// Copyright 2018 RED Software, LLC. All Rights Reserved.

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

namespace IgniteEngine
{
    /// <summary>
    /// Class that extends the use of the List class.
    /// </summary>
    public static class ListExtensions
    {
        /// <summary>
        /// The object to lock for list access.
        /// </summary>
        private static readonly object lockObject = new object();

        /// <summary>
        /// Adds an object to the list in a thread-safe, exception-safe
        /// manner.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="value">The value to add.</param>
        public static void AddSafe<T>(this List<T> source, T value)
        {
            if (value == null)
            {
                return;
            }

            lock (lockObject)
            {
                if (!source.Contains(value))
                {
                    source.Add(value);
                }
            }
        }

        /// <summary>
        /// Copies the elements from the source list to the output list.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="output">The output list.</param>
        public static void Copy<T>(this List<T> source, out List<T> output)
        {
            lock (lockObject)
            {
                output = new List<T>(source);
            }
        }

        /// <summary>
        /// Returns a new list filtered using the predicate provided.
        /// </summary>
        public static List<T> Filter<T>(this List<T> source, Func<T, bool> predicate)
        {
            lock (lockObject)
            {
                return new List<T>(source.Where(predicate));
            }
        }

        /// <summary>
        /// Performs an action on the filtered list of items in the list.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="predicate">The filter specifications.</param>
        /// <param name="action">The action to perform on the filtered items.</param>
        public static void FilteredAction<T>(this List<T> source, Func<T, bool> predicate, Action<T> action)
        {
            lock (lockObject)
            {
                source.Filter(predicate).ForEach(action);
            }
        }

        /// <summary>
        /// Returns the first matching element in the list.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="predicate">The filter specifications.</param>
        public static T First<T>(this List<T> source, Func<T, bool> predicate)
        {
            lock (lockObject)
            {
                var list = source.Filter(predicate);
                return list.Count <= 0 ? default(T) : list[0];
            }
        }


        /// <summary>
        /// Runs a for loop on list in a thread-safe manner.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="action">The action to perform on the item.</param>
        public static void For<T>(this List<T> source, Action<T> action)
        {
            lock (lockObject)
            {
                for (var i = 0; i < source.Count; i++)
                {
                    action(source[i]);
                }
            }
        }

        /// <summary>
        /// Runs a for loop on list, backwards, in a thread-safe manner.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="action">The action to perform on the item.</param>
        public static void ForBackwards<T>(this List<T> source, Action<T> action)
        {
            lock (lockObject)
            {
                for (var i = source.Count - 1; i >= 0; i--)
                {
                    action(source[i]);
                }
            }
        }

        /// <summary>
        /// Removes an object from a list in a thread-safe, exception-safe
        /// manner.
        /// </summary>
        /// <param name="source">The source list.</param>
        /// <param name="value">The value to remove.</param>
        public static void RemoveSafe<T>(this List<T> source, T value)
        {
            if (value == null)
            {
                return;
            }

            lock (lockObject)
            {
                if (source.Contains(value))
                {
                    source.Remove(value);
                }
            }
        }
    }
}