// ****************************************************************
// Copyright 2007, Charlie Poole
// This is free software licensed under the NUnit license. You may
// obtain a copy of the license at http://nunit.org/?p=license&r=2.4
// ****************************************************************

using System;
using System.Collections;

namespace NUnit.Framework.Constraints
{
    #region CollectionConstraint
    /// <summary>
    /// CollectionConstraint is the abstract base class for
    /// constraints that operate on collections.
    /// </summary>
    public abstract class CollectionConstraint : Constraint
    {
		protected static bool IsEmpty( IEnumerable enumerable )
		{
			ICollection collection = enumerable as ICollection;
			if ( collection != null )
				return collection.Count == 0;
			else
				return !enumerable.GetEnumerator().MoveNext();
		}

		/// <summary>
		/// CollectionTally counts (tallies) the number of
		/// occurences of each object in one or more enuerations.
		/// </summary>
		protected internal class CollectionTally
		{
			// Internal hash used to count occurences
			private Hashtable hash = new Hashtable();

			// We use this for any null entries found, since
			// the key to a hash may not be null.
			static object NULL = new object();

			private int getTally(object obj)
			{
				if ( obj == null ) obj = NULL;
				object val = hash[obj];
				return val == null ? 0 : (int)val;
			}

			private void setTally(object obj, int tally)
			{
				if ( obj == null ) obj = NULL;
				hash[obj] = tally;
			}

			/// <summary>
			/// Construct a CollectionTally object from a collection
			/// </summary>
			/// <param name="c"></param>
			public CollectionTally( IEnumerable c )
			{
				foreach( object obj in c )
					setTally( obj, getTally( obj ) + 1 );
			}

			/// <summary>
			/// Remove the counts for a collection from the tally,
			/// so long as their are sufficient items to remove.
			/// The tallies are not permitted to become negative.
			/// </summary>
			/// <param name="c">The collection to remove</param>
			/// <returns>True if there were enough items to remove, otherwise false</returns>
			public bool CanRemove( IEnumerable c )
			{
				foreach( object obj in c )
				{
					int tally = getTally(obj);
					if( tally > 0 )
						setTally(obj, tally - 1 );
					else
						return false;
				}

				return true;
			}

			/// <summary>
			/// Test whether all the counts are equal to a given value
			/// </summary>
			/// <param name="count">The value to be looked for</param>
			/// <returns>True if all counts are equal to the value, otherwise false</returns>
			public bool AllCountsEqualTo( int count )
			{
				foreach( DictionaryEntry entry in hash )
					if ( (int)entry.Value != count )
						return false;

				return true;
			}

			/// <summary>
			/// Get the count of the number of times an object is present in the tally
			/// </summary>
			public int this[object obj]
			{
				get	{ return getTally(obj); }
			}
		}

		/// <summary>
		/// Test whether the constraint is satisfied by a given value
		/// </summary>
		/// <param name="actual">The value to be tested</param>
		/// <returns>True for success, false for failure</returns>
		public override bool Matches(object actual)
		{
			this.actual = actual;

			IEnumerable enumerable = actual as IEnumerable;
			if ( enumerable == null )
				throw new ArgumentException( "The actual value must be an IEnumerable", "actual" );
		
			return doMatch( enumerable );
		}

		/// <summary>
		/// Protected method to be implemented by derived classes
		/// </summary>
		/// <param name="collection"></param>
		/// <returns></returns>
		protected abstract bool doMatch(IEnumerable collection);
    }
    #endregion

	#region EmptyCollectionConstraint
    /// <summary>
    /// EmptyCollectionConstraint tests whether a colletion is empty. 
    /// </summary>
    public class EmptyCollectionConstraint : CollectionConstraint
	{
		/// <summary>
		/// Check that the collection is empty
		/// </summary>
		/// <param name="collection"></param>
		/// <returns></returns>
		protected override bool doMatch(IEnumerable collection)
		{
			return IsEmpty( collection );
		}
	
		/// <summary>
		/// Write the constraint description to a MessageWriter
		/// </summary>
		/// <param name="writer"></param>
		public override void WriteDescriptionTo(MessageWriter writer)
		{
			writer.Write( "<empty>" );
		}
	}
	#endregion

	#region UniqueItemsConstraint
    /// <summary>
    /// UniqueItemsConstraint tests whether all the items in a 
    /// collection are unique.
    /// </summary>
    public class UniqueItemsConstraint : CollectionConstraint
    {
        /// <summary>
        /// Check that all items are unique.
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        protected override bool doMatch(IEnumerable actual)
        {
			return new CollectionTally( actual ).AllCountsEqualTo( 1 );
        }

        /// <summary>
        /// Write a description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.Write("all items unique");
        }
    }
    #endregion

    #region CollectionContainsConstraint
    /// <summary>
    /// CollectionContainsConstraint is used to test whether a collection
    /// contains an expected object as a member.
    /// </summary>
    public class CollectionContainsConstraint : CollectionConstraint
    {
        private object expected;

        /// <summary>
        /// Construct a CollectionContainsConstraint
        /// </summary>
        /// <param name="expected"></param>
        public CollectionContainsConstraint(object expected)
        {
            this.expected = expected;
        }

        /// <summary>
        /// Test whether the expected item is contained in the collection
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        protected override bool doMatch(IEnumerable actual)
        {
			foreach (object obj in actual)
				if ( Object.Equals( obj, expected ) )
					return true;

			return false;
		}

        /// <summary>
        /// Write a descripton of the constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WritePredicate( "collection containing" );
            writer.WriteExpectedValue(expected);
        }
    }
    #endregion

    #region CollectionEquivalentConstraint
    /// <summary>
    /// CollectionEquivalentCOnstraint is used to determine whether two
    /// collections are equivalent.
    /// </summary>
    public class CollectionEquivalentConstraint : CollectionConstraint
    {
        private IEnumerable expected;

        /// <summary>
        /// Construct a CollectionEquivalentConstraint
        /// </summary>
        /// <param name="expected"></param>
        public CollectionEquivalentConstraint(IEnumerable expected)
        {
            this.expected = expected;
        }

        /// <summary>
        /// Test whether two collections are equivalent
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        protected override bool doMatch(IEnumerable actual)
        {
			// This is just an optimization
			if( expected is ICollection && actual is ICollection )
				if( ((ICollection)actual).Count != ((ICollection)expected).Count )
					return false;

			CollectionTally tally = new CollectionTally( expected );
			return tally.CanRemove( actual ) && tally.AllCountsEqualTo( 0 );
        }

        /// <summary>
        /// Write a description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WritePredicate("equivalent to");
            writer.WriteExpectedValue(expected);
        }
    }
    #endregion

    #region CollectionSubsetConstraint
    /// <summary>
    /// CollectionSubsetConstraint is used to determine whether
    /// one collection is a subset of another
    /// </summary>
    public class CollectionSubsetConstraint : CollectionConstraint
    {
        private IEnumerable expected;

        /// <summary>
        /// Construct a CollectionSubsetConstraint
        /// </summary>
        /// <param name="expected">The collection that the actual value is expected to be a subset of</param>
        public CollectionSubsetConstraint(IEnumerable expected)
        {
            this.expected = expected;
        }

        /// <summary>
        /// Test whether the actual collection is a subset of 
        /// the expected collection provided.
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        protected override bool doMatch(IEnumerable actual)
        {
			return new CollectionTally( expected ).CanRemove( actual );
		}
        
        /// <summary>
        /// Write a description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WritePredicate( "subset of" );
            writer.WriteExpectedValue(expected);
        }
    }
    #endregion
}