Feature Chat Module

// Factory method with dependency injection
public func makeChatViewModel(conversationID: UUID) -> ChatViewModel {
    ChatViewModel(
        conversationID: conversationID,
        messageRepository: messageRepository,  // SwiftData repository
        llmClient: llmClient,                  // Proxy or Echo client
        paymentsStatusProvider: PaymentsStatusAdapter(paymentsClient: paymentsClient)
    )
}

// Create a dual-style chat container (renders the selected ChatUIStyle)
public func makeDualStyleChatView(
    conversationID: UUID,
    onRequireSubscription: (() -> Void)? = nil
) -> DualStyleChatView {
    let viewModel = makeChatViewModel(conversationID: conversationID)

    return DualStyleChatView(
        viewModel: viewModel,
        onRequireSubscription: onRequireSubscription
    )
}

@MainActor
@Observable
public final class ChatHistoryViewModel {
    var conversations: [ConversationDTO]
    var isLoading: Bool

    public func loadConversations() async
    public func createNewConversation() async -> ConversationDTO?
    public func renameConversation(id: UUID, newTitle: String) async
    public func deleteConversation(id: UUID) async
}

// In ChatViewModel.send(): accumulate streamed chunks into the message
var accumulatedText = ""
for try await chunk in llmClient.streamResponse(messages: messages) {
    accumulatedText += chunk
    messages[index].text = accumulatedText  // UI updates via @Observable
}

// InfinitePaginator handles:
// - Cursor-based pagination (MessageCursor)
// - Reverse chronological order
// - Prefetch before the user hits the end
// - State tracking (idle / loadingMore / endReached / error)

@MainActor
public final class InfinitePaginator {
    public init(pageSize: Int = 50, prefetchThreshold: Int = 5)

    public private(set) var state: State

    public func shouldLoadMore(visibleIndex: Int, totalCount: Int) -> Bool
    public func loadNext(
        using loader: (MessageCursor?) async throws -> (items: [MessageDTO], next: MessageCursor?)
    ) async -> Result<[ChatMessage], AppError>
    public func reset()
}

// Bubble colors resolve through DSColors (Packages/DesignSystem):
//   DSColors.bubbleUserOrFallback      -> AccentPrimary colorset
//   DSColors.bubbleAssistantOrFallback -> Surface colorset
//
// Edit those colorsets in
// Packages/DesignSystem/Sources/DesignSystem/Resources/Assets.xcassets
// and both chat styles update automatically.

// Add a context menu to MessageRow in ChatView.
// Copy works against the existing ChatMessage.text.
// Regenerate/Delete are methods you add to ChatViewModel yourself —
// they are not shipped on the view model.
.contextMenu {
    Button("Copy", systemImage: "doc.on.doc") {
        UIPasteboard.general.string = message.text
    }
    // Example extension points to implement on ChatViewModel:
    // Button("Regenerate", systemImage: "arrow.clockwise") { ... }
    // Button("Delete", systemImage: "trash", role: .destructive) { ... }
}

// In ChatViewModel. LLMMessage.role is a String: "user" | "assistant" | "system".
let systemPrompt = LLMMessage(
    role: "system",
    content: """
    You are a Swift expert.
    Provide clear answers with code examples.
    """
)

let messages = [systemPrompt] + history + [userMessage]

// ChatHistoryView.filteredConversations
viewModel.conversations.filter { conversation in
    conversation.title.localizedCaseInsensitiveContains(searchText) ||
    (conversation.personaName?.localizedCaseInsensitiveContains(searchText) ?? false)
}

struct TypingIndicatorView: View {
  @State private var isVisible = false
  var body: some View { /* minimal dots animation */ }
}
// TODO: drive from ChatMessage.isStreaming / ChatViewModel.isSending (throttle: 600ms)