import Combine
import Security
import SwiftUI
import WatchConnectivity

private enum SecureSnapshotStore {
    private static let service = "de.rfc1437.ironstorage.watch.snapshot"
    private static let account = "selected-totp"

    static func load() throws -> Data? {
        var result: CFTypeRef?
        let status = SecItemCopyMatching([
            kSecClass: kSecClassGenericPassword,
            kSecAttrService: service,
            kSecAttrAccount: account,
            kSecReturnData: true,
            kSecMatchLimit: kSecMatchLimitOne,
        ] as CFDictionary, &result)
        if status == errSecItemNotFound { return nil }
        guard status == errSecSuccess, let data = result as? Data else {
            throw SnapshotStoreError(status: status)
        }
        return data
    }

    static func replace(_ snapshot: Data) throws {
        let query = [
            kSecClass: kSecClassGenericPassword,
            kSecAttrService: service,
            kSecAttrAccount: account,
        ] as CFDictionary
        let status = SecItemUpdate(query, [kSecValueData: snapshot] as CFDictionary)
        if status == errSecItemNotFound {
            let added = SecItemAdd([
                kSecClass: kSecClassGenericPassword,
                kSecAttrService: service,
                kSecAttrAccount: account,
                kSecValueData: snapshot,
                kSecAttrAccessible: kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly,
            ] as CFDictionary, nil)
            guard added == errSecSuccess else { throw SnapshotStoreError(status: added) }
        } else if status != errSecSuccess {
            throw SnapshotStoreError(status: status)
        }
    }

    static func delete() throws {
        let status = SecItemDelete([
            kSecClass: kSecClassGenericPassword,
            kSecAttrService: service,
            kSecAttrAccount: account,
        ] as CFDictionary)
        guard status == errSecSuccess || status == errSecItemNotFound else {
            throw SnapshotStoreError(status: status)
        }
    }
}

private struct SnapshotStoreError: Error {
    let status: OSStatus
}

@MainActor
private final class WatchSnapshotTransport: NSObject, ObservableObject, WCSessionDelegate {
    private static let snapshotKey = "de.rfc1437.ironstorage.watch.snapshot"
    private static let receiptKey = "de.rfc1437.ironstorage.watch.delivered"

    @Published private(set) var presentation: WatchPresentation?
    private let core = watchCore()

    override init() {
        super.init()
        restoreSnapshot()
        guard WCSession.isSupported() else {
            try? core.syncUnavailable()
            refreshPresentation()
            return
        }
        let session = WCSession.default
        session.delegate = self
        try? core.syncStarted()
        refreshPresentation()
        session.activate()
    }

    func sceneBecameActive() {
        restoreSnapshot()
    }

    func sceneBecameInactive() {
        try? core.protectedDataUnavailable()
        refreshPresentation()
    }

    private func restoreSnapshot() {
        do {
            if var snapshot = try SecureSnapshotStore.load() {
                defer { snapshot.resetBytes(in: 0..<snapshot.count) }
                let update = try core.applySnapshot(snapshot: snapshot)
                if update.persistence == .delete { try SecureSnapshotStore.delete() }
            } else {
                try core.noPersistedSnapshot()
            }
            refreshPresentation()
        } catch {
            try? core.syncFailed()
            refreshPresentation()
        }
    }

    private func receive(_ applicationContext: [String: Any], session: WCSession) {
        try? core.syncStarted()
        guard var snapshot = applicationContext[Self.snapshotKey] as? Data else {
            try? core.syncFinished()
            refreshPresentation()
            return
        }
        defer { snapshot.resetBytes(in: 0..<snapshot.count) }
        do {
            let update = try core.applySnapshot(snapshot: snapshot)
            switch update.persistence {
            case .keep:
                break
            case .replace:
                try SecureSnapshotStore.replace(snapshot)
            case .delete:
                try SecureSnapshotStore.delete()
            }
            refreshPresentation()
            guard !update.receipt.isEmpty else { return }
            let acknowledgement = [Self.receiptKey: update.receipt]
            if session.isReachable {
                session.sendMessage(acknowledgement, replyHandler: nil) { _ in
                    session.transferUserInfo(acknowledgement)
                }
            } else {
                session.transferUserInfo(acknowledgement)
            }
        } catch {
            try? core.syncFailed()
            refreshPresentation()
        }
    }

    func refreshPresentation(at date: Date = .now) {
        presentation = try? core.presentationAt(
            unixSeconds: UInt64(date.timeIntervalSince1970)
        )
    }

    nonisolated func session(
        _ session: WCSession,
        activationDidCompleteWith activationState: WCSessionActivationState,
        error: Error?
    ) {
        Task { @MainActor [weak self] in
            guard let self else { return }
            guard activationState == .activated, error == nil else {
                try? self.core.syncUnavailable()
                self.refreshPresentation()
                return
            }
            self.receive(session.receivedApplicationContext, session: session)
        }
    }

    nonisolated func session(
        _ session: WCSession,
        didReceiveApplicationContext applicationContext: [String: Any]
    ) {
        Task { @MainActor [weak self] in
            self?.receive(applicationContext, session: session)
        }
    }
}

private struct WatchRootView: View {
    @ObservedObject var transport: WatchSnapshotTransport
    private let clock = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

    var body: some View {
        NavigationStack {
            if let presentation = transport.presentation {
                if presentation.records.isEmpty {
                    WatchStateView(presentation: presentation)
                } else {
                    List {
                        if presentation.state == .stale {
                            WatchStatusRow(presentation: presentation)
                        }
                        ForEach(presentation.records, id: \.path) { record in
                            NavigationLink {
                                WatchTotpDetail(path: record.path, transport: transport)
                            } label: {
                                VStack(alignment: .leading, spacing: 2) {
                                    Text(record.issuer ?? record.account)
                                        .font(.headline)
                                    if record.issuer != nil {
                                        Text(record.account)
                                            .font(.caption)
                                            .foregroundStyle(.secondary)
                                    }
                                }
                            }
                        }
                    }
                    .navigationTitle(presentation.title)
                }
            }
        }
        .onReceive(clock) { transport.refreshPresentation(at: $0) }
    }
}

private struct WatchTotpDetail: View {
    let path: String
    @ObservedObject var transport: WatchSnapshotTransport

    private var record: WatchTotpRecord? {
        transport.presentation?.records.first { $0.path == path }
    }

    var body: some View {
        if let record {
            ScrollView {
                VStack(spacing: 8) {
                    Text(record.issuer ?? record.account)
                        .font(.headline)
                        .multilineTextAlignment(.center)
                    Text(record.account)
                        .font(.caption)
                        .foregroundStyle(.secondary)
                        .multilineTextAlignment(.center)
                    Text(record.code)
                        .font(.system(size: 42, weight: .bold, design: .rounded))
                        .monospacedDigit()
                        .minimumScaleFactor(0.7)
                        .lineLimit(1)
                        .privacySensitive()
                    ProgressView(
                        value: Double(min(record.remaining, record.period)),
                        total: Double(record.period)
                    )
                    .accessibilityLabel("Code validity")
                    .accessibilityValue("\(record.remaining) seconds remaining")
                    Text("\(record.remaining)s")
                        .font(.caption.monospacedDigit())
                        .foregroundStyle(.secondary)
                }
                .frame(maxWidth: .infinity)
            }
            .navigationTitle(record.account)
        } else if let presentation = transport.presentation {
            WatchStateView(presentation: presentation)
        }
    }
}

private struct WatchStateView: View {
    let presentation: WatchPresentation

    var body: some View {
        ContentUnavailableView(
            presentation.title,
            systemImage: icon,
            description: Text(presentation.detail)
        )
    }

    private var icon: String {
        switch presentation.state {
        case .ready: "timer"
        case .empty: "iphone.and.arrow.forward"
        case .syncing: "arrow.triangle.2.circlepath"
        case .stale: "clock.badge.exclamationmark"
        case .locked: "lock"
        case .unavailable: "iphone.slash"
        case .error: "exclamationmark.triangle"
        }
    }
}

private struct WatchStatusRow: View {
    let presentation: WatchPresentation

    var body: some View {
        Label {
            VStack(alignment: .leading) {
                Text(presentation.title).font(.headline)
                Text(presentation.detail)
                    .font(.caption)
                    .foregroundStyle(.secondary)
            }
        } icon: {
            Image(systemName: "clock.badge.exclamationmark")
        }
    }
}

@main
struct IronStorageWatchApp: App {
    @Environment(\.scenePhase) private var scenePhase
    @StateObject private var transport = WatchSnapshotTransport()

    var body: some Scene {
        WindowGroup {
            WatchRootView(transport: transport)
                .onChange(of: scenePhase) { _, phase in
                    if phase == .active {
                        transport.sceneBecameActive()
                    } else {
                        transport.sceneBecameInactive()
                    }
                }
        }
    }
}