libs-gui/Source/NSCollectionView.m

/** <title>NSCollectionView</title>
 
   Copyright (C) 2013 Free Software Foundation, Inc.
 
   Author: Doug Simons (doug.simons@testplant.com)
           Frank LeGrand (frank.legrand@testplant.com)
   Date: February 2013
 
   This file is part of the GNUstep GUI Library.

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; see the file COPYING.LIB.
   If not, see <http://www.gnu.org/licenses/> or write to the 
   Free Software Foundation, 51 Franklin Street, Fifth Floor, 
   Boston, MA 02110-1301, USA.
*/

#import "AppKit/NSCollectionView.h"
#import "AppKit/NSCollectionViewItem.h"
#import "Foundation/NSKeyedArchiver.h"
#import <Foundation/NSGeometry.h>

#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSDebug.h>
#import <Foundation/NSDictionary.h>
#import <Foundation/NSEnumerator.h>
#import <Foundation/NSException.h>
#import <Foundation/NSFormatter.h>
#import <Foundation/NSIndexSet.h>
#import <Foundation/NSKeyValueCoding.h>
#import <Foundation/NSNotification.h>
#import <Foundation/NSSet.h>
#import <Foundation/NSSortDescriptor.h>
#import <Foundation/NSUserDefaults.h>
#import <Foundation/NSValue.h>
#import <Foundation/NSKeyedArchiver.h>
#import <Foundation/NSTimer.h>

#import "AppKit/NSView.h"
#import "AppKit/NSAnimation.h"
#import "AppKit/NSNibLoading.h"
#import "AppKit/NSTableView.h"
#import "AppKit/NSApplication.h"
#import "AppKit/NSCell.h"
#import "AppKit/NSClipView.h"
#import "AppKit/NSColor.h"
#import "AppKit/NSEvent.h"
#import "AppKit/NSImage.h"
#import "AppKit/NSGraphics.h"
#import "AppKit/NSKeyValueBinding.h"
#import "AppKit/NSScroller.h"
#import "AppKit/NSScrollView.h"
#import "AppKit/NSTableColumn.h"
#import "AppKit/NSTableHeaderView.h"
#import "AppKit/NSText.h"
#import "AppKit/NSTextFieldCell.h"
#import "AppKit/NSWindow.h"
#import "AppKit/PSOperators.h"
#import "AppKit/NSCachedImageRep.h"
#import "AppKit/NSPasteboard.h"
#import "AppKit/NSDragging.h"
#import "AppKit/NSCustomImageRep.h"
#import "AppKit/NSAttributedString.h"
#import "AppKit/NSStringDrawing.h"
#import "GNUstepGUI/GSTheme.h"
#import "GSBindingHelpers.h"

#include <math.h>




static NSString* NSCollectionViewMinItemSizeKey              = @"NSMinGridSize";
static NSString* NSCollectionViewMaxItemSizeKey              = @"NSMaxGridSize";
//static NSString* NSCollectionViewVerticalMarginKey           = @"NSCollectionViewVerticalMarginKey";
static NSString* NSCollectionViewMaxNumberOfRowsKey          = @"NSMaxNumberOfGridRows";
static NSString* NSCollectionViewMaxNumberOfColumnsKey       = @"NSMaxNumberOfGridColumns";
static NSString* NSCollectionViewSelectableKey               = @"NSSelectable";
static NSString* NSCollectionViewAllowsMultipleSelectionKey  = @"NSAllowsMultipleSelection";
static NSString* NSCollectionViewBackgroundColorsKey         = @"NSBackgroundColors";

/*
 * Class variables
 */
static NSString *placeholderItem = nil;

@interface NSCollectionView (CollectionViewInternalPrivate)

- (void) _initDefaults;
- (void) _resetItemSize;
- (void) _removeItemsViews;
- (NSInteger) _indexAtPoint: (NSPoint)point;

- (NSRect) _frameForRowOfItemAtIndex: (NSUInteger)theIndex;
- (NSRect) _frameForRowsAroundItemAtIndex: (NSUInteger)theIndex;

- (void) _modifySelectionWithNewIndex: (int)anIndex
                            direction: (int)aDirection
                                                       expand: (BOOL)shouldExpand;
                                                          
- (void) _moveDownAndExpandSelection: (BOOL)shouldExpand;
- (void) _moveUpAndExpandSelection: (BOOL)shouldExpand;
- (void) _moveLeftAndExpandSelection: (BOOL)shouldExpand;
- (void) _moveRightAndExpandSelection: (BOOL)shouldExpand;

- (BOOL) _writeItemsAtIndexes: (NSIndexSet *)indexes 
                 toPasteboard: (NSPasteboard *)pasteboard;

- (BOOL) _startDragOperationWithEvent: (NSEvent*)event 
                         clickedIndex: (NSUInteger)index;

- (void) _selectWithEvent: (NSEvent *)theEvent 
                    index: (NSUInteger)index;

@end


@implementation NSCollectionView

//
// Class methods
//
+ (void) initialize
{
  placeholderItem = @"Placeholder";
}

- (id) initWithFrame: (NSRect)frame
{
  if ((self = [super initWithFrame:frame]))
    {
          [self _initDefaults];
        }
  return self;
}

-(void) _initDefaults
{
//  _draggingSourceOperationMaskForLocal = NSDragOperationCopy | NSDragOperationLink | NSDragOperationGeneric | NSDragOperationPrivate;
  _draggingSourceOperationMaskForLocal = NSDragOperationGeneric | NSDragOperationMove | NSDragOperationCopy;
  _draggingSourceOperationMaskForRemote = NSDragOperationGeneric | NSDragOperationMove | NSDragOperationCopy;
  [self _resetItemSize];
  _content = [[NSArray alloc] init];
  _items = [[NSMutableArray alloc] init];
  _selectionIndexes = [[NSIndexSet alloc] init];
  _draggingOnIndex = NSNotFound;
}

- (void) _resetItemSize
{
  if (itemPrototype)
    {
      _itemSize = [[itemPrototype view] frame].size;
      _minItemSize = NSMakeSize (_itemSize.width, _itemSize.height);
      _maxItemSize = NSMakeSize (_itemSize.width, _itemSize.height);
    }
  else
    {
      // FIXME: This is just arbitrary.
          // What are we suppose to do when we don't have a prototype?
      _itemSize = NSMakeSize(120.0, 100.0);
      _minItemSize = NSMakeSize(120.0, 100.0);
      _maxItemSize = NSMakeSize(120.0, 100.0);
        }
}

- (void) drawRect: (NSRect)dirtyRect
{
  // TODO: Implement "use Alternating Colors"
  if (_backgroundColors && [_backgroundColors count] > 0)
    {
          NSColor *bgColor = [_backgroundColors objectAtIndex:0];
          [bgColor set];
          NSRectFill(dirtyRect);
        }

  NSPoint origin = dirtyRect.origin;
  NSSize size = dirtyRect.size;
  NSPoint oppositeOrigin = NSMakePoint (origin.x + size.width, origin.y + size.height);
  
  NSInteger firstIndexInRect = MAX(0, [self _indexAtPoint:origin]);
  NSInteger lastIndexInRect = MIN([_items count] - 1, [self _indexAtPoint:oppositeOrigin]);
  NSInteger index = firstIndexInRect;

  for (; index <= lastIndexInRect; index++)
    {
          // Calling itemAtIndex: will eventually instantiate the collection view item,
          // if it hasn't been done already.
      NSCollectionViewItem *collectionItem = [self itemAtIndex:index];
      NSView *view = [collectionItem view];
          [view setFrame:[self frameForItemAtIndex:index]];
    }
}

- (void) dealloc
{
  //[[NSNotificationCenter defaultCenter] removeObserver:self];

  DESTROY (_content);

  // FIXME: Not clear if we should destroy the top-level item "itemPrototype" loaded in the nib file.
  DESTROY (itemPrototype);
  
  DESTROY (_backgroundColors);
  DESTROY (_selectionIndexes);
  DESTROY (_items);
  //DESTROY (_mouseDownEvent);
  [super dealloc];
}

- (BOOL) isFlipped
{
  return YES;
}

- (BOOL) allowsMultipleSelection
{
  return _allowsMultipleSelection;
}

- (void) setAllowsMultipleSelection:(BOOL)flag
{
  _allowsMultipleSelection = flag;
}

- (NSArray *) backgroundColors
{
  return _backgroundColors;
}

- (void) setBackgroundColors: (NSArray *)colors
{
  _backgroundColors = [colors copy];
  [self setNeedsDisplay:YES];
}

- (NSArray *) content
{
  return _content;
}

- (void) setContent: (NSArray *)content
{
  RELEASE (_content);
  _content = [content retain];
  [self _removeItemsViews];
  
  RELEASE (_items);
  _items = [[NSMutableArray alloc] initWithCapacity:[_content count]];
  
  NSInteger i;
  for (i=0; i<[_content count]; i++)
    {
      [_items addObject:placeholderItem];
    }

  if (!itemPrototype)
    {
      return;
        }
  else
    {
      // Force recalculation of each item's frame
      _itemSize = _minItemSize;
      _tileWidth = -1;
      [self tile];
        }
}

- (id < NSCollectionViewDelegate >) delegate
{
  return delegate;
}

- (void) setDelegate: (id < NSCollectionViewDelegate >)aDelegate
{
  delegate = aDelegate;
}

- (NSCollectionViewItem *) itemPrototype
{
  return itemPrototype;
}

- (void) setItemPrototype: (NSCollectionViewItem *)prototype
{

  ASSIGN(itemPrototype, prototype);
  // RELEASE (itemPrototype);
  // itemPrototype = prototype;
  // RETAIN (itemPrototype);
  [self _resetItemSize];
}

- (CGFloat) verticalMargin
{
  return _verticalMargin;
}

- (void) setVerticalMargin: (CGFloat)margin
{
  if (_verticalMargin == margin)
    return;
    
  _verticalMargin = margin;
  [self tile];
}

- (NSSize) maxItemSize
{
  return _maxItemSize;
}

- (void) setMaxItemSize: (NSSize)size
{
  if (NSEqualSizes(_maxItemSize, size))
    return;
    
  _maxItemSize = size;
  [self tile];
}

- (NSUInteger) maxNumberOfColumns
{
  return _maxNumberOfColumns;
}

- (void) setMaxNumberOfColumns: (NSUInteger)number
{
  _maxNumberOfColumns = number;
}

- (NSUInteger) maxNumberOfRows
{
  return _maxNumberOfRows;
}

- (void) setMaxNumberOfRows: (NSUInteger)number
{
  _maxNumberOfRows = number;
}

- (NSSize) minItemSize
{
  return _minItemSize;
}

- (void) setMinItemSize: (NSSize)size
{
  if (NSEqualSizes(_minItemSize, size))
    return;
    
  _minItemSize = size;
  [self tile];
}

- (BOOL) isSelectable
{
  return _isSelectable;
}

- (void) setSelectable: (BOOL)flag
{
  _isSelectable = flag;
  if (!_isSelectable)
    {
      NSInteger index = -1;
      while ((index = [_selectionIndexes indexGreaterThanIndex:index]) != NSNotFound)
        {
              id item = [_items objectAtIndex:index];
              if ([item respondsToSelector:@selector(setSelected:)])
                    {
                          [item setSelected:NO];
                        }
            }
        }
}

- (NSIndexSet *) selectionIndexes
{
  return _selectionIndexes;
}

- (void) setSelectionIndexes: (NSIndexSet *)indexes
{
  if (!_isSelectable)
    {
      return;
    }
  
  if (![_selectionIndexes isEqual:indexes])
    {
      ASSIGN(_selectionIndexes,indexes);
      // RELEASE(_selectionIndexes);
      // _selectionIndexes = indexes;
      // RETAIN(_selectionIndexes);
    }
  
  NSUInteger index = 0;
  while (index < [_items count])
    {
      id item = [_items objectAtIndex:index];
      if ([item respondsToSelector:@selector(setSelected:)])
        {
          [item setSelected:NO];
        }
      index++;
    }
  
  index = -1;
  while ((index = [_selectionIndexes indexGreaterThanIndex:index]) != 
         NSNotFound)
    {
      id item = [_items objectAtIndex:index];
      if ([item respondsToSelector:@selector(setSelected:)])
        {
          [item setSelected:YES];
        }
    }
}

- (NSRect) frameForItemAtIndex: (NSUInteger)theIndex
{
  NSRect itemFrame = NSMakeRect (0,0,0,0);
  NSInteger index = 0;
  long count = (long)[_items count];
  
  if (_maxNumberOfColumns > 0 && _maxNumberOfRows > 0)
    count = MIN(count, _maxNumberOfColumns * _maxNumberOfRows);
  
  CGFloat x = _horizontalMargin;
  CGFloat y = -_itemSize.height;
  
  for (; index < count; ++index)
    {
      if (index % _numberOfColumns == 0)
        {
          x = _horizontalMargin;
          y += _verticalMargin + _itemSize.height;
        }
      
      if (index == theIndex)
        {
          NSInteger draggingOffset = 0;
          if (_draggingOnIndex != NSNotFound)
            {
              NSInteger draggingOnRow = (_draggingOnIndex / _numberOfColumns);
              NSInteger currentIndexRow = (theIndex / _numberOfColumns);
              if (draggingOnRow == currentIndexRow)
                {
                  if (index < _draggingOnIndex)
                    {
                      draggingOffset = -20;
                    }
                  else
                    {
                      draggingOffset = 20;
                    }
                }
            }
          itemFrame = NSMakeRect ((x + draggingOffset), y, _itemSize.width, _itemSize.height);
          break;
        }
      
      x += _itemSize.width + _horizontalMargin;
    }
  return itemFrame;
}

- (NSRect) _frameForRowOfItemAtIndex: (NSUInteger)theIndex
{
  NSRect itemFrame = [self frameForItemAtIndex:theIndex];
  NSPoint origin = NSMakePoint (0, itemFrame.origin.y);
  NSSize size = NSMakeSize([self bounds].size.width, itemFrame.size.height);
  return NSMakeRect (origin.x, origin.y, size.width, size.height);  
}

// Returns the frame of an item's row with the row above and the row below
- (NSRect) _frameForRowsAroundItemAtIndex: (NSUInteger)theIndex
{
  NSRect itemRowFrame = [self _frameForRowOfItemAtIndex:theIndex];
  CGFloat y = MAX (0, itemRowFrame.origin.y - itemRowFrame.size.height);
  CGFloat height = MIN (itemRowFrame.size.height * 3, [self bounds].size.height);
  NSRect rowsRect = NSMakeRect(0, y, itemRowFrame.size.width, height);
  return rowsRect;
}

- (NSCollectionViewItem *) itemAtIndex: (NSUInteger)index
{
  id item = [_items objectAtIndex:index];
  if (item == placeholderItem)
    {
      item = [self newItemForRepresentedObject:[_content objectAtIndex:index]];
      [_items replaceObjectAtIndex:index withObject:item];
      if ([[self selectionIndexes] containsIndex:index])
        {
          [item setSelected:YES];
        }
      [self addSubview:[item view]];
    }
  return item;
}

- (NSCollectionViewItem *) newItemForRepresentedObject: (id)object
{
  NSCollectionViewItem *collectionItem = nil;
  if (itemPrototype)
    {
      ASSIGN(collectionItem, [itemPrototype copy]);
      [collectionItem setRepresentedObject:object];
    }
  return AUTORELEASE (collectionItem);
}

- (void) _removeItemsViews
{
  if (!_items)
    return;
  
  long count = [_items count];
  
  while (count--)
    {
      if ([[_items objectAtIndex:count] respondsToSelector:@selector(view)])
        {
          [[[_items objectAtIndex:count] view] removeFromSuperview];
          [[_items objectAtIndex:count] setSelected:NO];
        }
    }
}

- (void) tile
{
  // TODO: - Animate items, Add Fade-in/Fade-out (as in Cocoa)
  //       - Put the tiling on a delay
  if (!_items)
    return;
  
  CGFloat width = [self bounds].size.width;
  
  if (width == _tileWidth)
    return;
  
  NSSize itemSize = NSMakeSize(_minItemSize.width, _minItemSize.height);
  
  _numberOfColumns = MAX(1.0, floor(width / itemSize.width));
  
  if (_maxNumberOfColumns > 0)
    {
      _numberOfColumns = MIN(_maxNumberOfColumns, _numberOfColumns);
    }
  
  CGFloat remaining = width - _numberOfColumns * itemSize.width;
  BOOL itemsNeedSizeUpdate = NO;
  
  if (remaining > 0 && itemSize.width < _maxItemSize.width)
    {
      itemSize.width = MIN(_maxItemSize.width, itemSize.width + 
                           floor(remaining / _numberOfColumns));
    }

  if (_maxNumberOfColumns == 1 && itemSize.width < 
      _maxItemSize.width && itemSize.width < width)
    {
      itemSize.width = MIN(_maxItemSize.width, width);
    }

  if (!NSEqualSizes(_itemSize, itemSize))
    {
      _itemSize = itemSize;
      itemsNeedSizeUpdate = YES;
    }
  
  NSInteger index = 0;
  long count = (long)[_items count];
  
  if (_maxNumberOfColumns > 0 && _maxNumberOfRows > 0)
    {
      count = MIN(count, _maxNumberOfColumns * _maxNumberOfRows);
    }

  _horizontalMargin = floor((width - _numberOfColumns * itemSize.width) / 
                            (_numberOfColumns + 1));
  CGFloat y = -itemSize.height;
  
  for (; index < count; ++index)
    {
      if (index % _numberOfColumns == 0)
        {
          y += _verticalMargin + itemSize.height;
        }
    }
  
  id superview = [self superview];
  CGFloat proposedHeight = y + itemSize.height + _verticalMargin;
  if ([superview isKindOfClass:[NSClipView class]])
    {
      NSSize superviewSize = [superview bounds].size;
      proposedHeight = MAX(superviewSize.height, proposedHeight);
    }
  
  _tileWidth = width;
  [self setFrameSize:NSMakeSize(width, proposedHeight)];
  [self setNeedsDisplay:YES];
}

- (void) resizeSubviewsWithOldSize: (NSSize)aSize
{
  NSSize currentSize = [self frame].size;
  if (!NSEqualSizes(currentSize, aSize))
    {
      [self tile];
    }
}

- (id) initWithCoder: (NSCoder *)aCoder
{
  self = [super initWithCoder:aCoder];
  
  if (self)
    {
      if([aCoder allowsKeyedCoding])
        {
          _items = [NSMutableArray array];
          _content = [NSArray array];
          
          _itemSize = NSMakeSize(0, 0);
          
          _minItemSize = [aCoder decodeSizeForKey:NSCollectionViewMinItemSizeKey];
          _maxItemSize = [aCoder decodeSizeForKey:NSCollectionViewMaxItemSizeKey];
          
          _maxNumberOfRows = [aCoder decodeInt64ForKey:NSCollectionViewMaxNumberOfRowsKey];
          _maxNumberOfColumns = [aCoder decodeInt64ForKey:NSCollectionViewMaxNumberOfColumnsKey];
          
          //_verticalMargin = [aCoder decodeFloatForKey:NSCollectionViewVerticalMarginKey];
          
          _isSelectable = [aCoder decodeBoolForKey:NSCollectionViewSelectableKey];
          _allowsMultipleSelection = [aCoder decodeBoolForKey:NSCollectionViewAllowsMultipleSelectionKey];
          
          [self setBackgroundColors:[aCoder decodeObjectForKey:NSCollectionViewBackgroundColorsKey]];
        
          _tileWidth = -1.0;
        
          _selectionIndexes = [NSIndexSet indexSet];
        }
      else
        {
        }
    }
  [self _initDefaults];
    
  return self;
}

- (void) encodeWithCoder: (NSCoder *)aCoder
{
  [super encodeWithCoder:aCoder];
  if([aCoder allowsKeyedCoding])
    {  
      if (!NSEqualSizes(_minItemSize, NSMakeSize(0, 0)))
        {
          [aCoder encodeSize:_minItemSize forKey:NSCollectionViewMinItemSizeKey];
        }
      
      if (!NSEqualSizes(_maxItemSize, NSMakeSize(0, 0)))
        {
          [aCoder encodeSize:_maxItemSize forKey:NSCollectionViewMaxItemSizeKey];
        }
      
      [aCoder encodeInt64:_maxNumberOfRows 
                   forKey:NSCollectionViewMaxNumberOfRowsKey];
      [aCoder encodeInt64:_maxNumberOfColumns 
                   forKey:NSCollectionViewMaxNumberOfColumnsKey];
      
      [aCoder encodeBool:_isSelectable 
                  forKey:NSCollectionViewSelectableKey];
      [aCoder encodeBool:_allowsMultipleSelection 
                  forKey:NSCollectionViewAllowsMultipleSelectionKey];
      
      //[aCoder encodeCGFloat:_verticalMargin forKey:NSCollectionViewVerticalMarginKey];
      [aCoder encodeObject:_backgroundColors 
                    forKey:NSCollectionViewBackgroundColorsKey];
    }
  else
    {
    }
}

- (void) mouseDown: (NSEvent *)theEvent
{
  NSPoint initialLocation = [theEvent locationInWindow];
  NSPoint location = [self convertPoint: initialLocation fromView: nil];
  NSInteger index = [self _indexAtPoint:location];
  NSEvent *lastEvent = theEvent;
  BOOL done = NO;

  NSUInteger eventMask = (NSLeftMouseUpMask 
                        | NSLeftMouseDownMask
                        | NSLeftMouseDraggedMask 
                        | NSPeriodicMask);
  NSDate *distantFuture = [NSDate distantFuture];

  while (!done)
    {
          lastEvent = [NSApp nextEventMatchingMask: eventMask 
                                                     untilDate: distantFuture
                                                        inMode: NSEventTrackingRunLoopMode 
                                                       dequeue: YES]; 
          NSEventType eventType = [lastEvent type];
          NSPoint mouseLocationWin = [lastEvent locationInWindow];
          switch (eventType)
            {
                  case NSLeftMouseDown:
                    break;
                  case NSLeftMouseDragged:
                    if (fabs(mouseLocationWin.x - initialLocation.x) >= 2
                          || fabs(mouseLocationWin.y - initialLocation.y) >= 2)
                          {
                if ([self _startDragOperationWithEvent:theEvent clickedIndex:index])
                                  {
                                    done = YES;
                                  }
                          }
                        break;
                  case NSLeftMouseUp:
                    [self _selectWithEvent:theEvent index:index];
                    done = YES;
                        break;
                  default:
                    done = NO;
                    break;
        }
        }
}

- (void) _selectWithEvent:(NSEvent *)theEvent index:(NSUInteger)index
{
  NSMutableIndexSet *currentIndexSet = [[NSMutableIndexSet alloc] initWithIndexSet:[self selectionIndexes]];
  
  if (_isSelectable && (index < [_items count]))
    {
      if (_allowsMultipleSelection
          && (([theEvent modifierFlags] & NSControlKeyMask) || ([theEvent modifierFlags] & NSShiftKeyMask)))
        
        {
          if ([theEvent modifierFlags] & NSControlKeyMask)
            {
              if ([currentIndexSet containsIndex:index])
                {
                  [currentIndexSet removeIndex:index];
                }
              else
                {
                  [currentIndexSet addIndex:index];
                }
              [self setSelectionIndexes:currentIndexSet];
            }
          else if ([theEvent modifierFlags] & NSShiftKeyMask)
            {
              long firstSelectedIndex = [currentIndexSet firstIndex];
              NSRange selectedRange;
              
              if (firstSelectedIndex == NSNotFound)
                {
                  selectedRange = NSMakeRange(index, index);
                }
              else if (index < firstSelectedIndex)
                {
                  selectedRange = NSMakeRange(index, (firstSelectedIndex - index + 1));
                }
              else
                {
                  selectedRange = NSMakeRange(firstSelectedIndex, (index - firstSelectedIndex + 1));
                }
              [currentIndexSet addIndexesInRange:selectedRange];
              [self setSelectionIndexes:currentIndexSet];
            }
        }
      else
        {
          [self setSelectionIndexes:[NSIndexSet indexSetWithIndex:index]];
        }
      [[self window] makeFirstResponder:self];
      
      
    }
  else
    {
      [self setSelectionIndexes:[NSIndexSet indexSet]];
    }
  RELEASE (currentIndexSet);
}

- (NSInteger) _indexAtPoint: (NSPoint)point
{
  NSInteger row = floor(point.y / (_itemSize.height + _verticalMargin));
  NSInteger column = floor(point.x / (_itemSize.width + _horizontalMargin));
  return (column + (row * _numberOfColumns));
}

- (BOOL) acceptsFirstResponder
{
  return YES;
}

/* MARK: Keyboard Interaction */

- (void) keyDown: (NSEvent *)theEvent
{
  [self interpretKeyEvents:[NSArray arrayWithObject:theEvent]];
}

-(void) moveUp: (id)sender
{
  [self _moveUpAndExpandSelection:NO];
}
 
-(void) moveUpAndModifySelection: (id)sender
{
  [self _moveUpAndExpandSelection:YES];
}

- (void) _moveUpAndExpandSelection: (BOOL)shouldExpand
{
  NSInteger index = [[self selectionIndexes] firstIndex];
  if (index != NSNotFound && (index - _numberOfColumns) >= 0)
    {
      [self _modifySelectionWithNewIndex:index - _numberOfColumns
                               direction:-1 
                                  expand:shouldExpand];
    }
}

-(void) moveDown: (id)sender
{
  [self _moveDownAndExpandSelection:NO];
}

-(void) moveDownAndModifySelection: (id)sender
{
  [self _moveDownAndExpandSelection:YES];
}

-(void) _moveDownAndExpandSelection: (BOOL)shouldExpand
{
  NSInteger index = [[self selectionIndexes] lastIndex];
  if (index != NSNotFound && (index + _numberOfColumns) < [_items count])
    {
      [self _modifySelectionWithNewIndex:index + _numberOfColumns
                               direction:1 
                                  expand:shouldExpand];
    }
}

-(void) moveLeft: (id)sender
{
  [self _moveLeftAndExpandSelection:NO];
}

-(void) moveLeftAndModifySelection: (id)sender
{
  [self _moveLeftAndExpandSelection:YES];
}

-(void) moveBackwardAndModifySelection: (id)sender
{
  [self _moveLeftAndExpandSelection:YES];
}

-(void) _moveLeftAndExpandSelection: (BOOL)shouldExpand
{
  NSInteger index = [[self selectionIndexes] firstIndex];
  if (index != NSNotFound && index != 0)
    {
      [self _modifySelectionWithNewIndex:index-1 direction:-1 expand:shouldExpand];
    }
}

-(void) moveRight: (id)sender
{
  [self _moveRightAndExpandSelection:NO];
}

-(void) moveRightAndModifySelection: (id)sender
{
  [self _moveRightAndExpandSelection:YES];
}

-(void) moveForwardAndModifySelection: (id)sender
{
  [self _moveRightAndExpandSelection:YES];
}

-(void) _moveRightAndExpandSelection: (BOOL)shouldExpand
{
  NSInteger index = [[self selectionIndexes] lastIndex];
  if (index != NSNotFound && index != ([_items count] - 1))
    {
      [self _modifySelectionWithNewIndex:index+1 direction:1 expand:shouldExpand];
    }
}

- (void) _modifySelectionWithNewIndex: (int)anIndex
                            direction: (int)aDirection
                            expand: (BOOL)shouldExpand
{
  anIndex = MIN (MAX (anIndex, 0), [_items count] - 1);
  
  if (_allowsMultipleSelection && shouldExpand)
    {
      NSMutableIndexSet *newIndexSet = [[NSMutableIndexSet alloc] initWithIndexSet:_selectionIndexes];
      NSInteger firstIndex = [newIndexSet firstIndex];
      NSInteger lastIndex = [newIndexSet lastIndex];
      if (aDirection == -1)
        {
          [newIndexSet addIndexesInRange:NSMakeRange (anIndex, firstIndex - anIndex + 1)];
        }
      else
        {
          [newIndexSet addIndexesInRange:NSMakeRange (lastIndex, anIndex - lastIndex + 1)];
        }
      [self setSelectionIndexes:newIndexSet];
      RELEASE (newIndexSet);
    }
  else
    {
      [self setSelectionIndexes:[NSIndexSet indexSetWithIndex:anIndex]];
    }
  
  [self scrollRectToVisible:[self frameForItemAtIndex:anIndex]];
}


/* MARK: Drag & Drop */

-(NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)isLocal
{
  if (isLocal)
    {
      return _draggingSourceOperationMaskForLocal;
    }
  else
    {
      return _draggingSourceOperationMaskForRemote;
    }
}

-(void)setDraggingSourceOperationMask:(NSDragOperation)mask
                             forLocal:(BOOL)isLocal
{
  if (isLocal)
    {
      _draggingSourceOperationMaskForLocal = mask;
    }
  else
    {
      _draggingSourceOperationMaskForRemote = mask;
    }
}

- (BOOL) _startDragOperationWithEvent:(NSEvent*)event 
clickedIndex:(NSUInteger)index
{
  NSIndexSet *dragIndexes = _selectionIndexes;
  if (![dragIndexes containsIndex:index]
      && (index < [_items count]))
    {
      dragIndexes = [NSIndexSet indexSetWithIndex:index];
    }
  
  if (![dragIndexes count])
    return NO;
  
  if (![delegate respondsToSelector:@selector(collectionView:writeItemsAtIndexes:toPasteboard:)])
    return NO;
  
  if ([delegate respondsToSelector:@selector(collectionView:canDragItemsAtIndexes:withEvent:)])
    {
      if (![delegate collectionView:self
              canDragItemsAtIndexes:dragIndexes
                          withEvent:event])
        {
          return NO;
        }
    }
  
  NSPoint downPoint = [event locationInWindow];
  NSPoint convertedDownPoint = [self convertPoint:downPoint fromView:nil];
  
  NSPasteboard *pasteboard = [NSPasteboard pasteboardWithName:NSDragPboard];
  if ([self _writeItemsAtIndexes:dragIndexes toPasteboard:pasteboard])
    {
      NSImage *dragImage = [self draggingImageForItemsAtIndexes:dragIndexes
                                                      withEvent:event
                                                         offset:NULL];
      
      [self dragImage:dragImage
                   at:convertedDownPoint
               offset:NSMakeSize(0,0)
                event:event
           pasteboard:pasteboard
               source:self
            slideBack:YES];
      
      return YES;
    }
  return NO;
}

- (NSImage *) draggingImageForItemsAtIndexes: (NSIndexSet *)indexes 
                                   withEvent: (NSEvent *)event 
                                      offset: (NSPointPointer)dragImageOffset
{
  if ([delegate respondsToSelector:@selector(collectionView:draggingImageForItemsAtIndexes:withEvent:offset:)])
    {
      return [delegate collectionView:self
                       draggingImageForItemsAtIndexes:indexes
                            withEvent:event
                               offset:dragImageOffset];
    }
  else
    {
      return [[NSImage alloc] initWithData:[self dataWithPDFInsideRect:[self bounds]]];
    }
}

- (BOOL) _writeItemsAtIndexes: (NSIndexSet *)indexes 
                 toPasteboard: (NSPasteboard *)pasteboard
{
  if (![delegate respondsToSelector:@selector(collectionView:writeItemsAtIndexes:toPasteboard:)])
    {
      return NO;
    }
  else
    {
      return [delegate collectionView:self
                  writeItemsAtIndexes:indexes
                         toPasteboard:pasteboard];
    }
}

- (void) draggedImage: (NSImage *)image
              endedAt: (NSPoint)point
            operation: (NSDragOperation)operation
{
}

- (NSDragOperation) _draggingEnteredOrUpdated: (id<NSDraggingInfo>)sender
{
  NSDragOperation result = NSDragOperationNone;
  
  if ([delegate respondsToSelector:@selector(collectionView:validateDrop:proposedIndex:dropOperation:)])
    {
      NSPoint location = [self convertPoint: [sender draggingLocation] fromView: nil];
      NSInteger index = [self _indexAtPoint:location];
      index = (index > [_items count] - 1) ? [_items count] - 1 : index;
      _draggingOnIndex = index;
      
      NSInteger *proposedIndex = &index;
      NSInteger dropOperationInt = NSCollectionViewDropOn;
      NSCollectionViewDropOperation *dropOperation = &dropOperationInt;
      
      // TODO: We currently don't do anything with the proposedIndex & dropOperation that
      // may get altered by the delegate.
      result = [delegate collectionView:self
                           validateDrop:sender
                          proposedIndex:proposedIndex
                          dropOperation:dropOperation];
      
      if (result == NSDragOperationNone)
        {
          _draggingOnIndex = NSNotFound;
        }
      [self setNeedsDisplayInRect:[self _frameForRowsAroundItemAtIndex:index]];
    }
  
  return result;
}

- (NSDragOperation) draggingEntered: (id<NSDraggingInfo>)sender
{
  return [self _draggingEnteredOrUpdated:sender];
}

- (void) draggingExited: (id<NSDraggingInfo>)sender
{
  [self setNeedsDisplayInRect:[self _frameForRowsAroundItemAtIndex:_draggingOnIndex]];
  _draggingOnIndex = NSNotFound;
}

- (NSDragOperation) draggingUpdated: (id<NSDraggingInfo>)sender
{
  return [self _draggingEnteredOrUpdated:sender];
}

- (BOOL) prepareForDragOperation: (id<NSDraggingInfo>)sender
{
  _draggingOnIndex = NSNotFound;
  NSPoint location = [self convertPoint: [sender draggingLocation] fromView: nil];
  NSInteger index = [self _indexAtPoint:location];
  [self setNeedsDisplayInRect:[self _frameForRowsAroundItemAtIndex:index]];
  return YES;
}

- (BOOL) performDragOperation: (id<NSDraggingInfo>)sender
{
  NSPoint location = [self convertPoint: [sender draggingLocation] fromView: nil];
  NSInteger index = [self _indexAtPoint:location];
  index = (index > [_items count] - 1) ? [_items count] - 1 : index;
  
  BOOL result = NO;
  if ([delegate respondsToSelector:@selector(collectionView:acceptDrop:index:dropOperation:)])
    {
      // TODO: dropOperation should be retrieved from the validateDrop delegate method.
      result = [delegate collectionView:self
                             acceptDrop:sender
                                  index:index
                          dropOperation:NSCollectionViewDropOn];
    }
  return result;
}

- (BOOL) wantsPeriodicDraggingUpdates
{
  return YES;
}

@end