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

namespace Chernobyl.Dependency
{
    /// <summary>
    /// A base class for <see cref="Attribute"/>s that are used to work with 
    /// services.
    /// </summary>
    public abstract class ServiceAttribute : Attribute
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="ServiceAttribute"/> 
        /// class.
        /// </summary>
        protected ServiceAttribute() : this(Array<Type>.Empty)
        {}

        /// <summary>
        /// Initializes a new instance of the <see cref="ServiceAttribute"/> 
        /// class.
        /// </summary>
        /// <param name="location">The location of the service within the
        /// <see cref="IEventCollection{T}"/> hierarchy or an empty array if the service 
        /// is at the root of the hierarchy. This <see cref="System.Type"/> array 
        /// represents the  "path" that must be taken through the hierarchy of 
        /// <see cref="IEventCollection{Object}"/> to get to the location where the service 
        /// specified by <see cref="Type"/> resides. Each 
        /// <see cref="System.Type"/> must implement the <see cref="IEventCollection{Object}"/> 
        /// interface. An example of what the service path might look like 
        /// (using '/' as separators):
        /// <example>/IEventCollection{Object}/IGraphicsServices/ITextureServices</example>
        /// In this example, the service represented by <see cref="Type"/>
        /// is located in the <see cref="IEventCollection{Object}"/> ITextureServices. That 
        /// <see cref="IEventCollection{Object}"/> is located within IGraphicsServices which 
        /// is located at the root <see cref="IEventCollection{Object}"/>.</param>
        protected ServiceAttribute(params Type[] location)
        {
            Location = location;
        }

        /// <summary>
        /// Performs the intended goal of this <see cref="ServiceAttribute"/>
        /// with relation to the attributed code element
        /// (<paramref name="attributeProvider"/>) and the <see cref="IEventCollection{Object}"/>
        /// (<paramref name="services"/>) that is processing that code element.
        /// </summary>
        /// <param name="services">The <see cref="IEventCollection{Object}"/> instance that
        /// allows access to the other services and provides adding or removing
        /// of specific services.</param>
        /// <param name="instance">The instance that contained a code element that
        /// was attributed with a <see cref="ServiceAttribute"/> derived instance.</param>
        /// <param name="attributeProvider">The code element that was attributed
        /// with a <see cref="ServiceAttribute"/> derived instance.</param>
        public abstract void Resolve(IEventCollection<Object> services, object instance,
                                     ICustomAttributeProvider attributeProvider);

        /// <summary>
        /// The location of the service within the <see cref="IEventCollection{Object}"/> 
        /// hierarchy or an empty array if the service is at the root of the 
        /// hierarchy. This <see cref="System.Type"/> array represents the "path"
        /// that must be taken through the hierarchy of <see cref="IEventCollection{Object}"/> 
        /// to get to the location where the service specified by 
        /// <see cref="Type"/> resides. Each <see cref="System.Type"/> must 
        /// implement the <see cref="IEventCollection{Object}"/> interface. An example of 
        /// what the service path might look like (using '/' as separators):
        /// <example>/IEventCollection{Object}/IGraphicsServices/ITextureServices</example>
        /// In this example, the service represented by <see cref="Type"/>
        /// is located in the <see cref="IEventCollection{Object}"/> ITextureServices. That 
        /// <see cref="IEventCollection{Object}"/> is located within IGraphicsServices which 
        /// is located at the root <see cref="IEventCollection{Object}"/>.
        /// </summary>
        /// <exception cref="ArgumentException">Thrown when any of the 
        /// <see cref="System.Type"/>s contained within the array set on this property
        /// are not of the <see cref="IEventCollection{Object}"/> <see cref="System.Type"/>.</exception>
        public Type[] Location
        {
            get { return _location; }
            set
            {
                if(value.All(type => typeof(IEventCollection<Object>).IsAssignableFrom(type)) == false)
                    throw new ArgumentException("All of the Types within the " +
                    "Location must be of type \"" + 
                    typeof(IEventCollection<Object>).FullName + "\" to allow for a hierarchy of " +
                    typeof(IEventCollection<Object>).FullName + "instances.", "value");
                
                _location = value;
            }
        }

        /// <summary>
        /// The type of the service being provided or injected. Set
        /// this property if the property type, return type, or 
        /// method parameter type does not depict the service type needed
        /// or provided.
        /// </summary>
        public Type Type { get; set; }

        /// <summary>
        /// The backing field to <see cref="Location"/>.
        /// </summary>
        Type[] _location;
    }

    /// <summary>
    /// Utility methods for <see cref="ServiceAttribute"/> or code that uses it.
    /// </summary>
    public static class ServiceAttributeExtensions
    {
        /// <summary>
        /// This method will set a service onto any member that has been
        /// attributed with the <see cref="InjectAttribute" /> attribute when that
        /// service is ready. For any member that has been attributed with the
        /// <see cref="ServiceAttribute" /> attribute, this method will take the
        /// value of that member as service. By default, this method uses
        /// <see cref="ServiceAttributeExtensions.DeclaredOnlyInstancePublicMembers" /> 
        /// to locate the <see cref="ICustomAttributeProvider" /> instances that 
        /// are to have services injected into or pulled from them.
        /// </summary>
        /// <typeparam name="T">The type of the object to take services
        /// from or give services to.</typeparam>
        /// <param name="services">The instance that will take or give services.</param>
        /// <param name="instance">The object that is to have services injected
        /// into or taken from it.</param>
        public static void Inject<T>(this IEventCollection<object> services, T instance)
        {
            services.Inject(instance, DeclaredOnlyInstancePublicMembers);
        }

        /// <summary>
        /// This method will set a service onto any member that has been 
        /// attributed with the <see cref="InjectAttribute"/> attribute when that
        /// service is ready. For any member that has been attributed with the 
        /// <see cref="ServiceAttribute"/> attribute, this method will take the 
        /// value of that member as service.
        /// </summary>
        /// <typeparam name="T">The type of the object to take services
        /// from or give services to.</typeparam>
        /// <param name="services">The instance that will take or give services.</param>
        /// <param name="instance">The object that is to have services injected
        /// into or taken from it.</param>
        /// <param name="attributeProviderRetriever">The method used to get the 
        /// <see cref="ICustomAttributeProvider"/>s on the 
        /// <paramref name="instance"/>. The 
        /// <see cref="ICustomAttributeProvider"/>s will be searched for 
        /// <see cref="ServiceAttribute"/>s that will be used for injection.</param>
        public static void Inject<T>(this IEventCollection<object> services, T instance,
                                     Func<Type, IEnumerable<ICustomAttributeProvider>> attributeProviderRetriever)
        {
            Type objectType = typeof(T);

            IEnumerable<ICustomAttributeProvider> attributeProviders = attributeProviderRetriever(objectType);
            foreach (ICustomAttributeProvider attributeProvider in attributeProviders)
            {
                object[] attributes = attributeProvider.GetCustomAttributes(typeof(ServiceAttribute), true);
                foreach (ServiceAttribute serviceAttribute in attributes.Cast<ServiceAttribute>())
                    serviceAttribute.Resolve(services, instance, attributeProvider);
            }
        }

        /// <summary>
        /// Returns the <see cref="BindingFlags.Instance"/>, 
        /// <see cref="BindingFlags.DeclaredOnly"/>, and 
        /// <see cref="BindingFlags.Public"/> <see cref="PropertyInfo"/> 
        /// instances of the <see cref="Type"/> passed in as 
        /// <see cref="ICustomAttributeProvider"/>s.
        /// </summary>
        /// <param name="type">The type whose <see cref="PropertyInfo"/>
        /// <see cref="ICustomAttributeProvider"/>s are to be retrieved.</param>
        /// <returns>The <see cref="PropertyInfo"/> of the <paramref name="type"/>
        /// as <see cref="ICustomAttributeProvider"/>s. </returns>
        public static IEnumerable<ICustomAttributeProvider> DeclaredOnlyInstancePublicMembers(Type type)
        {
            return type.GetProperties(BindingFlags.Instance | BindingFlags.DeclaredOnly | BindingFlags.Public);
        }
    }
}