import SwiftUI
import SwiftData

/// 매장 선택 후: 연도를 고르고 1~12월 그리드에서 달을 선택한다.
struct YearMonthView: View {
    let store: Store

    @Query private var allRecords: [ProductRecord]
    @State private var year: Int

    init(store: Store) {
        self.store = store
        _year = State(initialValue: KoreanCalendar.calendar.component(.year, from: .now))
    }

    private struct MonthRoute: Hashable {
        let year: Int
        let month: Int
    }

    private var storeRecords: [ProductRecord] {
        allRecords.filter { $0.store === store }
    }

    /// 이 연도의 월별 기록 개수
    private var countsByMonth: [Int: Int] {
        var counts: [Int: Int] = [:]
        for record in storeRecords {
            let c = KoreanCalendar.calendar.dateComponents([.year, .month], from: record.expiryDate)
            if c.year == year, let month = c.month {
                counts[month, default: 0] += 1
            }
        }
        return counts
    }

    var body: some View {
        ZStack {
            Theme.bg.ignoresSafeArea()
            ScrollView {
                VStack(spacing: 24) {
                    yearPicker
                    monthGrid
                    yearSummary
                }
                .padding(20)
            }
        }
        .navigationTitle(store.name)
        .navigationBarTitleDisplayMode(.inline)
        .navigationDestination(for: MonthRoute.self) { route in
            MonthCalendarView(store: store, year: route.year, month: route.month)
        }
    }

    // MARK: - 연도 선택

    private var yearPicker: some View {
        HStack {
            yearButton(systemName: "chevron.left") { year -= 1 }
            Spacer()
            Text(verbatim: "\(year)년")
                .font(.system(size: 26, weight: .bold, design: .rounded))
                .foregroundStyle(Theme.textPrimary)
                .contentTransition(.numericText())
            Spacer()
            yearButton(systemName: "chevron.right") { year += 1 }
        }
        .padding(.top, 8)
    }

    private func yearButton(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: 40, height: 40)
                .background(Circle().fill(Theme.surface))
                .overlay(Circle().strokeBorder(Theme.stroke, lineWidth: 1))
        }
    }

    // MARK: - 월 그리드

    private var monthGrid: some View {
        let columns = Array(repeating: GridItem(.flexible(), spacing: 12), count: 3)
        let now = KoreanCalendar.calendar.dateComponents([.year, .month], from: .now)
        return LazyVGrid(columns: columns, spacing: 12) {
            ForEach(1...12, id: \.self) { month in
                NavigationLink(value: MonthRoute(year: year, month: month)) {
                    monthCard(month: month, isCurrent: now.year == year && now.month == month)
                }
                .buttonStyle(.plain)
            }
        }
    }

    private func monthCard(month: Int, isCurrent: Bool) -> some View {
        let count = countsByMonth[month] ?? 0
        return VStack(alignment: .leading, spacing: 0) {
            Text(verbatim: "\(month)월")
                .font(.system(.title3, design: .rounded).weight(.bold))
                .foregroundStyle(count > 0 ? Theme.textPrimary : Theme.textSecondary)
            Spacer(minLength: 18)
            if count > 0 {
                Text(verbatim: "\(count)개")
                    .font(.caption.weight(.bold))
                    .foregroundStyle(Theme.onAccent)
                    .padding(.horizontal, 9)
                    .padding(.vertical, 4)
                    .background(Capsule().fill(Theme.accent))
            } else {
                Text("기록 없음")
                    .font(.caption2)
                    .foregroundStyle(Theme.textSecondary.opacity(0.6))
            }
        }
        .padding(14)
        .frame(maxWidth: .infinity, alignment: .leading)
        .frame(height: 96)
        .background(
            RoundedRectangle(cornerRadius: 18, style: .continuous)
                .fill(Theme.surface)
        )
        .overlay(
            RoundedRectangle(cornerRadius: 18, style: .continuous)
                .strokeBorder(isCurrent ? Theme.accent.opacity(0.8) : Theme.stroke, lineWidth: isCurrent ? 1.5 : 1)
        )
    }

    // MARK: - 연도 요약

    private var yearSummary: some View {
        let total = countsByMonth.values.reduce(0, +)
        return Group {
            if total > 0 {
                Text(verbatim: "\(year)년에 기록한 제품 \(total)개")
                    .font(.footnote)
                    .foregroundStyle(Theme.textSecondary)
            }
        }
    }
}