//
//  MonthTabView.swift
//  Schedule ICTIS
//
//  Created by G412 on 10.12.2024.
//

import SwiftUI

struct MonthTabView: View {
    @State private var currentMonthIndex: Int = 1
    @State private var monthSlider: [[Date.MonthWeek]] = []
    @State private var createMonth: Bool = false
    @State private var currentWeekIndex: Int = 0
    @ObservedObject var vm: ViewModel
    var body: some View {
        VStack {
            HStack (spacing: 34) {
                ForEach(MockData.daysOfWeek.indices, id: \.self) { index in
                    Text(MockData.daysOfWeek[index])
                        .font(.system(size: 15, weight: .semibold))
                        .foregroundColor(MockData.daysOfWeek[index] == "Вс" ? Color(.red) : Color("customGray2"))
                        .padding(.top, 13)
                        .foregroundColor(.gray)
                }
            }
            .padding(.top, 14)
            //.background(Color.red)
            TabView(selection: $currentMonthIndex) {
                ForEach(monthSlider.indices, id: \.self) { index in
                    let month = monthSlider[index]
                    MonthView(month)
                        .tag(index)
                }
            }
            .padding(.top, -25)
            .padding(.bottom, -10)
            .padding(.horizontal, -15)
            .tabViewStyle(.page(indexDisplayMode: .never))
            //.background(Color.green)
        }
        .onAppear(perform: {
            vm.updateSelectedDayIndex()
            if monthSlider.isEmpty {
                let currentMonth = Date().fetchMonth(vm.selectedDay)
                
                if let firstDate = currentMonth.first?.week[0].date {
                    monthSlider.append(firstDate.createPreviousMonth())
                }
                    
                monthSlider.append(currentMonth)
                
                if let lastDate = currentMonth.last?.week[6].date {
                    monthSlider.append(lastDate.createNextMonth())
                }
            }
        })
        .onChange(of: currentMonthIndex, initial: false) { oldValue, newValue in
            if newValue == 0 || newValue == (monthSlider.count - 1) {
                createMonth = true
            }
        }
    }
    
    @ViewBuilder
    func MonthView(_ month: [Date.MonthWeek]) -> some View {
        VStack (spacing: 10) {
            ForEach(month.indices, id: \.self) { index in
                let week = month[index].week
                WeekView(week)
            }
        }
        .background {
            GeometryReader {
                let minX = $0.frame(in: .global).minX
                
                Color.clear
                    .preference(key: OffsetKey.self, value: minX)
                    .onPreferenceChange(OffsetKey.self) { value in
                        if (abs(value.rounded()) - 20) < 5 && createMonth {
                            paginateMonth()
                            
                            createMonth = false
                        }
                    }
            }
        }
    }
    
    
    @ViewBuilder
    func WeekView(_ week: [Date.WeekDay]) -> some View {
        HStack (spacing: 23) {
            ForEach(week) { day in
                VStack {
                    Text(day.date.format("dd"))
                        .font(.system(size: 15, weight: .bold))
                        .foregroundStyle(isDateInCurrentMonth(day.date) ? isSameDate(day.date, vm.selectedDay) ? Color.white : Color.black: isSameDate(day.date, vm.selectedDay) ? Color.white : Color("greyForDaysInMonthTabView"))
                }
                .frame(width: 30, height: 30,  alignment: .center)
                .background( content: {
                    Group {
                        if isSameDate(day.date, vm.selectedDay) {
                            Color("blueColor")
                        }
                        else {
                            Color("background")
                        }
                        if isSameDate(day.date, vm.selectedDay) {
                            Color("blueColor")
                        }
                    }
                }
                )
                .overlay (
                    Group {
                        if day.date.isToday && !isSameDate(day.date, vm.selectedDay) {
                            RoundedRectangle(cornerRadius: 100)
                                .stroke(Color("blueColor"), lineWidth: 2)
                        }
                    }
                )
                .cornerRadius(15)
                .onTapGesture {
                    if isSameWeek(day.date, vm.selectedDay) {
                        print("На одной неделе")
                    }
                    else {
                        var difBetweenWeeks = weeksBetween(startDate: vm.selectedDay, endDate: day.date)
                        if day.date < vm.selectedDay {
                            difBetweenWeeks = difBetweenWeeks * -1
                        }
                        print(difBetweenWeeks)
                        vm.fetchWeekSchedule("", difBetweenWeeks)
                    }
                    vm.selectedDay = day.date
                    vm.updateSelectedDayIndex()
                }
            }
        }
    }
    
    func paginateMonth(_ indexOfWeek: Int = 0) {
        let calendar = Calendar.current
        if monthSlider.indices.contains(currentMonthIndex) {
            if let firstDate = monthSlider[currentMonthIndex].first?.week[0].date,
               currentMonthIndex == 0 {
//                switch (vm.numOfGroup) {
//                case "":
//                    vm.week -= 1
//                default:
//                    vm.fetchWeekSchedule("new week", -1)
//                }
                monthSlider.insert(firstDate.createPreviousMonth(), at: 0)
                monthSlider.removeLast()
                currentMonthIndex = 1
                vm.selectedDay = calendar.date(byAdding: .weekOfYear, value: -5, to: vm.selectedDay) ?? Date.init()
                vm.updateSelectedDayIndex()
                vm.fetchWeekSchedule("", -5)
            }
            
            if let lastDate = monthSlider[currentMonthIndex].last?.week[6].date,
               currentMonthIndex == (monthSlider.count - 1) {
//                switch (vm.numOfGroup) {
//                case "":
//                    vm.week += 1
//                default:
//                    vm.fetchWeekSchedule("new week", 1)
//                }
                monthSlider.append(lastDate.createNextMonth())
                monthSlider.removeFirst()
                currentMonthIndex = monthSlider.count - 2
                vm.selectedDay = calendar.date(byAdding: .weekOfYear, value: 5, to: vm.selectedDay) ?? Date.init()
                vm.updateSelectedDayIndex()
                vm.fetchWeekSchedule("", 5)
            }
        }
    }
}

#Preview {
    ContentView()
}