/**
 * @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 {ENGINE} from '../engine';
import {Select, SelectInputs} from '../kernel_names';
import {Tensor} from '../tensor';
import {NamedTensorMap} from '../tensor_types';
import {convertToTensor} from '../tensor_util_env';
import {TensorLike} from '../types';
import {assert, assertShapesMatch} from '../util';

import {broadcastTo} from './broadcast_to';
import {assertAndGetBroadcastShape} from './broadcast_util';
import {op} from './operation';

/**
 * Returns the elements, either `a` or `b` depending on the `condition`.
 *
 * If the condition is true, select from `a`, otherwise select from `b`.
 *
 * ```js
 * const cond = tf.tensor1d([false, false, true], 'bool');
 * const a = tf.tensor1d([1 , 2, 3]);
 * const b = tf.tensor1d([-1, -2, -3]);
 *
 * a.where(cond, b).print();
 * ```
 *
 * @param condition The input condition. Must be of dtype bool.
 * @param a If `condition` is rank 1, `a` may have a higher rank but
 *     its first dimension must match the size of `condition`.
 * @param b A tensor with the same dtype as `a` and with shape that is
 *     compatible with `a`.
 * @return A tensor with same dtype as `a` and `b`, and shape that is
 *     broadcastable from `a` and `b`.
 *
 * @doc {heading: 'Operations', subheading: 'Logical'}
 */
function where_<T extends Tensor>(
    condition: Tensor|TensorLike, a: T|TensorLike, b: T|TensorLike): T {
  const $a = convertToTensor(a, 'a', 'where');
  const $b = convertToTensor(b, 'b', 'where');
  const $condition = convertToTensor(condition, 'condition', 'where', 'bool');
  // TODO: move this logic to forward function when the broadcastTo op is
  // implemented in WASM.
  // Find the broadcastable shape for $a and $b.
  const broadcastShape = assertAndGetBroadcastShape($a.shape, $b.shape);
  const $broadcastedA = broadcastTo($a, broadcastShape);
  const $broadcastedB = broadcastTo($b, broadcastShape);
  if ($condition.rank === 1) {
    // If condition rank is 1, then the first dimension must match the size of
    // condition.
    assert(
        $condition.shape[0] === $a.shape[0],
        () => 'The first dimension of `a` must match the size of `condition`.');
  }

  if ($condition.rank !== 1) {
    // A must have the same shape as condition.
    assertShapesMatch(
        $condition.shape, $broadcastedB.shape, 'Error in where: ');
  }

  const inputs: SelectInputs = {
    condition: $condition,
    t: $broadcastedA,
    e: $broadcastedB
  };
  return ENGINE.runKernel(Select, inputs as unknown as NamedTensorMap);
}

export const where = op({where_});