A framework for comprehensive validation of user input

// Copyright (c) 2010 - 2012, Andreas Ganzer. All Rights reserved.

using System;
using System.Diagnostics;
using System.Globalization;
using System.Windows.Controls;
using System.Windows.Data;
using Ganzer.Validation;

namespace Ganzer.Wpf.Validation
{
	//############################################################################
	/// <summary>
	/// The ValidatorValidationRule class defines a validation rule that uses
	/// a <see cref="Validator"/> object for input validation.
	/// </summary>
	/// 
	public class ValidatorValidationRule : ValidationRule
	{
		#region properties

		private Validator _validator;

		/// <summary>
		/// Gets or sets the validator to use.
		/// </summary>
		/// 
		/// <returns>The validator to use or <c>null</c> if no validator is set.
		///   </returns>
		///   
		/// <remarks>
		/// This property can be set in XAML but cannot be filled by a data binding.
		/// </remarks>
		/// 
		public Validator Validator
		{
			get
			{
				return _validator;
			}
			set
			{
				_validator = value;
			}
		}

		private string _propertyName;

		/// <summary>
		/// Gets or sets the name of the property to validate.
		/// </summary>
		/// 
		/// <returns>The name of the property to validate or <c>null</c> if no
		///   name is set.</returns>
		/// 
		/// <remarks>
		/// <para>This is necessary to validate a binding group. This property is
		/// ignored if this validation rule is not defined within a binding group.
		/// </para>
		/// <para>This property can be set in XAML but cannot be filled by a data
		/// binding.</para>
		/// </remarks>
		/// 
		public string PropertyName
		{
			get
			{
				return _propertyName;
			}
			set
			{
				_propertyName = value;
			}
		}

		private int _itemIndex;

		/// <summary>
		/// Gets or sets the item index of the binding group data to validate.
		/// </summary>
		/// 
		/// <returns>The item index of the binding group data.</returns>
		/// 
		/// <exception cref="ArgumentException">The value to set is less than zero.
		///   </exception>
		/// 
		/// <remarks>
		/// <para>This is necessary to validate a binding group. This property is
		/// ignored if this validation rule is not defined within a binding group.
		/// </para>
		/// <para>This property can be set in XAML but cannot be filled by a data
		/// binding.</para>
		/// </remarks>
		/// 
		public int ItemIndex
		{
			get
			{
				return _itemIndex;
			}
			set
			{
				Debug.Assert(value >= 0);

				if( value < 0 )
					throw new ArgumentException("The value to set must not be less than zero.", "value");

				_itemIndex = value;
			}
		}

		#endregion

		#region ctor/dtor

		/// <summary>
		/// Creates an empty rule.
		/// </summary>
		/// 
		public ValidatorValidationRule()
		{
		}

		/// <summary>
		/// Initializes this object with the specified arguments.
		/// </summary>
		/// 
		/// <param name="validator">The validator to use.</param>
		/// 
		public ValidatorValidationRule( Validator validator )
		{
			_validator = validator;
		}

		#endregion

		#region methods

		/// <summary>
		/// This is called by the framework to validate the specifed value.
		/// </summary>
		/// 
		/// <param name="value">The value to validate.</param>
		/// <param name="cultureInfo">The culture to use.</param>
		/// 
		/// <returns><see cref="ValidationResult.ValidResult"/> if <paramref name="value"/>
		///   is valid or <see cref="Validator"/> is <c>null</c>; otherwise, another
		///   <see cref="ValidationResult"/> instance is returned.</returns>
		/// 
		public override ValidationResult Validate( object value, CultureInfo cultureInfo )
		{
			if( _validator != null )
			{
				BindingGroup group = value as BindingGroup;

				if( group != null )
					return ValidateGroup(group, cultureInfo);

				return ValidateInput(value, cultureInfo);
			}

			return ValidationResult.ValidResult;
		}

		/// <summary>
		/// Validates the specifed value.
		/// </summary>
		/// 
		/// <param name="value">The value to validate.</param>
		/// <param name="cultureInfo">The culture to use.</param>
		/// 
		/// <returns><see cref="ValidationResult.ValidResult"/> if <paramref name="value"/>
		///   is valid; otherwise, another <see cref="ValidationResult"/> instance is
		///   returned.</returns>
		/// 
		private ValidationResult ValidateInput( object value, CultureInfo cultureInfo )
		{
			ValidatorException vx;

			if( !_validator.Validate(value != null ? value.ToString() : string.Empty, cultureInfo, out vx) )
				return new ValidationResult(false, vx.Message);

			return ValidationResult.ValidResult;
		}

		/// <summary>
		/// Validates the specified binding group.
		/// </summary>
		/// 
		/// <param name="group">The binding group to validate.</param>
		/// <param name="cultureInfo">The culture to use.</param>
		/// 
		/// <returns><see cref="ValidationResult.ValidResult"/> if <see cref="ItemIndex"/>
		///   is a valid index, <see cref="PropertyName"/> is neither <c>null</c> nor empty and
		///   the received value is valid; otherwise, another <see cref="ValidationResult"/>
		///   instance is returned.</returns>
		/// 
		private ValidationResult ValidateGroup( BindingGroup group, CultureInfo cultureInfo )
		{
			if( group.Items.Count > _itemIndex && !string.IsNullOrWhiteSpace(_propertyName) )
			{
				object value;
				group.TryGetValue(group.Items[_itemIndex], _propertyName, out value);

				return ValidateInput(value, cultureInfo);
			}

			return ValidationResult.ValidResult;
		}

		#endregion
	}
}