poc-links/include/iterators/BFSIterator.h

#pragma once
#include <queue>

#include "iterators/BaseIterator.h"

template <typename T>
class BFSIterator : public BaseIterator<T> {
public:
	explicit BFSIterator(T* ptr) : BaseIterator<T>(ptr) {
		if (!this->current())
			return;

		for (auto& it : this->current()->children())
			q.push({it.get(), 1});
	}

	IIterator<T>& operator++() override {
		advance();
		return *this;
	}

protected:
	std::queue<std::pair<T*, size_t>> q;

	void advance() {
		if (q.empty()) {
			this->set_current(nullptr);
			return;
		}

		auto& [node, lvl] = q.front();
		q.pop();

		this->set_current(node);
		this->set_level(lvl);

		for (auto& it : this->current()->children())
			q.push({it.get(), lvl + 1});
	}
};