EntityUtil.h

#include "Core/Entity.h"

#include <vector>

namespace DYE::DYEditor::EntityUtil
{
	bool IsFirstDegreeChildOf(Entity potentialChild, Entity potentialParent);

	/// Check recursively if potential child is under potential parent's hierarchy.
	bool IsChildOf(Entity potentialChild, Entity potentialParent);

	/// Get an array including the given root entity and its children recursively in depth-first order.
	std::vector<Entity> GetEntityAndAllChildrenPreorder(Entity root);

	/// Get an array of children of the given entity recursively in depth-first order.
	std::vector<Entity> GetAllChildrenPreorder(Entity root);

	/// Iterate through the entity and its all children (including nth degree children)
	/// using depth-first order (preorder). You should not destroy any entity during the iteration.
	template<typename Func>
	void ForEntityAndEachChildPreorder(Entity root, Func func)
	{
		std::stack<Entity> entityStack;
		entityStack.push(root);

		while (!entityStack.empty())
		{
			Entity entity = entityStack.top();

			func(entity);

			entityStack.pop();
			auto tryGetChild = entity.TryGetComponent<ChildrenComponent>();
			if (!tryGetChild.has_value())
			{
				// No child, nothing to push into the stack.
				continue;
			}

			auto &childrenGUIDs = tryGetChild.value().get().ChildrenGUIDs;
			for (int i = childrenGUIDs.size() - 1; i >= 0; i--)
			{
				auto childGUID = childrenGUIDs[i];
				auto tryGetEntityWithGUID = root.GetWorld().TryGetEntityWithGUID(childGUID);
				if (!tryGetEntityWithGUID.has_value())
				{
					continue;
				}
				// Push the child into the stack.
				entityStack.push(tryGetEntityWithGUID.value());
			}
		}
	}

	/// Iterate through the entity and its all children (including nth degree children)
	/// using depth-first order (preorder). The second parameter of the function will be the relative depth to the root entity.
	/// You should not destroy any entity during the iteration.
	template<typename Func>
	void ForEntityAndEachChildPreorderWithDepth(Entity root, Func func)
	{
		struct Element
		{
			Entity Entity;
			int Depth = 0;
		};

		std::stack<Element> entityStack;
		entityStack.push({ .Entity = root, .Depth = 0 });

		while (!entityStack.empty())
		{
			Element element = entityStack.top();
			Entity entity = element.Entity;

			func(entity, element.Depth);

			entityStack.pop();
			auto tryGetChild = entity.TryGetComponent<ChildrenComponent>();
			if (!tryGetChild.has_value())
			{
				// No child, nothing to push into the stack.
				continue;
			}

			auto &childrenGUIDs = tryGetChild.value().get().ChildrenGUIDs;
			for (int i = childrenGUIDs.size() - 1; i >= 0; i--)
			{
				auto childGUID = childrenGUIDs[i];
				auto tryGetEntityWithGUID = root.GetWorld().TryGetEntityWithGUID(childGUID);
				if (!tryGetEntityWithGUID.has_value())
				{
					continue;
				}
				// Push the child into the stack.
				entityStack.push({ .Entity = tryGetEntityWithGUID.value(), .Depth = element.Depth + 1 });
			}
		}
	}

	/// Iterate through all children (including nth degree children)
	/// using depth-first order (preorder). You should not destroy any entity during the iteration.
	/// If you really have to, consider using GetAllChildrenPreorder to get an array of children.
	template<typename Func>
	void ForEachChildPreorder(Entity root, Func func)
	{
		std::stack<Entity> entityStack;
		entityStack.push(root);

		bool isRoot = true;

		while (!entityStack.empty())
		{
			Entity entity = entityStack.top();

			// We use a flag to skip the first entity in the stack (which is the parent).
			if (!isRoot)
			{
				func(entity);
			}
			isRoot = false;

			entityStack.pop();
			auto tryGetChild = entity.TryGetComponent<ChildrenComponent>();
			if (!tryGetChild.has_value())
			{
				// No child, nothing to push into the stack.
				continue;
			}

			auto &childrenGUIDs = tryGetChild.value().get().ChildrenGUIDs;
			for (int i = childrenGUIDs.size() - 1; i >= 0; i--)
			{
				auto childGUID = childrenGUIDs[i];
				auto tryGetEntityWithGUID = root.GetWorld().TryGetEntityWithGUID(childGUID);
				if (!tryGetEntityWithGUID.has_value())
				{
					continue;
				}
				// Push the child into the stack.
				entityStack.push(tryGetEntityWithGUID.value());
			}
		}
	}
}