TeachMate/TeachMate/Views/SemesterFormView.swift

//
//  SemesterFormView.swift
//  TeachMate
//
//  Created by Hongli on 2025/3/12.
//

import SwiftUI
import SwiftData

struct SemesterFormView: View {
    @Environment(\.dismiss) private var dismiss
    @Environment(\.modelContext) private var modelContext
    @Environment(\.colorScheme) private var colorScheme
    
    @State private var title: String = ""
    @State private var startDate: Date = Date()
    @State private var endDate: Date = Date()
    @State private var weeksCount: Int = 18
    
    @State private var showingAlert = false
    @State private var alertMessage = ""
    
    // Calculate the end of the week (Sunday) for a given date
    private func endOfWeek(for date: Date) -> Date {
        let calendar = Calendar.current
        let components = calendar.dateComponents([.yearForWeekOfYear, .weekOfYear], from: date)
        guard let sunday = calendar.date(from: components) else { return date }
        // Add 6 days to get to Sunday (assuming first day of week is Monday)
        return calendar.date(byAdding: .day, value: 6, to: sunday) ?? date
    }
    
    // Calculate the end date (last Sunday of the semester)
    private func calculateEndDate() -> Date {
        let calendar = Calendar.current
        // Add (weeksCount - 1) weeks to the start date to get to the beginning of the last week
        guard let lastWeekStart = calendar.date(byAdding: .day, value: (weeksCount - 1) * 7, to: startDate) else {
            return endDate
        }
        // Get the Sunday of the last week
        return endOfWeek(for: lastWeekStart)
    }
    
    // Format date for display
    private func formattedDate(_ date: Date) -> String {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        return formatter.string(from: date)
    }
    
    var body: some View {
        NavigationStack {
            ZStack {
                // Background
                (colorScheme == .dark ? Color.black : Color.gray.opacity(0.1))
                    .ignoresSafeArea()
                
                // Main content with horizontal layout
                HStack(spacing: 0) {
                    // Left side - Form content
                    ScrollView {
                        VStack(spacing: 24) {
                            // Title Section
                            FormSection(title: "学期标题") {
                                VStack(alignment: .leading, spacing: 8) {
                                    TextField("请输入标题", text: $title)
                                        .textFieldStyle(RoundedBorderTextFieldStyle())
                                        .autocorrectionDisabled()
                                        .frame(maxWidth: .infinity)
                                    
                                    Text("标题格式: YYYY-YYYY-N")
                                        .font(.caption)
                                        .foregroundStyle(.secondary)
                                }
                                .frame(maxWidth: .infinity)
                            }
                            
                            // Combined Teaching Weeks Section
                            FormSection(title: "教学周") {
                                VStack(spacing: 16) {
                                    // Weeks count
                                    HStack {
                                        Text("周数:")
                                            .foregroundStyle(.secondary)
                                        
                                        Spacer()
                                        
                                        Picker("周数", selection: $weeksCount) {
                                            ForEach(1...30, id: \.self) { week in
                                                Text("\(week) 周").tag(week)
                                            }
                                        }
                                        .pickerStyle(.menu)
                                        .onChange(of: weeksCount) { _, _ in
                                            // Update end date when weeks count changes
                                            endDate = calculateEndDate()
                                        }
                                    }
                                    
                                    Divider()
                                    
                                    // Start date
                                    HStack {
                                        Text("开始日期:")
                                            .foregroundStyle(.secondary)
                                        
                                        Spacer()
                                        
                                        DatePicker(
                                            "",
                                            selection: $startDate,
                                            displayedComponents: [.date]
                                        )
                                        .labelsHidden()
                                        .onChange(of: startDate) { _, _ in
                                            // Update end date when start date changes
                                            endDate = calculateEndDate()
                                        }
                                    }
                                }
                                .frame(maxWidth: .infinity)
                            }
                        }
                        .padding()
                        .frame(maxWidth: .infinity)
                    }
                    .frame(minWidth: 300, idealWidth: 350, maxWidth: .infinity)
                    
                    // Vertical divider
                    Divider()
                        .padding(.vertical)
                    
                    // Right side - Summary
                    VStack {
                        FormSection(title: "学期概览") {
                            VStack(alignment: .leading, spacing: 12) {
                                SummaryRow(label: "标题", value: title.isEmpty ? "未设置" : title)
                                SummaryRow(label: "周数", value: "\(weeksCount) 周")
                                SummaryRow(label: "开始日期", value: formattedDate(startDate))
                                SummaryRow(label: "结束日期", value: formattedDate(endDate))
                                SummaryRow(
                                    label: "总时长",
                                    value: "\(Calendar.current.dateComponents([.day], from: startDate, to: endDate).day ?? 0 + 1) 天"
                                )
                            }
                        }
                        
                        Spacer()
                    }
                    .padding()
                    .frame(minWidth: 250, idealWidth: 300, maxWidth: .infinity)
                    .background(colorScheme == .dark ? Color.black : Color.white)
                }
                .frame(minWidth: 600, idealWidth: 700, maxHeight: .infinity)
            }
            .navigationTitle("添加学期")
            .toolbarRole(.editor)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("取消") {
                        dismiss()
                    }
                }
                
                ToolbarItem(placement: .confirmationAction) {
                    Button("保存") {
                        saveSemester()
                    }
                }
            }
            .onAppear {
                // Set default end date
                endDate = calculateEndDate()
            }
            .alert("错误", isPresented: $showingAlert) {
                Button("确定", role: .cancel) { }
            } message: {
                Text(alertMessage)
            }
        }
    }
    
    private func saveSemester() {
        // Validate inputs
        if title.isEmpty {
            alertMessage = "请输入学期标题"
            showingAlert = true
            return
        }
        
        // Create and save the semester
        let semester = Semester(
            title: title,
            startDate: startDate,
            endDate: endDate,
            weeksCount: weeksCount
        )
        
        modelContext.insert(semester)
        dismiss()
    }
}

#Preview {
    SemesterFormView()
        .modelContainer(PreviewData.createSemesterContainer())
}