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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SandPit.Shaun.Algorithms.Collections
{
    /// <summary>
    /// These extension methods attempt to emulate the SetDefault method available to 
    /// python dictionaries. While they emulate them in spirit, they are probably
    /// not as perfomant
    /// 
    /// I decided to use the TryGetValue approach - though 
    /// try/catch/KeyNotFound or Contains/[] approach might be best depending on specific
    /// requirements (how often you expect to find the key already there etc)
    /// 
    /// Author: Shaun McCarthy - http://www.shaunmccarthy.com (me@shaunmccarthy.com)
    /// </summary>
    public static class SetDefaultExtension
    {
        /// <summary>
        /// This method checks to see if a key exists in the dictionary. If so, it returns
        /// that key, otherwise it returns a default value (and sets that default value to
        /// be the value in the dictionary)
        /// </summary>
        /// <typeparam name="TKey">The key type of the generic dictionary</typeparam>
        /// <typeparam name="TValue">The value type of the generic dictionary</typeparam>
        /// <param name="dictionary">Refernce to the dictionary you are using</param>
        /// <param name="key">The key to look for</param>
        /// <param name="defaultValue">The value to insert and use if it's not there</param>
        /// <returns>The value associated with the key</returns>
        public static TValue SetDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue)
        {
            TValue result;
            // If we can't find the value, return the default
            if (!dictionary.TryGetValue(key, out result))
                return dictionary[key] = defaultValue;
            return result;
        }

        /// <summary>
        /// This method checks to see if a key exists in the dictionary. If so, it returns
        /// that key, otherwise it creates a default value using the function passed in
        /// (and sets that default value to be the value in the dictionary)
        /// </summary>
        /// <typeparam name="TKey">The key type of the generic dictionary</typeparam>
        /// <typeparam name="TValue">The value type of the generic dictionary</typeparam>
        /// <param name="dictionary">Refernce to the dictionary you are using</param>
        /// <param name="key">The key to look for</param>
        /// <param name="initFunction">The method to use to create the value to insert and use if it's not there</param>
        /// <returns>The value associated with the key</returns>
        public static TValue SetDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, Func<TValue> initFunction)
        {
            TValue result;
            // If we can't find the value, run the default generation method
            if (!dictionary.TryGetValue(key, out result))
            {
                if (initFunction == null)
                {
                    throw new Exception("You haven't defined an initialization function with SetDefaultFunc");
                }
                return dictionary[key] = initFunction();
            }
            return result;
        }

        /// <summary>
        /// This method checks to see if a key exists in the dictionary. If so, it returns
        /// that key, otherwise it creates a default value using Activator.CreateInstance
        /// 
        /// NB: This calls the default constructor on the object - if it doesn't exist, 
        /// this will throw a MissingMethodException
        /// </summary>
        /// <typeparam name="TKey">The key type of the generic dictionary</typeparam>
        /// <typeparam name="TValue">The value type of the generic dictionary</typeparam>
        /// <param name="dictionary">Refernce to the dictionary you are using</param>
        /// <param name="key">The key to look for</param>
        /// <param name="initFunction">The method to use to create the value to insert and use if it's not there</param>
        /// <returns>The value associated with the key</returns>
        public static TValue SetDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key)
        {
            TValue result;
            if (!dictionary.TryGetValue(key, out result))
            {
                return dictionary[key] = (TValue)Activator.CreateInstance(typeof(TValue));
            }
            return result;
        }
    }
}