wordeck-native/Sources/Features/Study/StudySessionView.swift

import ManaCore
import SwiftData
import SwiftUI

#if canImport(UIKit)
    import UIKit
#endif

/// Vollbild-Study-View. Wird per Navigation aus DeckListView geöffnet.
struct StudySessionView: View {
    let deckId: String
    let deckName: String

    @Environment(AuthClient.self) private var auth
    @Environment(\.modelContext) private var context
    @Environment(\.dismiss) private var dismiss
    @State private var session: StudySession?

    var body: some View {
        ZStack {
            WordeckTheme.background.ignoresSafeArea()
            content
        }
        .navigationTitle(deckName)
        #if os(iOS)
            .navigationBarTitleDisplayMode(.inline)
        #endif
            .toolbar {
                ToolbarItem(placement: .topBarTrailing) {
                    if let session, case .studying = session.phase {
                        Text("\(session.remaining)")
                            .font(.subheadline.weight(.semibold))
                            .foregroundStyle(WordeckTheme.mutedForeground)
                            .accessibilityLabel("\(session.remaining) Karten übrig")
                    }
                }
            }
            .task {
                if session == nil {
                    let s = StudySession(deckId: deckId, deckName: deckName, auth: auth, context: context)
                    session = s
                    await s.start()
                }
            }
    }

    @ViewBuilder
    private var content: some View {
        if let session {
            switch session.phase {
            case .loading:
                ProgressView("Karten werden geladen …")
                    .tint(WordeckTheme.primary)
            case .studying:
                studyingView(session: session)
            case .finished:
                finishedView(session: session)
            case let .failed(message):
                failedView(message: message, session: session)
            }
        } else {
            ProgressView()
                .tint(WordeckTheme.primary)
        }
    }

    private func studyingView(session: StudySession) -> some View {
        VStack(spacing: 16) {
            if session.isOfflineSession {
                offlineBanner
            }
            if let due = session.current {
                cardSurface(due: due, isFlipped: session.isFlipped)
                    .onTapGesture {
                        flipHaptic()
                        session.flip()
                    }
                keyboardShortcuts(session: session)
                bottomBar(session: session)
            }
        }
        .padding(.bottom, 20)
        .animation(.easeInOut(duration: 0.2), value: session.isFlipped)
        .animation(.easeInOut(duration: 0.2), value: session.currentIndex)
    }

    /// Banner für Offline-Sessions. Erklärt dem User ehrlich, dass er
    /// gerade die Karten lernt, die zum letzten Sync fällig waren —
    /// neue Karten kommen erst nach Wiederverbindung.
    private var offlineBanner: some View {
        HStack(spacing: 8) {
            Image(systemName: "wifi.slash")
            Text("Offline — Karten vom letzten Sync")
        }
        .font(.caption.weight(.medium))
        .foregroundStyle(WordeckTheme.mutedForeground)
        .padding(.horizontal, 12)
        .padding(.vertical, 6)
        .background(WordeckTheme.muted, in: Capsule())
        .padding(.horizontal, 16)
        .padding(.top, 4)
        .transition(.opacity)
    }

    /// Fixe Höhe, damit der Wechsel zwischen "Antwort anzeigen" und
    /// `RatingBar` die Card oben nicht stauchen kann — sonst proportioniert
    /// `.aspectRatio(.fit)` die Card neu und das Layout springt.
    private func bottomBar(session: StudySession) -> some View {
        ZStack {
            if session.isFlipped {
                RatingBar { rating in
                    Task { await session.grade(rating) }
                }
                .transition(.opacity)
            } else {
                Button {
                    flipHaptic()
                    session.flip()
                } label: {
                    Text("Antwort anzeigen")
                        .font(.subheadline.weight(.semibold))
                        .frame(maxWidth: .infinity)
                        .padding(.vertical, 14)
                        .background(WordeckTheme.primary, in: RoundedRectangle(cornerRadius: 10))
                        .foregroundStyle(WordeckTheme.primaryForeground)
                }
                .buttonStyle(.plain)
                .padding(.horizontal, 16)
                .transition(.opacity)
            }
        }
        .frame(height: 52)
    }

    private func cardSurface(due: DueReview, isFlipped: Bool) -> some View {
        CardSurface(size: .hero, elevation: .raised) {
            CardRenderer(
                card: due.card,
                subIndex: due.review.subIndex,
                isFlipped: isFlipped
            )
            .frame(maxWidth: .infinity, maxHeight: .infinity)
        }
        .padding(.horizontal, 16)
        .padding(.top, 12)
    }

    private func finishedView(session: StudySession) -> some View {
        VStack(spacing: 16) {
            Image(systemName: "checkmark.seal.fill")
                .font(.system(size: 64))
                .foregroundStyle(WordeckTheme.success)
            Text(session.totalGraded == 0 ? "Keine Karten fällig" : "Fertig!")
                .font(.title.bold())
                .foregroundStyle(WordeckTheme.foreground)
            if session.totalGraded > 0 {
                Text("\(session.totalGraded) Karten gelernt")
                    .font(.subheadline)
                    .foregroundStyle(WordeckTheme.mutedForeground)
            }
            if session.isOfflineSession {
                Text("Weitere Karten erst nach Verbindung verfügbar.")
                    .font(.caption)
                    .multilineTextAlignment(.center)
                    .foregroundStyle(WordeckTheme.mutedForeground)
                    .padding(.horizontal, 32)
                    .padding(.top, 4)
            }
            Button("Zurück") { dismiss() }
                .padding(.top, 24)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private func failedView(message: String, session: StudySession) -> some View {
        VStack(spacing: 16) {
            Image(systemName: "wifi.exclamationmark")
                .font(.system(size: 48))
                .foregroundStyle(WordeckTheme.error)
            Text("Karten konnten nicht geladen werden")
                .font(.headline)
                .foregroundStyle(WordeckTheme.foreground)
            Text(message)
                .font(.caption)
                .multilineTextAlignment(.center)
                .foregroundStyle(WordeckTheme.mutedForeground)
                .padding(.horizontal, 32)
            Button("Erneut versuchen") {
                Task { await session.start() }
            }
            .padding(.top, 16)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    /// Unsichtbare Buttons mit Keyboard-Shortcuts. Funktionieren auf
    /// iPad (Magic Keyboard) und macOS. Space = flip, 1-4 = Rating.
    private func keyboardShortcuts(session: StudySession) -> some View {
        Group {
            Button("Flip") {
                flipHaptic()
                session.flip()
            }
            .keyboardShortcut(.space, modifiers: [])

            if session.isFlipped {
                ForEach(Rating.allCases, id: \.self) { rating in
                    Button(rating.label) {
                        Task { await session.grade(rating) }
                    }
                    .keyboardShortcut(KeyEquivalent(Character(rating.shortcut)), modifiers: [])
                }
            }
        }
        .frame(width: 0, height: 0)
        .opacity(0)
        .accessibilityHidden(true)
    }

    private func flipHaptic() {
        #if canImport(UIKit)
            UIImpactFeedbackGenerator(style: .soft).impactOccurred()
        #endif
    }
}