using System;
using System.Collections.Generic;
using System.Reflection;
using Chernobyl.Attribution;
using Chernobyl.Reflection;

namespace Chernobyl.Extensions.System.Collections.Generic
{
    /// <summary>
    /// Extensions for <see cref="KeyValuePair{TKey, TValue}"/> and related types.
    /// </summary>
    public static class KeyValuePairExtensions
    {
        /// <summary>
        /// Returns a method that, when invoked, invokes the specified callback
        /// with the value tied to a key.
        /// </summary>
        /// <typeparam name="TKey">The type of the key.</typeparam>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <param name="callback">The method to invoke with the key-value 
        /// pair.</param>
        /// <param name="createKey">The method that creates the key.</param>
        /// <returns>The method that converts the instance to a key-value pair.</returns>
        public static Callback<TValue> Key<TKey, TValue>(
            this Callback<KeyValuePair<TKey, TValue>> callback,
            Func<TValue, TKey> createKey)
        {
            return callback.Select<TValue, KeyValuePair<TKey, TValue>>(
                value =>
                {
                    var key = createKey(value);
                    return new KeyValuePair<TKey, TValue>(key, value);
                });
        }

        /// <summary>
        /// Returns a method that, when invoked, invokes the specified callback
        /// with the value tied to a key retrieved from the <see cref="GuidAttribute" />
        /// assigned to <paramref name="attributeProvider" />.
        /// </summary>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <param name="callback">The method to invoke with the key-value
        /// pair.</param>
        /// <param name="attributeProvider">The instance to pull the key from.</param>
        /// <param name="inherit">True to look up the hiearchy chain for the 
        /// attribute.</param>
        /// <returns>
        /// The method that converts the instance to a key-value pair.
        /// </returns>
        public static Callback<TValue> AttributeKey<TValue>(
            this Callback<KeyValuePair<Guid, TValue>> callback,
            ICustomAttributeProvider attributeProvider, bool inherit)
        {
            return callback.AttributeKey(attributeProvider, true, key => key);
        }

        /// <summary>
        /// Returns a method that, when invoked, invokes the specified callback
        /// with the value tied to a key retrieved from the <see cref="GuidAttribute" />
        /// assigned to <paramref name="attributeProvider" />.
        /// </summary>
        /// <typeparam name="TKey">The type of the key.</typeparam>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <param name="callback">The method to invoke with the key-value
        /// pair.</param>
        /// <param name="attributeProvider">The instance to pull the key from.</param>
        /// <param name="inherit">True to look up the hiearchy chain for the
        /// attribute.</param>
        /// <param name="keySelect">The method that converts the key.</param>
        /// <returns>
        /// The method that converts the instance to a key-value pair.
        /// </returns>
        public static Callback<TValue> AttributeKey<TKey, TValue>(
            this Callback<KeyValuePair<TKey, TValue>> callback,
            ICustomAttributeProvider attributeProvider, bool inherit,
            Func<Guid, TKey> keySelect)
        {
            return callback.Key(
                subscribe =>
                {
                    var key = attributeProvider.GetCustomAttribute<GuidAttribute>(inherit).Key;
                    return keySelect(key);
                });
        }
    }
}