initial commit: Proximity iOS app proposal, full Swift code scaffold, reference backend, testing docs, generated Xcode project

Proximity/ViewModels/ChatViewModel.swift

@@ -0,0 +1,109 @@
+import Foundation
+import Combine
+import CryptoKit
+
+/// View model for an E2E-encrypted conversation with a revealed connection.
+///
+/// Messages are encrypted with the session key established at reveal time
+/// (see `RevealFlow`). The server only ever sees ciphertext — it cannot read
+/// the conversation. This is the product's promise kept in the most intimate
+/// place: the words between two people who chose to meet.
+@MainActor
+final class ChatViewModel: ObservableObject {
+
+    @Published private(set) var messages: [ChatMessage] = []
+    @Published var draft: String = ""
+    @Published private(set) var isSending = false
+
+    private let apiClient: APIClient
+    private let cryptoManager: CryptoManager
+    private let graphStore: GraphStore
+    private let realtime: RealtimeClient
+
+    /// The active connection we're chatting with.
+    private var connection: Connection?
+    /// The E2E session key for this conversation.
+    private var sessionKey: SymmetricKey?
+    /// Decrypted plaintext cache keyed by message id.
+    @Published private(set) var plaintextByID: [UUID: String] = [:]
+
+    private var cancellables = Set<AnyCancellable>()
+
+    init(apiClient: APIClient, cryptoManager: CryptoManager, graphStore: GraphStore, realtime: RealtimeClient) {
+        self.apiClient = apiClient
+        self.cryptoManager = cryptoManager
+        self.graphStore = graphStore
+        self.realtime = realtime
+
+        // Live wire: decrypt and append incoming messages in real time.
+        realtime.incomingMessage
+            .sink { [weak self] message in
+                Task { await self?.receive(message) }
+            }
+            .store(in: &cancellables)
+    }
+
+    // MARK: - Setup
+
+    /// Begin a conversation with a revealed connection.
+    func start(with connection: Connection, sessionKey: SymmetricKey?) {
+        self.connection = connection
+        self.sessionKey = sessionKey
+        self.messages = graphStore.messages.filter { $0.connectionID == connection.id }
+    }
+
+    // MARK: - Sending
+
+    func send() async {
+        let text = draft.trimmingCharacters(in: .whitespacesAndNewlines)
+        guard !text.isEmpty,
+              let connection,
+              let sessionKey else { return }
+
+        isSending = true
+        defer { isSending = false }
+
+        do {
+            let plaintext = Data(text.utf8)
+            let ciphertext = try cryptoManager.encrypt(plaintext, using: sessionKey)
+
+            let message = ChatMessage(
+                connectionID: connection.id,
+                senderID: "me",
+                ciphertext: ciphertext
+            )
+            messages.append(message)
+            plaintextByID[message.id] = text
+            graphStore.addMessage(message)
+            draft = ""
+
+            try await apiClient.sendMessage(message)
+        } catch {
+            // Keep the message locally; surface send failure to the UI.
+        }
+    }
+
+    // MARK: - Receiving
+
+    /// Decrypt and append an incoming message (called live from the socket).
+    func receive(_ message: ChatMessage) async {
+        guard let sessionKey,
+              message.connectionID == connection?.id else { return }
+
+        // Deduplicate against messages we already have.
+        guard !messages.contains(where: { $0.id == message.id }) else { return }
+
+        // Decrypt and cache the plaintext for display.
+        if let plaintext = try? cryptoManager.decrypt(message.ciphertext, using: sessionKey),
+           let text = String(data: plaintext, encoding: .utf8) {
+            plaintextByID[message.id] = text
+            messages.append(message)
+            graphStore.addMessage(message)
+        }
+    }
+
+    /// The decrypted text for a message, for display.
+    func text(for message: ChatMessage) -> String {
+        plaintextByID[message.id] ?? "…"
+    }
+}