AboTracker/AboTracker/views/PaymentCalendarView.swift

import SwiftUI

struct PaymentCalendarView: View {
    @Binding var subs: [Subscription]
    let calendar = Calendar.current
    let dateFormatter = DateFormatter()
    
    @State private var currentDate = Date()
    private let initialDate = Date()
    
    var body: some View {
        VStack {
            Text("Payment Calendar")
                .font(.title)
                .padding()
            
            HStack {
                Button(action: {
                    self.currentDate = self.calendar.date(byAdding: .month, value: -1, to: self.currentDate)!
                }) {
                    Image(systemName: "chevron.left.circle.fill")
                        .font(.title)
                }
                
                Button(action: {
                    self.currentDate = self.initialDate
                }) {
                    Text("Current Month")
                        .font(.headline)
                }
                
                Button(action: {
                    self.currentDate = self.calendar.date(byAdding: .month, value: 1, to: self.currentDate)!
                }) {
                    Image(systemName: "chevron.right.circle.fill")
                        .font(.title)
                }
            }
            .padding(.horizontal)
            
            calendarView()
                .gesture(
                    DragGesture()
                        .onEnded { gesture in
                            if gesture.translation.width < 0 {
                                // Swipe left -> move to next month
                                self.currentDate = self.calendar.date(byAdding: .month, value: 1, to: self.currentDate)!
                            } else {
                                // Swipe right -> move to previous month
                                self.currentDate = self.calendar.date(byAdding: .month, value: -1, to: self.currentDate)!
                            }
                        }
                )
        }
        .padding()
    }
    
    func currentMonthYear() -> String {
        let formatter = DateFormatter()
        formatter.dateFormat = "MMMM yyyy"
        return formatter.string(from: currentDate)
    }
    
    func calendarView() -> some View {
        let days = daysInMonth(date: currentDate)
        let firstDay = firstDayOfMonth(date: currentDate)
        
        let columns = Array(repeating: GridItem(.flexible()), count: 7)
        let weeks = (days.count + firstDay) / 7 + ((days.count + firstDay) % 7 == 0 ? 0 : 1)
        
        return LazyVGrid(columns: columns, spacing: 20) {
            ForEach(0..<7, id: \.self) { index in
                Text(daySymbol(index: index))
                    .fontWeight(.bold)
            }
            
            ForEach(0..<(weeks * 7), id: \.self) { index in
                if index < firstDay || index - firstDay >= days.count {
                    Text("")
                } else {
                    let day = index - firstDay + 1
                    let dayDate = calendar.date(byAdding: .day, value: day - 1, to: startOfMonth(date: currentDate))!
                    let paymentColor = getPaymentColor(for: dayDate)
                    
                    Text("\(day)")
                        .frame(maxWidth: .infinity, maxHeight: .infinity)
                        .background(paymentColor)
                        .cornerRadius(8)
                }
            }
        }
    }
    
    func getPaymentColor(for date: Date) -> Color {
        for sub in subs {
            for payment in sub.payments {
                if isPaymentDue(payment: payment, for: date) {
                    return sub.color.opacity(0.3)
                }
            }
        }
        return Color.clear
    }
    
    func isPaymentDue(payment: Payment, for date: Date) -> Bool {
        switch payment.intervall {
        case .weekly:
            let startOfWeek = calendar.date(from: calendar.dateComponents([.yearForWeekOfYear, .weekOfYear], from: date))!
            let endOfWeek = calendar.date(byAdding: .day, value: 6, to: startOfWeek)!
            return date >= startOfWeek && date <= endOfWeek && calendar.component(.weekday, from: payment.startDate) == calendar.component(.weekday, from: date)
            
        case .monthly:
            return calendar.component(.day, from: payment.startDate) == calendar.component(.day, from: date)
            
        case .quarter:
            guard let quarterStartDate = calendar.date(byAdding: .month, value: -3, to: payment.startDate) else {
                return false
            }
            let startOfQuarter = calendar.date(from: calendar.dateComponents([.year, .month], from: quarterStartDate))!
            let endOfQuarter = calendar.date(byAdding: .month, value: 3, to: startOfQuarter)!
            return date >= startOfQuarter && date <= endOfQuarter
        
        case .yearly:
            return calendar.component(.year, from: payment.startDate) == calendar.component(.year, from: date)
        }
    }

    func daysInMonth(date: Date) -> [Date] {
        guard let range = calendar.range(of: .day, in: .month, for: date) else { return [] }
        return range.compactMap { day -> Date? in
            var components = calendar.dateComponents([.year, .month], from: date)
            components.day = day
            return calendar.date(from: components)
        }
    }
    
    func firstDayOfMonth(date: Date) -> Int {
        let components = calendar.dateComponents([.year, .month], from: date)
        guard let firstDay = calendar.date(from: components) else { return 0 }
        return calendar.component(.weekday, from: firstDay) - calendar.firstWeekday
    }
    
    func daySymbol(index: Int) -> String {
        dateFormatter.shortWeekdaySymbols[(index + calendar.firstWeekday - 1) % 7]
    }
    
    func startOfMonth(date: Date) -> Date {
        let components = calendar.dateComponents([.year, .month], from: date)
        return calendar.date(from: components) ?? date
    }
}

struct PaymentCalendarView_Previews: PreviewProvider {
    static var previews: some View {
        PaymentCalendarView(subs: .constant([
            Subscription(name: "Test", payments: [Payment(amount: 9.99, intervall: .monthly, startDate: Date())], color: .blue),
            Subscription(name: "Fitness First", payments: [
                Payment(amount: 7.9, intervall: .weekly, startDate: Date()),
                Payment(amount: 29, intervall: .quarter, startDate: Date())
            ], color: .red)
        ]))
    }
}