gecko-dev/accessible/src/html/nsHTMLTableAccessible.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Author: Aaron Leventhal (aaronl@netscape.com)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#include "nsHTMLTableAccessible.h"
#include "nsAccessibilityAtoms.h"
#include "nsIDOMElement.h"
#include "nsINameSpaceManager.h"
#include "nsIAccessibilityService.h"
#include "nsIDOMCSSStyleDeclaration.h"
#include "nsIDOMHTMLCollection.h"
#include "nsIDOMHTMLTableCaptionElem.h"
#include "nsIDOMHTMLTableCellElement.h"
#include "nsIDOMHTMLTableElement.h"
#include "nsIDOMHTMLTableRowElement.h"
#include "nsIDOMHTMLTableSectionElem.h"
#include "nsIDocument.h"
#include "nsIDOMDocument.h"
#include "nsIPresShell.h"
#include "nsIServiceManager.h"
#include "nsITableLayout.h"


NS_IMPL_ISUPPORTS_INHERITED0(nsHTMLTableCellAccessible, nsHyperTextAccessible)

nsHTMLTableCellAccessible::nsHTMLTableCellAccessible(nsIDOMNode* aDomNode, nsIWeakReference* aShell):
nsHyperTextAccessible(aDomNode, aShell)
{ 
}

/* unsigned long getRole (); */
NS_IMETHODIMP nsHTMLTableCellAccessible::GetRole(PRUint32 *aResult)
{
  *aResult = ROLE_CELL;
  return NS_OK;
}

NS_IMETHODIMP nsHTMLTableCellAccessible::GetState(PRUint32 *aResult)
{
  nsAccessible::GetState(aResult);
  *aResult &= ~STATE_FOCUSABLE;   // Inherit all states except focusable state since table cells cannot be focused
  return NS_OK;
}

NS_IMPL_ISUPPORTS_INHERITED0(nsHTMLTableAccessible, nsAccessible)

nsHTMLTableAccessible::nsHTMLTableAccessible(nsIDOMNode* aDomNode, nsIWeakReference* aShell):
nsAccessibleWrap(aDomNode, aShell)
{ 
}

/* unsigned long getRole (); */
NS_IMETHODIMP nsHTMLTableAccessible::GetRole(PRUint32 *aResult)
{
  *aResult = ROLE_TABLE;
  return NS_OK;
}

NS_IMETHODIMP nsHTMLTableAccessible::GetState(PRUint32 *aResult)
{
  nsAccessible::GetState(aResult);
  *aResult |= STATE_READONLY;
  *aResult &= ~STATE_FOCUSABLE;   // Inherit all states except focusable state since tables cannot be focused
  return NS_OK;
}

NS_IMETHODIMP nsHTMLTableAccessible::GetName(nsAString& aName)
{
  aName.Truncate();  // Default name is blank

  if (mRoleMapEntry) {
    nsAccessible::GetName(aName);
    if (!aName.IsEmpty()) {
      return NS_OK;
    }
  }

  nsCOMPtr<nsIDOMElement> element(do_QueryInterface(mDOMNode));
  if (element) {
    nsCOMPtr<nsIDOMNodeList> captions;
    nsAutoString nameSpaceURI;
    element->GetNamespaceURI(nameSpaceURI);
    element->GetElementsByTagNameNS(nameSpaceURI, NS_LITERAL_STRING("caption"), 
                                    getter_AddRefs(captions));
    if (captions) {
      nsCOMPtr<nsIDOMNode> captionNode;
      captions->Item(0, getter_AddRefs(captionNode));
      if (captionNode) {
        nsCOMPtr<nsIContent> captionContent(do_QueryInterface(captionNode));
        AppendFlatStringFromSubtree(captionContent, &aName);
      }
    }
    if (aName.IsEmpty()) {
      nsCOMPtr<nsIContent> content(do_QueryInterface(element));
      NS_ASSERTION(content, "No content for DOM element");
      content->GetAttr(kNameSpaceID_None, nsAccessibilityAtoms::summary, aName);
    }
  }
  return NS_OK;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetCaption(nsIAccessible **aCaption)
{
  *aCaption = nsnull;
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(table, NS_ERROR_FAILURE);

  nsCOMPtr<nsIDOMHTMLTableCaptionElement> caption;
  rv = table->GetCaption(getter_AddRefs(caption));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMNode> captionNode(do_QueryInterface(caption));
  NS_ENSURE_TRUE(captionNode, NS_ERROR_FAILURE);

  nsCOMPtr<nsIAccessibilityService>
    accService(do_GetService("@mozilla.org/accessibilityService;1"));
  NS_ENSURE_TRUE(accService, NS_ERROR_FAILURE);

  accService->GetCachedAccessible(captionNode, mWeakShell, aCaption);
  if (*aCaption)
    return NS_OK;

  accService->CreateHyperTextAccessible(captionNode, aCaption);
  nsCOMPtr<nsPIAccessNode> accessNode(do_QueryInterface(*aCaption));
  return accessNode ? accessNode->Init() : NS_ERROR_FAILURE;
}

NS_IMETHODIMP
nsHTMLTableAccessible::SetCaption(nsIAccessible *aCaption)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(table, NS_ERROR_FAILURE);

  nsCOMPtr<nsIAccessNode> accessNode(do_QueryInterface(aCaption));
  NS_ASSERTION(accessNode, "Unable to QI to nsIAccessNode");
  nsCOMPtr<nsIDOMNode> domNode;
  rv = accessNode->GetDOMNode(getter_AddRefs(domNode));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMNode> newDOMNode;
  rv = domNode->CloneNode(PR_TRUE, getter_AddRefs(newDOMNode));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMHTMLTableCaptionElement>
    captionElement(do_QueryInterface(newDOMNode));
  NS_ENSURE_TRUE(captionElement, NS_ERROR_FAILURE);

  return table->SetCaption(captionElement);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetSummary(nsAString &aSummary)
{
  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(table, NS_ERROR_FAILURE);

  return table->GetSummary(aSummary);
}

NS_IMETHODIMP
nsHTMLTableAccessible::SetSummary(const nsAString &aSummary)
{
  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(table, NS_ERROR_FAILURE);

  return table->SetSummary(aSummary);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetColumns(PRInt32 *aColumns)
{
  nsITableLayout *tableLayout;
  nsresult rv = GetTableLayout(&tableLayout);
  NS_ENSURE_SUCCESS(rv, rv);

  PRInt32 rows;
  return tableLayout->GetTableSize(rows, *aColumns);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetColumnHeader(nsIAccessibleTable **aColumnHeader)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(table, NS_ERROR_FAILURE);

  nsCOMPtr<nsIDOMHTMLTableSectionElement> section;
  rv = table->GetTHead(getter_AddRefs(section));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIAccessibilityService>
    accService(do_GetService("@mozilla.org/accessibilityService;1"));
  NS_ENSURE_TRUE(accService, NS_ERROR_FAILURE);

  nsCOMPtr<nsIAccessible> accHead;
  nsCOMPtr<nsIDOMNode> sectionNode(do_QueryInterface(section));
  if (sectionNode) {
    rv = accService->GetCachedAccessible(sectionNode, mWeakShell,
                                         getter_AddRefs(accHead));
    NS_ENSURE_SUCCESS(rv, rv);
  }

  if (!accHead) {
     accService->CreateHTMLTableHeadAccessible(section,
                                               getter_AddRefs(accHead));
                                                   
    nsCOMPtr<nsPIAccessNode> accessNode(do_QueryInterface(accHead));
    NS_ENSURE_TRUE(accHead, NS_ERROR_FAILURE);
    rv = accessNode->Init();
    NS_ENSURE_SUCCESS(rv, rv);
  }

  nsCOMPtr<nsIAccessibleTable> accTableHead(do_QueryInterface(accHead));
  NS_ENSURE_TRUE(accTableHead, NS_ERROR_FAILURE);

  *aColumnHeader = accTableHead;
  NS_IF_ADDREF(*aColumnHeader);

  return rv;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetRows(PRInt32 *aRows)
{
  nsITableLayout *tableLayout;
  nsresult rv = GetTableLayout(&tableLayout);
  NS_ENSURE_SUCCESS(rv, rv);

  PRInt32 columns;
  return tableLayout->GetTableSize(*aRows, columns);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetRowHeader(nsIAccessibleTable **aRowHeader)
{
  // Can not implement because there is no row header in html table
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetSelectedColumns(PRUint32 *aNumColumns,
                                          PRInt32 **aColumns)
{
  nsresult rv = NS_OK;

  PRInt32 columnCount;
  rv = GetColumns(&columnCount);
  NS_ENSURE_SUCCESS(rv, rv);

  PRBool *states = new PRBool[columnCount];
  NS_ENSURE_TRUE(states, NS_ERROR_OUT_OF_MEMORY);

  *aNumColumns = 0;
  PRInt32 index;
  for (index = 0; index < columnCount; index++) {
    rv = IsColumnSelected(index, &states[index]);
    NS_ENSURE_SUCCESS(rv, rv);

    if (states[index]) {
      (*aNumColumns)++;
    }
  }

  PRInt32 *outArray = (PRInt32 *)nsMemory::Alloc((*aNumColumns) * sizeof(PRInt32));
  if (!outArray) {
    delete []states;
    return NS_ERROR_OUT_OF_MEMORY;
  }

  PRInt32 curr = 0;
  for (index = 0; index < columnCount; index++) {
    if (states[index]) {
      outArray[curr++] = index;
    }
  }

  delete []states;
  *aColumns = outArray;
  return rv;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetSelectedRows(PRUint32 *aNumRows, PRInt32 **aRows)
{
  nsresult rv = NS_OK;

  PRInt32 rowCount;
  rv = GetRows(&rowCount);
  NS_ENSURE_SUCCESS(rv, rv);

  PRBool *states = new PRBool[rowCount];
  NS_ENSURE_TRUE(states, NS_ERROR_OUT_OF_MEMORY);

  *aNumRows = 0;
  PRInt32 index;
  for (index = 0; index < rowCount; index++) {
    rv = IsRowSelected(index, &states[index]);
    NS_ENSURE_SUCCESS(rv, rv);

    if (states[index]) {
      (*aNumRows)++;
    }
  }

  PRInt32 *outArray = (PRInt32 *)nsMemory::Alloc((*aNumRows) * sizeof(PRInt32));
  if (!outArray) {
    delete []states;
    return NS_ERROR_OUT_OF_MEMORY;
  }

  PRInt32 curr = 0;
  for (index = 0; index < rowCount; index++) {
    if (states[index]) {
      outArray[curr++] = index;
    }
  }

  delete []states;
  *aRows = outArray;
  return rv;
}

NS_IMETHODIMP
nsHTMLTableAccessible::CellRefAt(PRInt32 aRow, PRInt32 aColumn,
                                 nsIAccessible **aTableCellAccessible)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMElement> cellElement;
  rv = GetCellAt(aRow, aColumn, *getter_AddRefs(cellElement));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIAccessibilityService>
    accService(do_GetService("@mozilla.org/accessibilityService;1"));
  NS_ENSURE_TRUE(accService, NS_ERROR_FAILURE);

  return accService->GetAccessibleInWeakShell(cellElement, mWeakShell,
                                              aTableCellAccessible);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetIndexAt(PRInt32 aRow, PRInt32 aColumn,
                                  PRInt32 *_retval)
{
  NS_ENSURE_ARG_POINTER(_retval);

  nsresult rv = NS_OK;

  PRInt32 columns;
  rv = GetColumns(&columns);
  NS_ENSURE_SUCCESS(rv, rv);

  *_retval = aRow * columns + aColumn;

  return NS_OK;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetColumnAtIndex(PRInt32 aIndex, PRInt32 *_retval)
{
  NS_ENSURE_ARG_POINTER(_retval);

  nsresult rv = NS_OK;

  PRInt32 columns;
  rv = GetColumns(&columns);
  NS_ENSURE_SUCCESS(rv, rv);

  *_retval = aIndex % columns;

  return NS_OK;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetRowAtIndex(PRInt32 aIndex, PRInt32 *_retval)
{
  NS_ENSURE_ARG_POINTER(_retval);

  nsresult rv = NS_OK;

  PRInt32 columns;
  rv = GetColumns(&columns);
  NS_ENSURE_SUCCESS(rv, rv);

  *_retval = aIndex / columns;

  return NS_OK;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetColumnExtentAt(PRInt32 aRow, PRInt32 aColumn,
                                         PRInt32 *_retval)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMElement> domElement;
  rv = GetCellAt(aRow, aColumn, *getter_AddRefs(domElement));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMHTMLTableCellElement> cell(do_QueryInterface(domElement));
  NS_ENSURE_TRUE(cell, NS_ERROR_FAILURE);

  return cell->GetColSpan(_retval);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetRowExtentAt(PRInt32 aRow, PRInt32 aColumn,
                                      PRInt32 *_retval)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMElement> domElement;
  rv = GetCellAt(aRow, aColumn, *getter_AddRefs(domElement));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMHTMLTableCellElement> cell(do_QueryInterface(domElement));
  NS_ENSURE_TRUE(cell, NS_ERROR_FAILURE);

  return cell->GetRowSpan(_retval);
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetColumnDescription(PRInt32 aColumn, nsAString &_retval)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableAccessible::GetRowDescription(PRInt32 aRow, nsAString &_retval)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableAccessible::IsColumnSelected(PRInt32 aColumn, PRBool *_retval)
{
  NS_ENSURE_ARG_POINTER(_retval);

  nsresult rv = NS_OK;

  PRInt32 rows;
  rv = GetRows(&rows);
  NS_ENSURE_SUCCESS(rv, rv);

  for (PRInt32 index = 0; index < rows; index++) {
    rv = IsCellSelected(index, aColumn, _retval);
    NS_ENSURE_SUCCESS(rv, rv);
    if (!*_retval) {
      break;
    }
  }

  return rv;
}

NS_IMETHODIMP
nsHTMLTableAccessible::IsRowSelected(PRInt32 aRow, PRBool *_retval)
{
  NS_ENSURE_ARG_POINTER(_retval);

  nsresult rv = NS_OK;

  PRInt32 columns;
  rv = GetColumns(&columns);
  NS_ENSURE_SUCCESS(rv, rv);

  for (PRInt32 index = 0; index < columns; index++) {
    rv = IsCellSelected(aRow, index, _retval);
    NS_ENSURE_SUCCESS(rv, rv);
    if (!*_retval) {
      break;
    }
  }

  return rv;
}

NS_IMETHODIMP
nsHTMLTableAccessible::IsCellSelected(PRInt32 aRow, PRInt32 aColumn,
                                      PRBool *_retval)
{
  nsITableLayout *tableLayout;
  nsresult rv = GetTableLayout(&tableLayout);
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIDOMElement> domElement;
  PRInt32 startRowIndex = 0, startColIndex = 0,
          rowSpan, colSpan, actualRowSpan, actualColSpan;

  return tableLayout->GetCellDataAt(aRow, aColumn,
                                    *getter_AddRefs(domElement),
                                    startRowIndex, startColIndex, rowSpan,
                                    colSpan, actualRowSpan, actualColSpan,
                                    *_retval);
}

nsresult
nsHTMLTableAccessible::GetTableNode(nsIDOMNode **_retval)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMHTMLTableElement> table(do_QueryInterface(mDOMNode));
  if (table) {
    *_retval = table;
    NS_IF_ADDREF(*_retval);
    return rv;
  }

  nsCOMPtr<nsIDOMHTMLTableSectionElement> section(do_QueryInterface(mDOMNode));
  if (section) {
    nsCOMPtr<nsIDOMNode> parent;
    rv = section->GetParentNode(getter_AddRefs(parent));
    NS_ENSURE_SUCCESS(rv, rv);

    *_retval = parent;
    NS_IF_ADDREF(*_retval);
    return rv;
  }

  return NS_ERROR_FAILURE;
}

nsresult
nsHTMLTableAccessible::GetTableLayout(nsITableLayout **aLayoutObject)
{
  *aLayoutObject = nsnull;

  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMNode> tableNode;
  rv = GetTableNode(getter_AddRefs(tableNode));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIContent> content(do_QueryInterface(tableNode));
  NS_ENSURE_TRUE(content, NS_ERROR_FAILURE);

  nsIPresShell *presShell = content->GetDocument()->GetShellAt(0);

  nsCOMPtr<nsISupports> layoutObject;
  rv = presShell->GetLayoutObjectFor(content, getter_AddRefs(layoutObject));
  NS_ENSURE_SUCCESS(rv, rv);

  return CallQueryInterface(layoutObject, aLayoutObject);
}

nsresult
nsHTMLTableAccessible::GetCellAt(PRInt32        aRowIndex,
                                 PRInt32        aColIndex,
                                 nsIDOMElement* &aCell)
{
  PRInt32 startRowIndex = 0, startColIndex = 0,
          rowSpan, colSpan, actualRowSpan, actualColSpan;
  PRBool isSelected;

  nsITableLayout *tableLayout;
  nsresult rv = GetTableLayout(&tableLayout);
  NS_ENSURE_SUCCESS(rv, rv);

  return tableLayout->GetCellDataAt(aRowIndex, aColIndex, aCell,
                                    startRowIndex, startColIndex,
                                    rowSpan, colSpan,
                                    actualRowSpan, actualColSpan,
                                    isSelected);
}

#ifdef SHOW_LAYOUT_HEURISTIC
NS_IMETHODIMP nsHTMLTableAccessible::GetDescription(nsAString& aDescription)
{
  // Helpful for debugging layout vs. data tables
  aDescription.Truncate();
  PRBool isProbablyForLayout;
  IsProbablyForLayout(&isProbablyForLayout);
  aDescription = mLayoutHeuristic;
#ifdef DEBUG_A11Y
  printf("\nTABLE: %s\n", NS_ConvertUTF16toUTF8(mLayoutHeuristic).get());
#endif
  return NS_OK;
}
#endif

PRBool nsHTMLTableAccessible::HasDescendant(char *aTagName)
{
  nsCOMPtr<nsIDOMElement> tableElt(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(tableElt, PR_FALSE);

  nsCOMPtr<nsIDOMNodeList> nodeList;
  nsAutoString tagName;
  tagName.AssignWithConversion(aTagName);
  tableElt->GetElementsByTagName(tagName, getter_AddRefs(nodeList));
  NS_ENSURE_TRUE(nodeList, NS_ERROR_FAILURE);
  PRUint32 length;
  nodeList->GetLength(&length);
  
  if (length == 1) {
    // Make sure it's not the table itself
    nsCOMPtr<nsIDOMNode> firstItem;
    nodeList->Item(0, getter_AddRefs(firstItem));
    return firstItem != mDOMNode;
  }

  return length > 0;
}

NS_IMETHODIMP nsHTMLTableAccessible::IsProbablyForLayout(PRBool *aIsProbablyForLayout)
{
  // Implement a heuristic to determine if table is most likely used for layout
  // XXX do we want to look for rowspan or colspan, especialy that span all but a couple cells
  // at the beginning or end of a row/col, and especially when they occur at the edge of a table?
  // XXX expose this info via object attributes to AT-SPI

  // XXX For now debugging descriptions are always on via SHOW_LAYOUT_HEURISTIC
  // This will allow release trunk builds to be used by testers to refine the algorithm
  // Change to |#define SHOW_LAYOUT_HEURISTIC DEBUG| before final release
#ifdef SHOW_LAYOUT_HEURISTIC
#define RETURN_LAYOUT_ANSWER(isLayout, heuristic) \
  { *aIsProbablyForLayout = isLayout; \
    mLayoutHeuristic = isLayout ? NS_LITERAL_STRING("layout table: ") : NS_LITERAL_STRING("data table: "); \
    mLayoutHeuristic += NS_LITERAL_STRING(heuristic); return NS_OK; }
#else
#define RETURN_LAYOUT_ANSWER(isLayout, heuristic) { *aIsProbablyForLayout = isLayout; return NS_OK; }
#endif

  *aIsProbablyForLayout = PR_FALSE;
  
  nsCOMPtr<nsIContent> content(do_QueryInterface(mDOMNode));
  if (!content) {
    return NS_ERROR_FAILURE; // Table shut down
  }

  // Check role and role attribute
  PRBool hasNonTableRole = (Role(this) != ROLE_TABLE);
  if (hasNonTableRole) {
    RETURN_LAYOUT_ANSWER(PR_FALSE, "Has role attribute");
  }

  if (HasRoleAttribute(content)) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "Has role attribute, and role is table");
  }
  
  // Check for legitimate data table elements or attributes
  if (content->HasAttr(kNameSpaceID_None, nsAccessibilityAtoms::summary) || HasDescendant("summary") || 
      HasDescendant("th") || HasDescendant("thead") || HasDescendant("tfoot") || HasDescendant("colgroup")) {
    RETURN_LAYOUT_ANSWER(PR_FALSE, "Has caption, summary, th, thead, tfoot or colgroup -- legitimate table structures");
  }
  if (HasDescendant("table")) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "Has a nested table within it");
  }
  
  // If only 1 column or only 1 row, it's for layout
  PRInt32 columns, rows;
  GetColumns(&columns);
  if (columns <=1) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "Has only 1 column");
  }
  GetRows(&rows);
  if (rows <=1) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "Has only 1 row");
  }

  // Check for many columns
  if (columns >= 5) {
    RETURN_LAYOUT_ANSWER(PR_FALSE, ">=5 columns");
  }
  
  // Now we know there are 2-4 columns and 2 or more rows
  // Check to see if there are visible borders on the cells
  // XXX currently, we just check the first cell -- do we really need to do more?
  nsCOMPtr<nsIDOMElement> cellElement;
  GetCellAt(0, 0, *getter_AddRefs(cellElement));
  nsCOMPtr<nsIContent> cellContent(do_QueryInterface(cellElement));
  NS_ENSURE_TRUE(cellContent, NS_ERROR_FAILURE);
  nsCOMPtr<nsIPresShell> shell(GetPresShell());
  nsIFrame *cellFrame = shell->GetPrimaryFrameFor(cellContent);
  NS_ENSURE_TRUE(cellFrame, NS_ERROR_FAILURE);
  nsMargin border;
  cellFrame->GetBorder(border);
  if (border.top && border.bottom && border.left && border.right) {
    RETURN_LAYOUT_ANSWER(PR_FALSE, "Has nonzero border-width on table cell");
  }

  /**
   * Rules for non-bordered tables with 2-4 columns and 2+ rows from here on forward
   */

  // Check for styled background color across the row
  // Alternating background color is a common way 
  nsCOMPtr<nsIDOMNodeList> nodeList;
  nsCOMPtr<nsIDOMElement> tableElt(do_QueryInterface(mDOMNode));    
  tableElt->GetElementsByTagName(NS_LITERAL_STRING("tr"), getter_AddRefs(nodeList));
  NS_ENSURE_TRUE(nodeList, NS_ERROR_FAILURE);
  PRUint32 length;
  nodeList->GetLength(&length);
  nsAutoString color, lastRowColor;
  for (PRInt32 rowCount = 0; rowCount < rows; rowCount ++) {
    nsCOMPtr<nsIDOMNode> rowNode;
    nodeList->Item(rowCount, getter_AddRefs(rowNode));
    nsCOMPtr<nsIDOMElement> rowElement = do_QueryInterface(rowNode);
    nsCOMPtr<nsIDOMCSSStyleDeclaration> styleDecl;
    GetComputedStyleDeclaration(EmptyString(), rowElement, getter_AddRefs(styleDecl));
    NS_ENSURE_TRUE(styleDecl, NS_ERROR_FAILURE);
    lastRowColor = color;
    styleDecl->GetPropertyValue(NS_LITERAL_STRING("background-color"), color);
    if (rowCount > 0 && PR_FALSE == lastRowColor.Equals(color)) {
      RETURN_LAYOUT_ANSWER(PR_FALSE, "2 styles of row background color, non-bordered");
    }
  }

  // Check for many rows
  const PRInt32 kMaxLayoutRows = 20;
  if (rows > kMaxLayoutRows) { // A ton of rows, this is probably for data
    RETURN_LAYOUT_ANSWER(PR_TRUE, ">= kMaxLayoutRows (20) and non-bordered");
  }

  // Check for very wide table
  nsAutoString styledWidth;
  GetComputedStyleValue(EmptyString(), NS_LITERAL_STRING("width"), styledWidth);
  if (styledWidth.EqualsLiteral("100%")) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "<=4 columns and 100% width");
  }
  if (styledWidth.Find(NS_LITERAL_STRING("px"))) { // Hardcoded in pixels
    nsIFrame *tableFrame = GetFrame();
    NS_ENSURE_TRUE(tableFrame , NS_ERROR_FAILURE);
    nsSize tableSize  = tableFrame->GetSize();
    nsCOMPtr<nsIAccessibleDocument> docAccessible = GetDocAccessible();
    nsCOMPtr<nsPIAccessNode> docAccessNode(do_QueryInterface(docAccessible));
    NS_ENSURE_TRUE(docAccessNode, NS_ERROR_FAILURE);
    nsIFrame *docFrame = docAccessNode->GetFrame();
    NS_ENSURE_TRUE(docFrame , NS_ERROR_FAILURE);
    nsSize docSize = docFrame->GetSize();
    PRInt32 percentageOfDocWidth = (100 * tableSize.width) / docSize.width;
    if (percentageOfDocWidth > 95) {
      // 3-4 columns, no borders, not a lot of rows, and 95% of the doc's width
      // Probably for layout
      RETURN_LAYOUT_ANSWER(PR_TRUE, "<=4 columns, width hardcoded in pixels and 95% of document width");
    }
  }

  // Two column rules
  if (rows * columns <= 10) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "2-4 columns, 10 cells or less, non-bordered");
  }

  if (HasDescendant("embed") || HasDescendant("object") || HasDescendant("applet") || HasDescendant("iframe")) {
    RETURN_LAYOUT_ANSWER(PR_TRUE, "Has no borders, and has iframe, object, applet or iframe, typical of advertisements");
  }

  RETURN_LAYOUT_ANSWER(PR_FALSE, "no layout factor strong enough, so will guess data");
}

// --------------------------------------------------------
// nsHTMLTableHeadAccessible Accessible
// --------------------------------------------------------
NS_IMPL_ISUPPORTS_INHERITED0(nsHTMLTableHeadAccessible, nsHTMLTableAccessible)

nsHTMLTableHeadAccessible::nsHTMLTableHeadAccessible(nsIDOMNode *aDomNode, nsIWeakReference *aShell):
nsHTMLTableAccessible(aDomNode, aShell)
{
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::GetRole(PRUint32 *aResult)
{
  *aResult = ROLE_COLUMNHEADER;
  return NS_OK;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::GetCaption(nsIAccessible **aCaption)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::SetCaption(nsIAccessible *aCaption)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::GetSummary(nsAString &aSummary)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::SetSummary(const nsAString &aSummary)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::GetColumnHeader(nsIAccessibleTable **aColumnHeader)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP
nsHTMLTableHeadAccessible::GetRows(PRInt32 *aRows)
{
  nsresult rv = NS_OK;

  nsCOMPtr<nsIDOMHTMLTableSectionElement> head(do_QueryInterface(mDOMNode));
  NS_ENSURE_TRUE(head, NS_ERROR_FAILURE);

  nsCOMPtr<nsIDOMHTMLCollection> rows;
  rv = head->GetRows(getter_AddRefs(rows));
  NS_ENSURE_SUCCESS(rv, rv);

  return rows->GetLength((PRUint32 *)aRows);
}