using System.Collections.Generic;
using JD.Kernel.StaticHelpers;

namespace JD.Collections
{
    /// <summary>
    /// Counts the occurrences of key.
    /// </summary>
    public class OccurencesCounter<TKey>
    {
        #region Variables

        private readonly Dictionary<TKey, int> m_counts = new Dictionary<TKey, int>();

        #endregion

        #region Properties

        public ICollection<TKey> Keys
        {
            get { return m_counts.Keys; }
        }

        /// <summary>
        /// Enumerates all the items (in key) and the count of occurrences (the value).
        /// </summary>
        public ICollection<KeyValuePair<TKey, int>> Occurences
        {
            get { return m_counts; }
        }

        public bool IsEmpty
        {
            get { return m_counts.Count == 0; }
        }

        #endregion

        #region Methods

        public int OccurenceOf(TKey key)
        {
            Throw.IfNull(key, "key");

            int count;
            m_counts.TryGetValue(key, out count);
            return count;
        }

        /// <summary>
        /// Increments the occurence for the given <paramref name="key"/>. Returns 1 if it's the first time the key is referenced.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public int Increment(TKey key)
        {
            Throw.IfNull(key, "key");

            return Increment(key, 1);
        }

        /// <summary>
        /// Increments the occurence for the given <paramref name="key"/>.
        /// </summary>
        public int Increment(TKey key, int increment)
        {
            Throw.IfNull(key, "key");

            int count;
            if (!m_counts.TryGetValue(key, out count))
            {
                count = 0;
            }

            count += increment;
            SetValue(key, count);

            return count;
        }

        /// <summary>
        /// Decrements the occurence for the given <paramref name="key"/>. Returns 0 if it's the last time the key is referenced.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public int Decrement(TKey key)
        {
            Throw.IfNull(key, "key");

            int count;
            if (!m_counts.TryGetValue(key, out count))
            {
                count = 0;
            }

            count--;
            SetValue(key, count);

            return count;
        }

        /// <summary>
        /// Whether a key in the given collection has occurred at least one time.
        /// </summary>
        /// <param name="keys"></param>
        /// <returns></returns>
        public bool OccurenceOfAny(params TKey[] keys)
        {
            Throw.IfNull(keys, "keys");

            foreach (TKey currentKey in keys)
            {
                if (OccurenceOf(currentKey) > 0)
                {
                    return true;
                }
            }

            return false;
        }

        /// <summary>
        /// Clear.
        /// </summary>
        public void Clear()
        {
            m_counts.Clear();
        }

        /// <summary>
        /// Sets the occurence count directly.
        /// </summary>
        public void SetValue(TKey key, int count)
        {
            if (count == 0)
            {
                m_counts.Remove(key);
            }
            else
            {
                m_counts[key] = count;
            }
        }

        #endregion
    }
}