/**
 * Namespace: System.Web.UI.WebControls
 * Class:     PagedDataSource
 *
 * Author:  Gaurav Vaish
 * Maintainer: gvaish@iitk.ac.in
 * Contact: <my_scripts2001@yahoo.com>, <gvaish@iitk.ac.in>
 * Implementation: yes
 * Status:  100%
 *
 * (C) Gaurav Vaish (2002)
 */

using System;
using System.ComponentModel;
using System.Collections;
using System.Web;
using System.Web.UI;

namespace System.Web.UI.WebControls
{
	public sealed class PagedDataSource : ICollection, IEnumerable, ITypedList
	{
		private int  pageSize;
		private bool allowPaging;
		private int  currentPageIndex;
		private bool allowCustomPaging;
		private int  virtualCount;

		private IEnumerable dataSource;

		public PagedDataSource()
		{
			Initialize();
		}

		private void Initialize()
		{
			pageSize          = 10;
			allowPaging       = false;
			currentPageIndex  = 0;
			allowCustomPaging = false;
			virtualCount      = 0;
		}

		public bool AllowCustomPaging
		{
			get
			{
				return allowCustomPaging;
			}
			set
			{
				allowCustomPaging = value;
			}
		}

		public bool AllowPaging
		{
			get
			{
				return allowPaging;
			}
			set
			{
				allowPaging = value;
			}
		}

		public int Count
		{
			get
			{
				if(dataSource != null)
				{
					if(!IsPagingEnabled)
					{
						return DataSourceCount;
					}
					if(IsCustomPagingEnabled)
					{
						return pageSize;
					}
					if(IsLastPage)
					{
						return (DataSourceCount - FirstIndexInPage);
					}
					return pageSize;
				}
				return 0;
			}
		}

		public int CurrentPageIndex
		{
			get
			{
				return currentPageIndex;
			}

			set
			{
				currentPageIndex = value;
			}
		}

		public IEnumerable DataSource
		{
			get
			{
				return dataSource;
			}
			set
			{
				dataSource = value;
			}
		}

		public int DataSourceCount
		{
			get
			{
				if(dataSource != null)
				{
					if(IsCustomPagingEnabled)
					{
						return virtualCount;
					}
					if(dataSource is ICollection)
					{
						return ((ICollection)dataSource).Count;
					}
					throw new HttpException(HttpRuntime.FormatResourceString("PagedDataSource_Cannot_Get_Count"));
				}
				return 0;
			}
		}

		public int FirstIndexInPage
		{
			get
			{
				if(dataSource != null && IsPagingEnabled && !IsCustomPagingEnabled)
				{
					return (currentPageIndex * pageSize);
				}
				return 0;
			}
		}

		public bool IsCustomPagingEnabled
		{
			get
			{
				return (IsPagingEnabled && allowCustomPaging);
			}
		}

		public bool IsFirstPage
		{
			get
			{
				return (!IsPagingEnabled || (CurrentPageIndex == 0));
			}
		}

		public bool IsLastPage
		{
			get
			{
				return (!IsPagingEnabled || (CurrentPageIndex == (PageCount - 1)));
			}
		}

		public bool IsPagingEnabled
		{
			get
			{
				return (allowPaging && pageSize != 0);
			}
		}

		public bool IsReadOnly
		{
			get
			{
				return false;
			}
		}

		public bool IsSynchronized
		{
			get
			{
				return false;
			}
		}

		public int PageCount
		{
			get
			{
				if(dataSource != null)
				{
					int total = DataSourceCount;
					if(!IsPagingEnabled)
					{
						return total;
					}
					return (total + pageSize - 1)/pageSize;
				}
				return 0;
			}
		}

		public int PageSize
		{
			get
			{
				return pageSize;
			}
			set
			{
				pageSize = value;
			}
		}

		public object SyncRoot
		{
			get
			{
				return this;
			}
		}

		public int VirtualCount
		{
			get
			{
				return virtualCount;
			}
			set
			{
				virtualCount = value;
			}
		}

		public void CopyTo(Array array, int index)
		{
			foreach(object current in this)
			{
				array.SetValue(array, index++);
			}
		}

		public IEnumerator GetEnumerator()
		{
			int fInd = FirstIndexInPage;
			int count = -1;
			if(dataSource is ICollection)
			{
				count = Count;
			}

			if(dataSource is IList)
			{
				return (new PrivateListEnumerator((IList)dataSource, fInd, count));
			}
			if(dataSource is Array)
			{
				return (new PrivateArrayEnumerator((object[])dataSource, fInd, count));
			}
			if(dataSource is ICollection)
			{
				return (new PrivateICollectionEnumerator((ICollection)dataSource, fInd, count));
			}
			if(allowCustomPaging)
			{
				return (new PrivateIEnumeratorEnumerator(dataSource.GetEnumerator(), Count));
			}
			return dataSource.GetEnumerator();
		}

		class PrivateIEnumeratorEnumerator : IEnumerator
		{
			private int index;
			private int max;

			private IEnumerator enumerator;

			public PrivateIEnumeratorEnumerator(IEnumerator enumerator, int count)
			{
				this.enumerator = enumerator;
				index = -1;
				max   = count;
			}

			public bool MoveNext()
			{
				enumerator.MoveNext();
				index++;
				return (index < max);
			}

			public void Reset()
			{
				index = -1;
				enumerator.Reset();
			}

			public object Current
			{
				get
				{
					return enumerator.Current;
				}
			}
		}

		class PrivateICollectionEnumerator : IEnumerator
		{
			private int index;
			private int start;
			private int max;

			private ICollection collection;
			private IEnumerator collEnum;

			public PrivateICollectionEnumerator(ICollection collection, int start, int count)
			{
				this.collection = collection;
				this.start  = start;
				index = -1;
				max = start + count;
				if(max > collection.Count)
				{
					max = collection.Count;
				}
			}

			public bool MoveNext()
			{
				if(collEnum == null)
				{
					int cIndex = 0;
					collEnum = collection.GetEnumerator();
					while(cIndex < start)
					{
						collEnum.MoveNext();
					}
				}
				collEnum.MoveNext();
				index++;
				return (start + index < max);
			}

			public void Reset()
			{
				index = -1;
				collEnum = null;
			}

			public object Current
			{
				get
				{
					return collEnum.Current;
				}
			}
		}

		class PrivateArrayEnumerator : IEnumerator
		{
			private int index;
			private int start;
			private int max;
			private object[] values;

			public PrivateArrayEnumerator(object[] values, int start, int count)
			{
				this.values = values;
				this.start  = start;
				index = -1;
				max = start + count;
				if(max > this.values.Length)
				{
					max = this.values.Length;
				}
			}

			public bool MoveNext()
			{
				index++;
				return (index + start < max);
			}

			public void Reset()
			{
				index = -1;
			}

			public object Current
			{
				get
				{
					if(index >= 0)
					{
						return values[index + start];
					}
					throw new InvalidOperationException("Enumerator_MoveNext_Not_Called");
				}
			}
		}

		class PrivateListEnumerator : IEnumerator
		{
			private int   index;
			private int   start;
			private int   max;
			private IList collection;

			public PrivateListEnumerator(IList list, int start, int count)
			{
				collection = list;
				this.start = start;
				index = -1;
				max = start + count;
				if(max > list.Count)
				{
					max = list.Count;
				}
			}

			public bool MoveNext()
			{
				index++;
				return (index + start < max);
			}

			public void Reset()
			{
				index = -1;
			}

			public object Current
			{
				get
				{
					if(index >= 0)
					{
						return collection[index + start];
					}
					throw new InvalidOperationException("Enumerator_MoveNext_Not_Called");
				}
			}
		}

		public string GetListName(PropertyDescriptor[] listAccessors)
		{
			return String.Empty;
		}

		public PropertyDescriptorCollection GetItemProperties(PropertyDescriptor[] listAccessors)
		{
			if(dataSource != null)
			{
				if(dataSource is ITypedList)
				{
					return ((ITypedList)dataSource).GetItemProperties(listAccessors);
				}
			}
			return null;
		}
	}
}