import SwiftUI
import SwiftData

/// 특정 달의 캘린더. 날짜 칸마다 기록된 제품 사진 썸네일이 보인다.
struct MonthCalendarView: View {
    let store: Store

    @Query private var allRecords: [ProductRecord]
    @AppStorage(weekStartStorageKey) private var weekStartsMonday = false
    @State private var year: Int
    @State private var month: Int
    @State private var selectedDay: DaySelection?
    @State private var showCapture = false

    init(store: Store, year: Int, month: Int) {
        self.store = store
        _year = State(initialValue: year)
        _month = State(initialValue: month)
    }

    private struct DaySelection: Identifiable {
        let day: Int
        var id: Int { day }
    }

    private var monthRecords: [ProductRecord] {
        allRecords.filter {
            guard $0.store === store else { return false }
            let c = KoreanCalendar.calendar.dateComponents([.year, .month], from: $0.expiryDate)
            return c.year == year && c.month == month
        }
    }

    private var recordsByDay: [Int: [ProductRecord]] {
        Dictionary(grouping: monthRecords) {
            KoreanCalendar.calendar.component(.day, from: $0.expiryDate)
        }
        .mapValues { $0.sorted { $0.createdAt < $1.createdAt } }
    }

    var body: some View {
        ZStack {
            Theme.bg.ignoresSafeArea()
            VStack(spacing: 16) {
                monthHeader
                weekdayRow
                ScrollView {
                    calendarGrid
                        .padding(.bottom, 100)
                }
            }
            .padding(.horizontal, 16)
        }
        .overlay(alignment: .bottomTrailing) { scanButton }
        .navigationTitle(store.name)
        .navigationBarTitleDisplayMode(.inline)
        .sheet(item: $selectedDay) { selection in
            DayDetailView(store: store, year: year, month: month, day: selection.day)
        }
        .fullScreenCover(isPresented: $showCapture) {
            CaptureFlowView(store: store, year: year, month: month)
        }
    }

    // MARK: - 헤더

    private var monthHeader: some View {
        HStack(spacing: 12) {
            monthNavButton(systemName: "chevron.left") { moveMonth(-1) }
            Spacer()
            VStack(spacing: 2) {
                Text(verbatim: "\(year)년 \(month)월")
                    .font(.system(size: 22, weight: .bold, design: .rounded))
                    .foregroundStyle(Theme.textPrimary)
                    .contentTransition(.numericText())
                Text(monthRecords.isEmpty ? "기록 없음" : "제품 \(monthRecords.count)개")
                    .font(.caption)
                    .foregroundStyle(monthRecords.isEmpty ? Theme.textSecondary : Theme.accent)
            }
            Spacer()
            monthNavButton(systemName: "chevron.right") { moveMonth(1) }
        }
        .padding(.top, 8)
    }

    private func monthNavButton(systemName: String, action: @escaping () -> Void) -> some View {
        Button {
            withAnimation(.snappy) { action() }
            Haptics.tap()
        } label: {
            Image(systemName: systemName)
                .font(.body.weight(.semibold))
                .foregroundStyle(Theme.textPrimary)
                .frame(width: 38, height: 38)
                .background(Circle().fill(Theme.surface))
                .overlay(Circle().strokeBorder(Theme.stroke, lineWidth: 1))
        }
    }

    private func moveMonth(_ delta: Int) {
        var m = month + delta
        var y = year
        if m < 1 { m = 12; y -= 1 }
        if m > 12 { m = 1; y += 1 }
        month = m
        year = y
    }

    // MARK: - 요일 / 날짜 그리드

    private var weekdayRow: some View {
        let symbols = KoreanCalendar.weekdaySymbols(startsOnMonday: weekStartsMonday)
        return HStack(spacing: 6) {
            ForEach(0..<7, id: \.self) { index in
                Text(symbols[index])
                    .font(.caption.weight(.semibold))
                    .foregroundStyle(KoreanCalendar.weekdayColor(columnIndex: index, startsOnMonday: weekStartsMonday))
                    .frame(maxWidth: .infinity)
            }
        }
    }

    private var calendarGrid: some View {
        let columns = Array(repeating: GridItem(.flexible(), spacing: 6), count: 7)
        let days = KoreanCalendar.gridDays(year: year, month: month, startsOnMonday: weekStartsMonday)
        return LazyVGrid(columns: columns, spacing: 6) {
            ForEach(Array(days.enumerated()), id: \.offset) { index, day in
                if let day {
                    dayCell(day: day, columnIndex: index % 7)
                } else {
                    Color.clear.frame(height: 68)
                }
            }
        }
    }

    private func dayCell(day: Int, columnIndex: Int) -> some View {
        let records = recordsByDay[day] ?? []
        let isToday = KoreanCalendar.isToday(year: year, month: month, day: day)
        let hasPhoto = !records.isEmpty

        return Button {
            selectedDay = DaySelection(day: day)
            Haptics.tap()
        } label: {
            RoundedRectangle(cornerRadius: 12, style: .continuous)
                .fill(Theme.surface)
                .frame(height: 68)
                .overlay {
                    if let first = records.first, let image = UIImage(data: first.thumbnailData) {
                        Image(uiImage: image)
                            .resizable()
                            .scaledToFill()
                            .overlay(
                                LinearGradient(
                                    colors: [.black.opacity(0.55), .clear],
                                    startPoint: .top,
                                    endPoint: .center
                                )
                            )
                    }
                }
                .clipShape(RoundedRectangle(cornerRadius: 12, style: .continuous))
                .overlay(alignment: .topLeading) {
                    Text(verbatim: "\(day)")
                        .font(.system(size: 12, weight: isToday ? .heavy : .semibold, design: .rounded))
                        .foregroundStyle(dayNumberColor(columnIndex: columnIndex, hasPhoto: hasPhoto, isToday: isToday))
                        .padding(5)
                }
                .overlay(alignment: .bottomTrailing) {
                    if records.count > 1 {
                        Text(verbatim: "\(records.count)")
                            .font(.system(size: 10, weight: .bold, design: .rounded))
                            .foregroundStyle(Theme.onAccent)
                            .padding(.horizontal, 5)
                            .padding(.vertical, 2)
                            .background(Capsule().fill(Theme.accent))
                            .padding(4)
                    }
                }
                .overlay(
                    RoundedRectangle(cornerRadius: 12, style: .continuous)
                        .strokeBorder(
                            isToday ? Theme.accent : Theme.stroke,
                            lineWidth: isToday ? 1.5 : 1
                        )
                )
        }
        .buttonStyle(.plain)
    }

    private func dayNumberColor(columnIndex: Int, hasPhoto: Bool, isToday: Bool) -> Color {
        if isToday { return Theme.accent }
        if hasPhoto { return .white }
        return KoreanCalendar.weekdayColor(columnIndex: columnIndex, startsOnMonday: weekStartsMonday)
    }

    // MARK: - 스캔 버튼

    private var scanButton: some View {
        Button {
            showCapture = true
            Haptics.tap()
        } label: {
            Image(systemName: "camera.fill")
                .font(.title2.weight(.semibold))
                .foregroundStyle(Theme.onAccent)
                .frame(width: 62, height: 62)
                .background(Circle().fill(Theme.accentGradient))
                .shadow(color: Theme.accent.opacity(0.4), radius: 16, y: 6)
        }
        .padding(.trailing, 24)
        .padding(.bottom, 28)
    }
}