Add a code snippet for function calling (#187)

samples/FunctionCalling.swift

@@ -0,0 +1,109 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import GoogleGenerativeAI
+import XCTest
+
+// Set up your API Key
+// ====================
+// To use the Gemini API, you'll need an API key. To learn more, see the "Set up your API Key"
+// section in the Gemini API quickstart:
+// https://ai.google.dev/gemini-api/docs/quickstart?lang=swift#set-up-api-key
+
+@available(iOS 15.0, macOS 11.0, macCatalyst 15.0, *)
+final class FunctionCallingSnippets: XCTestCase {
+  override func setUpWithError() throws {
+    try XCTSkipIf(
+      APIKey.default.isEmpty,
+      "`\(APIKey.apiKeyEnvVar)` environment variable not set."
+    )
+  }
+
+  func testFunctionCalling() async throws {
+    // [BEGIN function_calling]
+    // Calls a hypothetical API to control a light bulb and returns the values that were set.
+    func controlLight(brightness: Double, colorTemperature: String) -> JSONObject {
+      return ["brightness": .number(brightness), "colorTemperature": .string(colorTemperature)]
+    }
+
+    let generativeModel =
+      GenerativeModel(
+        // Use a model that supports function calling, like a Gemini 1.5 model
+        name: "gemini-1.5-flash",
+        // Access your API key from your on-demand resource .plist file (see "Set up your API key"
+        // above)
+        apiKey: APIKey.default,
+        tools: [Tool(functionDeclarations: [
+          FunctionDeclaration(
+            name: "controlLight",
+            description: "Set the brightness and color temperature of a room light.",
+            parameters: [
+              "brightness": Schema(
+                type: .number,
+                format: "double",
+                description: "Light level from 0 to 100. Zero is off and 100 is full brightness."
+              ),
+              "colorTemperature": Schema(
+                type: .string,
+                format: "enum",
+                description: "Color temperature of the light fixture.",
+                enumValues: ["daylight", "cool", "warm"]
+              ),
+            ],
+            requiredParameters: ["brightness", "colorTemperature"]
+          ),
+        ])]
+      )
+
+    let chat = generativeModel.startChat()
+
+    let prompt = "Dim the lights so the room feels cozy and warm."
+
+    // Send the message to the model.
+    let response1 = try await chat.sendMessage(prompt)
+
+    // Check if the model responded with a function call.
+    // For simplicity, this sample uses the first function call found.
+    guard let functionCall = response1.functionCalls.first else {
+      fatalError("Model did not respond with a function call.")
+    }
+    // Print an error if the returned function was not declared
+    guard functionCall.name == "controlLight" else {
+      fatalError("Unexpected function called: \(functionCall.name)")
+    }
+    // Verify that the names and types of the parameters match the declaration
+    guard case let .number(brightness) = functionCall.args["brightness"] else {
+      fatalError("Missing argument: brightness")
+    }
+    guard case let .string(colorTemperature) = functionCall.args["colorTemperature"] else {
+      fatalError("Missing argument: colorTemperature")
+    }
+
+    // Call the executable function named in the FunctionCall with the arguments specified in the
+    // FunctionCall and let it call the hypothetical API.
+    let apiResponse = controlLight(brightness: brightness, colorTemperature: colorTemperature)
+
+    // Send the API response back to the model so it can generate a text response that can be
+    // displayed to the user.
+    let response2 = try await chat.sendMessage([ModelContent(
+      role: "function",
+      parts: [.functionResponse(FunctionResponse(name: "controlLight", response: apiResponse))]
+    )])
+
+    if let text = response2.text {
+      print(text)
+    }
+    // [END function_calling]
+  }
+}