/**
 * @license
 * Copyright 2021 Google LLC. All Rights Reserved.
 * 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 * as tflite from '@tensorflow/tfjs-tflite';
import {TaskModelLoader} from '../../task_model';
import {Runtime, Task, TFLiteCustomModelCommonLoadingOption} from '../common';
import {QuestionAnswererTFLite} from './tflite_common';

// The global namespace type.
type TFLiteNS = typeof tflite;

/** Loading options. */
export interface QACustomModelTFLiteLoadingOptions extends
    TFLiteCustomModelCommonLoadingOption {}

/**
 * Inference options.
 *
 * TODO: placeholder for now.
 */
export interface QACustomModelTFLiteInferenceOptions {}

/** Loader for custom Q&A TFLite model. */
export class QuestionAnswerCustomModelTFLiteLoader extends TaskModelLoader<
    TFLiteNS, QACustomModelTFLiteLoadingOptions, QACustomModelTFLite> {
  readonly metadata = {
    name: 'Question&Answer with TFLite models',
    description: 'A QuestionAnswerer backed by the TFLite Task Library. ' +
        'It can work with any models that meet the ' +
        '<a href="https://www.tensorflow.org/lite/inference_with_metadata/' +
        'task_library/bert_question_answerer#model_compatibility_requirements" ' +
        'target="_blank">model requirements</a>. Try models from this ' +
        '<a href="https://tfhub.dev/tensorflow/collections/lite/task-library/' +
        'bert-question-answerer/1" target="_blank">collection</a>.',
    resourceUrls: {
      'TFLite task library': 'https://www.tensorflow.org/lite/' +
          'inference_with_metadata/task_library/overview',
    },
    runtime: Runtime.TFLITE,
    version: '0.0.1-alpha.3',
    supportedTasks: [Task.QUESTION_AND_ANSWER],
  };
  readonly packageUrls =
      [[`https://cdn.jsdelivr.net/npm/@tensorflow/tfjs-tflite@${
          this.metadata.version}/dist/tf-tflite.min.js`]];
  readonly sourceModelGlobalNamespace = 'tflite';

  protected async transformSourceModel(
      sourceModelGlobal: TFLiteNS,
      loadingOptions?: QACustomModelTFLiteLoadingOptions):
      Promise<QACustomModelTFLite> {
    const tfliteQa = await sourceModelGlobal.BertQuestionAnswerer.create(
        loadingOptions.model);
    return new QACustomModelTFLite(tfliteQa);
  }
}

/**
 * A custom TFLite Q&A model loaded from a model url or an `ArrayBuffer` in
 * memory.
 *
 * The underlying question answerer is built on top of the [TFLite Task
 * Library](https://www.tensorflow.org/lite/inference_with_metadata/task_library/overview).
 * As a result, the custom model needs to meet the [metadata
 * requirements](https://www.tensorflow.org/lite/inference_with_metadata/task_library/bert_question_answerer#model_compatibility_requirements).
 *
 * Usage:
 *
 * ```js
 * // Load the model from a custom url.
 * const model = await tfTask.QuestionAndAnswer.CustomModel.TFLite.load({
 *   model:
 * 'https://tfhub.dev/tensorflow/lite-model/mobilebert/1/metadata/1?lite-format=tflite',
 * });
 *
 * // Run inference with question and context.
 * const result = await model.predict(question, context);
 * console.log(result.answers);
 *
 * // Clean up.
 * model.cleanUp();
 * ```
 *
 * Refer to `tfTask.QuestionAnswerer` for the `predict` and `cleanUp` method.
 *
 * @docextratypes [
 *   {description: 'Options for `load`', symbol:
 * 'QACustomModelTFLiteLoadingOptions'},
 *   {description: 'Options for `predict`', symbol:
 * 'QACustomModelTFLiteInferenceOptions'}
 * ]
 *
 *
 * @doc {heading: 'Question & Answer', subheading: 'Models'}
 */
export class QACustomModelTFLite extends
    QuestionAnswererTFLite<QACustomModelTFLiteInferenceOptions> {}

export const qaCustomModelTfliteLoader =
    new QuestionAnswerCustomModelTFLiteLoader();