SwiftUIとUIKitで Foundation Models を使ってみた：オンデバイス要約の最小実装

enum OnDeviceSummarizeError: LocalizedError {
    case unavailable(String)

    var errorDescription: String? {
        switch self {
        case .unavailable(let message): return message
        }
    }
}

final class OnDeviceSummarizer {
    private let model = SystemLanguageModel.default
    private let session = LanguageModelSession(instructions: """
    あなたは要約機能です。
    出力は日本語。
    300字以内で出力してください。
    """)

    func summarize(_ text: String) async throws -> String {
        try ensureAvailable()

        let prompt = """
        次の文章を要約してください。
        ---
        \(text)
        ---
        """

        let response = try await session.respond(to: prompt)
        return response.content
    }

    private func ensureAvailable() throws {
        switch model.availability {
        case .available:
            return
        case .unavailable(let reason):
            throw OnDeviceSummarizeError.unavailable("この端末では利用できません（\(reason)）。")
        }
    }
}

import SwiftUI

struct ContentView: View {
    @State private var inputText: String = ""
    @State private var outputText: String = ""
    @State private var errorText: String?
    @State private var isLoading: Bool = false

    private let summarizer = OnDeviceSummarizer()

    var body: some View {
        VStack(spacing: 12) {
            Text("オンデバイス要約（Foundation Models）")
                .font(.headline)

            TextEditor(text: $inputText)
                .frame(height: 180)
                .overlay(RoundedRectangle(cornerRadius: 8).stroke(.secondary.opacity(0.3)))

            Button {
                Task {
                    await summarize()
                }
            } label: {
                if isLoading {
                    ProgressView()
                } else {
                    Text("要約する")
                }
            }
            .disabled(isLoading || inputText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty)

            if let errorText {
                Text(errorText)
                    .foregroundStyle(.red)
                    .frame(maxWidth: .infinity, alignment: .leading)
            }

            ScrollView {
                Text(outputText)
                    .frame(maxWidth: .infinity, alignment: .leading)
            }
            .frame(maxHeight: .infinity)
            .overlay(RoundedRectangle(cornerRadius: 8).stroke(.secondary.opacity(0.3)))
        }
        .padding()
    }

    private func summarize() async {
        isLoading = true
        errorText = nil
        outputText = ""

        do {
            let result = try await summarizer.summarize(inputText)
            outputText = result
        } catch {
            errorText = (error as? LocalizedError)?.errorDescription ?? String(describing: error)
        }

        isLoading = false
    }
}

import UIKit

final class ViewController: UIViewController {

    private let inputTextView = UITextView()
    private let outputTextView = UITextView()
    private let summarizeButton = UIButton(type: .system)

    private let summarizer = OnDeviceSummarizer()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
        setupUI()
    }

    private func setupUI() {
        inputTextView.font = .systemFont(ofSize: 16)
        inputTextView.layer.borderWidth = 1
        inputTextView.layer.borderColor = UIColor.secondaryLabel.withAlphaComponent(0.3).cgColor
        inputTextView.layer.cornerRadius = 8

        outputTextView.font = .systemFont(ofSize: 16)
        outputTextView.isEditable = false
        outputTextView.layer.borderWidth = 1
        outputTextView.layer.borderColor = UIColor.secondaryLabel.withAlphaComponent(0.3).cgColor
        outputTextView.layer.cornerRadius = 8

        summarizeButton.setTitle("要約する", for: .normal)
        summarizeButton.addTarget(self, action: #selector(didTapSummarize), for: .touchUpInside)

        let stack = UIStackView(arrangedSubviews: [inputTextView, summarizeButton, outputTextView])
        stack.axis = .vertical
        stack.spacing = 12
        stack.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(stack)

        NSLayoutConstraint.activate([
            stack.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 16),
            stack.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16),
            stack.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16),
            stack.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -16),

            inputTextView.heightAnchor.constraint(equalToConstant: 180),
            outputTextView.heightAnchor.constraint(greaterThanOrEqualToConstant: 180),
        ])
    }

    @objc private func didTapSummarize() {
        let text = inputTextView.text ?? ""
        if text.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty { return }

        setLoading(true)
        outputTextView.text = ""

        Task {
            do {
                let result = try await summarizer.summarize(text)
                await MainActor.run {
                    self.outputTextView.text = result
                    self.setLoading(false)
                }
            } catch {
                let message = (error as? LocalizedError)?.errorDescription ?? String(describing: error)
                await MainActor.run {
                    self.outputTextView.text = message
                    self.setLoading(false)
                }
            }
        }
    }

    private func setLoading(_ isLoading: Bool) {
        summarizeButton.isEnabled = !isLoading
        if isLoading {
            summarizeButton.setTitle("要約中…", for: .disabled)
        } else {
            summarizeButton.setTitle("要約する", for: .normal)
        }
    }
}