import SwiftUI
import SharedModels
import SwiftData

struct VocabReviewView: View {
    @Environment(\.cloudModelContextProvider) private var cloudModelContextProvider
    @Environment(\.modelContext) private var localContext
    @Environment(\.dismiss) private var dismiss

    @State private var dueCards: [CourseReviewCard] = []
    @State private var currentIndex = 0
    @State private var isRevealed = false
    @State private var sessionCorrect = 0
    @State private var sessionTotal = 0
    @State private var isFinished = false

    private var cloudContext: ModelContext { cloudModelContextProvider() }

    var body: some View {
        VStack(spacing: 20) {
            if isFinished || dueCards.isEmpty {
                finishedView
            } else if let card = dueCards[safe: currentIndex] {
                cardView(card)
            }
        }
        .padding()
        .adaptiveContainer(maxWidth: 600)
        .navigationTitle("Vocab Review")
        .navigationBarTitleDisplayMode(.inline)
        .onAppear(perform: loadDueCards)
    }

    // MARK: - Card View

    @ViewBuilder
    private func cardView(_ card: CourseReviewCard) -> some View {
        VStack(spacing: 24) {
            // Progress
            Text("\(currentIndex + 1) of \(dueCards.count)")
                .font(.caption.weight(.medium))
                .foregroundStyle(.secondary)

            ProgressView(value: Double(currentIndex), total: Double(dueCards.count))
                .tint(.teal)

            Spacer()

            // Front (Spanish)
            Text(card.front)
                .font(.largeTitle.bold())
                .multilineTextAlignment(.center)

            if isRevealed {
                // Back (English)
                Text(card.back)
                    .font(.title2)
                    .foregroundStyle(.secondary)
                    .transition(.opacity.combined(with: .move(edge: .bottom)))

                Spacer()

                // Rating buttons
                HStack(spacing: 12) {
                    ratingButton("Again", color: .red, quality: .again)
                    ratingButton("Hard", color: .orange, quality: .hard)
                    ratingButton("Good", color: .green, quality: .good)
                    ratingButton("Easy", color: .blue, quality: .easy)
                }
            } else {
                Spacer()

                Button {
                    withAnimation { isRevealed = true }
                } label: {
                    Text("Show Answer")
                        .font(.headline)
                        .frame(maxWidth: .infinity)
                        .padding(.vertical, 12)
                }
                .buttonStyle(.borderedProminent)
                .tint(.teal)
            }
        }
    }

    // MARK: - Finished View

    private var finishedView: some View {
        VStack(spacing: 20) {
            Spacer()

            Image(systemName: dueCards.isEmpty ? "checkmark.seal.fill" : "star.fill")
                .font(.system(size: 60))
                .foregroundStyle(dueCards.isEmpty ? .green : .yellow)

            if dueCards.isEmpty {
                Text("All caught up!")
                    .font(.title2.bold())
                Text("No vocabulary cards are due for review.")
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            } else {
                Text("\(sessionCorrect) / \(sessionTotal)")
                    .font(.system(size: 48, weight: .bold).monospacedDigit())
                Text("Review complete!")
                    .font(.title3)
                    .foregroundStyle(.secondary)
            }

            Spacer()
        }
    }

    // MARK: - Helpers

    private func ratingButton(_ label: String, color: Color, quality: ReviewQuality) -> some View {
        Button {
            rate(quality: quality)
        } label: {
            Text(label)
                .font(.subheadline.weight(.semibold))
                .frame(maxWidth: .infinity)
                .padding(.vertical, 10)
        }
        .buttonStyle(.bordered)
        .tint(color)
    }

    private func rate(quality: ReviewQuality) {
        guard let card = dueCards[safe: currentIndex] else { return }

        let store = CourseReviewStore(context: cloudContext)
        let result = SRSEngine.review(
            quality: quality,
            currentEase: card.easeFactor,
            currentInterval: card.interval,
            currentReps: card.repetitions
        )
        card.easeFactor = result.easeFactor
        card.interval = result.interval
        card.repetitions = result.repetitions
        card.dueDate = SRSEngine.nextDueDate(interval: result.interval)
        card.lastReviewDate = Date()
        try? cloudContext.save()

        sessionTotal += 1
        if quality != .again { sessionCorrect += 1 }

        isRevealed = false
        if currentIndex + 1 < dueCards.count {
            currentIndex += 1
        } else {
            withAnimation { isFinished = true }
        }
    }

    private func loadDueCards() {
        let now = Date()
        let descriptor = FetchDescriptor<CourseReviewCard>(
            predicate: #Predicate<CourseReviewCard> { $0.dueDate <= now },
            sortBy: [SortDescriptor(\CourseReviewCard.dueDate)]
        )
        dueCards = (try? cloudContext.fetch(descriptor)) ?? []
    }

    static func dueCount(context: ModelContext) -> Int {
        let now = Date()
        let descriptor = FetchDescriptor<CourseReviewCard>(
            predicate: #Predicate<CourseReviewCard> { $0.dueDate <= now }
        )
        return (try? context.fetchCount(descriptor)) ?? 0
    }
}

private extension Collection {
    subscript(safe index: Index) -> Element? {
        indices.contains(index) ? self[index] : nil
    }
}