Templates, Inversion of Control, Factories, and so on

using System;
using Pfz.Databasing.Managers;
using System.Linq;

namespace Pfz.Databasing.Filtering
{
	/// <summary>
	/// Class used to represent a single filter in the sense of
	/// DatabaseField Operation Value.
	/// Example: Name LIKE 'Test%';
	/// </summary>
	[Serializable]
	public sealed class FilterItem:
		ICloneable<FilterItem>,
		IEquatable<FilterItem>
	{
		/// <summary>
		/// Creates the new filter object with the given property path, operation
		/// and value.
		/// </summary>
		public FilterItem(ExtendedPropertyInfoPath path, FilterOperation operation, object value)
		{
			if (!path.HasValue)
				throw new ArgumentException("path must have a value.", "path");
				
			if (value == null)
			{
				switch(operation)
				{
					case FilterOperation.DifferentThan:
					case FilterOperation.EqualTo:
						break;
					
					default:
						throw new DatabaseException("Only EqualTo and DifferentThan can receive null values.\r\nPath: " + path.ToString() + "\r\nOperation: " + operation);
				}
			}
		
			Path = path;
			Operation = operation;
			Value = value;
		}
		
		/// <summary>
		/// Gets the path of the properties used for the field.
		/// </summary>
		public ExtendedPropertyInfoPath Path { get; private set; }
		
		/// <summary>
		/// Gets the operation performed by the filter.
		/// </summary>
		public FilterOperation Operation { get; private set; }
		
		/// <summary>
		/// Gets the value used by the filter.
		/// </summary>
		public object Value { get; private set; }

		/// <summary>
		/// Compares the Filter structure with another object.
		/// The value is ignored, as this is used to refill prepared queries.
		/// </summary>
		public override bool Equals(object obj)
		{
			FilterItem other = obj as FilterItem;
			if (other == null)
				return false;
			
			return Equals(other);
		}

		/// <summary>
		/// Compares the Filter structure with another Filter.
		/// The value is ignored, as this is used to refill prepared queries.
		/// </summary>
		public bool Equals(FilterItem other)
		{
			if (other == null)
				return false;

			if (Operation != other.Operation)
				return false;

			if (Path != other.Path)
				return false;

			if ((Value == null) != (other.Value == null))
				return false;

			return true;
		}

		/// <summary>
		/// Gets the hashcode for this filter.
		/// </summary>
		public override int GetHashCode()
		{
			return Path.GetHashCode();
		}
		
		/// <summary>
		/// Clones the actual filter.
		/// </summary>
		public FilterItem Clone()
		{
			FilterItem result = new FilterItem(Path, Operation, Value);
			return result;
		}
		
		object ICloneable.Clone()
		{
			return Clone();
		}
	}
}