import SwiftUI

struct AuthView: View {
    @EnvironmentObject var authStore: AuthStore
    @State private var mode: Mode = .login
    @State private var username: String = ""
    @State private var password: String = ""
    @State private var confirmPassword: String = ""
    @FocusState private var focusedField: Field?

    enum Mode { case login, register }
    enum Field { case username, password, confirmPassword }

    var body: some View {
        NavigationStack {
            VStack(spacing: 0) {
                // Logo / header
                VStack(spacing: 8) {
                    Image(systemName: "books.vertical.fill")
                        .font(.system(size: 56))
                        .foregroundStyle(.amber)
                    Text("LibNovel")
                        .font(.largeTitle.bold())
                }
                .padding(.top, 60)
                .padding(.bottom, 40)

                // Tab switcher
                Picker("Mode", selection: $mode) {
                    Text("Sign In").tag(Mode.login)
                    Text("Create Account").tag(Mode.register)
                }
                .pickerStyle(.segmented)
                .padding(.horizontal, 24)
                .padding(.bottom, 32)

                // Form
                VStack(spacing: 16) {
                    TextField("Username", text: $username)
                        .textFieldStyle(.roundedBorder)
                        .textInputAutocapitalization(.never)
                        .autocorrectionDisabled()
                        .focused($focusedField, equals: .username)
                        .submitLabel(.next)
                        .onSubmit { focusedField = .password }

                    SecureField("Password", text: $password)
                        .textFieldStyle(.roundedBorder)
                        .focused($focusedField, equals: .password)
                        .submitLabel(mode == .register ? .next : .go)
                        .onSubmit {
                            if mode == .register { focusedField = .confirmPassword }
                            else { submit() }
                        }

                    if mode == .register {
                        SecureField("Confirm Password", text: $confirmPassword)
                            .textFieldStyle(.roundedBorder)
                            .focused($focusedField, equals: .confirmPassword)
                            .submitLabel(.go)
                            .onSubmit { submit() }
                            .transition(.opacity.combined(with: .move(edge: .top)))
                    }
                }
                .padding(.horizontal, 24)
                .animation(.easeInOut(duration: 0.2), value: mode)

                if let error = authStore.error {
                    Text(error)
                        .font(.footnote)
                        .foregroundStyle(.red)
                        .multilineTextAlignment(.center)
                        .padding(.horizontal, 24)
                        .padding(.top, 8)
                }

                Button(action: submit) {
                    Group {
                        if authStore.isLoading {
                            ProgressView()
                                .progressViewStyle(.circular)
                                .tint(.white)
                        } else {
                            Text(mode == .login ? "Sign In" : "Create Account")
                                .fontWeight(.semibold)
                        }
                    }
                    .frame(maxWidth: .infinity)
                    .frame(height: 50)
                }
                .buttonStyle(.borderedProminent)
                .tint(.amber)
                .padding(.horizontal, 24)
                .padding(.top, 24)
                .disabled(authStore.isLoading || !formIsValid)

                Spacer()
            }
            .toolbar(.hidden, for: .navigationBar)
        }
        .onChange(of: mode) { _, _ in
            authStore.error = nil
            confirmPassword = ""
        }
    }

    private var formIsValid: Bool {
        let base = !username.isEmpty && password.count >= 4
        if mode == .register { return base && password == confirmPassword }
        return base
    }

    private func submit() {
        focusedField = nil
        Task {
            if mode == .login {
                await authStore.login(username: username, password: password)
            } else {
                await authStore.register(username: username, password: password)
            }
        }
    }
}