[Vertex AI] Add POC for initializing function declarations from JSON

Author: andrewheard

FirebaseVertexAI/Sources/FunctionCalling.swift

@@ -48,6 +48,22 @@ public struct FunctionDeclaration {
       nullable: false
     )
   }
+
+  /// Constructs a new `FunctionDeclaration`.
+  ///
+  /// - Parameters:
+  ///   - jsonString: A string representing a function declaration in JSON format; see the [REST
+  ///   documentation]( https://cloud.google.com/vertex-ai/generative-ai/docs/reference/rest/v1/Tool#FunctionDeclaration)
+  ///   for details.
+  public init(jsonString: String) throws {
+    guard let jsonData = jsonString.data(using: .utf8) else {
+      throw DecodingError.dataCorrupted(DecodingError.Context(
+        codingPath: [],
+        debugDescription: "Could not parse JSON string as UTF8."
+      ))
+    }
+    self = try JSONDecoder().decode(Self.self, from: jsonData)
+  }
 }
 
 /// A helper tool that the model may use when generating responses.
@@ -146,7 +162,7 @@ public struct ToolConfig {
 // MARK: - Codable Conformance
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-extension FunctionDeclaration: Encodable {
+extension FunctionDeclaration: Codable {
   enum CodingKeys: String, CodingKey {
     case name
     case description

FirebaseVertexAI/Sources/Types/Internal/DataType.swift

@@ -37,4 +37,4 @@ enum DataType: String {
 
 // MARK: - Codable Conformance
 
-extension DataType: Encodable {}
+extension DataType: Codable {}

FirebaseVertexAI/Sources/Types/Public/Schema.swift

@@ -19,7 +19,7 @@ import Foundation
 /// These types can be objects, but also primitives and arrays. Represents a select subset of an
 /// [OpenAPI 3.0 schema object](https://spec.openapis.org/oas/v3.0.3#schema).
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-public class Schema {
+public final class Schema {
   /// Modifiers describing the expected format of a string `Schema`.
   @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
   public struct StringFormat: EncodableProtoEnum {
@@ -319,7 +319,7 @@ public class Schema {
 // MARK: - Codable Conformance
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-extension Schema: Encodable {
+extension Schema: Codable {
   enum CodingKeys: String, CodingKey {
     case dataType = "type"
     case format

FirebaseVertexAI/Tests/Unit/Snippets/FunctionCallingSnippets.swift

@@ -29,6 +29,27 @@ final class FunctionCallingSnippets: XCTestCase {
     await FirebaseApp.deleteDefaultAppForSnippets()
   }
 
+  func testFunctionDeclaration_jsonString() throws {
+    let json = """
+    {
+      "name": "getWeather",
+      "description": "gets the weather for a requested city",
+      "parameters": {
+        "type": "OBJECT",
+        "properties": {
+          "city": {
+            "type": "STRING"
+          }
+        }
+      }
+    }
+    """
+
+    let functionDeclaration = try FunctionDeclaration(jsonString: json)
+
+    print(functionDeclaration)
+  }
+
   func testFunctionCalling() async throws {
     // This function calls a hypothetical external API that returns
     // a collection of weather information for a given location on a given date.