feat: adds fallback models support for OpenRouter

Playground/Playground/Views/AppView.swift

@@ -34,6 +34,12 @@ struct AppView: View {
                                     ResponseFormatView(provider: provider)
                                 }
                             }
+
+                            if provider == .openRouter {
+                                NavigationLink("Fallback Model") {
+                                    FallbackModelView(provider: provider)
+                                }
+                            }
                         }
                         .disabled(provider == .openai && viewModel.openaiAPIKey.isEmpty)
                         .disabled(provider == .openRouter && viewModel.openRouterAPIKey.isEmpty)

Playground/Playground/Views/FallbackModelView.swift

@@ -0,0 +1,150 @@
+//
+//  FallbackModelView.swift
+//  Playground
+//
+//  Created by Kevin Hermawan on 10/19/24.
+//
+
+import SwiftUI
+import LLMChatOpenAI
+
+struct FallbackModelView: View {
+    let provider: ServiceProvider
+
+    @Environment(AppViewModel.self) private var viewModel
+    @State private var isPreferencesPresented: Bool = false
+
+    @State private var fallbackModel: String = ""
+
+    @State private var prompt: String = "Hi!"
+    @State private var response: String = ""
+    @State private var inputTokens: Int = 0
+    @State private var outputTokens: Int = 0
+    @State private var totalTokens: Int = 0
+
+    var body: some View {
+        @Bindable var viewModelBindable = viewModel
+
+        VStack {
+            Form {
+                Section("Models") {
+                    Picker("Primary Model", selection: $viewModelBindable.selectedModel) {
+                        ForEach(viewModelBindable.models, id: \.self) { model in
+                            Text(model).tag(model)
+                        }
+                    }
+
+                    Picker("Fallback Model", selection: $fallbackModel) {
+                        ForEach(viewModelBindable.models, id: \.self) { model in
+                            Text(model).tag(model)
+                        }
+                    }
+                }
+                .disabled(viewModel.models.isEmpty)
+
+                Section("Prompt") {
+                    TextField("Prompt", text: $prompt)
+                }
+
+                Section("Response") {
+                    Text(response)
+                }
+
+                UsageSection(inputTokens: inputTokens, outputTokens: outputTokens, totalTokens: totalTokens)
+            }
+
+            VStack {
+                SendButton(stream: viewModel.stream, onSend: onSend, onStream: onStream)
+                    .disabled(viewModel.models.isEmpty)
+            }
+        }
+        .toolbar {
+            ToolbarItem(placement: .principal) {
+                NavigationTitle("Fallback Model")
+            }
+
+            ToolbarItem(placement: .primaryAction) {
+                Button("Preferences", systemImage: "gearshape", action: { isPreferencesPresented.toggle() })
+            }
+        }
+        .sheet(isPresented: $isPreferencesPresented) {
+            PreferencesView()
+        }
+        .onAppear {
+            viewModel.setup(for: provider)
+        }
+        .onDisappear {
+            viewModel.selectedModel = ""
+        }
+        .onChange(of: viewModel.models) { _, models in
+            if let firstModel = models.first {
+                fallbackModel = firstModel
+            }
+        }
+    }
+
+    private func onSend() {
+        clear()
+
+        let messages = [
+            ChatMessage(role: .system, content: viewModel.systemPrompt),
+            ChatMessage(role: .user, content: prompt)
+        ]
+
+        let options = ChatOptions(temperature: viewModel.temperature)
+
+        Task {
+            do {
+                let completion = try await viewModel.chat.send(models: [viewModel.selectedModel, fallbackModel], messages: messages, options: options)
+
+                if let content = completion.choices.first?.message.content {
+                    self.response = content
+                }
+
+                if let usage = completion.usage {
+                    self.inputTokens = usage.promptTokens
+                    self.outputTokens = usage.completionTokens
+                    self.totalTokens = usage.totalTokens
+                }
+            } catch {
+                print(String(describing: error))
+            }
+        }
+    }
+
+    private func onStream() {
+        clear()
+
+        let messages = [
+            ChatMessage(role: .system, content: viewModel.systemPrompt),
+            ChatMessage(role: .user, content: prompt)
+        ]
+
+        let options = ChatOptions(temperature: viewModel.temperature)
+
+        Task {
+            do {
+                for try await chunk in viewModel.chat.stream(models: [viewModel.selectedModel, fallbackModel], messages: messages, options: options) {
+                    if let content = chunk.choices.first?.delta.content {
+                        self.response += content
+                    }
+
+                    if let usage = chunk.usage {
+                        self.inputTokens = usage.promptTokens ?? 0
+                        self.outputTokens = usage.completionTokens ?? 0
+                        self.totalTokens = usage.totalTokens ?? 0
+                    }
+                }
+            } catch {
+                print(String(describing: error))
+            }
+        }
+    }
+
+    private func clear() {
+        response = ""
+        inputTokens = 0
+        outputTokens = 0
+        totalTokens = 0
+    }
+}

README.md

@@ -99,6 +99,34 @@ let task = Task {
 task.cancel()
 ```
 
+#### Using Fallback Models (OpenRouter only)
+
+```swift
+Task {
+    do {
+        let completion = try await chat.send(models: ["openai/gpt-4o", "mistralai/mixtral-8x7b-instruct"], messages: messages)
+
+        print(completion.choices.first?.message.content ?? "No response")
+    } catch {
+        print(String(describing: error))
+    }
+}
+
+Task {
+    do {
+        for try await chunk in chat.stream(models: ["openai/gpt-4o", "mistralai/mixtral-8x7b-instruct"], messages: messages) {
+            if let content = chunk.choices.first?.delta.content {
+                print(content, terminator: "")
+            }
+        }
+    } catch {
+        print(String(describing: error))
+    }
+}
+```
+
+> **Note**: Fallback model functionality is only supported when using OpenRouter. If you use the fallback models method (`send(models:)` or `stream(models:)`) with other providers, only the first model in the array will be used, and the rest will be ignored. To learn more about fallback models, check out the [OpenRouter documentation](https://openrouter.ai/docs/model-routing).
+
 ### Advanced Usage
 
 #### Vision

Sources/LLMChatOpenAI/Documentation.docc/Documentation.md

@@ -70,6 +70,34 @@ let task = Task {
 task.cancel()
 ```
 
+#### Using Fallback Models (OpenRouter only)
+
+```swift
+Task {
+    do {
+        let completion = try await chat.send(models: ["openai/gpt-4o", "mistralai/mixtral-8x7b-instruct"], messages: messages)
+
+        print(completion.choices.first?.message.content ?? "No response")
+    } catch {
+        print(String(describing: error))
+    }
+}
+
+Task {
+    do {
+        for try await chunk in chat.stream(models: ["openai/gpt-4o", "mistralai/mixtral-8x7b-instruct"], messages: messages) {
+            if let content = chunk.choices.first?.delta.content {
+                print(content, terminator: "")
+            }
+        }
+    } catch {
+        print(String(describing: error))
+    }
+}
+```
+
+> **Note**: Fallback model functionality is only supported when using OpenRouter. If you use the fallback models method (`send(models:)` or `stream(models:)`) with other providers, only the first model in the array will be used, and the rest will be ignored. To learn more about fallback models, check out the [OpenRouter documentation](https://openrouter.ai/docs/model-routing).
+
 ### Advanced Usage
 
 #### Vision