import Foundation
import CoreData
import Combine

class CategoryRepository: ObservableObject {
    private let context: NSManagedObjectContext

    @Published private(set) var categories: [Category] = []

    init(context: NSManagedObjectContext = CoreDataStack.shared.viewContext) {
        self.context = context
        fetchCategories()
        setupNotificationObserver()
    }

    private func setupNotificationObserver() {
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(contextDidChange),
            name: .NSManagedObjectContextObjectsDidChange,
            object: context
        )
    }

    @objc private func contextDidChange(_ notification: Notification) {
        fetchCategories()
    }

    // MARK: - Fetch

    func fetchCategories() {
        let request: NSFetchRequest<Category> = Category.fetchRequest()
        request.sortDescriptors = [
            NSSortDescriptor(keyPath: \Category.sortOrder, ascending: true),
            NSSortDescriptor(keyPath: \Category.name, ascending: true)
        ]

        do {
            categories = try context.fetch(request)
        } catch {
            print("Failed to fetch categories: \(error)")
            categories = []
        }
    }

    func fetchCategory(by id: UUID) -> Category? {
        let request: NSFetchRequest<Category> = Category.fetchRequest()
        request.predicate = NSPredicate(format: "id == %@", id as CVarArg)
        request.fetchLimit = 1
        return try? context.fetch(request).first
    }

    // MARK: - Create

    @discardableResult
    func createCategory(
        name: String,
        colorHex: String,
        icon: String
    ) -> Category {
        let category = Category(context: context)
        category.name = name
        category.colorHex = colorHex
        category.icon = icon
        category.sortOrder = Int16(categories.count)

        save()
        return category
    }

    func createDefaultCategoriesIfNeeded() {
        guard categories.isEmpty else { return }
        Category.createDefaultCategories(in: context)
        fetchCategories()
    }

    // MARK: - Update

    func updateCategory(
        _ category: Category,
        name: String? = nil,
        colorHex: String? = nil,
        icon: String? = nil
    ) {
        if let name = name {
            category.name = name
        }
        if let colorHex = colorHex {
            category.colorHex = colorHex
        }
        if let icon = icon {
            category.icon = icon
        }

        save()
    }

    func updateSortOrder(_ categories: [Category]) {
        for (index, category) in categories.enumerated() {
            category.sortOrder = Int16(index)
        }
        save()
    }

    // MARK: - Delete

    func deleteCategory(_ category: Category) {
        context.delete(category)
        save()
    }

    func deleteCategory(at offsets: IndexSet) {
        for index in offsets {
            guard index < categories.count else { continue }
            context.delete(categories[index])
        }
        save()
    }

    // MARK: - Statistics

    var totalValue: Decimal {
        categories.reduce(Decimal.zero) { $0 + $1.totalValue }
    }

    func categoryAllocation() -> [(category: Category, percentage: Double)] {
        let total = totalValue
        guard total > 0 else { return [] }

        return categories.map { category in
            let percentage = NSDecimalNumber(decimal: category.totalValue / total).doubleValue * 100
            return (category: category, percentage: percentage)
        }.sorted { $0.percentage > $1.percentage }
    }

    // MARK: - Save

    private func save() {
        guard context.hasChanges else { return }
        do {
            try context.save()
            fetchCategories()
        } catch {
            print("Failed to save context: \(error)")
        }
    }
}