/**
 * @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 {Unpack, UnpackAttrs, UnpackInputs} from '../kernel_names';
import {NamedAttrMap} from '../kernel_registry';
import {Tensor} from '../tensor';
import {NamedTensorMap} from '../tensor_types';
import {convertToTensor} from '../tensor_util_env';
import {TensorLike} from '../types';
import * as util from '../util';

import {op} from './operation';

/**
 * Unstacks a `tf.Tensor` of rank-`R` into a list of rank-`(R-1)` `tf.Tensor`s.
 *
 * ```js
 * const a = tf.tensor2d([1, 2, 3, 4], [2, 2]);
 *
 * tf.unstack(a).forEach(tensor => tensor.print());
 * ```
 *
 * @param x A tensor object.
 * @param axis The axis to unstack along. Defaults to 0 (the first dim).
 *
 * @doc {heading: 'Tensors', subheading: 'Slicing and Joining'}
 */
function unstack_(x: Tensor|TensorLike, axis = 0): Tensor[] {
  const $x = convertToTensor(x, 'x', 'unstack', 'string_or_numeric');
  util.assert(
      axis >= -$x.shape.length && axis < $x.shape.length,
      () =>
          `Axis = ${axis} is not in [-${$x.shape.length}, ${$x.shape.length})`);

  const inputs: UnpackInputs = {value: $x};
  const attrs: UnpackAttrs = {axis};

  return ENGINE.runKernel(
      Unpack, inputs as {} as NamedTensorMap, attrs as {} as NamedAttrMap);
}

export const unstack = op({unstack_});