LLM Search with SpotlightSearchTool

import SwiftUI
import CoreSpotlight
import FoundationModels

// MARK: - Index Delegate (supplies full item metadata to the model)
final class TrailIndexDelegate: NSObject, CSSearchableIndexDelegate {
    func searchableIndex(_ searchableIndex: CSSearchableIndex,
                         reindexAllSearchableItemsWithAcknowledgementHandler acknowledgementHandler: @escaping () -> Void) {
        acknowledgementHandler()
    }

    func searchableIndex(_ searchableIndex: CSSearchableIndex,
                         reindexSearchableItemsWithIdentifiers identifiers: [String],
                         acknowledgementHandler: @escaping () -> Void) {
        acknowledgementHandler()
    }

    // New iOS 27 method: called by SpotlightSearchTool to recover full item data
    func searchableItems(forIdentifiers identifiers: [String]) async -> [CSSearchableItem] {
        return identifiers.map { id in
            let attrs = CSSearchableItemAttributeSet(contentType: .text)
            attrs.title = "Sample Trail"
            attrs.contentDescription = "A beautiful coastal hike with ocean views."
            attrs.namedLocation = "Point Reyes, CA"
            // Add any extra metadata not stored compactly in the index
            attrs.completionDate = Date()
            attrs.distance = 12.4
            return CSSearchableItem(uniqueIdentifier: id,
                                    domainIdentifier: "com.example.trails",
                                    attributeSet: attrs)
        }
    }
}

// MARK: - Trail Search View
struct TrailAssistantView: View {
    @State private var question: String = ""
    @State private var answer: String = ""
    @State private var isLoading: Bool = false

    private let indexDelegate = TrailIndexDelegate()

    var body: some View {
        NavigationStack {
            VStack(spacing: 16) {
                TextField("Ask about your hikes…", text: $question)
                    .textFieldStyle(.roundedBorder)
                    .padding(.horizontal)

                Button("Ask") {
                    Task { await askModel() }
                }
                .buttonStyle(.borderedProminent)
                .disabled(question.isEmpty || isLoading)

                if isLoading {
                    ProgressView("Thinking…")
                }

                ScrollView {
                    Text(answer)
                        .padding()
                        .frame(maxWidth: .infinity, alignment: .leading)
                }
            }
            .navigationTitle("Trail Journal")
        }
        .onAppear { setupIndex() }
    }

    private func setupIndex() {
        // Register delegate so SpotlightSearchTool can recover full metadata
        CSSearchableIndex.default().indexDelegate = indexDelegate
    }

    private func askModel() async {
        isLoading = true
        answer = ""
        defer { isLoading = false }

        // Create the SpotlightSearchTool scoped to this app's bundle
        let searchTool = SpotlightSearchTool()

        // Build a session with the on-device model and attach the tool
        let session = LanguageModelSession(
            model: SystemLanguageModel.default,
            tools: [searchTool]
        )

        do {
            let response = try await session.respond(to: question)
            answer = response.content
        } catch {
            answer = "Error: \(error.localizedDescription)"
        }
    }
}