Simple Data Access in C#

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Globalization;

using Yap.Data.Client.Properties;


namespace Yap.Data.Client
{
	/// <summary>
	/// Simplifies access to properties of an entity. Used by entity commands to get/set entity property values.
	/// </summary>
	public class Accessor
	{
		private static readonly Object _Sync = new Object();

		private static readonly Dictionary<Type, Accessor> _Instances
			= new Dictionary<Type, Accessor>();


		/// <summary>
		/// Returns existing or initializes new <see cref="Yap.Data.Client.Accessor"/> instance for specified entity type.
		/// </summary>
		/// <param name="entityType">The type of entity.</param>
		/// <returns>The accessor.</returns>
		/// <exception cref="System.ArgumentNullException">entityType is null.</exception>
		public static Accessor GetInstance(Type entityType)
		{
			lock (_Sync)
			{
				if (entityType == null)
				{
					throw new ArgumentNullException("entityType");
				}
				Accessor accessor;
				if (!_Instances.TryGetValue(entityType, out accessor))
				{
					accessor = new Accessor(entityType);
					_Instances.Add(entityType, accessor);
				}
				return accessor;
			}
		}

		private readonly Type _Type;

		private readonly Dictionary<String, PropertyInfo> _Properties =
			new Dictionary<String, PropertyInfo>();

		private Accessor(Type entityType)
		{
			_Type = entityType;

			PropertyInfo[] properties = _Type.GetProperties(
				BindingFlags.Instance |
				BindingFlags.Public);

			foreach (PropertyInfo property in properties)
			{
				if (!_Properties.ContainsKey(property.Name))
				{
					_Properties.Add(
						property.Name, property);
				}
			}
		}

		/// <summary>
		/// Gets collection of entity properties.
		/// </summary>
		public ICollection<PropertyInfo> Properties
		{
			get
			{
				return _Properties.Values;
			}
		}

		/// <summary>
		/// Sets value into entity property by path specified.
		/// </summary>
		/// <param name="entity">Property owner.</param>
		/// <param name="propertyPath">The property path to set value to.</param>
		/// <param name="value">The value to set.</param>
		/// <exception cref="System.InvalidOperationException">Entity property was not found by specified path.</exception>
		public void SetPropertyValue(Object entity, String propertyPath, Object value)
		{
			Int32 indexOfDelimiter = propertyPath.IndexOf('.');
			String propertyName = indexOfDelimiter > 0 ? propertyPath.Substring(0, indexOfDelimiter) : propertyPath;
			PropertyInfo property;
			if (!TryGetProperty(propertyName, out property))
			{
				throw new InvalidOperationException(
					String.Format(
						CultureInfo.CurrentCulture,
						Resources.PropertyWasNotFoundInTypeException,
						propertyName,
						_Type.Name));
			}
			if (indexOfDelimiter == -1)
			{
				property.SetValue(
					entity, value, null);
			}
			else
			{
				Type propertyType = property.PropertyType;
				Object propertyValue = GetPropertyValue(entity, propertyName) ?? Activator.CreateInstance(propertyType);
				Accessor accessor = GetInstance(propertyType);
				accessor.SetPropertyValue(
					propertyValue,
					propertyPath.Substring(
						indexOfDelimiter + 1,
						propertyPath.Length - propertyName.Length - 1),
					value);
				SetPropertyValue(entity, propertyName, propertyValue);
			}
		}

		/// <summary>
		/// Gets entity property value.
		/// </summary>
		/// <param name="entity">Property owner.</param>
		/// <param name="propertyPath">The property path to get value from.</param>
		/// <returns>The value of entity property.</returns>
		/// <exception cref="System.InvalidOperationException">Entity property was not found by specified path.</exception>
		public Object GetPropertyValue(Object entity, String propertyPath)
		{
			Int32 indexOfDelimiter = propertyPath.IndexOf('.');
			String propertyName = indexOfDelimiter > 0 ? propertyPath.Substring(0, indexOfDelimiter) : propertyPath;
			PropertyInfo property;
			if (!TryGetProperty(propertyName, out property))
			{
				throw new InvalidOperationException(
					String.Format(
						CultureInfo.CurrentCulture,
						Resources.PropertyWasNotFoundInTypeException,
						propertyName,
						_Type.Name));
			}
			if (indexOfDelimiter == -1)
			{
				return property.GetValue(
					entity, null);
			}
			
			Object propertyValue = GetPropertyValue(entity, propertyName);
			if (propertyValue == null)
			{
				return null;
			}
			Accessor accessor = GetInstance(property.PropertyType);
			return accessor.GetPropertyValue(
				propertyValue,
				propertyPath.Substring(
					indexOfDelimiter + 1,
					propertyPath.Length - propertyName.Length - 1));
		}

		/// <summary>
		/// Gets entity property <see cref="System.Reflection.PropertyInfo"/> by property path.
		/// </summary>
		/// <param name="propertyPath">The property path to get <see cref="System.Reflection.PropertyInfo"/> from.</param>
		/// <returns>The <see cref="System.Reflection.PropertyInfo"/> of entity property.</returns>
		/// <exception cref="System.InvalidOperationException">Entity property was not found by specified path.</exception>
		public PropertyInfo GetProperty(String propertyPath)
		{
			PropertyInfo property;
			if (!TryGetProperty(propertyPath, out property))
			{
				throw new InvalidOperationException(
					String.Format(
						CultureInfo.CurrentCulture,
						Resources.PropertyWasNotFoundInTypeException,
						propertyPath,
						_Type.Name));
			}
			return property;
		}

		/// <summary>
		/// Gets entity property <see cref="System.Reflection.PropertyInfo"/> by property path.
		/// </summary>
		/// <param name="propertyPath">The property path to get <see cref="System.Reflection.PropertyInfo"/> from.</param>
		/// <param name="property">When this method returns, contains the <see cref="System.Reflection.PropertyInfo"/> of entity property, if property is found; otherwise, null.</param>
		/// <returns>true if entity contains an property with specified path; otherwise, false.</returns>
		public Boolean TryGetProperty(String propertyPath, out PropertyInfo property)
		{
			Int32 indexOfDelimiter = propertyPath.IndexOf('.');
			String propertyName = indexOfDelimiter > 0 ? propertyPath.Substring(0, indexOfDelimiter) : propertyPath;

			if (_Properties.TryGetValue(propertyName, out property))
			{
				if (indexOfDelimiter == -1)
				{
					return property != null;
				}
				Accessor accessor = GetInstance(property.PropertyType);
				return accessor.TryGetProperty(
					propertyPath.Substring(
						indexOfDelimiter + 1,
						propertyPath.Length - propertyName.Length - 1),
					out property);
			}
			return false;
		}
	}
}