RmlUi/Source/Core/StyleSheetSelector.cpp

#include "StyleSheetSelector.h"
#include "../../Include/RmlUi/Core/Element.h"
#include "StyleSheetNode.h"
#include <tuple>

namespace Rml {

static inline bool IsTextElement(const Element* element)
{
	return element->GetTagName() == "#text";
}

// Returns true if a positive integer can be found for n in the equation an + b = count.
static bool IsNth(int a, int b, int count)
{
	int x = count;
	x -= b;
	if (a != 0)
		x /= a;

	return (x >= 0 && x * a + b == count);
}

bool operator==(const AttributeSelector& a, const AttributeSelector& b)
{
	return a.type == b.type && a.name == b.name && a.value == b.value;
}
bool operator<(const AttributeSelector& a, const AttributeSelector& b)
{
	return std::tie(a.type, a.name, a.value) < std::tie(b.type, b.name, b.value);
}

bool operator==(const StructuralSelector& a, const StructuralSelector& b)
{
	// Currently sub-selectors (selector_tree) are only superficially compared. This mainly has the consequence that selectors with a sub-selector
	// which are instantiated separately will never compare equal, even if they have the exact same sub-selector expression. This further results in
	// such selectors not being de-duplicated. This should not lead to any functional differences but leads to potentially missed memory/performance
	// optimizations. E.g. 'div a, div b' will combine the two div nodes, while ':not(div) a, :not(div) b' will not combine the two not-div nodes.
	return a.type == b.type && a.a == b.a && a.b == b.b && a.selector_tree == b.selector_tree;
}
bool operator<(const StructuralSelector& a, const StructuralSelector& b)
{
	return std::tie(a.type, a.a, a.b, a.selector_tree) < std::tie(b.type, b.a, b.b, b.selector_tree);
}

bool operator==(const CompoundSelector& a, const CompoundSelector& b)
{
	if (a.tag != b.tag)
		return false;
	if (a.id != b.id)
		return false;
	if (a.class_names != b.class_names)
		return false;
	if (a.pseudo_class_names != b.pseudo_class_names)
		return false;
	if (a.attributes != b.attributes)
		return false;
	if (a.structural_selectors != b.structural_selectors)
		return false;
	if (a.combinator != b.combinator)
		return false;
	return true;
}

bool IsSelectorApplicable(const Element* element, const StructuralSelector& selector, const Element* scope)
{
	RMLUI_ASSERT(element);

	switch (selector.type)
	{
	case StructuralSelectorType::Nth_Child:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		// Start counting elements until we find this one.
		int element_index = 1;
		for (int i = 0; i < parent->GetNumChildren(); i++)
		{
			Element* child = parent->GetChild(i);

			// Skip text nodes.
			if (IsTextElement(child))
				continue;

			// If we've found our element, then break; the current index is our element's index.
			if (child == element)
				break;

			element_index++;
		}

		return IsNth(selector.a, selector.b, element_index);
	}
	break;
	case StructuralSelectorType::Nth_Last_Child:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		// Start counting elements until we find this one.
		int element_index = 1;
		for (int i = parent->GetNumChildren() - 1; i >= 0; --i)
		{
			Element* child = parent->GetChild(i);

			// Skip text nodes.
			if (IsTextElement(child))
				continue;

			// If we've found our element, then break; the current index is our element's index.
			if (child == element)
				break;

			element_index++;
		}

		return IsNth(selector.a, selector.b, element_index);
	}
	break;
	case StructuralSelectorType::Nth_Of_Type:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		// Start counting elements until we find this one.
		int element_index = 1;
		const int num_children = parent->GetNumChildren();
		for (int i = 0; i < num_children; i++)
		{
			Element* child = parent->GetChild(i);

			// If we've found our element, then break; the current index is our element's index.
			if (child == element)
				break;

			// Skip nodes that don't share our tag.
			if (child->GetTagName() != element->GetTagName())
				continue;

			element_index++;
		}

		return IsNth(selector.a, selector.b, element_index);
	}
	break;
	case StructuralSelectorType::Nth_Last_Of_Type:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		// Start counting elements until we find this one.
		int element_index = 1;
		for (int i = parent->GetNumChildren() - 1; i >= 0; --i)
		{
			Element* child = parent->GetChild(i);

			// If we've found our element, then break; the current index is our element's index.
			if (child == element)
				break;

			// Skip nodes that don't share our tag.
			if (child->GetTagName() != element->GetTagName())
				continue;

			element_index++;
		}

		return IsNth(selector.a, selector.b, element_index);
	}
	break;
	case StructuralSelectorType::First_Child:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		int child_index = 0;
		while (child_index < parent->GetNumChildren())
		{
			// If this child (the first non-text child) is our element, then the selector succeeds.
			Element* child = parent->GetChild(child_index);
			if (child == element)
				return true;

			// If this child is not a text element, then the selector fails; this element is non-trivial.
			if (!IsTextElement(child))
				return false;

			// Otherwise, skip over the text element to find the last non-trivial element.
			child_index++;
		}

		return false;
	}
	break;
	case StructuralSelectorType::Last_Child:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		int child_index = parent->GetNumChildren() - 1;
		while (child_index >= 0)
		{
			// If this child (the last non-text child) is our element, then the selector succeeds.
			Element* child = parent->GetChild(child_index);
			if (child == element)
				return true;

			// If this child is not a text element, then the selector fails; this element is non-trivial.
			if (!IsTextElement(child))
				return false;

			// Otherwise, skip over the text element to find the last non-trivial element.
			child_index--;
		}

		return false;
	}
	break;
	case StructuralSelectorType::First_Of_Type:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		int child_index = 0;
		while (child_index < parent->GetNumChildren())
		{
			// If this child is our element, then it's the first one we've found with our tag; the selector succeeds.
			Element* child = parent->GetChild(child_index);
			if (child == element)
				return true;

			// Otherwise, if this child shares our element's tag, then our element is not the first tagged child; the selector fails.
			if (child->GetTagName() == element->GetTagName())
				return false;

			child_index++;
		}

		return false;
	}
	break;
	case StructuralSelectorType::Last_Of_Type:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		int child_index = parent->GetNumChildren() - 1;
		while (child_index >= 0)
		{
			// If this child is our element, then it's the first one we've found with our tag; the selector succeeds.
			Element* child = parent->GetChild(child_index);
			if (child == element)
				return true;

			// Otherwise, if this child shares our element's tag, then our element is not the first tagged child; the selector fails.
			if (child->GetTagName() == element->GetTagName())
				return false;

			child_index--;
		}

		return false;
	}
	break;
	case StructuralSelectorType::Only_Child:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		const int num_children = parent->GetNumChildren();
		for (int i = 0; i < num_children; i++)
		{
			Element* child = parent->GetChild(i);

			// Skip the child if it is our element.
			if (child == element)
				continue;

			// Skip the child if it is trivial.
			if (IsTextElement(child))
				continue;

			return false;
		}

		return true;
	}
	break;
	case StructuralSelectorType::Only_Of_Type:
	{
		Element* parent = element->GetParentNode();
		if (!parent)
			return false;

		const int num_children = parent->GetNumChildren();
		for (int i = 0; i < num_children; i++)
		{
			Element* child = parent->GetChild(i);

			// Skip the child if it is our element.
			if (child == element)
				continue;

			// Skip the child if it does not share our tag.
			if (child->GetTagName() != element->GetTagName())
				continue;

			// We've found a similarly-tagged child to our element; selector fails.
			return false;
		}

		return true;
	}
	break;
	case StructuralSelectorType::Empty:
	{
		return element->GetNumChildren() == 0;
	}
	break;
	case StructuralSelectorType::Not:
	{
		if (!selector.selector_tree)
		{
			RMLUI_ERROR;
			return false;
		}

		bool inner_selector_matches = false;

		for (const StyleSheetNode* node : selector.selector_tree->leafs)
		{
			if (node->IsApplicable(element, scope))
			{
				inner_selector_matches = true;
				break;
			}
		}

		return !inner_selector_matches;
	}
	break;
	case StructuralSelectorType::Scope:
	{
		return scope && element == scope;
	}
	break;
	case StructuralSelectorType::Invalid:
	{
		RMLUI_ERROR;
	}
	break;
	}

	return false;
}

} // namespace Rml