//
// HashSet.cs
//
// Authors:
//  Jb Evain  <jbevain@novell.com>
//
// Copyright (C) 2007 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Permissions;
using System.Diagnostics;

// HashSet is basically implemented as a reduction of Dictionary<K, V>

namespace System.Collections.Generic {

	[Serializable]
	[DebuggerDisplay ("Count={Count}")]
	[DebuggerTypeProxy (typeof (CollectionDebuggerView<,>))]
	public class HashSet<T> : ICollection<T>, ISerializable, IDeserializationCallback
#if NET_4_0
							, ISet<T>
#endif
	{
		const int INITIAL_SIZE = 10;
		const float DEFAULT_LOAD_FACTOR = (90f / 100);
		const int NO_SLOT = -1;
		const int HASH_FLAG = -2147483648;

		struct Link {
			public int HashCode;
			public int Next;
		}

		// The hash table contains indices into the "links" array
		int [] table;

		Link [] links;
		T [] slots;

		// The number of slots in "links" and "slots" that
		// are in use (i.e. filled with data) or have been used and marked as
		// "empty" later on.
		int touched;

		// The index of the first slot in the "empty slots chain".
		// "Remove ()" prepends the cleared slots to the empty chain.
		// "Add ()" fills the first slot in the empty slots chain with the
		// added item (or increases "touched" if the chain itself is empty).
		int empty_slot;

		// The number of items in this set.
		int count;

		// The number of items the set can hold without
		// resizing the hash table and the slots arrays.
		int threshold;

		IEqualityComparer<T> comparer;
		SerializationInfo si;

		// The number of changes made to this set. Used by enumerators
		// to detect changes and invalidate themselves.
		int generation;

		public int Count {
			get { return count; }
		}

		public HashSet ()
		{
			Init (INITIAL_SIZE, null);
		}

		public HashSet (IEqualityComparer<T> comparer)
		{
			Init (INITIAL_SIZE, comparer);
		}

		public HashSet (IEnumerable<T> collection) : this (collection, null)
		{
		}

		public HashSet (IEnumerable<T> collection, IEqualityComparer<T> comparer)
		{
			if (collection == null)
				throw new ArgumentNullException ("collection");

			int capacity = 0;
			var col = collection as ICollection<T>;
			if (col != null)
				capacity = col.Count;

			Init (capacity, comparer);
			foreach (var item in collection)
				Add (item);
		}

		protected HashSet (SerializationInfo info, StreamingContext context)
		{
			si = info;
		}

		void Init (int capacity, IEqualityComparer<T> comparer)
		{
			if (capacity < 0)
				throw new ArgumentOutOfRangeException ("capacity");

			this.comparer = comparer ?? EqualityComparer<T>.Default;
			if (capacity == 0)
				capacity = INITIAL_SIZE;

			/* Modify capacity so 'capacity' elements can be added without resizing */
			capacity = (int) (capacity / DEFAULT_LOAD_FACTOR) + 1;

			InitArrays (capacity);
			generation = 0;
		}

		void InitArrays (int size)
		{
			table = new int [size];

			links = new Link [size];
			empty_slot = NO_SLOT;

			slots = new T [size];
			touched = 0;

			threshold = (int) (table.Length * DEFAULT_LOAD_FACTOR);
			if (threshold == 0 && table.Length > 0)
				threshold = 1;
		}

		bool SlotsContainsAt (int index, int hash, T item)
		{
			int current = table [index] - 1;
			while (current != NO_SLOT) {
				Link link = links [current];
				if (link.HashCode == hash && ((hash == HASH_FLAG && (item == null || null == slots [current])) ? (item == null && null == slots [current]) : comparer.Equals (item, slots [current])))
					return true;

				current = link.Next;
			}

			return false;
		}

		public void CopyTo (T [] array)
		{
			CopyTo (array, 0, count);
		}
		
		public void CopyTo (T [] array, int arrayIndex)
		{
			CopyTo (array, arrayIndex, count);
		}

		public void CopyTo (T [] array, int arrayIndex, int count)
		{
			if (array == null)
				throw new ArgumentNullException ("array");
			if (arrayIndex < 0)
				throw new ArgumentOutOfRangeException ("arrayIndex");
			if (arrayIndex > array.Length)
				throw new ArgumentException ("index larger than largest valid index of array");
			if (array.Length - arrayIndex < count)
				throw new ArgumentException ("Destination array cannot hold the requested elements!");

			for (int i = 0, items = 0; i < touched && items < count; i++) {
				if (GetLinkHashCode (i) != 0)
					array [arrayIndex++] = slots [i];
			}
		}

		void Resize ()
		{
			int newSize = HashPrimeNumbers.ToPrime ((table.Length << 1) | 1);

			// allocate new hash table and link slots array
			var newTable = new int [newSize];
			var newLinks = new Link [newSize];

			for (int i = 0; i < table.Length; i++) {
				int current = table [i] - 1;
				while (current != NO_SLOT) {
					int hashCode = newLinks [current].HashCode = GetItemHashCode (slots [current]);
					int index = (hashCode & int.MaxValue) % newSize;
					newLinks [current].Next = newTable [index] - 1;
					newTable [index] = current + 1;
					current = links [current].Next;
				}
			}

			table = newTable;
			links = newLinks;

			// allocate new data slots, copy data
			var newSlots = new T [newSize];
			Array.Copy (slots, 0, newSlots, 0, touched);
			slots = newSlots;

			threshold = (int) (newSize * DEFAULT_LOAD_FACTOR);
		}

		int GetLinkHashCode (int index)
		{
			return links [index].HashCode & HASH_FLAG;
		}

		int GetItemHashCode (T item)
		{
			if (item == null)
				return HASH_FLAG;
			return comparer.GetHashCode (item) | HASH_FLAG;
		}

		public bool Add (T item)
		{
			int hashCode = GetItemHashCode (item);
			int index = (hashCode & int.MaxValue) % table.Length;

			if (SlotsContainsAt (index, hashCode, item))
				return false;

			if (++count > threshold) {
				Resize ();
				index = (hashCode & int.MaxValue) % table.Length;
			}

			// find an empty slot
			int current = empty_slot;
			if (current == NO_SLOT)
				current = touched++;
			else
				empty_slot = links [current].Next;

			// store the hash code of the added item,
			// prepend the added item to its linked list,
			// update the hash table
			links [current].HashCode = hashCode;
			links [current].Next = table [index] - 1;
			table [index] = current + 1;

			// store item
			slots [current] = item;

			generation++;

			return true;
		}

		public IEqualityComparer<T> Comparer {
			get { return comparer; }
		}

		public void Clear ()
		{
			count = 0;

			Array.Clear (table, 0, table.Length);
			Array.Clear (slots, 0, slots.Length);
			Array.Clear (links, 0, links.Length);

			// empty the "empty slots chain"
			empty_slot = NO_SLOT;

			touched = 0;
			generation++;
		}

		public bool Contains (T item)
		{
			int hashCode = GetItemHashCode (item);
			int index = (hashCode & int.MaxValue) % table.Length;

			return SlotsContainsAt (index, hashCode, item);
		}

		public bool Remove (T item)
		{
			// get first item of linked list corresponding to given key
			int hashCode = GetItemHashCode (item);
			int index = (hashCode & int.MaxValue) % table.Length;
			int current = table [index] - 1;

			// if there is no linked list, return false
			if (current == NO_SLOT)
				return false;

			// walk linked list until right slot (and its predecessor) is
			// found or end is reached
			int prev = NO_SLOT;
			do {
				Link link = links [current];
				if (link.HashCode == hashCode && ((hashCode == HASH_FLAG && (item == null || null == slots [current])) ? (item == null && null == slots [current]) : comparer.Equals (slots [current], item)))
					break;

				prev = current;
				current = link.Next;
			} while (current != NO_SLOT);

			// if we reached the end of the chain, return false
			if (current == NO_SLOT)
				return false;

			count--;

			// remove slot from linked list
			// is slot at beginning of linked list?
			if (prev == NO_SLOT)
				table [index] = links [current].Next + 1;
			else
				links [prev].Next = links [current].Next;

			// mark slot as empty and prepend it to "empty slots chain"
			links [current].Next = empty_slot;
			empty_slot = current;

			// clear slot
			links [current].HashCode = 0;
			slots [current] = default (T);

			generation++;

			return true;
		}

		public int RemoveWhere (Predicate<T> match)
		{
			if (match == null)
				throw new ArgumentNullException ("match");

			var candidates = new List<T> ();

			foreach (var item in this)
				if (match (item)) 
					candidates.Add (item);

			foreach (var item in candidates)
				Remove (item);

			return candidates.Count;
		}

		public void TrimExcess ()
		{
			Resize ();
		}

		// set operations

		public void IntersectWith (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			var other_set = ToSet (other);

			RemoveWhere (item => !other_set.Contains (item));
		}

		public void ExceptWith (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in other)
				Remove (item);
		}

		public bool Overlaps (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in other)
				if (Contains (item))
					return true;

			return false;
		}

		public bool SetEquals (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			var other_set = ToSet (other);

			if (count != other_set.Count)
				return false;

			foreach (var item in this)
				if (!other_set.Contains (item))
					return false;

			return true;
		}

		public void SymmetricExceptWith (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in ToSet (other))
				if (!Add (item))
					Remove (item);
		}

		HashSet<T> ToSet (IEnumerable<T> enumerable)
		{
			var set = enumerable as HashSet<T>;
			if (set == null || !Comparer.Equals (set.Comparer))
				set = new HashSet<T> (enumerable, Comparer);

			return set;
		}

		public void UnionWith (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in other)
				Add (item);
		}

		bool CheckIsSubsetOf (HashSet<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in this)
				if (!other.Contains (item))
					return false;

			return true;
		}

		public bool IsSubsetOf (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			if (count == 0)
				return true;

			var other_set = ToSet (other);

			if (count > other_set.Count)
				return false;

			return CheckIsSubsetOf (other_set);
		}

		public bool IsProperSubsetOf (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			if (count == 0)
				return true;

			var other_set = ToSet (other);

			if (count >= other_set.Count)
				return false;

			return CheckIsSubsetOf (other_set);
		}

		bool CheckIsSupersetOf (HashSet<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			foreach (var item in other)
				if (!Contains (item))
					return false;

			return true;
		}

		public bool IsSupersetOf (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			var other_set = ToSet (other);

			if (count < other_set.Count)
				return false;

			return CheckIsSupersetOf (other_set);
		}

		public bool IsProperSupersetOf (IEnumerable<T> other)
		{
			if (other == null)
				throw new ArgumentNullException ("other");

			var other_set = ToSet (other);

			if (count <= other_set.Count)
				return false;

			return CheckIsSupersetOf (other_set);
		}

		public static IEqualityComparer<HashSet<T>> CreateSetComparer ()
		{
			return HashSetEqualityComparer<T>.Instance;
		}

		[SecurityPermission (SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.SerializationFormatter)]
		public virtual void GetObjectData (SerializationInfo info, StreamingContext context)
		{
			if (info == null) {
				throw new ArgumentNullException("info");
			}
			info.AddValue("Version", generation);
			info.AddValue("Comparer", comparer, typeof(IEqualityComparer<T>));
			info.AddValue("Capacity", (table == null) ? 0 : table.Length);
			if (table != null) {
				T[] tableArray = new T[count];
				CopyTo(tableArray);
				info.AddValue("Elements", tableArray, typeof(T[]));
			}
		}

		public virtual void OnDeserialization (object sender)
		{
			if (si != null)
			{
				generation = (int) si.GetValue("Version", typeof(int));
				comparer = (IEqualityComparer<T>) si.GetValue("Comparer", 
									      typeof(IEqualityComparer<T>));
				int capacity = (int) si.GetValue("Capacity", typeof(int));

				empty_slot = NO_SLOT;
				if (capacity > 0) {
					InitArrays(capacity);

					T[] tableArray = (T[]) si.GetValue("Elements", typeof(T[]));
					if (tableArray == null) 
						throw new SerializationException("Missing Elements");

					for (int iElement = 0; iElement < tableArray.Length; iElement++) {
						Add(tableArray[iElement]);
					}
				} else 
					table = null;

				si = null;
			}
		}


		IEnumerator<T> IEnumerable<T>.GetEnumerator ()
		{
			return new Enumerator (this);
		}

		bool ICollection<T>.IsReadOnly {
			get { return false; }
		}

		void ICollection<T>.Add (T item)
		{
			Add (item);
		}

		IEnumerator IEnumerable.GetEnumerator ()
		{
			return new Enumerator (this);
		}

		public Enumerator GetEnumerator ()
		{
			return new Enumerator (this);
		}

		[Serializable]
		public struct Enumerator : IEnumerator<T>, IDisposable {

			HashSet<T> hashset;
			int next;
			int stamp;

			T current;

			internal Enumerator (HashSet<T> hashset)
				: this ()
			{
				this.hashset = hashset;
				this.stamp = hashset.generation;
			}

			public bool MoveNext ()
			{
				CheckState ();

				if (next < 0)
					return false;

				while (next < hashset.touched) {
					int cur = next++;
					if (hashset.GetLinkHashCode (cur) != 0) {
						current = hashset.slots [cur];
						return true;
					}
				}

				next = NO_SLOT;
				return false;
			}

			public T Current {
				get { return current; }
			}

			object IEnumerator.Current {
				get {
					CheckState ();
					if (next <= 0)
						throw new InvalidOperationException ("Current is not valid");
					return current;
				}
			}

			void IEnumerator.Reset ()
			{
				CheckState ();
				next = 0;
			}

			public void Dispose ()
			{
				hashset = null;
			}

			void CheckState ()
			{
				if (hashset == null)
					throw new ObjectDisposedException (null);
				if (hashset.generation != stamp)
					throw new InvalidOperationException ("HashSet have been modified while it was iterated over");
			}
		}
	}
	
	sealed class HashSetEqualityComparer<T> : IEqualityComparer<HashSet<T>>
	{
		public static readonly HashSetEqualityComparer<T> Instance = new HashSetEqualityComparer<T> ();
			
		public bool Equals (HashSet<T> lhs, HashSet<T> rhs)
		{
			if (lhs == rhs)
				return true;

			if (lhs == null || rhs == null || lhs.Count != rhs.Count)
				return false;

			foreach (var item in lhs)
				if (!rhs.Contains (item))
					return false;

			return true;
		}

		public int GetHashCode (HashSet<T> hashset)
		{
			if (hashset == null)
				return 0;

			IEqualityComparer<T> comparer = EqualityComparer<T>.Default;
			int hash = 0;
			foreach (var item in hashset)
				hash ^= comparer.GetHashCode (item);

			return hash;
		}
	}
}