using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Text;

namespace Dfs.WayneChina.SpsDataCourier
{
    /// <summary>
    /// Taken from the link below:
    /// https://stackoverflow.com/questions/3189861/pass-a-lambda-expression-in-place-of-icomparer-or-iequalitycomparer-or-any-singl
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <typeparam name="TKey"></typeparam>
    public class GenericComparer<T, TKey> : IComparer<T>, IEqualityComparer<T>
    {
        private readonly Expression<Func<T, TKey>> _KeyExpr;
        private readonly Func<T, TKey> _CompiledFunc;
        
        // Constructor
        public GenericComparer(Expression<Func<T, TKey>> getKey)
        {
            _KeyExpr = getKey;
            _CompiledFunc = _KeyExpr.Compile();
        }

        public int Compare(T obj1, T obj2)
        {
            return Comparer<TKey>.Default.Compare(_CompiledFunc(obj1), _CompiledFunc(obj2));
        }

        public bool Equals(T obj1, T obj2)
        {
            return EqualityComparer<TKey>.Default.Equals(_CompiledFunc(obj1), _CompiledFunc(obj2));
        }

        public int GetHashCode(T obj)
        {
            return EqualityComparer<TKey>.Default.GetHashCode(_CompiledFunc(obj));
        }
    }
}