Local Agentic AI on Mac with MLX

import SwiftUI

// MARK: - OpenAI-compatible request/response models
struct ChatMessage: Codable {
    let role: String
    let content: String
}

struct ChatRequest: Codable {
    let model: String
    let messages: [ChatMessage]
    let stream: Bool
}

struct ChatChoice: Codable {
    struct Delta: Codable {
        let content: String?
    }
    let delta: Delta
}

struct ChatStreamChunk: Codable {
    let choices: [ChatChoice]
}

// MARK: - View Model
@MainActor
final class LocalLLMViewModel: ObservableObject {
    @Published var response: String = ""
    @Published var isLoading = false

    // MLX-LM Server default endpoint
    private let serverURL = URL(string: "http://localhost:8080/v1/chat/completions")!

    func send(prompt: String) async {
        isLoading = true
        response = ""

        let body = ChatRequest(
            model: "mlx-community/Qwen2.5-7B-Instruct-4bit",
            messages: [ChatMessage(role: "user", content: prompt)],
            stream: true
        )

        var request = URLRequest(url: serverURL)
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.httpBody = try? JSONEncoder().encode(body)

        do {
            let (bytes, _) = try await URLSession.shared.bytes(for: request)
            for try await line in bytes.lines {
                guard line.hasPrefix("data: "),
                      let data = line.dropFirst(6).data(using: .utf8),
                      let chunk = try? JSONDecoder().decode(ChatStreamChunk.self, from: data),
                      let token = chunk.choices.first?.delta.content
                else { continue }
                response += token
            }
        } catch {
            response = "Error: \(error.localizedDescription)"
        }
        isLoading = false
    }
}

// MARK: - SwiftUI View
struct LocalLLMView: View {
    @StateObject private var vm = LocalLLMViewModel()
    @State private var prompt = "Summarize what MLX is in one sentence."

    var body: some View {
        VStack(alignment: .leading, spacing: 16) {
            Text("Local LLM (MLX-LM Server)")
                .font(.headline)
            TextEditor(text: $prompt)
                .frame(height: 80)
                .overlay(RoundedRectangle(cornerRadius: 8).stroke(.secondary))
            Button("Send") {
                Task { await vm.send(prompt: prompt) }
            }
            .disabled(vm.isLoading)
            .buttonStyle(.borderedProminent)
            ScrollView {
                Text(vm.response.isEmpty ? (vm.isLoading ? "Thinking…" : "Response appears here") : vm.response)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .padding(8)
            }
            .frame(maxHeight: .infinity)
            .overlay(RoundedRectangle(cornerRadius: 8).stroke(.secondary))
        }
        .padding()
    }
}

#Preview {
    LocalLLMView()
        .frame(width: 480, height: 400)
}