using System.Collections.Generic;

namespace Chernobyl.Values
{
    /// <summary>
    /// An <see cref="IValue{T}"/> that gets its value from another
    /// <see cref="IContainer{T}"/> that may not always be present.
    /// </summary>
    public class SourceContainer<T> : SourceValue<T>, IContainer<T>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="SourceContainer{T}"/> class
        /// that uses null for the <see cref="Source"/> and
        /// <see cref="System.Collections.Generic.Comparer{T}.Default"/> for the
        /// <see cref="BasicValue{T}.Comparer"/>.
        /// </summary>
        public SourceContainer() : this(null)
        {}

        /// <summary>
        /// Initializes a new instance of the <see cref="SourceContainer{T}"/> class
        /// that uses <see cref="EqualityComparer{T}.Default"/>
        /// for the <see cref="BasicValue{T}.Comparer"/>.
        /// </summary>
        /// <param name="source">The <see cref="IContainer{T}"/> that acts as the 
        /// source for <see cref="Value"/> or null if this source has not yet 
        /// been provided.</param>
        public SourceContainer(IContainer<T> source)
            : this(source, EqualityComparer<T>.Default)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="SourceContainer{T}"/> class.
        /// </summary>
        /// <param name="source">The <see cref="IContainer{T}"/> that acts as the 
        /// source for <see cref="Value"/> or null if this source has not yet 
        /// been provided.</param>
        /// <param name="comparer">The instance used to compare new and previous
        /// values of <see cref="Value"/> to determine if 
        /// <see cref="IValue{T}.Provide"/> should be raised.</param>
        public SourceContainer(IContainer<T> source, IEqualityComparer<T> comparer)
            : base(source, comparer)
        {
            Source = source;
        }

        /// <summary>
        /// The value held by this instance or <c>default(T)</c> if
        /// <see cref="Source"/> has not been provided.
        /// </summary>
        T IContainer<T>.Value
        {
            get { return _source != null ? _source.Value : default(T); }
        }

        /// <summary>
        /// The <see cref="IValue{T}"/> that acts as the source for
        /// <see cref="Value"/> or null if this source has not yet been
        /// provided.
        /// </summary>
        public new IContainer<T> Source
        {
            get { return _source; }
            set
            {
                if (_source != value)
                    base.Source = _source = value;
            }
        }

        /// <summary>
        /// The backing field to <see cref="Source"/>.
        /// </summary>
        IContainer<T> _source;
    }
}