using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;

namespace Unosquare.Swan.Components {
  /// <summary>
  /// A thread-safe collection cache repository for types.
  /// </summary>
  /// <typeparam name="TValue">The type of member to cache.</typeparam>
  public class CollectionCacheRepository<TValue> {
    private readonly Lazy<ConcurrentDictionary<Type, IEnumerable<TValue>>> _data =
        new Lazy<ConcurrentDictionary<Type, IEnumerable<TValue>>>(() =>
            new ConcurrentDictionary<Type, IEnumerable<TValue>>(), true);

    /// <summary>
    /// Determines whether the cache contains the specified key.
    /// </summary>
    /// <param name="key">The key.</param>
    /// <returns><c>true</c> if the cache contains the key, otherwise <c>false</c>.</returns>
    public Boolean ContainsKey(Type key) => this._data.Value.ContainsKey(key);

    /// <summary>
    /// Retrieves the properties stored for the specified type.
    /// If the properties are not available, it calls the factory method to retrieve them
    /// and returns them as an array of PropertyInfo.
    /// </summary>
    /// <param name="key">The key.</param>
    /// <param name="factory">The factory.</param>
    /// <returns>
    /// An array of the properties stored for the specified type.
    /// </returns>
    /// <exception cref="System.ArgumentNullException">type.</exception>
    public IEnumerable<TValue> Retrieve(Type key, Func<Type, IEnumerable<TValue>> factory) {
      if(factory == null) {
        throw new ArgumentNullException(nameof(factory));
      }

      return this._data.Value.GetOrAdd(key, k => factory.Invoke(k).Where(item => item != null));
    }
  }
}