import SwiftUI
import SwiftData

/// 自由周期提醒的创建 / 编辑表单。
/// `reminder == nil` 为新建;否则为编辑(多一个删除按钮)。
/// 本地 @State 暂存,保存时才写 SwiftData + 调度通知;取消即丢弃。
struct CustomReminderEditSheet: View {
    @Environment(\.modelContext) private var ctx
    @Environment(\.dismiss) private var dismiss

    /// nil = 新建模式。
    let reminder: CustomReminder?

    @State private var title = ""
    @State private var note = ""
    @State private var pickedTime: Date = .now
    @State private var frequency: CustomReminder.Frequency = .daily
    @State private var weekdays: Set<Int> = Set(1...7)
    @State private var dayOfMonth = 1
    @State private var month = 1
    @State private var hydrated = false
    @State private var showAuthDeniedAlert = false

    /// 常用时间快捷预设(时, 分):早 / 午 / 傍晚 / 睡前。
    private let timePresets: [(h: Int, m: Int)] = [(8, 0), (12, 0), (18, 0), (22, 0)]

    init(reminder: CustomReminder? = nil) {
        self.reminder = reminder
    }

    private var isEditing: Bool { reminder != nil }
    private var trimmedTitle: String {
        title.trimmingCharacters(in: .whitespacesAndNewlines)
    }
    private var canSave: Bool {
        guard !trimmedTitle.isEmpty else { return false }
        if frequency == .weekly { return !weekdays.isEmpty }
        return true
    }

    var body: some View {
        NavigationStack {
            Form {
                Section {
                    TextField(String(appLoc: "做点什么?例:跑步5公里 / 吃2片护肝片"),
                              text: $title, axis: .vertical)
                        .lineLimit(1...3)
                    TextField(String(appLoc: "备注(可选)"), text: $note, axis: .vertical)
                        .lineLimit(1...3)
                        .foregroundStyle(Tj.Palette.text2)
                }

                Section {
                    Picker(String(appLoc: "重复"), selection: $frequency) {
                        Text(String(appLoc: "每日")).tag(CustomReminder.Frequency.daily)
                        Text(String(appLoc: "每周")).tag(CustomReminder.Frequency.weekly)
                        Text(String(appLoc: "每月")).tag(CustomReminder.Frequency.monthly)
                        Text(String(appLoc: "每年")).tag(CustomReminder.Frequency.yearly)
                    }
                    .pickerStyle(.segmented)
                    .listRowBackground(Color.clear)

                    frequencyDetail
                } header: {
                    Text("重复")
                }

                Section {
                    timePresetRow
                    DatePicker(String(appLoc: "时间"), selection: $pickedTime,
                               displayedComponents: .hourAndMinute)
                } header: {
                    Text("时间")
                }

                if isEditing {
                    Section {
                        Button(role: .destructive) { deleteReminder() } label: {
                            Label(String(appLoc: "删除提醒"), systemImage: "trash")
                        }
                    }
                }
            }
            .scrollContentBackground(.hidden)
            .background(Tj.Palette.sand.ignoresSafeArea())
            .navigationTitle(isEditing ? String(appLoc: "编辑提醒") : String(appLoc: "新建提醒"))
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button(String(appLoc: "取消")) { dismiss() }
                }
                ToolbarItem(placement: .topBarTrailing) {
                    Button(String(appLoc: "保存")) { save() }
                        .fontWeight(.semibold)
                        .disabled(!canSave)
                }
            }
            .onAppear(perform: hydrate)
            .onChange(of: month) { _, newMonth in
                // 切月份后,把超出该月最大天数的「日」收回(避免「2月31日」这种永不触发的组合)。
                let maxD = Self.daysInMonth(newMonth)
                if dayOfMonth > maxD { dayOfMonth = maxD }
            }
            .alert(String(appLoc: "通知未开启"), isPresented: $showAuthDeniedAlert) {
                Button(String(appLoc: "好")) { dismiss() }
            } message: {
                Text("提醒已保存,但系统通知权限未开启,到点不会弹出。请在「设置 · 通知 · 康康」中允许。")
            }
        }
    }

    // MARK: - 频率子控件

    @ViewBuilder
    private var frequencyDetail: some View {
        switch frequency {
        case .daily:
            EmptyView()
        case .weekly:
            weekdayRow
        case .monthly:
            Picker(String(appLoc: "日期"), selection: $dayOfMonth) {
                ForEach(1...31, id: \.self) { d in
                    Text(String(appLoc: "\(d)日")).tag(d)
                }
            }
            if dayOfMonth >= 29 { skipHint }
        case .yearly:
            Picker(String(appLoc: "月份"), selection: $month) {
                ForEach(1...12, id: \.self) { mo in
                    Text(String(appLoc: "\(mo)月")).tag(mo)
                }
            }
            Picker(String(appLoc: "日期"), selection: $dayOfMonth) {
                ForEach(1...Self.daysInMonth(month), id: \.self) { d in
                    Text(String(appLoc: "\(d)日")).tag(d)
                }
            }
            if month == 2 && dayOfMonth == 29 { skipHint }   // 仅闰年的 2/29
        }
    }

    private var skipHint: some View {
        Text(String(appLoc: "部分月份无此日,该月将跳过"))
            .font(.system(size: 11))
            .foregroundStyle(Tj.Palette.text3)
    }

    /// 某月最大天数(2 月取 29,允许设闰年 2/29)。
    private static func daysInMonth(_ month: Int) -> Int {
        switch month {
        case 2:           return 29
        case 4, 6, 9, 11: return 30
        default:          return 31
        }
    }

    // MARK: - 时间快捷预设

    private var timePresetRow: some View {
        let cal = Calendar.current
        let curH = cal.component(.hour, from: pickedTime)
        let curM = cal.component(.minute, from: pickedTime)
        return HStack(spacing: 8) {
            ForEach(Array(timePresets.enumerated()), id: \.offset) { _, preset in
                let on = curH == preset.h && curM == preset.m
                Button {
                    pickedTime = cal.date(bySettingHour: preset.h, minute: preset.m,
                                          second: 0, of: pickedTime) ?? pickedTime
                } label: {
                    Text(String(format: "%d:%02d", preset.h, preset.m))
                        .font(.system(size: 13, weight: on ? .semibold : .regular))
                        .foregroundStyle(on ? Tj.Palette.paper : Tj.Palette.text)
                        .frame(maxWidth: .infinity, minHeight: 30)
                        .background(
                            RoundedRectangle(cornerRadius: 8, style: .continuous)
                                .fill(on ? Tj.Palette.ink : Tj.Palette.paper)
                        )
                        .overlay(
                            RoundedRectangle(cornerRadius: 8, style: .continuous)
                                .strokeBorder(Tj.Palette.line, lineWidth: on ? 0 : 1)
                        )
                }
                .buttonStyle(.plain)
            }
        }
        .listRowBackground(Color.clear)
    }

    // MARK: - 周几选择(与 RemindersListView 同款)

    private var weekdayRow: some View {
        let names = [
            String(appLoc: "一"), String(appLoc: "二"), String(appLoc: "三"),
            String(appLoc: "四"), String(appLoc: "五"), String(appLoc: "六"),
            String(appLoc: "日"),
        ]
        let values = [2, 3, 4, 5, 6, 7, 1]
        return HStack(spacing: 6) {
            ForEach(Array(values.enumerated()), id: \.offset) { idx, w in
                let on = weekdays.contains(w)
                Button {
                    if on { weekdays.remove(w) } else { weekdays.insert(w) }
                } label: {
                    Text(names[idx])
                        .font(.system(size: 13, weight: on ? .semibold : .regular))
                        .foregroundStyle(on ? Tj.Palette.paper : Tj.Palette.text)
                        .frame(maxWidth: .infinity, minHeight: 30)
                        .background(
                            RoundedRectangle(cornerRadius: 8, style: .continuous)
                                .fill(on ? Tj.Palette.ink : Tj.Palette.paper)
                        )
                        .overlay(
                            RoundedRectangle(cornerRadius: 8, style: .continuous)
                                .strokeBorder(Tj.Palette.line, lineWidth: on ? 0 : 1)
                        )
                }
                .buttonStyle(.plain)
            }
        }
        .listRowBackground(Color.clear)
    }

    // MARK: - 数据

    private func hydrate() {
        guard !hydrated else { return }
        hydrated = true
        if let r = reminder {
            title = r.title
            note = r.note
            frequency = r.frequency
            weekdays = Set(r.weekdays)
            dayOfMonth = r.dayOfMonth
            month = r.month
            pickedTime = Calendar.current.date(
                bySettingHour: r.hour, minute: r.minute, second: 0, of: .now
            ) ?? .now
        }
    }

    private func save() {
        guard canSave else { return }
        let cal = Calendar.current
        let hour = cal.component(.hour, from: pickedTime)
        let minute = cal.component(.minute, from: pickedTime)
        let sortedDays = weekdays.sorted()

        let target: CustomReminder
        if let r = reminder {
            r.title = trimmedTitle
            r.note = note.trimmingCharacters(in: .whitespacesAndNewlines)
            r.hour = hour
            r.minute = minute
            r.weekdays = sortedDays
            r.frequency = frequency
            r.dayOfMonth = dayOfMonth
            r.month = month
            r.updatedAt = .now
            target = r
        } else {
            let new = CustomReminder(
                title: trimmedTitle,
                note: note.trimmingCharacters(in: .whitespacesAndNewlines),
                hour: hour,
                minute: minute,
                weekdays: sortedDays,
                frequency: frequency,
                dayOfMonth: dayOfMonth,
                month: month
            )
            ctx.insert(new)
            target = new
        }
        try? ctx.save()

        Task { @MainActor in
            let state = await ReminderService.requestAuthorization()
            await ReminderService.sync(target)
            if state == .denied {
                showAuthDeniedAlert = true
            } else {
                dismiss()
            }
        }
    }

    private func deleteReminder() {
        guard let r = reminder else { return }
        ReminderService.cancel(customId: r.id)
        ctx.delete(r)
        try? ctx.save()
        dismiss()
    }
}

#Preview("新建") {
    CustomReminderEditSheet()
        .modelContainer(for: [CustomReminder.self], inMemory: true)
}