/**
 * @license
 * Copyright 2020 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 {Softmax, SoftmaxAttrs} from '../kernel_names';
import {GradConfig, NamedAttrMap} from '../kernel_registry';
import {mul} from '../ops/mul';
import {sub} from '../ops/sub';
import {sum} from '../ops/sum';
import {Tensor} from '../tensor';

export const softmaxGradConfig: GradConfig = {
  kernelName: Softmax,
  outputsToSave: [true],
  gradFunc: (dy: Tensor, saved: Tensor[], attrs: NamedAttrMap) => {
    const [y] = saved;
    const {dim} = attrs as {} as SoftmaxAttrs;
    const keepDims = true;

    const dyTimesY = mul(dy, y);
    return {
      logits: () => sub(dyTimesY, mul(sum(dyTimesY, [dim], keepDims), y))
    };
  }
};