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

// This base class comes from Jimmy Bogard, but with support of inheritance
// http://grabbagoft.blogspot.com/2007/06/generic-value-object-equality.html

public abstract class ValueObject<T> : IEquatable<T>
  where T : ValueObject<T>
{
    public override bool Equals(object obj)
    {
        if (obj == null)
            return false;

        var other = obj as T;

        return Equals(other);
    }

    public override int GetHashCode()
    {
        var fields = GetFields(this);

        var startValue = 17;
        var multiplier = 59;

        return fields
            .Select(field => field.GetValue(this))
            .Where(value => value != null)
            .Aggregate(
                startValue,
                    (current, value) => current * multiplier + value.GetHashCode());
    }

    public virtual bool Equals(T other)
    {
        if (other == null)
            return false;

        var t = GetType();
        var otherType = other.GetType();

        if (t != otherType)
            return false;

        var fields = GetFields(this);

        foreach (var field in fields)
        {
            var value1 = field.GetValue(other);
            var value2 = field.GetValue(this);

            if (value1 == null)
            {
                if (value2 != null)
                    return false;
            }
            else if (!value1.Equals(value2))
                return false;
        }

        return true;
    }

    private static IEnumerable<FieldInfo> GetFields(object obj)
    {
        var t = obj.GetType();

        var fields = new List<FieldInfo>();

        while (t != typeof(object))
        {
            if (t == null) continue;
            fields.AddRange(t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public));

            t = t.BaseType;
        }

        return fields;
    }

    public static bool operator ==(ValueObject<T> x, ValueObject<T> y)
    {
        if (ReferenceEquals(x, y))
        {
            return true;
        }

        if (((object)x == null) || ((object)y == null))
        {
            return false;
        }

        return x.Equals(y);
    }

    public static bool operator !=(ValueObject<T> x, ValueObject<T> y)
    {
        return !(x == y);
    }
}