/**
 * LocalStorage utilities for persisting user data
 */

export interface ConversionRecord {
  id: string;
  timestamp: number;
  from: {
    value: number;
    unit: string;
  };
  to: {
    value: number;
    unit: string;
  };
  measure: string;
}

const HISTORY_KEY = 'units-ui-history';
const FAVORITES_KEY = 'units-ui-favorites';
const MAX_HISTORY = 50;

/**
 * Save conversion to history
 */
export function saveToHistory(record: Omit<ConversionRecord, 'id' | 'timestamp'>): void {
  if (typeof window === 'undefined') return;

  const history = getHistory();
  const newRecord: ConversionRecord = {
    ...record,
    id: crypto.randomUUID(),
    timestamp: Date.now(),
  };

  // Add to beginning and limit size
  const updated = [newRecord, ...history].slice(0, MAX_HISTORY);
  localStorage.setItem(HISTORY_KEY, JSON.stringify(updated));
}

/**
 * Get conversion history
 */
export function getHistory(): ConversionRecord[] {
  if (typeof window === 'undefined') return [];

  try {
    const stored = localStorage.getItem(HISTORY_KEY);
    return stored ? JSON.parse(stored) : [];
  } catch {
    return [];
  }
}

/**
 * Clear conversion history
 */
export function clearHistory(): void {
  if (typeof window === 'undefined') return;
  localStorage.removeItem(HISTORY_KEY);
}

/**
 * Get favorite units
 */
export function getFavorites(): string[] {
  if (typeof window === 'undefined') return [];

  try {
    const stored = localStorage.getItem(FAVORITES_KEY);
    return stored ? JSON.parse(stored) : [];
  } catch {
    return [];
  }
}

/**
 * Add unit to favorites
 */
export function addToFavorites(unit: string): void {
  if (typeof window === 'undefined') return;

  const favorites = getFavorites();
  if (!favorites.includes(unit)) {
    favorites.push(unit);
    localStorage.setItem(FAVORITES_KEY, JSON.stringify(favorites));
  }
}

/**
 * Remove unit from favorites
 */
export function removeFromFavorites(unit: string): void {
  if (typeof window === 'undefined') return;

  const favorites = getFavorites();
  const filtered = favorites.filter(u => u !== unit);
  localStorage.setItem(FAVORITES_KEY, JSON.stringify(filtered));
}

/**
 * Toggle favorite status
 */
export function toggleFavorite(unit: string): boolean {
  const favorites = getFavorites();
  const isFavorite = favorites.includes(unit);

  if (isFavorite) {
    removeFromFavorites(unit);
    return false;
  } else {
    addToFavorites(unit);
    return true;
  }
}