[CSS Grid Layout] Introduce an explicit type for resolved grid positions

Source/core/rendering/style/GridResolvedPosition.cpp

Index: Source/core/rendering/style/GridResolvedPosition.cpp
diff --git a/Source/core/rendering/style/GridResolvedPosition.cpp b/Source/core/rendering/style/GridResolvedPosition.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..7249b15e739b0e8d7dac18dabeae7a6dd85219bb
--- /dev/null
+++ b/Source/core/rendering/style/GridResolvedPosition.cpp
@@ -0,0 +1,189 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/rendering/style/GridResolvedPosition.h"
+
+#include "core/rendering/RenderBox.h"
+#include "core/rendering/style/GridCoordinate.h"
+
+namespace WebCore {
+
+GridSpan GridResolvedPosition::resolveGridPositionsFromAutoPlacementPosition(const RenderBox&, GridTrackSizingDirection, const GridResolvedPosition& initialPosition)
+{
+    // FIXME: We don't support spanning with auto positions yet. Once we do, this is wrong. Also we should make
+    // sure the grid can accomodate the new item as we only grow 1 position in a given direction.
+    return GridSpan(initialPosition, initialPosition);
+}
+
+PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionsFromStyle(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction)
+{
+    GridPosition initialPosition = (direction == ForColumns) ? gridItem.style()->gridColumnStart() : gridItem.style()->gridRowStart();
+    const GridPositionSide initialPositionSide = (direction == ForColumns) ? ColumnStartSide : RowStartSide;
+    GridPosition finalPosition = (direction == ForColumns) ? gridItem.style()->gridColumnEnd() : gridItem.style()->gridRowEnd();
+    const GridPositionSide finalPositionSide = (direction == ForColumns) ? ColumnEndSide : RowEndSide;
+
+    // We must handle the placement error handling code here instead of in the StyleAdjuster because we don't want to
+    // overwrite the specified values.
+    if (initialPosition.isSpan() && finalPosition.isSpan())
+        finalPosition.setAutoPosition();
+
+    if (initialPosition.isNamedGridArea() && !gridContainerStyle.namedGridArea().contains(initialPosition.namedGridLine()))
+        initialPosition.setAutoPosition();
+
+    if (finalPosition.isNamedGridArea() && !gridContainerStyle.namedGridArea().contains(finalPosition.namedGridLine()))
+        finalPosition.setAutoPosition();
+
+    if (initialPosition.shouldBeResolvedAgainstOppositePosition() && finalPosition.shouldBeResolvedAgainstOppositePosition()) {
+        if (gridContainerStyle.gridAutoFlow() == AutoFlowNone)
+            return adoptPtr(new GridSpan(0, 0));
+
+        // We can't get our grid positions without running the auto placement algorithm.
+        return nullptr;
+    }
+
+    if (initialPosition.shouldBeResolvedAgainstOppositePosition()) {
+        // Infer the position from the final position ('auto / 1' or 'span 2 / 3' case).
+        GridResolvedPosition finalResolvedPosition = resolveGridPositionFromStyle(gridContainerStyle, finalPosition, finalPositionSide);
+        return resolveGridPositionAgainstOppositePosition(gridContainerStyle, finalResolvedPosition, initialPosition, initialPositionSide);
+    }
+
+    if (finalPosition.shouldBeResolvedAgainstOppositePosition()) {
+        // Infer our position from the initial position ('1 / auto' or '3 / span 2' case).
+        GridResolvedPosition initialResolvedPosition = resolveGridPositionFromStyle(gridContainerStyle, initialPosition, initialPositionSide);
+        return resolveGridPositionAgainstOppositePosition(gridContainerStyle, initialResolvedPosition, finalPosition, finalPositionSide);
+    }
+
+    GridResolvedPosition resolvedInitialPosition = resolveGridPositionFromStyle(gridContainerStyle, initialPosition, initialPositionSide);
+    GridResolvedPosition resolvedFinalPosition = resolveGridPositionFromStyle(gridContainerStyle, finalPosition, finalPositionSide);
+
+    // If 'grid-after' specifies a line at or before that specified by 'grid-before', it computes to 'span 1'.
+    if (resolvedFinalPosition < resolvedInitialPosition)
+        resolvedFinalPosition = resolvedInitialPosition;
+
+    return adoptPtr(new GridSpan(resolvedInitialPosition, resolvedFinalPosition));
+}
+
+size_t GridResolvedPosition::explicitGridColumnCount(const RenderStyle& gridContainerStyle)
+{
+    return gridContainerStyle.gridTemplateColumns().size();
+}
+
+size_t GridResolvedPosition::explicitGridRowCount(const RenderStyle& gridContainerStyle)
+{
+    return gridContainerStyle.gridTemplateRows().size();
+}
+
+size_t GridResolvedPosition::explicitGridSizeForSide(const RenderStyle& gridContainerStyle, GridPositionSide side)
+{
+    return (side == ColumnStartSide || side == ColumnEndSide) ? explicitGridColumnCount(gridContainerStyle) : explicitGridRowCount(gridContainerStyle);
+}
+
+GridResolvedPosition GridResolvedPosition::resolveNamedGridLinePositionFromStyle(const RenderStyle& gridContainerStyle, const GridPosition& position, GridPositionSide side)
+{
+    ASSERT(!position.namedGridLine().isNull());
+
+    const NamedGridLinesMap& gridLinesNames = (side == ColumnStartSide || side == ColumnEndSide) ? gridContainerStyle.namedGridColumnLines() : gridContainerStyle.namedGridRowLines();
+    NamedGridLinesMap::const_iterator it = gridLinesNames.find(position.namedGridLine());
+    if (it == gridLinesNames.end()) {
+        if (position.isPositive())
+            return GridResolvedPosition(0);
+        const size_t lastLine = explicitGridSizeForSide(gridContainerStyle, side);
+        return adjustGridPositionForSide(lastLine, side);
+    }
+
+    size_t namedGridLineIndex;
+    if (position.isPositive())
+        namedGridLineIndex = std::min<size_t>(position.integerPosition(), it->value.size()) - 1;
+    else
+        namedGridLineIndex = std::max<int>(it->value.size() - abs(position.integerPosition()), 0);
+    return adjustGridPositionForSide(it->value[namedGridLineIndex], side);
+}
+
+GridResolvedPosition GridResolvedPosition::resolveGridPositionFromStyle(const RenderStyle& gridContainerStyle, const GridPosition& position, GridPositionSide side)
+{
+    switch (position.type()) {
+    case ExplicitPosition: {
+        ASSERT(position.integerPosition());
+
+        if (!position.namedGridLine().isNull())
+            return resolveNamedGridLinePositionFromStyle(gridContainerStyle, position, side);
+
+        // Handle <integer> explicit position.
+        if (position.isPositive())
+            return adjustGridPositionForSide(position.integerPosition() - 1, side);
+
+        size_t resolvedPosition = abs(position.integerPosition()) - 1;
+        const size_t endOfTrack = explicitGridSizeForSide(gridContainerStyle, side);
+
+        // Per http://lists.w3.org/Archives/Public/www-style/2013Mar/0589.html, we clamp negative value to the first line.
+        if (endOfTrack < resolvedPosition)
+            return GridResolvedPosition(0);
+
+        return adjustGridPositionForSide(endOfTrack - resolvedPosition, side);
+    }
+    case NamedGridAreaPosition:
+    {
+        NamedGridAreaMap::const_iterator it = gridContainerStyle.namedGridArea().find(position.namedGridLine());
+        // Unknown grid area should have been computed to 'auto' by now.
+        ASSERT_WITH_SECURITY_IMPLICATION(it != gridContainerStyle.namedGridArea().end());
+        const GridCoordinate& gridAreaCoordinate = it->value;
+        switch (side) {
+        case ColumnStartSide:
+            return gridAreaCoordinate.columns.resolvedInitialPosition;
+        case ColumnEndSide:
+            return gridAreaCoordinate.columns.resolvedFinalPosition;
+        case RowStartSide:
+            return gridAreaCoordinate.rows.resolvedInitialPosition;
+        case RowEndSide:
+            return GridResolvedPosition(gridAreaCoordinate.rows.resolvedFinalPosition);
+        }
+        ASSERT_NOT_REACHED();
+        return GridResolvedPosition(0);
+    }
+    case AutoPosition:
+    case SpanPosition:
+        // 'auto' and span depend on the opposite position for resolution (e.g. grid-row: auto / 1 or grid-column: span 3 / "myHeader").
+        ASSERT_NOT_REACHED();
+        return GridResolvedPosition(0);
+    }
+    ASSERT_NOT_REACHED();
+    return GridResolvedPosition(0);
+}
+
+PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionAgainstOppositePosition(const RenderStyle& gridContainerStyle, const GridResolvedPosition& resolvedOppositePosition, const GridPosition& position, GridPositionSide side)
+{
+    if (position.isAuto())
+        return GridSpan::create(resolvedOppositePosition, resolvedOppositePosition);
+
+    ASSERT(position.isSpan());
+    ASSERT(position.spanPosition() > 0);
+
+    if (!position.namedGridLine().isNull()) {
+        // span 2 'c' -> we need to find the appropriate grid line before / after our opposite position.
+        return resolveNamedGridLinePositionAgainstOppositePosition(gridContainerStyle, resolvedOppositePosition, position, side);
+    }
+
+    return GridSpan::createWithSpanAgainstOpposite(resolvedOppositePosition, position, side);
+}
+
+PassOwnPtr<GridSpan> GridResolvedPosition::resolveNamedGridLinePositionAgainstOppositePosition(const RenderStyle& gridContainerStyle, const GridResolvedPosition& resolvedOppositePosition, const GridPosition& position, GridPositionSide side)
+{
+    ASSERT(position.isSpan());
+    ASSERT(!position.namedGridLine().isNull());
+    // Negative positions are not allowed per the specification and should have been handled during parsing.
+    ASSERT(position.spanPosition() > 0);
+
+    const NamedGridLinesMap& gridLinesNames = (side == ColumnStartSide || side == ColumnEndSide) ? gridContainerStyle.namedGridColumnLines() : gridContainerStyle.namedGridRowLines();
+    NamedGridLinesMap::const_iterator it = gridLinesNames.find(position.namedGridLine());
+
+    // If there is no named grid line of that name, we resolve the position to 'auto' (which is equivalent to 'span 1' in this case).
+    // See http://lists.w3.org/Archives/Public/www-style/2013Jun/0394.html.
+    if (it == gridLinesNames.end())
+        return GridSpan::create(resolvedOppositePosition, resolvedOppositePosition);
+
+    return GridSpan::createWithNamedSpanAgainstOpposite(resolvedOppositePosition, position, side, it->value);
+}
+
+} // namespace WebCore