using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace BlueWest.Core.Tests
{
   public static class PocoToDictionary
{
    private static readonly MethodInfo AddToDicitonaryMethod = typeof(IDictionary<string, object>).GetMethod("Add");
    private static readonly ConcurrentDictionary<Type, Func<object, IDictionary<string, object>>> Converters = new ConcurrentDictionary<Type, Func<object, IDictionary<string, object>>>();
    private static readonly ConstructorInfo DictionaryConstructor = typeof(Dictionary<string, object>).GetConstructors().FirstOrDefault(c => c.IsPublic && !c.GetParameters().Any());
 
    public static IDictionary<string, object> ToDictionary(this object obj) => obj == null ? null : Converters.GetOrAdd(obj.GetType(), o =>
    {
        var outputType = typeof(IDictionary<string, object>);
        var inputType = obj.GetType();
        var inputExpression = Expression.Parameter(typeof(object), "input");
        var typedInputExpression = Expression.Convert(inputExpression, inputType);
        var outputVariable = Expression.Variable(outputType, "output");
        var returnTarget = Expression.Label(outputType);
        var body = new List<Expression>
        {
            Expression.Assign(outputVariable, Expression.New(DictionaryConstructor))
        };
        body.AddRange(
            from prop in inputType.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy)
            where prop.CanRead && (prop.PropertyType.IsPrimitive || prop.PropertyType == typeof(string))
            let getExpression = Expression.Property(typedInputExpression, prop.GetMethod)
            let convertExpression = Expression.Convert(getExpression, typeof(object))
            select Expression.Call(outputVariable, AddToDicitonaryMethod, Expression.Constant(prop.Name), convertExpression));
        body.Add(Expression.Return(returnTarget, outputVariable));
        body.Add(Expression.Label(returnTarget, Expression.Constant(null, outputType)));
 
        var lambdaExpression = Expression.Lambda<Func<object, IDictionary<string, object>>>(
            Expression.Block(new[] { outputVariable }, body),
            inputExpression);
 
        return lambdaExpression.Compile();
    })(obj);
}
}