replaced functionCall with functionCalls (google-gemini#137)

Co-authored-by: David Motsonashvili <davidmotson@google.com>
Co-authored-by: Rodrigo Lazo <rlazo@users.noreply.github.com>

.changes/common/bath-advertisement-attempt-car.json

@@ -0,0 +1 @@
+{"type":"MINOR","changes":["Add GenerateContentResponse#functionCalls and mark GenerateContentResponse#functionCall deprecated"]}

.changes/generativeai/badge-cake-arithmetic-cook.json

@@ -0,0 +1 @@
+{"type":"MINOR","changes":["Add GenerateContentResponse#functionCalls and mark GenerateContentResponse#functionCall deprecated"]}

generativeai/src/main/java/com/google/ai/client/generativeai/type/GenerateContentResponse.kt

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2023 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.
+ */
+
+package com.google.ai.client.generativeai.type
+
+import android.util.Log
+
+/**
+ * Represents a response from the model.
+ *
+ * @property candidates a list of possible responses generated from the model
+ * @property promptFeedback optional feedback for the given prompt. When streaming, it's only
+ *   populated in the first response.
+ */
+class GenerateContentResponse(
+  val candidates: List<Candidate>,
+  val promptFeedback: PromptFeedback?,
+  val usageMetadata: UsageMetadata?
+) {
+  /** Convenience field representing the first text part in the response, if it exists. */
+  val text: String? by lazy { firstPartAs<TextPart>()?.text }
+
+  /** Convenience field representing the first function call part in the request, if it exists */
+  @Deprecated("Use functionCallParts instead", ReplaceWith("functionCallParts"))
+  val functionCall: FunctionCallPart? by lazy { firstPartAs() }
+
+  /** Convenience field to get all the function call parts in the request, if they exist */
+  val functionCalls: List<FunctionCallPart> by lazy {
+    candidates.first().content.parts.filterIsInstance<FunctionCallPart>()
+  }
+
+  /**
+   * Convenience field representing the first function response part in the response, if it exists.
+   */
+  val functionResponse: FunctionResponsePart? by lazy { firstPartAs() }
+
+  private inline fun <reified T : Part> firstPartAs(): T? {
+    if (candidates.isEmpty()) {
+      warn("No candidates were found, but was asked to get a candidate.")
+      return null
+    }
+
+    val (parts, otherParts) = candidates.first().content.parts.partition { it is T }
+    val type = T::class.simpleName ?: "of the part type you asked for"
+
+    if (parts.isEmpty()) {
+      if (otherParts.isNotEmpty()) {
+        warn(
+          "We didn't find any $type, but we did find other part types. Did you ask for the right type?"
+        )
+      }
+
+      return null
+    }
+
+    if (parts.size > 1) {
+      warn("Multiple $type were found, returning the first one.")
+    } else if (otherParts.isNotEmpty()) {
+      warn("Returning the only $type found, but other part types were present as well.")
+    }
+
+    return parts.first() as T
+  }
+
+  private fun warn(message: String) {
+    Log.w("GenerateContentResponse", message)
+  }
+}