import SwiftUI

// MARK: - AuthView
// Full-screen login / register view.
// Mirrors the web UI's login page: zinc-900 background, tab switcher with
// amber underline indicator, zinc-800 text fields with amber focus ring,
// amber CTA button, inline error banner, loading state.

struct AuthView: View {
    @EnvironmentObject var authStore: AuthStore
    @EnvironmentObject var networkMonitor: NetworkMonitor

    @State private var mode: AuthMode = .login

    // Login fields
    @State private var loginUsername: String = ""
    @State private var loginPassword: String = ""

    // Register fields
    @State private var regUsername: String = ""
    @State private var regPassword: String = ""
    @State private var regConfirm: String  = ""

    // Focus management
    @FocusState private var focus: AuthField?

    // Local validation error (client-side, e.g. password mismatch)
    @State private var localError: String?

    private var displayError: String? { localError ?? authStore.error }

    var body: some View {
        ZStack {
            Color.appBackground.ignoresSafeArea()

            ScrollView {
                VStack(spacing: 0) {
                    Spacer(minLength: 60)

                    // ── Wordmark ──────────────────────────────────────────
                    wordmark

                    Spacer(minLength: 48)

                    // ── Card ──────────────────────────────────────────────
                    VStack(spacing: 0) {
                        tabSwitcher
                        formContent
                    }
                    .background(Color.cardBackground)
                    .clipShape(RoundedRectangle(cornerRadius: 14, style: .continuous))
                    .padding(.horizontal, 24)

                    Spacer(minLength: 40)
                }
            }
            .scrollDismissesKeyboard(.interactively)
        }
        .onChange(of: mode) { _, _ in
            localError = nil
            authStore.error = nil
        }
    }

    // MARK: - Wordmark

    private var wordmark: some View {
        VStack(spacing: 6) {
            Image(systemName: "books.vertical.fill")
                .font(.system(size: 44))
                .foregroundStyle(Color.amber)
                .symbolEffect(.bounce, value: mode)

            Text("libnovel")
                .font(.title.bold())
                .fontDesign(.serif)
                .foregroundStyle(.primary)
        }
    }

    // MARK: - Tab switcher

    private var tabSwitcher: some View {
        HStack(spacing: 0) {
            tabButton(label: "Sign in",        tab: .login)
            tabButton(label: "Create account", tab: .register)
        }
        .overlay(alignment: .bottom) {
            Rectangle()
                .fill(Color.cardBorder)
                .frame(height: 1)
        }
    }

    @ViewBuilder
    private func tabButton(label: String, tab: AuthMode) -> some View {
        let isActive = mode == tab
        Button {
            UIImpactFeedbackGenerator(style: .light).impactOccurred()
            withAnimation(.spring(response: 0.3, dampingFraction: 0.7)) {
                mode = tab
            }
        } label: {
            VStack(spacing: 0) {
                Text(label)
                    .font(.subheadline.weight(.medium))
                    .foregroundStyle(isActive ? Color.amber : Color.secondary)
                    .padding(.vertical, 14)
                    .frame(maxWidth: .infinity)

                // Active underline indicator
                Rectangle()
                    .fill(isActive ? Color.amber : Color.clear)
                    .frame(height: 2)
                    .offset(y: 1)           // sits on top of the border
            }
        }
        .accessibilityAddTraits(isActive ? [.isSelected] : [])
    }

    // MARK: - Form content

    @ViewBuilder
    private var formContent: some View {
        VStack(spacing: 16) {
            // Error banner
            if let err = displayError {
                errorBanner(err)
                    .transition(.move(edge: .top).combined(with: .opacity))
            }

            switch mode {
            case .login:    loginForm
            case .register: registerForm
            }
        }
        .padding(20)
        .animation(.spring(response: 0.3, dampingFraction: 0.7), value: displayError)
        .animation(.spring(response: 0.35, dampingFraction: 0.75), value: mode)
    }

    // MARK: - Error banner

    private func errorBanner(_ message: String) -> some View {
        HStack(spacing: 8) {
            Image(systemName: "exclamationmark.triangle.fill")
                .foregroundStyle(Color.errorText)
                .font(.footnote)
            Text(message)
                .font(.footnote)
                .foregroundStyle(Color.errorText)
                .multilineTextAlignment(.leading)
        }
        .padding(.horizontal, 12)
        .padding(.vertical, 10)
        .frame(maxWidth: .infinity, alignment: .leading)
        .background(Color.errorBackground)
        .overlay(
            RoundedRectangle(cornerRadius: 8, style: .continuous)
                .stroke(Color.errorBorder, lineWidth: 1)
        )
        .clipShape(RoundedRectangle(cornerRadius: 8, style: .continuous))
    }

    // MARK: - Login form

    private var loginForm: some View {
        VStack(spacing: 16) {
            AuthInputField(
                label: "Username",
                placeholder: "your_username",
                text: $loginUsername,
                contentType: .username,
                keyboardType: .default,
                focusState: $focus,
                field: .loginUsername,
                nextField: .loginPassword
            )

            AuthInputField(
                label: "Password",
                placeholder: "••••••••",
                text: $loginPassword,
                contentType: .password,
                isSecure: true,
                focusState: $focus,
                field: .loginPassword,
                onSubmit: submitLogin
            )

            ctaButton(label: "Sign in", action: submitLogin)
        }
    }

    // MARK: - Register form

    private var registerForm: some View {
        VStack(spacing: 16) {
            VStack(spacing: 4) {
                AuthInputField(
                    label: "Username",
                    placeholder: "your_username",
                    text: $regUsername,
                    contentType: .username,
                    focusState: $focus,
                    field: .regUsername,
                    nextField: .regPassword
                )
                Text("3–32 characters: letters, numbers, _ or -")
                    .font(.caption)
                    .foregroundStyle(.tertiary)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .padding(.leading, 2)
            }

            VStack(spacing: 4) {
                AuthInputField(
                    label: "Password",
                    placeholder: "••••••••",
                    text: $regPassword,
                    contentType: .newPassword,
                    isSecure: true,
                    focusState: $focus,
                    field: .regPassword,
                    nextField: .regConfirm
                )
                Text("At least 8 characters")
                    .font(.caption)
                    .foregroundStyle(.tertiary)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .padding(.leading, 2)
            }

            AuthInputField(
                label: "Confirm password",
                placeholder: "••••••••",
                text: $regConfirm,
                contentType: .newPassword,
                isSecure: true,
                focusState: $focus,
                field: .regConfirm,
                onSubmit: submitRegister
            )

            ctaButton(label: "Create account", action: submitRegister)
        }
    }

    // MARK: - CTA button

    private func ctaButton(label: String, action: @escaping () -> Void) -> some View {
        Button(action: action) {
            ZStack {
                if authStore.isLoading {
                    ProgressView()
                        .tint(Color(uiColor: .systemBackground))
                } else {
                    Text(label)
                        .font(.subheadline.bold())
                        .foregroundStyle(Color.ctaText)
                }
            }
            .frame(maxWidth: .infinity)
            .frame(height: 44)
        }
        .background(Color.amber)
        .clipShape(RoundedRectangle(cornerRadius: 10, style: .continuous))
        .disabled(authStore.isLoading || !networkMonitor.isConnected)
        .opacity(authStore.isLoading ? 0.8 : 1)
        .animation(.easeInOut(duration: 0.15), value: authStore.isLoading)
        .accessibilityLabel(label)
    }

    // MARK: - Actions

    private func submitLogin() {
        guard !authStore.isLoading else { return }
        localError = nil
        focus = nil
        UIImpactFeedbackGenerator(style: .medium).impactOccurred()
        Task { await authStore.login(username: loginUsername, password: loginPassword) }
    }

    private func submitRegister() {
        guard !authStore.isLoading else { return }
        localError = nil
        // Client-side validation
        if regUsername.count < 3 || regUsername.count > 32 {
            localError = "Username must be 3–32 characters."
            return
        }
        if regPassword.count < 8 {
            localError = "Password must be at least 8 characters."
            return
        }
        if regPassword != regConfirm {
            localError = "Passwords do not match."
            return
        }
        focus = nil
        UIImpactFeedbackGenerator(style: .medium).impactOccurred()
        Task { await authStore.register(username: regUsername, password: regPassword) }
    }
}

// MARK: - Auth mode enum

private enum AuthMode: Equatable { case login, register }

// MARK: - Focus field enum

private enum AuthField: Hashable {
    case loginUsername, loginPassword
    case regUsername, regPassword, regConfirm
}

// MARK: - AuthInputField component

private struct AuthInputField: View {
    let label: String
    let placeholder: String
    @Binding var text: String
    var contentType: UITextContentType? = nil
    var keyboardType: UIKeyboardType = .default
    var isSecure: Bool = false
    @FocusState.Binding var focusState: AuthField?
    let field: AuthField
    var nextField: AuthField? = nil
    var onSubmit: (() -> Void)? = nil

    private var isFocused: Bool { focusState == field }

    var body: some View {
        VStack(alignment: .leading, spacing: 4) {
            Text(label)
                .font(.caption)
                .foregroundStyle(.secondary)

            Group {
                if isSecure {
                    SecureField(placeholder, text: $text)
                } else {
                    TextField(placeholder, text: $text)
                        .keyboardType(keyboardType)
                        .autocorrectionDisabled()
                        .textInputAutocapitalization(.never)
                }
            }
            .textContentType(contentType)
            .focused($focusState, equals: field)
            .submitLabel(nextField != nil ? .next : .done)
            .onSubmit {
                if let next = nextField {
                    focusState = next
                } else {
                    onSubmit?()
                }
            }
            .padding(.horizontal, 12)
            .frame(height: 44)
            .background(Color.fieldBackground)
            .overlay(
                RoundedRectangle(cornerRadius: 8, style: .continuous)
                    .stroke(
                        isFocused ? Color.amber : Color.cardBorder,
                        lineWidth: isFocused ? 1.5 : 1
                    )
            )
            .clipShape(RoundedRectangle(cornerRadius: 8, style: .continuous))
            .animation(.spring(response: 0.2, dampingFraction: 0.7), value: isFocused)
        }
    }
}

// MARK: - Local color helpers

private extension Color {
    static let appBackground  = Color(uiColor: UIColor { t in t.userInterfaceStyle == .dark ? UIColor(red: 0.09, green: 0.09, blue: 0.11, alpha: 1) : UIColor.systemGroupedBackground })
    static let cardBackground = Color(uiColor: UIColor { t in t.userInterfaceStyle == .dark ? UIColor(red: 0.14, green: 0.14, blue: 0.16, alpha: 1) : UIColor.secondarySystemGroupedBackground })
    static let cardBorder     = Color(uiColor: UIColor { t in t.userInterfaceStyle == .dark ? UIColor(white: 0.25, alpha: 1) : UIColor.separator })
    static let fieldBackground = Color(uiColor: UIColor { t in t.userInterfaceStyle == .dark ? UIColor(red: 0.11, green: 0.11, blue: 0.13, alpha: 1) : UIColor.secondarySystemBackground })
    static let ctaText        = Color(uiColor: UIColor(red: 0.11, green: 0.09, blue: 0.04, alpha: 1)) // zinc-900
    static let errorBackground = Color(red: 0.40, green: 0.05, blue: 0.05).opacity(0.40)
    static let errorBorder    = Color(red: 0.70, green: 0.20, blue: 0.20).opacity(0.60)
    static let errorText      = Color(red: 0.98, green: 0.60, blue: 0.60)
}