using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using Chernobyl.Attribution;
using Chernobyl.Collections.Generic.Event;
using Chernobyl.Values;
using Chernobyl.Reflection;

namespace Chernobyl.Dependency
{
    /// <summary>
    /// Interface for attributes which get the value of an attributable item. 
    /// </summary>
    public interface IGetAttribute
    {
        /// <summary>
        /// Returns the value of the specified attribute provider. The attribute
        /// provider must be the instance that this 
        /// <see cref="IGetAttribute{TCustomAttributeProvider}"/> was attributing.
        /// </summary>
        /// <param name="attributeProvider">The instance this 
        /// <see cref="IGetAttribute{TCustomAttributeProvider}"/> was 
        /// attributing.</param>
        /// <returns>The value of the requested item.</returns>
        IValue<object> Get(ICustomAttributeProvider attributeProvider);
    }

    /// <summary>
    /// Interface for attributes which get the value of an attributable item.
    /// </summary>
    /// <typeparam name="TCustomAttributeProvider">The type being attributed.</typeparam>
    public interface IGetAttribute<TCustomAttributeProvider> : IGetAttribute
        where TCustomAttributeProvider : ICustomAttributeProvider
    {
        /// <summary>
        /// Returns the value of the specified attribute provider. The attribute
        /// provider must be the instance that this 
        /// <see cref="IGetAttribute{TCustomAttributeProvider}"/> was attributing.
        /// </summary>
        /// <param name="attributeProvider">The instance this 
        /// <see cref="IGetAttribute{TCustomAttributeProvider}"/> was 
        /// attributing.</param>
        /// <returns>The value of the requested item.</returns>
        IValue<object> Get(TCustomAttributeProvider attributeProvider);
    }

    /// <summary>
    /// Extensions and utilities for <see cref="IGetAttribute"/> and related types.
    /// </summary>
    public static class GetAttributeExtensions
    {
        /// <summary>
        /// Retrieves the values from the provided 
        /// <typeparamref name="TCustomAttributeProvider"/> instances using the
        /// <see cref="IGetAttribute"/> on each 
        /// <typeparamref name="TCustomAttributeProvider"/> to retrieve the value.
        /// </summary>
        /// <typeparam name="TCustomAttributeProvider">The type that can be 
        /// attributed.</typeparam>
        /// <param name="providers">The instances to pull the values from.</param>
        /// <returns>The list of values pulled from <paramref name="providers"/>.</returns>
        public static IEnumerable<IValue<Object>> Get<TCustomAttributeProvider>(this IEnumerable<TCustomAttributeProvider> providers)
            where TCustomAttributeProvider : ICustomAttributeProvider
        {
            // Go through all of the parameters on the method, grab the 
            // IGetAttribute for each, and get the IValue<T> parameter from each.
            return from parameterInfo in providers
                   let getAttribute = parameterInfo.GetCustomAttributes<IGetAttribute>(true).First()
                   select getAttribute.Get(parameterInfo);
        }

        /// <summary>
        /// Returns an <see cref="IValue{T}"/> that holds the value of return
        /// parameter on a static method.
        /// </summary>
        /// <param name="returnParameter">The instance that represents the return
        /// parameter. This instance's <see cref="ParameterInfo.Member"/> must be
        /// a static <see cref="MethodInfo"/>. The static method's input parameters
        /// must be attributed with <see cref="GetAttribute"/>.</param>
        /// <returns>The instance that holds the return value.</returns>
        /// <exception cref="InvalidTypeException">Thrown when the 
        /// <paramref name="returnParameter"/> instance's
        /// <see cref="ParameterInfo.Member"/> is not a <see cref="MethodBase"/>.</exception>
        /// <exception cref="MethodException">Thrown when the 
        /// <paramref name="returnParameter"/> instance's 
        /// <see cref="ParameterInfo.Member"/> is not static.</exception>
        public static IValue<Object> ToReturnValue(this ParameterInfo returnParameter)
        {
            MethodBase method = returnParameter.Member.Require<MethodBase>();
            method.ThrowWhenStaticIs(false);

            // Create the IValue<T> that will create the instance from the method.
            var parameters = method.GetParameters().Get().ToEventList();
            return new ReturnValue<object>(method, parameters);
        }
    }
}