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

namespace Chernobyl
{
    /// <summary>
    /// Extension and utility methods for <see cref="Object"/> types.
    /// </summary>
    public static class ObjectExtensions
    {
        /// <summary>
        /// Returns a single item as an <see cref="IEnumerable{T}"/>. For example:
        /// <example>
        /// DateTime example = new DateTime();
        /// IEnumerable{DateTime} dates = example.ToEnumerable();
        /// </example>
        /// This is used in cases where you need a single object in the form of a collection of objects.
        /// </summary>
        /// <typeparam name="T">The type that is to be turned into an <see cref="IEnumerable{T}"/>.</typeparam>
        /// <param name="item">The item that is to be turned into an <see cref="IEnumerable{T}"/>.</param>
        /// <returns>The <paramref name="item"/> as an <see cref="IEnumerable{T}"/></returns>
        public static IEnumerable<T> ToEnumerable<T>(this T item)
        {
            yield return item;
        }

        /// <summary>
        /// Returns a single item as an <see cref="IEnumerable{T}"/> if it is not null. If it is null,
        /// then it returns an empty <see cref="IEnumerable{T}"/>. For example:
        /// <example>
        /// DateTime example = new DateTime();
        /// IEnumerable{DateTime} dates = example.ToEnumerableOrEmpty();
        /// </example>
        /// This is used in cases where you need a single object in the form of a collection of objects.
        /// </summary>
        /// <typeparam name="T">The type that is to be turned into an <see cref="IEnumerable{T}"/>.</typeparam>
        /// <param name="item">The item that is to be turned into an <see cref="IEnumerable{T}"/>.</param>
        /// <returns>The <paramref name="item"/> as an <see cref="IEnumerable{T}"/></returns>
        public static IEnumerable<T> ToEnumerableOrEmpty<T>(this T item) where T : class =>
            item != null ? item.ToEnumerable() : Enumerable.Empty<T>();

        /// <summary>
        /// Invokes <paramref name="method"/> with <paramref name="item"/> as
        /// its parameter.
        /// </summary>
        /// <typeparam name="T">The type of the item to give to the
        /// <paramref name="method"/>.</typeparam>
        /// <param name="item">The item to give to the <paramref name="method"/>.</param>
        /// <param name="method">The method to invoke with <paramref name="item"/>.</param>
        public static void To<T>(this T item, Action<T> method) => method(item);
    }
}