using System;
using System.ComponentModel;
using System.Reflection;
using BLToolkit.Mapping;
using BLToolkit.Reflection;

namespace BLToolkit.Validation
{
    public class ValidationContext
    {
        public delegate bool IsNullHandler(ValidationContext context);

        private object _object;
        public  object  Object
        {
            get { return _object;  }
            set { _object = value; }
        }

        private TypeAccessor _typeAccessor;
        public  TypeAccessor  TypeAccessor
        {
            get
            {
                if (_typeAccessor == null)
                    _typeAccessor = TypeAccessor.GetAccessor(_object.GetType());

                return _typeAccessor;
            }
        }

        private PropertyDescriptor _propertyDescriptor;
        public  PropertyDescriptor  PropertyDescriptor
        {
            get { return _propertyDescriptor;  }
            set { _propertyDescriptor = value; }
        }

        private IsNullHandler _isNull;
        public  IsNullHandler  IsNull
        {
            get { return _isNull;  }
            set { _isNull = value; }
        }

        public  bool IsValueNull
        {
            get { return _isNull(this);  }
        }

        private object _value;
        public  object  Value
        {
            get { return _value;  }
            set
            {
                _value     = value;
                _nullValue = null;
            }
        }

        private MemberAccessor _memberAccessor;
        public  MemberAccessor  MemberAccessor
        {
            get { return _memberAccessor; }
            set 
            {
                _memberAccessor = value;
                _memberInfo     = value != null? value.MemberInfo: null;
            }
        }

        private MemberInfo _memberInfo;
        public  MemberInfo  MemberInfo
        {
            get { return _memberInfo;  }
        }

        private object _nullValue;
        public  object  NullValue
        {
            get
            {
                if (_nullValue == null)
                {
                    if (_value == null)
                        throw new InvalidOperationException("NullValue is undefined when Value == null");

                    ObjectMapper om = Map.GetObjectMapper(Object.GetType());
                    MemberMapper mm = om[MemberName, true];

                    _nullValue =
                        mm != null && mm.MapMemberInfo.Nullable && mm.MapMemberInfo.NullValue != null?
                            mm.MapMemberInfo.NullValue:
                            TypeAccessor.GetNullValue(Value.GetType());

                    if (_nullValue == null)
                        _nullValue = DBNull.Value;
                }

                return _nullValue;

            }
        }

        public string MemberName
        {
            get
            {
                return
                    _memberInfo         != null? _memberInfo.Name:
                    _propertyDescriptor != null? _propertyDescriptor.Name:
                        null;
            }
        }
    }
}