// ==++==
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--==
//=============================================================================
//
// Class: Queue
//
// Purpose: A circular-array implementation of a queue.
//
//=============================================================================  
namespace System.Collections
{
    using System;

    // A simple Queue of objects.  Internally it is implemented as a circular
    // buffer, so Enqueue can be O(n).  Dequeue is O(1).
    //| <include path='docs/doc[@for="Queue"]/*' />
    public class Queue : ICollection, ICloneable {
        private Object[] _array;
        private int _head;       // First valid element in the queue
        private int _tail;       // Last valid element in the queue
        private int _size;       // Number of elements.
        private int _growFactor; // 100 == 1.0, 130 == 1.3, 200 == 2.0
        private int _version;

        private const int _MinimumGrow = 4;
        private const int _ShrinkThreshold = 32;

        // Creates a queue with room for capacity objects. The default initial
        // capacity and grow factor are used.
        //| <include path='docs/doc[@for="Queue.Queue"]/*' />
        public Queue()
            : this(32, 200) {
        }

        // Creates a queue with room for capacity objects. The default grow factor
        // is used.
        //
        //| <include path='docs/doc[@for="Queue.Queue1"]/*' />
        public Queue(int capacity)
            : this(capacity, 200) {
        }

        // Creates a queue with room for capacity objects. When full, the new
        // capacity is set to the old capacity * growFactor.
        //
        //| <include path='docs/doc[@for="Queue.Queue2"]/*' />
        public Queue(int capacity, int growFactorPercent) {
            if (capacity < 0)
                throw new ArgumentOutOfRangeException("capacity", "ArgumentOutOfRange_NeedNonNegNum");
            if (!(growFactorPercent >= 100 && growFactorPercent <= 1000)) {
                throw new ArgumentOutOfRangeException("growFactor", String.Format("ArgumentOutOfRange_QueueGrowFactor", 1, 10));
            }

            _array = new Object[capacity];
            _head = 0;
            _tail = 0;
            _size = 0;
            _growFactor = growFactorPercent;
        }

        // Fills a Queue with the elements of an ICollection.  Uses the enumerator
        // to get each of the elements.
        //
        //| <include path='docs/doc[@for="Queue.Queue3"]/*' />
        public Queue(ICollection col) : this((col==null ? 32 : col.Count))
        {
            if (col == null)
                throw new ArgumentNullException("col");
            IEnumerator en = col.GetEnumerator();
            while (en.MoveNext())
                Enqueue(en.Current);
        }


        //| <include path='docs/doc[@for="Queue.Count"]/*' />
        public virtual int Count {
            get { return _size; }
        }

        //| <include path='docs/doc[@for="Queue.Clone"]/*' />
        public virtual Object Clone() {
            Queue q = new Queue(_size);
            q._size = _size;
            Array.Copy(_array, 0, q._array, 0, _size);
            q._version = _version;
            return q;
        }

        //| <include path='docs/doc[@for="Queue.IsSynchronized"]/*' />
        public virtual bool IsSynchronized {
            get { return false; }
        }

        //| <include path='docs/doc[@for="Queue.SyncRoot"]/*' />
        public virtual Object SyncRoot {
            get { return this; }
        }

        // Removes all Objects from the queue.
        //| <include path='docs/doc[@for="Queue.Clear"]/*' />
        public virtual void Clear() {
            if (_head < _tail)
                Array.Clear(_array, _head, _size);
            else {
                Array.Clear(_array, _head, _array.Length - _head);
                Array.Clear(_array, 0, _tail);
            }

            _head = 0;
            _tail = 0;
            _size = 0;
            _version++;
        }

        // CopyTo copies a collection into an Array, starting at a particular
        // index into the array.
        //
        //| <include path='docs/doc[@for="Queue.CopyTo"]/*' />
        public virtual void CopyTo(Array array, int index)
        {
            if (array == null)
                throw new ArgumentNullException("array");
            if (array.Rank != 1)
                throw new ArgumentException("Arg_RankMultiDimNotSupported");
            if (index < 0)
                throw new ArgumentOutOfRangeException("index", "ArgumentOutOfRange_Index");
            int arrayLen = array.Length;
            if (arrayLen - index < _size)
                throw new ArgumentException("Argument_InvalidOffLen");

            int numToCopy = (arrayLen-index < _size) ? arrayLen-index : _size;
            if (numToCopy == 0)
                return;
            if (_head < _tail) {
                Array.Copy(_array, _head, array, index, numToCopy);
            }
            else {
                int firstPart = (_array.Length - _head < numToCopy) ? _array.Length - _head : numToCopy;
                Array.Copy(_array, _head, array, index, firstPart);
                numToCopy -= firstPart;
                Array.Copy(_array, 0, array, index+_array.Length - _head, numToCopy);
            }
        }

        // Adds obj to the tail of the queue.
        //
        //| <include path='docs/doc[@for="Queue.Enqueue"]/*' />
        public virtual void Enqueue(Object obj) {
            if (_size == _array.Length) {
                int newcapacity = (int)((long)_array.Length * (long)_growFactor / 100);
                if (newcapacity < _array.Length + _MinimumGrow) {
                    newcapacity = _array.Length + _MinimumGrow;
                }
                SetCapacity(newcapacity);
            }

            _array[_tail] = obj;
            _tail = (_tail + 1) % _array.Length;
            _size++;
            _version++;
        }

        // GetEnumerator returns an IEnumerator over this Queue.  This
        // Enumerator will support removing.
        //
        //| <include path='docs/doc[@for="Queue.GetEnumerator"]/*' />
        public virtual IEnumerator GetEnumerator()
        {
            return new QueueEnumerator(this);
        }

        // Removes the object at the head of the queue and returns it. If the queue
        // is empty, this method simply returns null.
        //| <include path='docs/doc[@for="Queue.Dequeue"]/*' />
        public virtual Object Dequeue() {
            if (_size == 0)
                throw new InvalidOperationException("InvalidOperation_EmptyQueue");

            Object removed = _array[_head];
            _array[_head] = null;
            _head = (_head + 1) % _array.Length;
            _size--;
            _version++;
            return removed;
        }

        // Returns the object at the head of the queue. The object remains in the
        // queue. If the queue is empty, this method throws an
        // InvalidOperationException.
        //| <include path='docs/doc[@for="Queue.Peek"]/*' />
        public virtual Object Peek() {
            if (_size == 0)
                throw new InvalidOperationException("InvalidOperation_EmptyQueue");

            return _array[_head];
        }

        public virtual Object PeekAt(int index)
        {
            if (index < 0 || index >= _size) {
                throw new ArgumentOutOfRangeException("index");
            }
            return GetElement(index);
        }

        // Returns a synchronized Queue.  Returns a synchronized wrapper
        // class around the queue - the caller must not use references to the
        // original queue.
        //
        //| <include path='docs/doc[@for="Queue.Synchronized"]/*' />
        public static Queue Synchronized(Queue queue)
        {
            if (queue == null)
                throw new ArgumentNullException("queue");
            return new SynchronizedQueue(queue);
        }

        // Returns true if the queue contains at least one object equal to obj.
        // Equality is determined using obj.Equals().
        //
        // Exceptions: ArgumentNullException if obj == null.
        //| <include path='docs/doc[@for="Queue.Contains"]/*' />
        public virtual bool Contains(Object obj) {
            int index = _head;
            int count = _size;

            while (count-- > 0) {
                if (obj == null) {
                    if (_array[index] == null)
                        return true;
                }
                else if (obj.Equals(_array[index])) {
                    return true;
                }
                index = (index + 1) % _array.Length;
            }

            return false;
        }

        internal Object GetElement(int i)
        {
            return _array[(_head + i) % _array.Length];
        }

        // Iterates over the objects in the queue, returning an array of the
        // objects in the Queue, or an empty array if the queue is empty.
        // The order of elements in the array is first in to last in, the same
        // order produced by successive calls to Dequeue.
        //| <include path='docs/doc[@for="Queue.ToArray"]/*' />
        public virtual Object[] ToArray()
        {
            Object[] arr = new Object[_size];
            if (_size == 0)
                return arr;

            if (_head < _tail) {
                Array.Copy(_array, _head, arr, 0, _size);
            }
            else {
                Array.Copy(_array, _head, arr, 0, _array.Length - _head);
                Array.Copy(_array, 0, arr, _array.Length - _head, _tail);
            }

            return arr;
        }


        // PRIVATE Grows or shrinks the buffer to hold capacity objects. Capacity
        // must be >= _size.
        private void SetCapacity(int capacity) {
            Object[] newarray = new Object[capacity];
            if (_size > 0) {
                if (_head < _tail) {
                    Array.Copy(_array, _head, newarray, 0, _size);
                }
                else {
                    Array.Copy(_array, _head, newarray, 0, _array.Length - _head);
                    Array.Copy(_array, 0, newarray, _array.Length - _head, _tail);
                }
            }

            _array = newarray;
            _head = 0;
            _tail = _size;
            _version++;
        }

        //| <include path='docs/doc[@for="Queue.TrimToSize"]/*' />
        public virtual void TrimToSize()
        {
            SetCapacity(_size);
        }


        // Implements a synchronization wrapper around a queue.
        private class SynchronizedQueue : Queue
        {
            private Queue _q;
            private Object root;

            internal SynchronizedQueue(Queue q) {
                this._q = q;
                root = _q.SyncRoot;
            }

            public override bool IsSynchronized {
                get { return true; }
            }

            public override Object SyncRoot {
                get {
                    return root;
                }
            }

            public override int Count {
                get {
                    lock (root) {
                        return _q.Count;
                    }
                }
            }

            public override void Clear() {
                lock (root) {
                    _q.Clear();
                }
            }

            public override Object Clone() {
                lock (root) {
                    return new SynchronizedQueue((Queue)_q.Clone());
                }
            }

            public override bool Contains(Object obj) {
                lock (root) {
                    return _q.Contains(obj);
                }
            }

            public override void CopyTo(Array array, int arrayIndex) {
                lock (root) {
                    _q.CopyTo(array, arrayIndex);
                }
            }

            public override void Enqueue(Object value) {
                lock (root) {
                    _q.Enqueue(value);
                }
            }

            public override Object Dequeue() {
                lock (root) {
                    return _q.Dequeue();
                }
            }

            public override IEnumerator GetEnumerator() {
                lock (root) {
                    return _q.GetEnumerator();
                }
            }

            public override Object Peek() {
                lock (root) {
                    return _q.Peek();
                }
            }

            public override Object[] ToArray() {
                lock (root) {
                    return _q.ToArray();
                }
            }

            public override void TrimToSize() {
               lock (root) {
                    _q.TrimToSize();
                }
            }
        }


        // Implements an enumerator for a Queue.  The enumerator uses the
        // internal version number of the list to ensure that no modifications are
        // made to the list while an enumeration is in progress.
        private class QueueEnumerator : IEnumerator, ICloneable
        {
            private Queue _q;
            private int _index;
            private int _version;
            private Object currentElement;

            internal QueueEnumerator(Queue q) {
                _q = q;
                _version = _q._version;
                _index = 0;
                currentElement = _q._array;
                if (_q._size == 0)
                    _index = -1;
            }

            public Object Clone()
            {
                return MemberwiseClone();
            }

            public virtual bool MoveNext() {
                if (_version != _q._version) throw new InvalidOperationException("InvalidOperation_EnumFailedVersion");

                if (_index < 0) {
                    currentElement = _q._array;
                    return false;
                }

                currentElement = _q.GetElement(_index);
                _index++;

                if (_index == _q._size)
                    _index = -1;
                return true;
            }

            public virtual Object Current {
                get {
                    if (currentElement == _q._array) {
                        if (_index == 0)
                            throw new InvalidOperationException("InvalidOperation_EnumNotStarted");
                        else
                            throw new InvalidOperationException("InvalidOperation_EnumEnded");
                    }
                    return currentElement;
                }
            }

            public virtual void Reset() {
                if (_version != _q._version) throw new InvalidOperationException("InvalidOperation_EnumFailedVersion");
                if (_q._size == 0)
                    _index = -1;
                 else
                     _index = 0;
                currentElement = _q._array;
            }
        }
    }
}