {
  mkdirSync(DATA_DIR, { recursive: true });
  if (!existsSync(UNITS_PATH) && existsSync(DEFAULT_UNITS_PATH)) {
    copyFileSync(DEFAULT_UNITS_PATH, UNITS_PATH);
    console.log('[humor-units] First run: seeded data/units.json from defaults/units.json');
  }
  if (!existsSync(CONFIG_PATH) && existsSync(DEFAULT_CONFIG_PATH)) {
    copyFileSync(DEFAULT_CONFIG_PATH, CONFIG_PATH);
    console.log('[humor-units] First run: seeded data/config.json from defaults/config.json');
  }
}

/** Read units.json synchronously. Seeds from defaults on first run. */
export function loadData(): UnitsData {
  ensureDataDir();
  if (!existsSync(UNITS_PATH)) {
    throw new Error(`[humor-units] units.json not found at ${UNITS_PATH} and no default available.`);
  }
  const raw = readFileSync(UNITS_PATH, 'utf8');
  return JSON.parse(raw) as UnitsData;
}

/** Write full UnitsData atomically (write to temp, rename). */
export function saveData(data: UnitsData): void {
  const tmp = UNITS_PATH + '.tmp';
  writeFileSync(tmp, JSON.stringify(data, null, 2) + '\n', 'utf8');
  renameSync(tmp, UNITS_PATH);
}

/** Read config.json synchronously. Seeds from defaults on first run. */
export function loadConfig(): AppConfig {
  ensureDataDir();
  if (!existsSync(CONFIG_PATH)) {
    throw new Error(`[humor-units] config.json not found at ${CONFIG_PATH} and no default available.`);
  }
  const raw = readFileSync(CONFIG_PATH, 'utf8');
  return JSON.parse(raw) as AppConfig;
}

/** Write config.json atomically. */
export function saveConfig(config: AppConfig): void {
  const tmp = CONFIG_PATH + '.tmp';
  writeFileSync(tmp, JSON.stringify(config, null, 2) + '\n', 'utf8');
  renameSync(tmp, CONFIG_PATH);
}