Support drag&drop for startup pages

chrome/browser/custom_home_pages_table_model.cc

Index: chrome/browser/custom_home_pages_table_model.cc
diff --git a/chrome/browser/custom_home_pages_table_model.cc b/chrome/browser/custom_home_pages_table_model.cc
index 5f2cf6124e8e41fd4e9b907ee1f983742663d153..ffa565de62b9cd4141851dd186f74517bd4c007d 100644
--- a/chrome/browser/custom_home_pages_table_model.cc
+++ b/chrome/browser/custom_home_pages_table_model.cc
@@ -66,6 +66,63 @@ void CustomHomePagesTableModel::SetURLs(const std::vector<GURL>& urls) {
     observer_->OnModelChanged();
 }
 
+/**
+ * Move a number of existing entries to a new position, reordering the table.
+ *
+ * We determine the range of elements affected by the move, save the moved
+ * elements, compact the remaining ones, and re-insert moved elements.
+ */
+void CustomHomePagesTableModel::MoveURLs(int insert_before,
+                                         const std::vector<int>& index_list)

[csilv, 2011/06/13 22:57:02]

Should we be concerned about this not working properly if index_list is not in
sorted order?  This won't happen in the current implementation, just thinking
defensively against future changes.

[groby-ooo-7-16, 2011/06/13 23:45:27]

Since the underlying SelectionModel uses Object.keys it's guaranteed to return
an ordered list. And it seems all other JS referring to selected items also
relies on the selection being ordered.

I've added a comment to that effect so people will at least be aware of this.

[csilv, 2011/06/14 00:06:12]

A comment is prefect, thanks.

On 2011/06/13 23:45:27, groby wrote:

+{
+  DCHECK(insert_before >= 0 && insert_before <= RowCount());
+
+  // The range of elements that needs to be reshuffled is [ |first|, |last| ).

[csilv, 2011/06/13 22:57:02]

nit picky: the end of the comment opens with a bracket and closes with a
parenthesis.

[groby-ooo-7-16, 2011/06/13 23:45:27]

Actually intentional - that's the standard range notation STL uses. In this
case, indicating a half-open range including first, excluding last.

[csilv, 2011/06/14 00:06:12]

Ah, that thought crossed my mind.  (I'm not familiar w/ STL notation as you can
see.)

On 2011/06/13 23:45:27, groby wrote:

+  int first = std::min(insert_before,index_list.front());

[csilv, 2011/06/13 22:57:02]

style nit: space after comma

[groby-ooo-7-16, 2011/06/13 23:45:27]

Done.

+  int last = std::max(insert_before, index_list.back() + 1);
+
+  // Save the dragged elements. Also, adjust insertion point if it is before a
+  // dragged element.
+  std::vector<Entry> moved_entries;
+  for (size_t i = 0; i < index_list.size(); ++i) {
+    moved_entries.push_back(entries_[index_list[i]]);
+    if (index_list[i] == insert_before)
+      insert_before++;
+  }
+
+  // Compact the range between beginning and insertion point, moving downwards.
+  size_t skip_count = 0;
+  for (int i = first; i < insert_before; ++i) {
+    if (skip_count < index_list.size() && index_list[skip_count] == i)
+      skip_count++;
+    else
+      entries_[i - skip_count]=entries_[i];
+  }
+
+  // Moving items down created a gap. We start compacting up after it.
+  first = insert_before;
+  insert_before -= skip_count;
+
+  // Now compact up for elements after the insertion point.
+  skip_count = 0;
+  for (int i = last - 1; i >= first; --i) {
+    if (skip_count < index_list.size() &&
+        index_list[index_list.size() - skip_count - 1] == i) {
+      skip_count++;
+    } else {
+      entries_[i + skip_count] = entries_[i];
+    }
+  }
+
+  // Insert moved elements.
+  std::copy(moved_entries.begin(), moved_entries.end(),
+      entries_.begin() + insert_before);
+
+  // Possibly large change, so tell the view to just rebuild itself.
+  if (observer_)
+    observer_->OnModelChanged();
+}
+
 void CustomHomePagesTableModel::Add(int index, const GURL& url) {
   DCHECK(index >= 0 && index <= RowCount());
   entries_.insert(entries_.begin() + static_cast<size_t>(index), Entry());