Added java implementation for imagen

Author: David Motsonashvili

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/java/ImageModelFutures.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2025 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.firebase.vertexai.java
+
+import androidx.concurrent.futures.SuspendToFutureAdapter
+import com.google.common.util.concurrent.ListenableFuture
+import com.google.firebase.vertexai.ImageModel
+import com.google.firebase.vertexai.type.ImagenGCSImage
+import com.google.firebase.vertexai.type.ImagenGenerationConfig
+import com.google.firebase.vertexai.type.ImagenGenerationResponse
+import com.google.firebase.vertexai.type.ImagenInlineImage
+
+/**
+ * Wrapper class providing Java compatible methods for [ImageModel].
+ *
+ * @see [ImageModel]
+ */
+public abstract class ImageModelFutures internal constructor() {
+  /**
+   * Generates an image, returning the result directly to the caller.
+   *
+   * @param prompt The main text prompt from which the image is generated.
+   * @param config contains secondary image generation parameters.
+   */
+  public abstract fun generateImage(
+    prompt: String,
+    config: ImagenGenerationConfig?,
+  ): ListenableFuture<ImagenGenerationResponse<ImagenInlineImage>>
+
+  /**
+   * Generates an image, storing the result in Google Cloud Storage and returning a URL
+   *
+   * @param prompt The main text prompt from which the image is generated.
+   * @param gcsUri Specifies the GCS bucket in which to store the image.
+   * @param config contains secondary image generation parameters.
+   */
+  public abstract fun generateImage(
+    prompt: String,
+    gcsUri: String,
+    config: ImagenGenerationConfig?,
+  ): ListenableFuture<ImagenGenerationResponse<ImagenGCSImage>>
+
+  /** Returns the [ImageModel] object wrapped by this object. */
+  public abstract fun getImageModel(): ImageModel
+
+  private class FuturesImpl(private val model: ImageModel) : ImageModelFutures() {
+    override fun generateImage(
+      prompt: String,
+      config: ImagenGenerationConfig?,
+    ): ListenableFuture<ImagenGenerationResponse<ImagenInlineImage>> =
+      SuspendToFutureAdapter.launchFuture { model.generateImage(prompt, config) }
+
+    override fun generateImage(
+      prompt: String,
+      gcsUri: String,
+      config: ImagenGenerationConfig?,
+    ): ListenableFuture<ImagenGenerationResponse<ImagenGCSImage>> =
+      SuspendToFutureAdapter.launchFuture { model.generateImage(prompt, gcsUri, config) }
+
+    override fun getImageModel(): ImageModel = model
+  }
+
+  public companion object {
+
+    /** @return a [ImageModelFutures] created around the provided [ImageModel] */
+    @JvmStatic public fun from(model: ImageModel): ImageModelFutures = FuturesImpl(model)
+  }
+}