import SwiftUI

// MARK: - Colours

extension Color {
    init(hex: UInt32) {
        self.init(.sRGB, red: Double((hex >> 16) & 0xFF) / 255, green: Double((hex >> 8) & 0xFF) / 255, blue: Double(hex & 0xFF) / 255)
    }

    /// The app's blue (#0061A4 in light, #9ECAFF in dark), from the asset catalog.
    static let brand = Color("AccentColor")
    /// Text and icons on the brand blue: white on the dark light-theme blue, black on the pale dark-theme one.
    static let onBrand = Color(.systemBackground)
    // Color.greenWeek, the university's green weeks, is generated from the asset catalog.
}

/// A subject's colours: `strong`/`onStrong` for small fills (dots, week grid),
/// `soft`/`onSoft` for lesson cards; every pair keeps 4.5:1 contrast.
struct SubjectColor {
    var strong: Color
    var onStrong: Color
    var soft: Color
    var onSoft: Color
}

// Material 700 tones (strong in light theme) and 200 tones (strong in dark theme), as on Android.
private let tone700: [UInt32] = [0x1565C0, 0x7B1FA2, 0xC62828, 0x2E7D32, 0xD84315, 0x00695C, 0x283593, 0xAD1457, 0x5D4037, 0x00838F, 0x4527A0, 0x455A64]
private let tone200: [UInt32] = [0x90CAF9, 0xCE93D8, 0xEF9A9A, 0xA5D6A7, 0xFFAB91, 0x80CBC4, 0x9FA8DA, 0xF48FB1, 0xBCAAA4, 0x80DEEA, 0xB39DDB, 0xB0BEC5]

private func mix(_ a: UInt32, _ b: UInt32, _ t: Double) -> Color {
    func c(_ v: UInt32, _ s: UInt32) -> Double { Double((v >> s) & 0xFF) / 255 }
    func m(_ s: UInt32) -> Double { c(a, s) + (c(b, s) - c(a, s)) * t }
    return Color(.sRGB, red: m(16), green: m(8), blue: m(0))
}

/// Subject colours of the open timetable, put into the environment at the root.
struct Palette {
    var slots: [String: Int] = [:]
    var enabled = true

    func color(_ subject: String, dark: Bool) -> SubjectColor {
        guard enabled else {
            return SubjectColor(strong: .brand, onStrong: dark ? .black : .white, soft: Color(.secondarySystemGroupedBackground), onSoft: .primary)
        }
        let key = subjectKey(subject)
        // Subjects of other groups (search results) still get a stable colour.
        let i = slots[key].map { $0 % tone700.count } ?? Int(UInt(bitPattern: key.hashValue) % UInt(tone700.count))
        return dark
            ? SubjectColor(strong: Color(hex: tone200[i]), onStrong: Color(hex: 0x1D1B20), soft: mix(0x211F26, tone700[i], 0.5), onSoft: mix(tone200[i], 0xFFFFFF, 0.4))
            : SubjectColor(strong: Color(hex: tone700[i]), onStrong: .white, soft: mix(tone200[i], 0xFFFFFF, 0.35), onSoft: mix(tone700[i], 0x000000, 0.35))
    }
}

extension EnvironmentValues {
    @Entry var palette = Palette()
    @Entry var display = Display()
}

/// Reads a subject's colours inside a view body.
struct WithSubjectColor<Content: View>: View {
    @Environment(\.palette) private var palette
    @Environment(\.colorScheme) private var scheme
    var subject: String
    @ViewBuilder var content: (SubjectColor) -> Content
    var body: some View { content(palette.color(subject, dark: scheme == .dark)) }
}

struct SubjectDot: View {
    var subject: String
    var size: CGFloat = 12
    var body: some View {
        WithSubjectColor(subject: subject) { c in
            Circle().fill(c.strong).frame(width: size, height: size)
        }
        .accessibilityHidden(true)
    }
}

// MARK: - Cards

extension View {
    /// Content cards lie on the grouped background; Liquid Glass is kept for the controls above them.
    func card(padding: CGFloat = 20) -> some View {
        self.padding(padding)
            .frame(maxWidth: .infinity, alignment: .leading)
            .background(Color(.secondarySystemGroupedBackground), in: .rect(cornerRadius: 26, style: .continuous))
    }

    /// A readable column on iPad and in landscape.
    func readableWidth(_ width: CGFloat = 720) -> some View {
        frame(maxWidth: width).frame(maxWidth: .infinity)
    }
}

/// A titled card: the overview's building block.
struct SectionCard<Content: View>: View {
    var symbol: String
    var title: String
    var trailing: String?
    @ViewBuilder var content: Content

    var body: some View {
        VStack(alignment: .leading, spacing: 14) {
            HStack(spacing: 10) {
                Image(systemName: symbol)
                    .font(.footnote.weight(.bold))
                    .foregroundStyle(Color.onBrand)
                    .frame(width: 30, height: 30)
                    .background(Color.brand, in: .circle)
                Text(title).font(.headline).foregroundStyle(Color.brand)
                    .accessibilityAddTraits(.isHeader)
                Spacer()
                if let trailing { Text(trailing).font(.headline).foregroundStyle(.secondary) }
            }
            content
        }
        .card()
    }
}

/// An error or offline message with "Повторить" and "OK".
struct Banner: View {
    var text: String
    var offline: Bool
    var onClose: (() -> Void)?
    var onRetry: (() -> Void)?

    var body: some View {
        HStack(alignment: .center, spacing: 12) {
            Image(systemName: offline ? "icloud.slash" : "exclamationmark.triangle")
                .foregroundStyle(offline ? Color.secondary : Color.red)
            Text(text).font(.subheadline).frame(maxWidth: .infinity, alignment: .leading)
            if let onRetry { Button("Повторить", action: onRetry).font(.subheadline.weight(.semibold)) }
            if let onClose { Button("OK", action: onClose).font(.subheadline.weight(.semibold)) }
        }
        .padding(.horizontal, 16)
        .padding(.vertical, 12)
        .background(
            (offline ? Color(.tertiarySystemFill) : Color.red.opacity(0.12)),
            in: .rect(cornerRadius: 18, style: .continuous)
        )
    }
}

/// "Занятия в Полоцке" above a day's lessons: Word marks the days a group spends in another
/// town, and every lesson of that day is there.
struct DayPlaces: View {
    var places: [DayPlace]

    var body: some View {
        if !places.isEmpty {
            VStack(alignment: .leading, spacing: 10) {
                ForEach(places, id: \.self) { p in
                    HStack(spacing: 14) {
                        Image(systemName: "building.2")
                            .font(.title3)
                            .foregroundStyle(Color.indigo)
                            .accessibilityHidden(true)
                        VStack(alignment: .leading, spacing: 2) {
                            Text(p.text).font(.headline)
                            Text(p.subgroup.map { "\($0) · пометка в Word на этот день" } ?? "Пометка в Word на этот день")
                                .font(.subheadline)
                                .foregroundStyle(.secondary)
                        }
                        Spacer(minLength: 0)
                    }
                    .accessibilityElement(children: .combine)
                }
            }
            .padding(.horizontal, 16)
            .padding(.vertical, 12)
            .background(Color.indigo.opacity(0.14), in: .rect(cornerRadius: 18, style: .continuous))
        }
    }
}

/// The town under a day's date in the week grid: short, in the note's colour.
struct DayPlaceMark: View {
    var places: [DayPlace]

    var body: some View {
        if let first = places.first {
            Text(first.place)
                .font(.caption2.weight(.semibold))
                .lineLimit(1)
                .padding(.horizontal, 4)
                .padding(.vertical, 1)
                .foregroundStyle(Color.indigo)
                .background(Color.indigo.opacity(0.14), in: .rect(cornerRadius: 4, style: .continuous))
        }
    }
}

/// The status banner of the app model, if it has something to say.
struct StatusBanner: View {
    @Environment(AppModel.self) private var model
    var body: some View {
        if let message = model.status.message {
            Banner(
                text: message,
                offline: model.status.offline,
                onClose: { model.dismissMessage() },
                onRetry: model.status.offline ? { Task { await model.retry() } } : nil
            )
        }
    }
}

/// An empty state: a symbol, a title, a calm explanation and an optional action.
struct EmptyState: View {
    var title: String
    var text: String
    var symbol: String = "calendar.badge.exclamationmark"
    var action: (label: String, run: () -> Void)?

    var body: some View {
        ContentUnavailableView {
            Label(title, systemImage: symbol)
        } description: {
            Text(text)
        } actions: {
            if let action {
                Button(action.label, action: action.run).buttonStyle(.glassProminent)
            }
        }
    }
}

// MARK: - Weeks

/// "белая неделя" / "зелёная неделя": the university's week colour, never by colour alone.
struct WeekMark: View {
    var week: Week
    var short = false
    var body: some View {
        HStack(spacing: 5) {
            Circle()
                .fill(week.white ? Color.white : Color.greenWeek)
                .overlay(Circle().strokeBorder(Color.secondary.opacity(0.5), lineWidth: week.white ? 1 : 0))
                .frame(width: 10, height: 10)
            Text(short ? (week.white ? "белая" : "зелёная") : (week.white ? "белая неделя" : "зелёная неделя"))
                .font(.footnote)
                .foregroundStyle(.secondary)
        }
        .accessibilityElement(children: .combine)
    }
}

/// The tint a week's glass header takes: none for white weeks, a light green for green ones.
func weekTint(_ week: Week?) -> Color? {
    guard let week, !week.white else { return nil }
    return Color.greenWeek.opacity(0.28)
}

// MARK: - Layout

/// Chips that wrap onto the next line.
struct FlowLayout: Layout {
    var spacing: CGFloat = 8

    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
        let rows = arrange(proposal.width ?? .infinity, subviews)
        let height = rows.last.map { $0.y + $0.height } ?? 0
        let width = rows.map(\.width).max() ?? 0
        return CGSize(width: proposal.width ?? width, height: height)
    }

    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
        for row in arrange(bounds.width, subviews) {
            var x = bounds.minX
            for i in row.items {
                let size = subviews[i].sizeThatFits(.unspecified)
                subviews[i].place(at: CGPoint(x: x, y: bounds.minY + row.y), proposal: ProposedViewSize(size))
                x += size.width + spacing
            }
        }
    }

    private struct Row { var items: [Int] = []; var y: CGFloat = 0; var width: CGFloat = 0; var height: CGFloat = 0 }

    private func arrange(_ maxWidth: CGFloat, _ subviews: Subviews) -> [Row] {
        var rows: [Row] = []
        var row = Row()
        for (i, view) in subviews.enumerated() {
            let size = view.sizeThatFits(.unspecified)
            if !row.items.isEmpty && row.width + spacing + size.width > maxWidth {
                rows.append(row)
                row = Row(y: row.y + row.height + spacing)
            }
            row.width += (row.items.isEmpty ? 0 : spacing) + size.width
            row.height = max(row.height, size.height)
            row.items.append(i)
        }
        if !row.items.isEmpty { rows.append(row) }
        return rows
    }
}

/// A small rounded tag: "Лекция", "белые недели", "общее занятие".
struct Tag: View {
    var text: String
    var symbol: String?
    var foreground: Color = .secondary
    var background: Color = Color(.tertiarySystemFill)
    var body: some View {
        HStack(spacing: 4) {
            if let symbol { Image(systemName: symbol).font(.caption.weight(.bold)) }
            Text(text.prefix(1).uppercased() + text.dropFirst()).font(.footnote.weight(.medium))
        }
        .padding(.horizontal, 8)
        .padding(.vertical, 3)
        .foregroundStyle(foreground)
        .background(background, in: .rect(cornerRadius: 8, style: .continuous))
    }
}

/// An icon and a line of text, for rooms, teachers and other details.
struct Meta: View {
    var symbol: String
    var text: String
    var body: some View {
        Label {
            Text(text)
        } icon: {
            Image(systemName: symbol).imageScale(.small)
        }
        .font(.subheadline)
        .labelStyle(.titleAndIcon)
    }
}