CoreDataStuff

private func buildTree(allProducts:[Product], handler: @escaping(()->Void)) {
        let group = DispatchGroup()
        
        let asyncQueue = DispatchQueue(label: "com.shop.tree.build.queue", qos: .utility, attributes: .concurrent, autoreleaseFrequency: .inherit, target: nil)
        
        var byCategory:[ProductSection] = []
        
        group.enter()
        asyncQueue.async {
            for product in allProducts {
                // If we have same section already
                if let sectionIndex = byCategory.firstIndex(where: { (section) -> Bool in
                    section.category == product.category
                }) {
                    // If we have same subsection already
                    if let subSectionIndex = byCategory[sectionIndex].subSections.firstIndex(where: { (subSection) -> Bool in
                        subSection.subCategory == product.category
                    }) {
                        byCategory[sectionIndex].subSections[subSectionIndex].products.append(product)
                    } else {
                        guard let subCategory = product.subCategory else { return }
                        let newSubSection = ProductSubSection(subCategory: subCategory, products: [product])
                        byCategory[sectionIndex].subSections.append(newSubSection)
                    }
                } else {
                    // If we have to create a new one section
                    guard let category = product.category, let subCategory = product.subCategory else { return }
                    let newSection = ProductSection(category: category)
                    let newSubSection = ProductSubSection(subCategory: subCategory, products: [product])
                    newSection.subSections.append(newSubSection)
                    byCategory.append(newSection)
                }
            }
        }
        
        group.notify(queue: .main) {
            handler()
        }
        
    }