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 {
            CardsTheme.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(CardsTheme.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(CardsTheme.primary)
            case .studying:
                studyingView(session: session)
            case .finished:
                finishedView(session: session)
            case let .failed(message):
                failedView(message: message, session: session)
            }
        } else {
            ProgressView()
                .tint(CardsTheme.primary)
        }
    }

    private func studyingView(session: StudySession) -> some View {
        VStack(spacing: 16) {
            if let due = session.current {
                cardSurface(due: due, isFlipped: session.isFlipped)
                    .onTapGesture {
                        flipHaptic()
                        session.flip()
                    }
                if session.isFlipped {
                    RatingBar { rating in
                        Task { await session.grade(rating) }
                    }
                    .transition(.move(edge: .bottom).combined(with: .opacity))
                } else {
                    Button {
                        flipHaptic()
                        session.flip()
                    } label: {
                        Text("Antwort anzeigen")
                            .font(.subheadline.weight(.semibold))
                            .frame(maxWidth: .infinity)
                            .padding(.vertical, 14)
                            .background(CardsTheme.primary, in: RoundedRectangle(cornerRadius: 10))
                            .foregroundStyle(CardsTheme.primaryForeground)
                    }
                    .buttonStyle(.plain)
                    .padding(.horizontal, 16)
                }
            }
        }
        .padding(.bottom, 20)
        .animation(.easeInOut(duration: 0.2), value: session.isFlipped)
        .animation(.easeInOut(duration: 0.2), value: session.currentIndex)
    }

    private func cardSurface(due: DueReview, isFlipped: Bool) -> some View {
        RoundedRectangle(cornerRadius: 16)
            .fill(CardsTheme.surface)
            .overlay(
                CardRenderer(
                    card: due.card,
                    subIndex: due.review.subIndex,
                    isFlipped: isFlipped
                )
            )
            .overlay(
                RoundedRectangle(cornerRadius: 16)
                    .stroke(CardsTheme.border, lineWidth: 1)
            )
            .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(CardsTheme.success)
            Text(session.totalGraded == 0 ? "Keine Karten fällig" : "Fertig!")
                .font(.title.bold())
                .foregroundStyle(CardsTheme.foreground)
            if session.totalGraded > 0 {
                Text("\(session.totalGraded) Karten gelernt")
                    .font(.subheadline)
                    .foregroundStyle(CardsTheme.mutedForeground)
            }
            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(CardsTheme.error)
            Text("Karten konnten nicht geladen werden")
                .font(.headline)
                .foregroundStyle(CardsTheme.foreground)
            Text(message)
                .font(.caption)
                .multilineTextAlignment(.center)
                .foregroundStyle(CardsTheme.mutedForeground)
                .padding(.horizontal, 32)
            Button("Erneut versuchen") {
                Task { await session.start() }
            }
            .padding(.top, 16)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

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