/main/contrib/NGit/NGit.Util/BlockList.cs

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using System;
using NGit.Util;
using Sharpen;

namespace NGit.Util
{
	/// <summary>Random access list that allocates entries in blocks.</summary>
	/// <remarks>
	/// Random access list that allocates entries in blocks.
	/// <p>
	/// Unlike
	/// <see cref="System.Collections.ArrayList{E}">System.Collections.ArrayList&lt;E&gt;
	/// 	</see>
	/// , this type does not need to reallocate the
	/// internal array in order to expand the capacity of the list. Access to any
	/// element is constant time, but requires two array lookups instead of one.
	/// <p>
	/// To handle common usages,
	/// <see cref="BlockList{T}.AddItem(object)">BlockList&lt;T&gt;.AddItem(object)</see>
	/// and
	/// <see cref="BlockList{T}.Iterator()">BlockList&lt;T&gt;.Iterator()</see>
	/// use
	/// internal code paths to amortize out the second array lookup, making addition
	/// and simple iteration closer to one array operation per element processed.
	/// <p>
	/// Similar to
	/// <code>ArrayList</code>
	/// , adding or removing from any position except the
	/// end of the list requires O(N) time to copy all elements between the
	/// modification point and the end of the list. Applications are strongly
	/// encouraged to not use this access pattern with this list implementation.
	/// </remarks>
	/// <?></?>
	public class BlockList<T> : AbstractList<T>
	{
		private const int BLOCK_BITS = 10;

		internal const int BLOCK_SIZE = 1 << BLOCK_BITS;

		private const int BLOCK_MASK = BLOCK_SIZE - 1;

		private T[][] directory;

		private int size;

		private int tailDirIdx;

		private int tailBlkIdx;

		private T[] tailBlock;

		/// <summary>Initialize an empty list.</summary>
		/// <remarks>Initialize an empty list.</remarks>
		public BlockList()
		{
			directory = NGit.Util.BlockList<T>.NewDirectory(256);
			directory[0] = NGit.Util.BlockList<T>.NewBlock();
			tailBlock = directory[0];
		}

		/// <summary>Initialize an empty list with an expected capacity.</summary>
		/// <remarks>Initialize an empty list with an expected capacity.</remarks>
		/// <param name="capacity">number of elements expected to be in the list.</param>
		public BlockList(int capacity)
		{
			int dirSize = ToDirectoryIndex(capacity);
			if ((capacity & BLOCK_MASK) != 0 || dirSize == 0)
			{
				dirSize++;
			}
			directory = NGit.Util.BlockList<T>.NewDirectory(dirSize);
			directory[0] = NGit.Util.BlockList<T>.NewBlock();
			tailBlock = directory[0];
		}

		public override int Count
		{
			get
			{
				return size;
			}
		}

		public override void Clear()
		{
			foreach (T[] block in directory)
			{
				if (block != null)
				{
					Arrays.Fill(block, default(T));
				}
			}
			size = 0;
			tailDirIdx = 0;
			tailBlkIdx = 0;
			tailBlock = directory[0];
		}

		public override T Get(int index)
		{
			if (index < 0 || size <= index)
			{
				throw new IndexOutOfRangeException(index.ToString());
			}
			return directory[ToDirectoryIndex(index)][ToBlockIndex(index)];
		}

		public override T Set(int index, T element)
		{
			if (index < 0 || size <= index)
			{
				throw new IndexOutOfRangeException(index.ToString());
			}
			T[] blockRef = directory[ToDirectoryIndex(index)];
			int blockIdx = ToBlockIndex(index);
			T old = blockRef[blockIdx];
			blockRef[blockIdx] = element;
			return old;
		}

		/// <summary>Quickly append all elements of another BlockList.</summary>
		/// <remarks>Quickly append all elements of another BlockList.</remarks>
		/// <param name="src">the list to copy elements from.</param>
		public virtual void AddAll(NGit.Util.BlockList<T> src)
		{
			if (src.size == 0)
			{
				return;
			}
			int srcDirIdx = 0;
			for (; srcDirIdx < src.tailDirIdx; srcDirIdx++)
			{
				AddAll(src.directory[srcDirIdx], 0, BLOCK_SIZE);
			}
			if (src.tailBlkIdx != 0)
			{
				AddAll(src.tailBlock, 0, src.tailBlkIdx);
			}
		}

		/// <summary>Quickly append all elements from an array.</summary>
		/// <remarks>Quickly append all elements from an array.</remarks>
		/// <param name="src">the source array.</param>
		/// <param name="srcIdx">first index to copy.</param>
		/// <param name="srcCnt">number of elements to copy.</param>
		public virtual void AddAll(T[] src, int srcIdx, int srcCnt)
		{
			while (0 < srcCnt)
			{
				int i = tailBlkIdx;
				int n = Math.Min(srcCnt, BLOCK_SIZE - i);
				if (n == 0)
				{
					// Our tail is full, expand by one.
					AddItem(src[srcIdx++]);
					srcCnt--;
					continue;
				}
				System.Array.Copy(src, srcIdx, tailBlock, i, n);
				tailBlkIdx += n;
				size += n;
				srcIdx += n;
				srcCnt -= n;
			}
		}

		public override bool AddItem(T element)
		{
			int i = tailBlkIdx;
			if (i < BLOCK_SIZE)
			{
				// Fast-path: Append to current tail block.
				tailBlock[i] = element;
				tailBlkIdx = i + 1;
				size++;
				return true;
			}
			// Slow path: Move to the next block, expanding if necessary.
			if (++tailDirIdx == directory.Length)
			{
				T[][] newDir = NGit.Util.BlockList<T>.NewDirectory(directory.Length << 1);
				System.Array.Copy(directory, 0, newDir, 0, directory.Length);
				directory = newDir;
			}
			T[] blockRef = directory[tailDirIdx];
			if (blockRef == null)
			{
				blockRef = NGit.Util.BlockList<T>.NewBlock();
				directory[tailDirIdx] = blockRef;
			}
			blockRef[0] = element;
			tailBlock = blockRef;
			tailBlkIdx = 1;
			size++;
			return true;
		}

		public override void Add(int index, T element)
		{
			if (index == size)
			{
				// Fast-path: append onto the end of the list.
				AddItem(element);
			}
			else
			{
				if (index < 0 || size < index)
				{
					throw new IndexOutOfRangeException(index.ToString());
				}
				else
				{
					// Slow-path: the list needs to expand and insert.
					// Do this the naive way, callers shouldn't abuse
					// this class by entering this code path.
					//
					AddItem(default(T));
					// expand the list by one
					for (int oldIdx = size - 2; index <= oldIdx; oldIdx--)
					{
						Set(oldIdx + 1, this[oldIdx]);
					}
					Set(index, element);
				}
			}
		}

		public override T Remove(int index)
		{
			if (index == size - 1)
			{
				// Fast-path: remove the last element.
				T[] blockRef = directory[ToDirectoryIndex(index)];
				int blockIdx = ToBlockIndex(index);
				T old = blockRef[blockIdx];
				blockRef[blockIdx] = default(T);
				size--;
				if (0 < tailBlkIdx)
				{
					tailBlkIdx--;
				}
				else
				{
					ResetTailBlock();
				}
				return old;
			}
			else
			{
				if (index < 0 || size <= index)
				{
					throw new IndexOutOfRangeException(index.ToString());
				}
				else
				{
					// Slow-path: the list needs to contract and remove.
					// Do this the naive way, callers shouldn't abuse
					// this class by entering this code path.
					//
					T old = this[index];
					for (; index < size - 1; index++)
					{
						Set(index, this[index + 1]);
					}
					Set(size - 1, default(T));
					size--;
					ResetTailBlock();
					return old;
				}
			}
		}

		private void ResetTailBlock()
		{
			tailDirIdx = ToDirectoryIndex(size);
			tailBlkIdx = ToBlockIndex(size);
			tailBlock = directory[tailDirIdx];
		}

		public override Sharpen.Iterator<T> Iterator()
		{
			return new BlockList<T>.MyIterator(this);
		}

		private static int ToDirectoryIndex(int index)
		{
			return (int)(((uint)index) >> BLOCK_BITS);
		}

		private static int ToBlockIndex(int index)
		{
			return index & BLOCK_MASK;
		}

		private static T[][] NewDirectory(int size)
		{
			return new T[size][];
		}

		private static T[] NewBlock()
		{
			return new T[BLOCK_SIZE];
		}

		private class MyIterator : Iterator<T>
		{
			private int index;

			private int dirIdx;

			private int blkIdx;

			private T[] block;

			public override bool HasNext()
			{
				return this.index < this._enclosing.size;
			}

			public override T Next()
			{
				if (this._enclosing.size <= this.index)
				{
					throw new NoSuchElementException();
				}
				T res = this.block[this.blkIdx];
				if (++this.blkIdx == BlockList<T>.BLOCK_SIZE)
				{
					if (++this.dirIdx < this._enclosing.directory.Length)
					{
						this.block = this._enclosing.directory[this.dirIdx];
					}
					else
					{
						this.block = null;
					}
					this.blkIdx = 0;
				}
				this.index++;
				return res;
			}

			public override void Remove()
			{
				if (this.index == 0)
				{
					throw new InvalidOperationException();
				}
				this._enclosing.Remove(--this.index);
				this.dirIdx = BlockList<T>.ToDirectoryIndex(this.index);
				this.blkIdx = BlockList<T>.ToBlockIndex(this.index);
				this.block = this._enclosing.directory[this.dirIdx];
			}

			internal MyIterator(BlockList<T> _enclosing)
			{
				this._enclosing = _enclosing;
				block = this._enclosing.directory[0];
			}

			private readonly BlockList<T> _enclosing;
		}
	}
}