using System;
using System.Collections.Generic;

using DataStructures.Common;

namespace DataStructures.Heaps
{
    /// <summary>
    /// Implements the Priority Queue Data Structure.
    /// <typeparam name="TKey">Node's Value type</typeparam>
    /// <typeparam name="TPriority">Node's Priority type</typeparam>
    /// </summary>
    public class MinPriorityQueue<TKey, TPriority>
        where TKey : IComparable<TKey>
        where TPriority : IComparable<TPriority>
    {
        /// <summary>
        /// Instance variables
        /// </summary>
        // A dictionary of keys and number of copies in the heap.
        private Dictionary<TKey, long> _keys { get; set; }

        // The internal heap.
        private BinaryMinHeap<PriorityQueueNode<TKey, TPriority>> _heap { get; set; }

        // The priorities value comparer.
        private Comparer<PriorityQueueNode<TKey, TPriority>> _priorityComparer { get; set; }


        /// <summary>
        /// CONSTRUCTOR
        /// </summary>
        public MinPriorityQueue() : this(0, null) { }

        public MinPriorityQueue(uint capacity) : this(capacity, null) { }

        public MinPriorityQueue(uint capacity, Comparer<PriorityQueueNode<TKey, TPriority>> priorityComparer)
        {
            // Make sure the TPriority is elegible for a priority
            if (!_validPriorityType())
                throw new NotSupportedException("The priority type is not supported.");

            // Initialize comparer
            if (priorityComparer == null)
                _priorityComparer = Comparer<PriorityQueueNode<TKey, TPriority>>.Default;
            else
                _priorityComparer = priorityComparer;

            // Initialize.
            _keys = new Dictionary<TKey, long>();
            _heap = new BinaryMinHeap<PriorityQueueNode<TKey, TPriority>>((int)capacity, this._priorityComparer);
        }


        /// <summary>
        /// Validates the Type of TPriority. Returns true if acceptable, false otherwise.
        /// </summary>
        /// <returns></returns>
        private bool _validPriorityType()
        {
            bool isValid = false;
            TypeCode typeCode = Type.GetTypeCode(typeof(TPriority));

            switch (typeCode)
            {
                //case TypeCode.DateTime:
                case TypeCode.Byte:
                case TypeCode.Char:
                case TypeCode.Decimal:
                case TypeCode.Double:
                case TypeCode.Int16:
                case TypeCode.Int32:
                case TypeCode.Int64:
                case TypeCode.SByte:
                case TypeCode.Single:
                case TypeCode.UInt16:
                case TypeCode.UInt32:
                case TypeCode.UInt64:
                    isValid = true;
                    break;
                default:
                    isValid = false;
                    break;
            }

            return isValid;
        }


        /// <summary>
        /// Returns the count of elements in the queue.
        /// </summary>
        public int Count
        {
            get { return _heap.Count; }
        }

        /// <summary>
        /// Checks if the queue is empty
        /// </summary>
        public bool IsEmpty
        {
            get { return _heap.IsEmpty; }
        }

        /// <summary>
        /// Get the default max priority, if set, raises an exception if not set.
        /// Also sets the default max priority.
        /// </summary>
        public TPriority DefaultMaxPriority
        {
            get
            {
                object maxValue = default(TPriority);
                TypeCode typeCode = Type.GetTypeCode(typeof(TPriority));
                switch (typeCode)
                {
                    case TypeCode.Byte:
                        maxValue = byte.MaxValue;
                        break;
                    case TypeCode.Char:
                        maxValue = char.MaxValue;
                        break;
                    case TypeCode.DateTime:
                        maxValue = DateTime.MaxValue;
                        break;
                    case TypeCode.Decimal:
                        maxValue = decimal.MaxValue;
                        break;
                    case TypeCode.Double:
                        maxValue = decimal.MaxValue;
                        break;
                    case TypeCode.Int16:
                        maxValue = short.MaxValue;
                        break;
                    case TypeCode.Int32:
                        maxValue = int.MaxValue;
                        break;
                    case TypeCode.Int64:
                        maxValue = long.MaxValue;
                        break;
                    case TypeCode.SByte:
                        maxValue = sbyte.MaxValue;
                        break;
                    case TypeCode.Single:
                        maxValue = float.MaxValue;
                        break;
                    case TypeCode.UInt16:
                        maxValue = ushort.MaxValue;
                        break;
                    case TypeCode.UInt32:
                        maxValue = uint.MaxValue;
                        break;
                    case TypeCode.UInt64:
                        maxValue = ulong.MaxValue;
                        break;
                }

                return (TPriority)maxValue;
            }
        }

        /// <summary>
        /// Returns the highest priority element.
        /// </summary>
        /// <returns>The at highest priority.</returns>
        public TKey PeekAtMinPriority()
        {
            if (_heap.IsEmpty)
            {
                throw new ArgumentOutOfRangeException("Queue is empty.");
            }

            return _heap.Peek().Key;
        }

        /// <summary>
        /// Checks for the existence of a key in the queue
        /// </summary>
        public bool Contains(TKey key)
        {
            return _keys.ContainsKey(key);
        }

        /// <summary>
        /// Enqueue the specified key, with the default-max-priority value.
        /// </summary>
        public void Enqueue(TKey key)
        {
            Enqueue(key, DefaultMaxPriority);
        }

        /// <summary>
        /// Enqueue the specified key, value and priority.
        /// </summary>
        /// <param name="value">Value.</param>
        /// <param name="priority">Priority.</param>
        public void Enqueue(TKey key, TPriority priority)
        {
            var newNode = new PriorityQueueNode<TKey, TPriority>(key, priority);
            _heap.Add(newNode);

            if (_keys.ContainsKey(key))
                _keys[key] += 1;
            else
                _keys.Add(key, 1);
        }

        /// <summary>
        /// Dequeue this instance.
        /// </summary>
        public TKey DequeueMin()
        {
            if (_heap.IsEmpty)
                throw new ArgumentOutOfRangeException("Queue is empty.");

            var key = _heap.ExtractMin().Key;

            // Decrease the key count.
            _keys[key] = _keys[key] - 1;

            // Remove key if its count is zero
            if (_keys[key] == 0)
                _keys.Remove(key);

            return key;
        }

        /// <summary>
        /// Sets the priority.
        /// </summary>
        public void UpdatePriority(TKey key, TPriority newPriority)
        {
            // Handle boundaries errors
            if (_heap.IsEmpty)
                throw new ArgumentOutOfRangeException("Queue is empty.");
            if (!_keys.ContainsKey(key))
                throw new KeyNotFoundException();

            int i;
            for (i = 0; i < _heap.Count; ++i)
                if (_heap[i].Key.IsEqualTo(key))
                    break;

            _heap[i].Priority = newPriority;
        }

        /// <summary>
        /// Clear this priority queue.
        /// </summary>
        public void Clear()
        {
            _heap.Clear();
            _keys.Clear();
        }
    }



    /// <summary>
    /// The Priority-queue node.
    /// </summary>
    /// <typeparam name="K">Node's Key type</typeparam>
    /// <typeparam name="TKey">Node's Value type</typeparam>
    public class PriorityQueueNode<TKey, TPriority> : IComparable<PriorityQueueNode<TKey, TPriority>>
        where TKey : IComparable<TKey>
        where TPriority : IComparable<TPriority>
    {
        public TKey Key { get; set; }
        public TPriority Priority { get; set; }

        public PriorityQueueNode() : this(default(TKey), default(TPriority)) { }

        public PriorityQueueNode(TKey value, TPriority priority)
        {
            this.Key = value;
            this.Priority = priority;
        }

        public int CompareTo(PriorityQueueNode<TKey, TPriority> other)
        {
            if (other == null)
                return -1;

            return this.Priority.CompareTo(other.Priority);
        }
    }//end-of-node-class

}