/**
 * @license
 * Copyright 2018 Google Inc. 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 {Tensor} from '../tensor';
import {convertToTensor} from '../tensor_util_env';
import {TensorLike} from '../types';
import * as util from '../util';
import * as axis_util from './axis_util';
import {op} from './operation';

/**
 * Transposes the `tf.Tensor`. Permutes the dimensions according to `perm`.
 *
 * The returned `tf.Tensor`'s dimension `i` will correspond to the input
 * dimension `perm[i]`. If `perm` is not given, it is set to `[n-1...0]`,
 * where `n` is the rank of the input `tf.Tensor`. Hence by default, this
 * operation performs a regular matrix transpose on 2-D input `tf.Tensor`s.
 *
 * ```js
 * const a = tf.tensor2d([1, 2, 3, 4, 5, 6], [2, 3]);
 *
 * a.transpose().print();  // or tf.transpose(a)
 * ```
 *
 * @param x The tensor to transpose.
 * @param perm The permutation of the dimensions of a.
 */
/** @doc {heading: 'Operations', subheading: 'Matrices'} */
function transpose_<T extends Tensor>(x: T|TensorLike, perm?: number[]): T {
  const $x = convertToTensor(x, 'x', 'transpose');

  if (perm == null) {
    perm = $x.shape.map((s, i) => i).reverse();
  }
  util.assert(
      $x.rank === perm.length,
      () => `Error in transpose: rank of input ${$x.rank} ` +
          `must match length of perm ${perm}.`);
  perm.forEach(axis => {
    util.assert(
        axis >= 0 && axis < $x.rank,
        () => `All entries in 'perm' must be between 0 and ${$x.rank - 1}` +
            ` but got ${perm}`);
  });

  if ($x.rank <= 1) {
    return $x.clone();
  }

  const der = (dy: T) => {
    const undoPerm = axis_util.getUndoAxesPermutation(perm);
    return {$x: () => dy.transpose(undoPerm)};
  };
  return ENGINE.runKernel(backend => backend.transpose($x, perm), {$x}, der);
}

export const transpose = op({transpose_});