/* Copyright 2016 The TensorFlow Authors. 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.
==============================================================================*/

package org.tensorflow;

import java.util.Arrays;

/** The possibly partially known shape of a tensor produced by an operation. */
public final class Shape {

  /** Create a Shape representing an unknown number of dimensions. */
  public static Shape unknown() {
    return new Shape(null);
  }

  /** Create a Shape representing a scalar value. */
  public static Shape scalar() {
    return new Shape(new long[0]);
  }

  /**
   * Create a Shape representing an N-dimensional value.
   *
   * <p>Creates a Shape representing an N-dimensional value (N being at least 1), with the provided
   * size for each dimension. A -1 indicates that the size of the corresponding dimension is
   * unknown. For example:
   *
   * <pre>{@code
   * // A 2-element vector.
   * Shape vector = Shape.create(2);
   *
   * // A 2x3 matrix.
   * Shape matrix = Shape.create(2, 3);
   *
   * // A matrix with 4 columns but an unknown number of rows.
   * // This is typically used to indicate the shape of tensors that represent
   * // a variable-sized batch of values. The Shape below might represent a
   * // variable-sized batch of 4-element vectors.
   * Shape batch = Shape.create(-1, 4);
   * }</pre>
   */
  public static Shape make(long firstDimensionSize, long... otherDimensionSizes) {
    long[] shape = new long[otherDimensionSizes.length + 1];
    shape[0] = firstDimensionSize;
    System.arraycopy(otherDimensionSizes, 0, shape, 1, otherDimensionSizes.length);
    return new Shape(shape);
  }

  /**
   * Number of dimensions represented by this shape.
   *
   * @return -1 if the number of dimensions is unknown, 0 if the shape represents a scalar, 1 for a
   *     vector, 2 for a matrix etc.
   */
  public int numDimensions() {
    return shape == null ? -1 : shape.length;
  }

  /**
   * The size of the i-th dimension.
   *
   * @return The size of the requested dimension or -1 if it is unknown.
   */
  public long size(int i) {
    return shape[i];
  }

  /** Succinct description of the shape meant for debugging. */
  @Override
  public String toString() {
    if (shape == null) {
      return "<unknown>";
    }
    return Arrays.toString(shape).replace("-1", "?");
  }

  // Package-private constructor.
  Shape(long[] shape) {
    this.shape = shape;
  }

  // Package-private accessor.
  // The idea is that the public API does not expose the internal array.
  long[] asArray() {
    return shape;
  }

  private long[] shape;
}
