How to Implement a Message Filter Extension in SwiftUI

// ─────────────────────────────────────────────────────────────────
// MARK: FilterRulesStore.swift
// Shared by BOTH the host app target AND the extension target.
// Add this file to both targets in Xcode (File Inspector → Target Membership).
// ─────────────────────────────────────────────────────────────────
import Foundation

final class FilterRulesStore {
    static let shared = FilterRulesStore()

    // Replace with your actual App Group identifier.
    private let defaults = UserDefaults(suiteName: "group.com.yourapp.messagefilter")!

    private init() {}

    var blockedSenders: Set<String> {
        get { Set(defaults.stringArray(forKey: "blockedSenders") ?? []) }
        set { defaults.set(Array(newValue), forKey: "blockedSenders") }
    }
}

// ─────────────────────────────────────────────────────────────────
// MARK: MessageFilterExtension.swift  (Extension target only)
// ─────────────────────────────────────────────────────────────────
import IdentityLookup

final class MessageFilterExtension: ILMessageFilterExtension {}

extension MessageFilterExtension: ILMessageFilterQueryHandling {

    func handle(
        _ queryRequest: ILMessageFilterQueryRequest,
        context: ILMessageFilterExtensionContext,
        completion: @escaping (ILMessageFilterQueryResponse) -> Void
    ) {
        let response = ILMessageFilterQueryResponse()

        guard let rawBody = queryRequest.messageBody else {
            response.action = .none
            completion(response)
            return
        }

        let body   = rawBody.lowercased()
        let sender = queryRequest.sender ?? ""

        switch classify(body: body, sender: sender) {
        case .junk(let sub):
            response.action = .junk
            response.junkSubAction = sub
        case .promotion(let sub):
            response.action = .promotion
            response.promotionSubAction = sub
        case .transaction(let sub):
            response.action = .transaction
            response.transactionSubAction = sub
        case .allow:
            response.action = .allow
        case .unknown:
            // Hand off to carrier / Apple network for uncertain messages.
            context.deferQueryRequestToNetwork()
            return
        }

        completion(response)
    }

    // MARK: - Classification

    private enum Classification {
        case junk(ILMessageFilterJunkAction)
        case promotion(ILMessageFilterPromotionAction)
        case transaction(ILMessageFilterTransactionAction)
        case allow
        case unknown
    }

    private func classify(body: String, sender: String) -> Classification {
        // 1. Check user-managed blocked sender list (App Group container).
        if FilterRulesStore.shared.blockedSenders.contains(sender) {
            return .junk(.junkMarketing)
        }

        // 2. Junk / scam signals.
        let junkTerms = ["winner", "you've won", "prize", "click here now",
                         "free gift", "claim your reward", "urgent action required"]
        if junkTerms.contains(where: body.contains) {
            let isScam = body.contains("bank") || body.contains("verify") || body.contains("account")
            return .junk(isScam ? .junkScam : .junkMarketing)
        }

        // 3. Promotional signals.
        let promoTerms = ["% off", "discount", "sale ends", "coupon", "promo code",
                          "shop now", "deal of the day", "limited offer"]
        if promoTerms.contains(where: body.contains) {
            let hasCoupon = body.contains("code") || body.contains("coupon")
            return .promotion(hasCoupon ? .promotionCoupon : .promotionOffer)
        }

        // 4. Transactional signals.
        let txTerms = ["order confirmed", "has shipped", "out for delivery", "delivered",
                       "payment received", "your receipt", "appointment reminder", "invoice"]
        if txTerms.contains(where: body.contains) {
            let isReminder = body.contains("reminder") || body.contains("appointment")
            return .transaction(isReminder ? .transactionReminder : .transactionOrder)
        }

        return .unknown
    }
}

// ─────────────────────────────────────────────────────────────────
// MARK: FilterSettingsView.swift  (Host app target only)
// ─────────────────────────────────────────────────────────────────
import SwiftUI

struct FilterSettingsView: View {
    @State private var blockedSenders: [String] = []
    @State private var newSender = ""
    @FocusState private var fieldFocused: Bool

    var body: some View {
        NavigationStack {
            List {
                Section("Blocked Senders") {
                    HStack(spacing: 10) {
                        TextField("Phone number or short code", text: $newSender)
                            .keyboardType(.phonePad)
                            .focused($fieldFocused)
                            .submitLabel(.done)
                            .onSubmit(addSender)
                            .accessibilityLabel("New blocked sender number")
                        Button("Add", action: addSender)
                            .buttonStyle(.borderedProminent)
                            .controlSize(.small)
                            .disabled(newSender.trimmingCharacters(in: .whitespaces).isEmpty)
                    }

                    if blockedSenders.isEmpty {
                        Text("No blocked senders yet.")
                            .foregroundStyle(.secondary)
                            .font(.footnote)
                    } else {
                        ForEach(blockedSenders, id: \.self) { sender in
                            Text(sender)
                                .accessibilityLabel("Blocked sender: \(sender)")
                        }
                        .onDelete(perform: removeSenders)
                    }
                }

                Section {
                    Label {
                        Text("Messages are classified on-device. Your message content never leaves your iPhone.")
                            .font(.footnote)
                    } icon: {
                        Image(systemName: "lock.shield.fill")
                            .foregroundStyle(.green)
                    }
                }
            }
            .navigationTitle("Message Filter")
            .navigationBarTitleDisplayMode(.large)
            .toolbar { EditButton() }
            .onAppear { reload() }
        }
    }

    // MARK: - Helpers

    private func reload() {
        blockedSenders = Array(FilterRulesStore.shared.blockedSenders).sorted()
    }

    private func addSender() {
        let trimmed = newSender.trimmingCharacters(in: .whitespaces)
        guard !trimmed.isEmpty else { return }
        FilterRulesStore.shared.blockedSenders.insert(trimmed)
        reload()
        newSender = ""
        fieldFocused = false
    }

    private func removeSenders(at offsets: IndexSet) {
        let toRemove = offsets.map { blockedSenders[$0] }
        toRemove.forEach { FilterRulesStore.shared.blockedSenders.remove($0) }
        blockedSenders.remove(atOffsets: offsets)
    }
}

#Preview {
    // Seed some sample data so the preview shows a populated list.
    FilterRulesStore.shared.blockedSenders = ["+18005550199", "SPAMCO", "+14155550123"]
    return FilterSettingsView()
}