using System;
using System.Collections;
using System.Collections.Generic;

namespace Prism.Regions
{
    /// <summary>
    /// A collection of <see cref="IRegionBehavior"/> instances, that are stored and retrieved by Key.
    /// </summary>
    public class RegionBehaviorCollection : IRegionBehaviorCollection
    {
        private readonly IRegion region;
        private readonly Dictionary<string, IRegionBehavior> behaviors = new Dictionary<string, IRegionBehavior>();

        /// <summary>
        /// Initializes a new instance of the <see cref="RegionBehaviorCollection"/> class and associates it with a region.
        /// </summary>
        /// <param name="region">The region to associate the behavior collection with.</param>
        public RegionBehaviorCollection(IRegion region)
        {
            this.region = region;
        }

        /// <summary>
        /// Gets the <see cref="IRegionBehavior"/> with the specified key.
        /// </summary>
        /// <value>The RegionBehavior that's registered with the key.</value>
        public IRegionBehavior this[string key] => behaviors[key];

        /// <summary>
        /// Adds a <see cref="IRegionBehavior"/> to the collection, using the specified key as an indexer.
        /// </summary>
        /// <param name="key">The key that specifies the type of <see cref="IRegionBehavior"/> that's added.</param>
        /// <param name="regionBehavior">The <see cref="IRegionBehavior"/> to add.</param>
        /// <exception cref="ArgumentNullException">
        /// Thrown is the <paramref name="key"/> parameter is Null,
        /// or if the <paramref name="regionBehavior"/> parameter is Null.
        /// </exception>
        /// <exception cref="ArgumentException">Thrown if a behavior with the specified Key parameter already exists.</exception>
        public void Add(string key, IRegionBehavior regionBehavior)
        {
            if (key == null)
                throw new ArgumentNullException(nameof(key));

            if (regionBehavior == null)
                throw new ArgumentNullException(nameof(regionBehavior));

            if (behaviors.ContainsKey(key))
                throw new ArgumentException("Could not add duplicate behavior with same key.", nameof(key));

            behaviors.Add(key, regionBehavior);
            regionBehavior.Region = region;

            regionBehavior.Attach();
        }

        /// <summary>
        /// Checks if a <see cref="IRegionBehavior"/> with the specified key is already present.
        /// </summary>
        /// <param name="key">The key to use to find a particular <see cref="IRegionBehavior"/>.</param>
        /// <returns></returns>
        public bool ContainsKey(string key) => behaviors.ContainsKey(key);

        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
        /// </returns>
        public IEnumerator<KeyValuePair<string, IRegionBehavior>> GetEnumerator() => behaviors.GetEnumerator();

        /// <summary>
        /// Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
        /// </returns>
        IEnumerator IEnumerable.GetEnumerator() => behaviors.GetEnumerator();
    }
}
