// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.

using System.Reflection;

namespace System.Web.Helpers.Claims
{
    // Represents a Claim; serves as an abstraction around the WIF SDK and 4.5 Claim types since
    // we can't compile directly against them.
    internal sealed class Claim
    {
        public Claim(string claimType, string value)
        {
            ClaimType = claimType;
            Value = value;
        }

        public string ClaimType { get; private set; }

        public string Value { get; private set; }

        // Creates a Claim from a TClaim object (duck typing).
        //
        // The TClaim must have the following shape:
        // class TClaim {
        //   string ClaimType { get; } // or just 'Type'
        //   string Value { get; }
        // }
        internal static Claim Create<TClaim>(TClaim claim)
        {
            return ClaimFactory<TClaim>.Create(claim);
        }

        private static class ClaimFactory<TClaim>
        {
            private static readonly Func<TClaim, string> _claimTypeGetter = CreateClaimTypeGetter();
            private static readonly Func<TClaim, string> _valueGetter = CreateValueGetter();

            public static Claim Create(TClaim claim)
            {
                return new Claim(_claimTypeGetter(claim), _valueGetter(claim));
            }

            private static Func<TClaim, string> CreateClaimTypeGetter()
            {
                // the claim type might go by one of two different property names
                return CreateGeneralPropertyGetter("ClaimType") ?? CreateGeneralPropertyGetter("Type");
            }

            private static Func<TClaim, string> CreateGeneralPropertyGetter(string propertyName)
            {
                PropertyInfo propInfo = typeof(TClaim).GetProperty(propertyName, BindingFlags.Public | BindingFlags.Instance, null, typeof(string), Type.EmptyTypes, null);
                if (propInfo == null)
                {
                    return null;
                }

                MethodInfo propGetter = propInfo.GetGetMethod();

                // For improved perf, instance methods can be treated as static methods by leaving
                // the 'this' parameter unbound. Virtual dispatch for the property getter will
                // still take place as expected.
                return (Func<TClaim, string>)Delegate.CreateDelegate(typeof(Func<TClaim, string>), propGetter);
            }

            private static Func<TClaim, string> CreateValueGetter()
            {
                return CreateGeneralPropertyGetter("Value");
            }
        }
    }
}
