/** Numeric VITE_UI_THEME index → semantic data-theme id (UI layer only; 3D unchanged). */
export const THEME_MAP = {
  '1': 'obsidian_slate',
  '2': 'amber_charcoal',
  '3': 'nordic_forest',
  '4': 'titanium_oxide',
  '5': 'midnight_ink',
  '6': 'basalt_copper',
  '7': 'swiss_brutalist',
  '8': 'ibm_as400',
  '9': 'amiga_os13',
  '10': 'blueprint_heliography',
};

/** Human-readable labels (design-system/README.md catalog). */
export const THEME_LABELS = {
  '1': 'Obsidian Slate',
  '2': 'Amber & Warm Charcoal',
  '3': 'Nordic Forest',
  '4': 'Titanium Oxide',
  '5': 'Midnight Ink',
  '6': 'Basalt & Raw Copper',
  '7': 'Swiss Brutalist',
  '8': 'IBM AS/400 Terminal',
  '9': 'Amiga Workbench 1.3',
  '10': 'Blue-Line Blueprint',
};

export const THEME_STORAGE_KEY = 'ui_theme_index';
const DEFAULT_THEME_INDEX = 1;
const MIN_THEME_INDEX = 1;
const MAX_THEME_INDEX = 10;

/** @type {number} */
let currentThemeIndex = DEFAULT_THEME_INDEX;

/**
 * @param {string | number | undefined | null} rawIndex
 * @returns {number}
 */
export function normalizeThemeIndex(rawIndex) {
  const n = Number.parseInt(String(rawIndex ?? '').trim(), 10);
  if (!Number.isFinite(n) || n < MIN_THEME_INDEX || n > MAX_THEME_INDEX) {
    return DEFAULT_THEME_INDEX;
  }
  return n;
}

/**
 * Resolve env index to a theme id. Invalid or missing values fall back to obsidian_slate.
 * @param {string | number | undefined | null} rawIndex
 * @returns {string}
 */
export function resolveThemeName(rawIndex) {
  const key = String(normalizeThemeIndex(rawIndex));
  return THEME_MAP[key] ?? THEME_MAP[String(DEFAULT_THEME_INDEX)];
}

/**
 * @returns {number | null}
 */
export function readStoredThemeIndex() {
  if (typeof localStorage === 'undefined') return null;
  try {
    const raw = localStorage.getItem(THEME_STORAGE_KEY);
    if (raw == null || raw === '') return null;
    const n = Number.parseInt(raw, 10);
    if (!Number.isFinite(n) || n < MIN_THEME_INDEX || n > MAX_THEME_INDEX) return null;
    return n;
  } catch {
    return null;
  }
}

/**
 * Boot priority: localStorage → VITE_UI_THEME → default 1.
 * @returns {number}
 */
export function resolveInitialThemeIndex() {
  const stored = readStoredThemeIndex();
  if (stored != null) return stored;
  const fromEnv = import.meta.env.VITE_UI_THEME;
  if (fromEnv != null && String(fromEnv).trim() !== '') {
    return normalizeThemeIndex(fromEnv);
  }
  return DEFAULT_THEME_INDEX;
}

/**
 * @param {number} index
 * @param {{ persist?: boolean }} [options]
 * @returns {{ index: number, id: string, label: string }}
 */
export function applyUiThemeByIndex(index, options = {}) {
  const { persist = true } = options;
  const normalized = normalizeThemeIndex(index);
  const id = resolveThemeName(normalized);
  const label = THEME_LABELS[String(normalized)] ?? THEME_LABELS[String(DEFAULT_THEME_INDEX)];

  currentThemeIndex = normalized;

  if (typeof document !== 'undefined' && document.body) {
    document.body.setAttribute('data-theme', id);
  }

  if (persist && typeof localStorage !== 'undefined') {
    try {
      localStorage.setItem(THEME_STORAGE_KEY, String(normalized));
    } catch {
      /* quota / private mode — theme still applied for this session */
    }
  }

  return { index: normalized, id, label };
}

/** Apply saved/env/default theme at boot without overwriting localStorage. */
export function bootstrapUiTheme() {
  return applyUiThemeByIndex(resolveInitialThemeIndex(), { persist: false });
}

/**
 * Advance 1→10→1 and persist.
 * @returns {{ index: number, id: string, label: string }}
 */
export function cycleUiTheme() {
  const next = currentThemeIndex >= MAX_THEME_INDEX ? MIN_THEME_INDEX : currentThemeIndex + 1;
  return applyUiThemeByIndex(next, { persist: true });
}

/**
 * @returns {{ index: number, id: string, label: string }}
 */
export function getUiThemeSummary() {
  const normalized = normalizeThemeIndex(currentThemeIndex);
  return {
    index: normalized,
    id: resolveThemeName(normalized),
    label: THEME_LABELS[String(normalized)] ?? THEME_LABELS[String(DEFAULT_THEME_INDEX)],
  };
}

/**
 * Read VITE_UI_THEME and set body[data-theme]. Safe in SSR/test when document is absent.
 * @param {string | number | undefined | null} [rawIndex]
 * @returns {string} Applied theme id
 */
export function applyUiThemeFromEnv(rawIndex = import.meta.env.VITE_UI_THEME) {
  return applyUiThemeByIndex(rawIndex, { persist: false }).id;
}