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// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Web.Razor.Resources;
using System.Web.Razor.Utils;
namespace System.Web.Razor.Text
{
public class BufferingTextReader : LookaheadTextReader
{
private Stack<BacktrackContext> _backtrackStack = new Stack<BacktrackContext>();
private int _currentBufferPosition;
private int _currentCharacter;
private SourceLocationTracker _locationTracker;
public BufferingTextReader(TextReader source)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
InnerReader = source;
_locationTracker = new SourceLocationTracker();
UpdateCurrentCharacter();
}
internal StringBuilder Buffer { get; set; }
internal bool Buffering { get; set; }
internal TextReader InnerReader { get; private set; }
public override SourceLocation CurrentLocation
{
get { return _locationTracker.CurrentLocation; }
}
protected virtual int CurrentCharacter
{
get { return _currentCharacter; }
}
public override int Read()
{
int ch = CurrentCharacter;
NextCharacter();
return ch;
}
// TODO: Optimize Read(char[],int,int) to copy direct from the buffer where possible
public override int Peek()
{
return CurrentCharacter;
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
InnerReader.Dispose();
}
base.Dispose(disposing);
}
public override IDisposable BeginLookahead()
{
// Is this our first lookahead?
if (Buffer == null)
{
// Yes, setup the backtrack buffer
Buffer = new StringBuilder();
}
if (!Buffering)
{
// We're not already buffering, so we need to expand the buffer to hold the first character
ExpandBuffer();
Buffering = true;
}
// Mark the position to return to when we backtrack
// Use the closures and the "using" statement rather than an explicit stack
BacktrackContext context = new BacktrackContext()
{
BufferIndex = _currentBufferPosition,
Location = CurrentLocation
};
_backtrackStack.Push(context);
return new DisposableAction(() =>
{
EndLookahead(context);
});
}
// REVIEW: This really doesn't sound like the best name for this...
public override void CancelBacktrack()
{
if (_backtrackStack.Count == 0)
{
throw new InvalidOperationException(RazorResources.CancelBacktrack_Must_Be_Called_Within_Lookahead);
}
// Just pop the current backtrack context so that when the lookahead ends, it won't be backtracked
_backtrackStack.Pop();
}
private void EndLookahead(BacktrackContext context)
{
// If the specified context is not the one on the stack, it was popped by a call to DoNotBacktrack
if (_backtrackStack.Count > 0 && ReferenceEquals(_backtrackStack.Peek(), context))
{
_backtrackStack.Pop();
_currentBufferPosition = context.BufferIndex;
_locationTracker.CurrentLocation = context.Location;
UpdateCurrentCharacter();
}
}
protected virtual void NextCharacter()
{
int prevChar = CurrentCharacter;
if (prevChar == -1)
{
return; // We're at the end of the source
}
if (Buffering)
{
if (_currentBufferPosition >= Buffer.Length - 1)
{
// If there are no more lookaheads (thus no need to continue with the buffer) we can just clean up the buffer
if (_backtrackStack.Count == 0)
{
// Reset the buffer
Buffer.Length = 0;
_currentBufferPosition = 0;
Buffering = false;
}
else if (!ExpandBuffer())
{
// Failed to expand the buffer, because we're at the end of the source
_currentBufferPosition = Buffer.Length; // Force the position past the end of the buffer
}
}
else
{
// Not at the end yet, just advance the buffer pointer
_currentBufferPosition++;
}
}
else
{
// Just act like normal
InnerReader.Read(); // Don't care about the return value, Peek() is used to get characters from the source
}
UpdateCurrentCharacter();
_locationTracker.UpdateLocation((char)prevChar, (char)CurrentCharacter);
}
protected bool ExpandBuffer()
{
// Pull another character into the buffer and update the position
int ch = InnerReader.Read();
// Only append the character to the buffer if there actually is one
if (ch != -1)
{
Buffer.Append((char)ch);
_currentBufferPosition = Buffer.Length - 1;
return true;
}
return false;
}
private void UpdateCurrentCharacter()
{
if (Buffering && _currentBufferPosition < Buffer.Length)
{
// Read from the buffer
_currentCharacter = (int)Buffer[_currentBufferPosition];
}
else
{
// No buffer? Peek from the source
_currentCharacter = InnerReader.Peek();
}
}
private class BacktrackContext
{
public int BufferIndex { get; set; }
public SourceLocation Location { get; set; }
}
}
}
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