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

namespace Chernobyl.Reflection
{
    /// <summary>
    /// Extension and utility methods for <see cref="ICustomAttributeProvider"/>.
    /// </summary>
    public static class CustomAttributeProviderExtensions
    {
        /// <summary>
        /// Returns the <typeparamref name="TAttribute"/> custom 
        /// attribute instances defined on this member or an empty 
        /// <see cref="IEnumerable{T}"/> if there are no custom attributes of 
        /// that type. Effectively, this method does the exact same thing as
        /// <see cref="ICustomAttributeProvider.GetCustomAttributes(Type, bool)"/>.
        /// </summary>
        /// <typeparam name="TAttribute">The type of the attribute
        /// instances to return.</typeparam>
        /// <param name="provider">The instance to retrieve the attribute 
        /// instances from.</param>
        /// <param name="inherit">When true, look up the hierarchy chain for the 
        /// inherited custom attributes.</param>
        /// <returns>The attribute instances defined on
        /// <paramref name="provider"/>.</returns>
        public static IEnumerable<TAttribute> GetCustomAttributes<TAttribute>(
            this ICustomAttributeProvider provider, bool inherit)
        {
            return provider.GetCustomAttributes(typeof(TAttribute), inherit)
                           .Cast<TAttribute>();
        }

        /// <summary>
        /// Returns the <typeparamref name="TAttribute"/> custom 
        /// attribute instance defined on this member or null if there are no 
        /// custom attributes of that type. Effectively, this method does the 
        /// exact same thing as
        /// <see cref="ICustomAttributeProvider.GetCustomAttributes(Type, bool)"/>.
        /// </summary>
        /// <typeparam name="TAttribute">The type of the attribute
        /// instance to return.</typeparam>
        /// <param name="provider">The instance to retrieve the 
        /// attribute instance from.</param>
        /// <param name="inherit">When true, look up the hierarchy chain for the 
        /// inherited custom attribute.</param>
        /// <returns>The attribute instance defined on
        /// <paramref name="provider"/> or null if there is no attribute of type
        /// <typeparamref name="TAttribute"/>.</returns>
        public static TAttribute GetCustomAttribute<TAttribute>(
            this ICustomAttributeProvider provider, bool inherit)
        {
            return provider.GetCustomAttributes<TAttribute>(inherit)
                           .FirstOrDefault();
        }

        /// <summary>
        /// Returns true if the specified <see cref="ICustomAttributeProvider"/>
        /// has an attribute of the type specified by <paramref name="attributeType"/>.
        /// </summary>
        /// <param name="provider">The instance to check for the attribute.</param>
        /// <param name="attributeType">The type of attribute to check for on
        /// the instance.</param>
        /// <param name="inherit">When true, look up the hierarchy chain for the 
        /// inherited custom attribute.</param>
        /// <returns>True if the provider has the attribute, false if otherwise.</returns>
        public static bool HasAttribute(this ICustomAttributeProvider provider, 
                                        Type attributeType, 
                                        bool inherit)
        {
            return provider.GetCustomAttributes(attributeType, inherit)
                           .IsEmpty() == false;
        }

        /// <summary>
        /// Returns true if the specified <see cref="ICustomAttributeProvider" />
        /// has an attribute of the type specified by <typeparamref name="TAttribute"/>.
        /// </summary>
        /// <typeparam name="TAttribute">The type of attribute to check for on
        /// the instance.</typeparam>
        /// <param name="provider">The instance to check for the attribute.</param>
        /// <param name="inherit">When true, look up the hierarchy chain for the
        /// inherited custom attribute.</param>
        /// <returns>True if the provider has the attribute, false if otherwise.</returns>
        public static bool HasAttribute<TAttribute>(this ICustomAttributeProvider provider,
                                                    bool inherit)
        {
            return provider.HasAttribute(typeof (TAttribute), inherit);
        }
    }
}