import ManaCore
import Observation
import SwiftUI

/// Account-Sheet: Email-Adresse ändern.
///
/// Schickt eine Verifikations-Mail an die **neue** Adresse. Bis der
/// User klickt, bleibt die alte Email aktiv.
///
/// **Server-Limitation (v0.1.0):** funktioniert erst nach Phase-3-
/// Server-PR (`mana-auth` braucht Bearer-Plugin). Die UI ist fertig,
/// der Wire ist fertig, der Server muss nachziehen.
public struct ManaChangeEmailView: View {
    @Environment(\.manaBrand) private var brand
    @State private var model: ChangeEmailViewModel
    private let onDone: () -> Void

    public init(auth: AuthClient, callbackUniversalLink: URL? = nil, onDone: @escaping () -> Void) {
        _model = State(initialValue: ChangeEmailViewModel(
            auth: auth,
            callbackUniversalLink: callbackUniversalLink
        ))
        self.onDone = onDone
    }

    public var body: some View {
        switch model.status {
        case .done:
            doneView
        default:
            formView
        }
    }

    @ViewBuilder
    private var formView: some View {
        ManaAuthScaffold(showsHeader: false) {
            VStack(spacing: 16) {
                Text("Email ändern")
                    .font(.title2)
                    .fontWeight(.semibold)
                    .foregroundStyle(brand.foreground)
                    .frame(maxWidth: .infinity, alignment: .leading)

                Text(
                    "Wir schicken eine Bestätigungs-Mail an die neue Adresse. "
                        + "Bis du klickst, bleibt die alte Email aktiv."
                )
                .font(.subheadline)
                .foregroundStyle(brand.mutedForeground)
                .frame(maxWidth: .infinity, alignment: .leading)

                ManaTextField("Neue Email", text: $model.newEmail)
                    .manaEmailField()

                ManaPrimaryButton(
                    "Email ändern",
                    isLoading: model.isSubmitting,
                    isEnabled: model.canSubmit
                ) {
                    Task { await model.submit() }
                }

                if case let .error(message) = model.status {
                    Text(message)
                        .font(.footnote)
                        .foregroundStyle(brand.error)
                        .multilineTextAlignment(.center)
                        .padding(.top, 4)
                }
            }
            .padding(.top, 16)

            Button("Abbrechen", action: onDone)
                .font(.subheadline)
                .foregroundStyle(brand.mutedForeground)
                .padding(.top, 12)
        }
    }

    @ViewBuilder
    private var doneView: some View {
        ManaAuthScaffold(showsHeader: false) {
            VStack(spacing: 16) {
                Image(systemName: "envelope.fill")
                    .font(.system(size: 56, weight: .light))
                    .foregroundStyle(brand.primary)

                Text("Bestätigungs-Mail verschickt")
                    .font(.title2)
                    .fontWeight(.semibold)
                    .foregroundStyle(brand.foreground)

                Text(
                    "Klicke den Link in der Mail, um die Änderung zu bestätigen."
                )
                .font(.subheadline)
                .foregroundStyle(brand.mutedForeground)
                .multilineTextAlignment(.center)

                ManaPrimaryButton("Fertig") { onDone() }
                    .padding(.top, 16)
            }
        }
    }
}

@MainActor
@Observable
final class ChangeEmailViewModel {
    enum Status: Equatable {
        case idle
        case submitting
        case done
        case error(String)
    }

    var newEmail: String = ""
    private(set) var status: Status = .idle

    private let auth: AuthClient
    private let callbackUniversalLink: URL?

    init(auth: AuthClient, callbackUniversalLink: URL?) {
        self.auth = auth
        self.callbackUniversalLink = callbackUniversalLink
    }

    var canSubmit: Bool {
        guard !newEmail.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty else { return false }
        if case .submitting = status { return false }
        return true
    }

    var isSubmitting: Bool {
        if case .submitting = status { return true }
        return false
    }

    func submit() async {
        let trimmed = newEmail.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }

        status = .submitting
        do {
            try await auth.changeEmail(newEmail: trimmed, callbackUniversalLink: callbackUniversalLink)
            status = .done
        } catch let error as AuthError {
            status = .error(error.errorDescription ?? "Änderung fehlgeschlagen")
        } catch {
            status = .error(String(describing: error))
        }
    }
}