import SwiftUI

/// Week page — Calendar-app style: day number in a circle on the left (today
/// filled in coral), meals with tinted icons on the right.
///
/// Swipes horizontally between every week the phone sent, so the weeks already
/// planned ahead are reachable from the wrist.
struct WeekView: View {
    @EnvironmentObject private var store: WatchWeekStore
    @State private var selection: Date?

    /// Weeks from the snapshot, or the single week of a pre-2.1.2 payload.
    private var weeks: [WatchWeekPayload.Week] {
        if let weeks = store.payload?.weeks, !weeks.isEmpty { return weeks }
        guard let payload = store.payload else { return [] }
        return [WatchWeekPayload.Week(
            weekStartDate: payload.weekStartDate ?? payload.updatedAt.startOfWeekOnWatch(),
            weekTitle: payload.weekTitle,
            days: payload.days
        )]
    }

    var body: some View {
        Group {
            if weeks.isEmpty {
                EmptySyncView()
            } else {
                TabView(selection: $selection) {
                    ForEach(weeks) { week in
                        weekPage(week)
                            .tag(Optional(week.weekStartDate))
                    }
                }
                .tabViewStyle(.verticalPage(transitionStyle: .blur))
                .onAppear {
                    // Land on the current week, not on the oldest one.
                    if selection == nil {
                        selection = weeks.first(where: { $0.isCurrentWeek() })?.weekStartDate
                            ?? weeks.first?.weekStartDate
                    }
                }
            }
        }
    }

    private func weekPage(_ week: WatchWeekPayload.Week) -> some View {
        ScrollView {
            VStack(alignment: .leading, spacing: 6) {
                HStack(spacing: 4) {
                    Text(week.weekTitle)
                        .font(.system(.footnote, design: .rounded, weight: .bold))
                        .foregroundStyle(WatchTheme.coral)
                    if !week.isCurrentWeek() {
                        Image(systemName: "chevron.up.chevron.down")
                            .font(.system(size: 8, weight: .bold))
                            .foregroundStyle(.secondary)
                    }
                }
                .padding(.horizontal, 2)

                ForEach(week.days, id: \.dayOfWeek) { day in
                    // Only the current week can contain today.
                    DayRow(day: day, isToday: week.isCurrentWeek() && day.isCurrentDay())
                }
            }
        }
    }
}

private struct DayRow: View {
    let day: WatchWeekPayload.Day
    /// Resolved by the payload when the view renders, not by the snapshot's own
    /// frozen `isToday`.
    let isToday: Bool

    /// "Lun 8" → ("Lun", "8")
    private var parts: (name: String, number: String) {
        let pieces = day.title.split(separator: " ", maxSplits: 1)
        guard pieces.count == 2 else { return (day.title, "") }
        return (String(pieces[0]), String(pieces[1]))
    }

    var body: some View {
        HStack(alignment: .top, spacing: 8) {
            VStack(spacing: 0) {
                Text(parts.name.uppercased())
                    .font(.system(size: 9, weight: .bold, design: .rounded))
                    .foregroundStyle(isToday ? WatchTheme.coral : .secondary)
                Text(parts.number)
                    .font(.system(size: 15, weight: .bold, design: .rounded))
                    .foregroundStyle(isToday ? .white : .primary)
                    .frame(width: 26, height: 26)
                    .background(
                        Circle().fill(isToday ? WatchTheme.coral : .clear)
                    )
            }
            .frame(width: 32)

            VStack(alignment: .leading, spacing: 3) {
                ForEach(Array(day.meals.enumerated()), id: \.offset) { _, meal in
                    HStack(spacing: 4) {
                        Image(systemName: WatchWeekPayload.icon(for: meal.type))
                            .font(.system(size: 9, weight: .semibold))
                            .foregroundStyle(WatchTheme.accent(for: meal.type))
                            .frame(width: 12)
                        Text(meal.name ?? "—")
                            .font(.system(size: 13, design: .rounded))
                            .lineLimit(1)
                    }
                }
            }
            .frame(maxWidth: .infinity, alignment: .leading)
            .padding(.vertical, 5)
            .padding(.horizontal, 7)
            .background(
                isToday ? WatchTheme.coral.opacity(0.16) : Color.white.opacity(0.07),
                in: RoundedRectangle(cornerRadius: 9)
            )
        }
    }
}