import SwiftUI
import WidgetKit

struct TimetableDayView: View {
    let entry: TimetableEntry
    @Environment(\.widgetPalette) private var palette

    var body: some View {
        ZStack {
            if !entry.isLoggedIn {
                placeholder("Bitte einloggen, um den Stundenplan zu laden")
            } else if let data = entry.data {
                content(data: data)
            } else {
                placeholder("Lade…")
            }
        }
        .background(MarianumWatermark())
    }

    @ViewBuilder
    private func content(data: WidgetTimetableData) -> some View {
        VStack(alignment: .leading, spacing: GRID_MARGIN_TOP) {
            header(data: data)
            if data.isHoliday {
                emptyState(text: data.holidayName ?? "Ferien")
            } else if data.lessons.isEmpty {
                emptyState(text: "Keine Stunden")
            } else {
                GeometryReader { geo in
                    let periods = trimTrailingPeriods(data.periods, lessons: data.lessons)
                    HStack(alignment: .top, spacing: 0) {
                        PeriodRuler(
                            periods: periods,
                            hourHeight: resolveHourHeight(forGridHeight: geo.size.height, periods: periods)
                        )
                        Rectangle()
                            .fill(palette.divider)
                            .frame(width: 1)
                        TimeGridView(
                            lessons: data.lessons,
                            periods: periods,
                            hourHeight: resolveHourHeight(forGridHeight: geo.size.height, periods: periods)
                        )
                    }
                }
            }
        }
    }

    private func header(data: WidgetTimetableData) -> some View {
        HStack(spacing: 6) {
            Text(dayLabel(for: data.anchorDate, relativeTo: entry.date))
                .font(.system(size: 14, weight: .bold))
                .foregroundStyle(palette.textPrimary)
                .lineLimit(1)
                .minimumScaleFactor(0.65)
                .frame(maxWidth: .infinity, alignment: .leading)
            Text("Stand: \(freshnessLabel(for: data.fetchedAt, relativeTo: entry.date))")
                .font(.system(size: 10))
                .foregroundStyle(palette.textSecondary)
                .lineLimit(1)
                .fixedSize()
        }
        .frame(height: TITLE_ROW_HEIGHT)
    }

    private func emptyState(text: String) -> some View {
        VStack {
            Spacer()
            Text(text)
                .font(.caption)
                .foregroundStyle(palette.textSecondary)
            Spacer()
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private func placeholder(_ message: String) -> some View {
        VStack(spacing: 4) {
            Text("Marianum Stundenplan")
                .font(.system(size: 14, weight: .semibold))
                .foregroundStyle(palette.textPrimary)
            Text(message)
                .font(.caption)
                .foregroundStyle(palette.textSecondary)
                .multilineTextAlignment(.center)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}

/// Mirrors the in-app _PeriodLabel: period number centred, start time above,
/// end time below, a cup in the breaks.
struct PeriodRuler: View {
    let periods: [WidgetPeriod]
    let hourHeight: CGFloat

    @Environment(\.widgetPalette) private var palette

    private var totalHeight: CGFloat {
        CGFloat(totalVirtualMinutes(periods)) * hourHeight / 60.0
    }

    var body: some View {
        // Every child has layout-y 0 (`.offset` only shifts the rendering),
        // so both the ZStack and its frame need `.top` — the default
        // `.center` would anchor the whole ruler at the column's midpoint.
        ZStack(alignment: .top) {
            ForEach(periodBoundaries(periods), id: \.self) { virtualMin in
                Rectangle()
                    .fill(palette.divider)
                    .frame(height: 1)
                    .offset(y: CGFloat(virtualMin) * hourHeight / 60.0)
            }
            ForEach(periods, id: \.startMinutes) { period in
                cell(period)
            }
            ForEach(periodBreaks(periods), id: \.self) { pause in
                let height = CGFloat(pause.virtualMinutes) * hourHeight / 60.0
                if height >= BREAK_ICON_MIN_HEIGHT {
                    Image(systemName: "cup.and.saucer")
                        .font(.system(size: 8))
                        .foregroundStyle(palette.textSecondary)
                        .frame(width: RULER_WIDTH, height: height)
                        .offset(y: CGFloat(pause.virtualStart) * hourHeight / 60.0)
                }
            }
        }
        .frame(width: RULER_WIDTH, height: totalHeight, alignment: .top)
    }

    private func cell(_ period: WidgetPeriod) -> some View {
        let height = CGFloat(period.virtualEndMinutes - period.virtualStartMinutes) * hourHeight / 60.0
        let timeFont = max(6, min(8.5, height * 0.19))
        return ZStack {
            Text(period.name)
                .font(.system(size: max(8, min(13, height * 0.3)), weight: .medium))
                .foregroundStyle(palette.textPrimary)
                .lineLimit(1)
            if height >= RULER_TIMES_MIN_CELL {
                VStack(spacing: 0) {
                    Text(formatHm(period.startMinutes))
                    Spacer(minLength: 0)
                    Text(formatHm(period.endMinutes))
                }
                .font(.system(size: timeFont))
                .foregroundStyle(palette.textSecondary)
                .lineLimit(1)
                .padding(.vertical, 2)
            }
        }
        .frame(width: RULER_WIDTH, height: height)
        .offset(y: CGFloat(period.virtualStartMinutes) * hourHeight / 60.0)
    }

    private func formatHm(_ minutes: Int) -> String {
        String(format: "%02d:%02d", minutes / 60, minutes % 60)
    }
}

/// One day column: grid lines, break bands and the lesson tiles. Shared by
/// the day widget and each of the week widget's five columns.
struct TimeGridView: View {
    let lessons: [WidgetLesson]
    let periods: [WidgetPeriod]
    let hourHeight: CGFloat
    var holiday: WidgetDayInfo? = nil
    var isToday: Bool = false

    @Environment(\.widgetPalette) private var palette

    private var totalHeight: CGFloat {
        CGFloat(totalVirtualMinutes(periods)) * hourHeight / 60.0
    }

    var body: some View {
        GeometryReader { geo in
            let metrics = TileMetrics(periods: periods, hourHeight: hourHeight)
            let innerWidth = geo.size.width - 2 * (TILE_MARGIN_H + TILE_PADDING_H)
            ZStack(alignment: .top) {
                if let holiday {
                    holidayColumn(holiday)
                } else {
                    if isToday {
                        palette.todayTint.frame(height: totalHeight)
                    }
                    gridLines
                    breakBlocks
                }
                ForEach(lessons.indices, id: \.self) { idx in
                    lessonBlock(lessons[idx], metrics: metrics, innerWidth: innerWidth)
                }
            }
            .frame(width: geo.size.width, height: totalHeight, alignment: .top)
        }
        .frame(height: totalHeight)
    }

    private var gridLines: some View {
        // `.top` on both the ZStack and the frame — see PeriodRuler.
        ZStack(alignment: .top) {
            ForEach(periodBoundaries(periods), id: \.self) { virtualMin in
                Rectangle()
                    .fill(palette.divider)
                    .frame(height: 1)
                    .offset(y: CGFloat(virtualMin) * hourHeight / 60.0)
            }
        }
        .frame(height: totalHeight, alignment: .top)
    }

    private var breakBlocks: some View {
        ZStack(alignment: .top) {
            ForEach(periodBreaks(periods), id: \.self) { pause in
                let height = CGFloat(pause.virtualMinutes) * hourHeight / 60.0
                ZStack {
                    palette.breakBlock
                    if height >= BREAK_ICON_MIN_HEIGHT {
                        Image(systemName: "fork.knife")
                            .font(.system(size: 9))
                            .foregroundStyle(palette.accent)
                    }
                }
                .frame(height: height)
                .offset(y: CGFloat(pause.virtualStart) * hourHeight / 60.0)
            }
        }
        .frame(height: totalHeight, alignment: .top)
    }

    /// Mirrors the in-app holiday region: icon and "Schulfrei" on top, the
    /// holiday name rotated along the column.
    private func holidayColumn(_ holiday: WidgetDayInfo) -> some View {
        let nameLength = max(40, totalHeight - 2 * HOLIDAY_NAME_INSET)
        return ZStack {
            palette.holidayTint
            VStack(spacing: 2) {
                Image(systemName: "calendar")
                    .font(.system(size: 12))
                Text("Schulfrei")
                    .font(.system(size: 9))
                    .lineLimit(1)
                    .minimumScaleFactor(0.6)
            }
            .padding(.top, 8)
            .padding(.horizontal, 2)
            .frame(maxHeight: .infinity, alignment: .top)
            // The outer frame carries the rotated footprint: rotationEffect
            // alone leaves the layout box at its unrotated size.
            Text(holiday.holidayName ?? "")
                .font(.system(size: 11, weight: .bold))
                .kerning(1)
                .lineLimit(1)
                .minimumScaleFactor(0.6)
                .frame(width: nameLength, height: 14)
                .rotationEffect(.degrees(90))
                .frame(width: 14, height: nameLength)
        }
        .foregroundStyle(palette.textPrimary)
        .frame(height: totalHeight)
    }

    @ViewBuilder
    private func lessonBlock(
        _ lesson: WidgetLesson,
        metrics: TileMetrics,
        innerWidth: CGFloat
    ) -> some View {
        let startMinutes = minutesOfDay(lesson.start)
        let durationMinutes = max(15, Int(lesson.end.timeIntervalSince(lesson.start) / 60))
        let virtualStart = realMinutesToVirtual(startMinutes, periods: periods)
        let virtualEnd = realMinutesToVirtual(startMinutes + durationMinutes, periods: periods)

        if virtualEnd > virtualStart {
            // Half the gap above + half below so the grid line under the
            // tile stays visible.
            let top = virtualStart * hourHeight / 60.0 + LESSON_GAP / 2
            let height = max(
                MIN_BLOCK_HEIGHT,
                (virtualEnd - virtualStart) * hourHeight / 60.0 - LESSON_GAP
            )
            LessonTile(
                lesson: lesson,
                height: height,
                metrics: metrics,
                layout: TileTextLayout(
                    lesson: lesson,
                    innerHeight: height - 2 * TILE_PADDING_V,
                    innerWidth: innerWidth,
                    metrics: metrics
                )
            )
            .offset(y: top)
        }
    }
}

/// Mirrors the in-app AppointmentTile: title on top, room and teacher
/// stacked below, each line shrinking on its own to fit the tile width.
private struct LessonTile: View {
    let lesson: WidgetLesson
    let height: CGFloat
    let metrics: TileMetrics
    let layout: TileTextLayout

    private static let cancelledRed =
        Color(red: 244 / 255, green: 67 / 255, blue: 54 / 255).opacity(200 / 255)

    var body: some View {
        let shape = RoundedRectangle(cornerRadius: TILE_CORNER_RADIUS)
        VStack(alignment: .leading, spacing: 0) {
            titleRow
            ForEach(Array(layout.body.enumerated()), id: \.offset) { index, line in
                Text(line)
                    .font(.system(size: metrics.bodyFont))
                    .lineLimit(1)
                    .minimumScaleFactor(MIN_BODY_LINE_FONT / metrics.bodyFont)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .frame(height: metrics.bodyBox)
                    .padding(.trailing, badgeInset(line: index + 1))
            }
        }
        .foregroundStyle(.white)
        .padding(.horizontal, TILE_PADDING_H)
        .padding(.vertical, TILE_PADDING_V)
        .frame(maxWidth: .infinity, alignment: .topLeading)
        .frame(height: height, alignment: .topLeading)
        .background(lesson.tileColor)
        .clipShape(shape)
        .overlay(alignment: .bottomTrailing) {
            if let count = lesson.siblingCount, count > 0 {
                Text("+\(count)")
                    .font(.system(size: 9, weight: .bold))
                    .foregroundStyle(.white)
                    .padding(.trailing, TILE_PADDING_H)
                    .padding(.bottom, TILE_PADDING_V)
            }
        }
        .overlay {
            if lesson.status == .cancelled {
                ZStack {
                    shape.strokeBorder(LessonTile.cancelledRed, lineWidth: 2)
                    GeometryReader { geo in
                        Path { p in
                            p.move(to: .zero)
                            p.addLine(to: CGPoint(x: geo.size.width, y: geo.size.height))
                            p.move(to: CGPoint(x: geo.size.width, y: 0))
                            p.addLine(to: CGPoint(x: 0, y: geo.size.height))
                        }
                        .stroke(LessonTile.cancelledRed, lineWidth: 2)
                    }
                }
                .clipShape(shape)
            }
        }
        .padding(.horizontal, TILE_MARGIN_H)
    }

    private var titleRow: some View {
        HStack(alignment: .center, spacing: 3) {
            Text(layout.title)
                .font(.system(size: layout.titleFont, weight: .medium))
                .lineLimit(layout.titleLines)
                .minimumScaleFactor(min(1, MIN_TITLE_FONT / layout.titleFont))
                .frame(maxWidth: .infinity, alignment: .leading)
            if let inline = layout.inline {
                Text(inline)
                    .font(.system(size: metrics.bodyFont))
                    .lineLimit(1)
                    .fixedSize()
            }
        }
        .frame(height: layout.titleBox)
        .padding(.trailing, badgeInset(line: 0))
    }

    private func badgeInset(line: Int) -> CGFloat {
        layout.badgeLine == line ? BADGE_WIDTH : 0
    }
}

/// Fixed-locale formatters cached once — DateFormatter setup is the
/// expensive part and the multi-entry timelines render up to ~8 entries per
/// reload. Only touched from WidgetKit's archival rendering, so the shared
/// instances are safe.
enum WidgetDateFormatters {
    static let shortDate = make("dd.MM.")
    static let weekdayShort = make("EE")
    static let weekdayDate = make("EEEE · dd.MM.")
    static let time = make("HH:mm")
    static let dateTime = make("dd.MM. HH:mm")

    private static func make(_ format: String) -> DateFormatter {
        let f = DateFormatter()
        f.locale = Locale(identifier: "de_DE")
        f.dateFormat = format
        return f
    }
}

/// `now` is the timeline entry's date, not `Date()`: WidgetKit archives
/// entries ahead of time, so wall-clock reads would be wrong for every
/// entry after the first.
func dayLabel(for date: Date, relativeTo now: Date) -> String {
    let cal = Calendar.current
    let today = cal.startOfDay(for: now)
    let anchor = cal.startOfDay(for: date)
    if anchor == today {
        return "Heute · \(shortDate(date))"
    }
    if let tomorrow = cal.date(byAdding: .day, value: 1, to: today), anchor == tomorrow {
        return "Morgen · \(shortDate(date))"
    }
    return WidgetDateFormatters.weekdayDate.string(from: date)
}

func shortDate(_ date: Date) -> String {
    WidgetDateFormatters.shortDate.string(from: date)
}

func freshnessLabel(for fetchedAt: Date, relativeTo now: Date) -> String {
    let cal = Calendar.current
    let today = cal.startOfDay(for: now)
    let fetchedDay = cal.startOfDay(for: fetchedAt)
    if fetchedDay == today {
        return WidgetDateFormatters.time.string(from: fetchedAt)
    }
    if let yesterday = cal.date(byAdding: .day, value: -1, to: today),
       fetchedDay == yesterday {
        return "gestern \(WidgetDateFormatters.time.string(from: fetchedAt))"
    }
    return WidgetDateFormatters.dateTime.string(from: fetchedAt)
}