using System;
using System.Collections.Generic;

namespace Unosquare.Swan {
  /// <summary>
  /// Extension methods.
  /// </summary>
  public static partial class Extensions {
    /// <summary>
    /// Gets the value if exists or default.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TValue">The type of the value.</typeparam>
    /// <param name="dict">The dictionary.</param>
    /// <param name="key">The key.</param>
    /// <param name="defaultValue">The default value.</param>
    /// <returns>
    /// The value of the provided key or default.
    /// </returns>
    /// <exception cref="ArgumentNullException">dict.</exception>
    public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dict, TKey key, TValue defaultValue = default) {
      if(dict == null) {
        throw new ArgumentNullException(nameof(dict));
      }

      return dict.ContainsKey(key) ? dict[key] : defaultValue;
    }

    /// <summary>
    /// Adds a key/value pair to the Dictionary if the key does not already exist.
    /// If the value is null, the key will not be updated.
    ///
    /// Based on <c>ConcurrentDictionary.GetOrAdd</c> method.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TValue">The type of the value.</typeparam>
    /// <param name="dict">The dictionary.</param>
    /// <param name="key">The key.</param>
    /// <param name="valueFactory">The value factory.</param>
    /// <returns>The value for the key.</returns>
    public static TValue GetOrAdd<TKey, TValue>(this IDictionary<TKey, TValue> dict, TKey key, Func<TKey, TValue> valueFactory) {
      if(dict == null) {
        throw new ArgumentNullException(nameof(dict));
      }

      if(!dict.ContainsKey(key)) {
        TValue value = valueFactory(key);
        if(Equals(value, default)) {
          return default;
        }

        dict[key] = value;
      }

      return dict[key];
    }

    /// <summary>
    /// Executes the item action for each element in the Dictionary.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TValue">The type of the value.</typeparam>
    /// <param name="dict">The dictionary.</param>
    /// <param name="itemAction">The item action.</param>
    /// <exception cref="ArgumentNullException">dict.</exception>
    public static void ForEach<TKey, TValue>(this IDictionary<TKey, TValue> dict, Action<TKey, TValue> itemAction) {
      if(dict == null) {
        throw new ArgumentNullException(nameof(dict));
      }

      foreach(KeyValuePair<TKey, TValue> kvp in dict) {
        itemAction(kvp.Key, kvp.Value);
      }
    }
  }
}