/*!
 *  Copyright (c) 2019 by Contributors
 * \file dgl/samplinig/randomwalks.h
 * \brief Random walk functions.
 */
#ifndef DGL_SAMPLING_RANDOMWALKS_H_
#define DGL_SAMPLING_RANDOMWALKS_H_

#include <dgl/base_heterograph.h>
#include <dgl/array.h>
#include <vector>
#include <utility>
#include <tuple>

namespace dgl {

namespace sampling {

/*!
 * \brief Metapath-based random walk.
 * \param hg The heterograph.
 * \param seeds A 1D array of seed nodes, with the type the source type of the first
 *        edge type in the metapath.
 * \param metapath A 1D array of edge types representing the metapath.
 * \param prob A vector of 1D float arrays, indicating the transition probability of
 *        each edge by edge type.  An empty float array assumes uniform transition.
 * \return A pair of
 *         1. One 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *            paths that terminated early are padded with -1.
 *         2. One 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *            paths that terminated early are padded with -1.
 *         3. One 1D array of shape (len(metapath) + 1) with node type IDs.
 */
std::tuple<IdArray, IdArray, TypeArray> RandomWalk(
    const HeteroGraphPtr hg,
    const IdArray seeds,
    const TypeArray metapath,
    const std::vector<FloatArray> &prob);

/*!
 * \brief Metapath-based random walk with restart probability.
 * \param hg The heterograph.
 * \param seeds A 1D array of seed nodes, with the type the source type of the first
 *        edge type in the metapath.
 * \param metapath A 1D array of edge types representing the metapath.
 * \param prob A vector of 1D float arrays, indicating the transition probability of
 *        each edge by edge type.  An empty float array assumes uniform transition.
 * \param restart_prob Restart probability
 * \return A pair of
 *         1. One 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *            paths that terminated early are padded with -1.
 *         2. One 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *            paths that terminated early are padded with -1.
 *         3. One 1D array of shape (len(metapath) + 1) with node type IDs.
 */
std::tuple<IdArray, IdArray, TypeArray> RandomWalkWithRestart(
    const HeteroGraphPtr hg,
    const IdArray seeds,
    const TypeArray metapath,
    const std::vector<FloatArray> &prob,
    double restart_prob);

/*!
 * \brief Metapath-based random walk with stepwise restart probability.  Useful
 *        for PinSAGE-like models.
 * \param hg The heterograph.
 * \param seeds A 1D array of seed nodes, with the type the source type of the first
 *        edge type in the metapath.
 * \param metapath A 1D array of edge types representing the metapath.
 * \param prob A vector of 1D float arrays, indicating the transition probability of
 *        each edge by edge type.  An empty float array assumes uniform transition.
 * \param restart_prob Restart probability array which has the same number of elements
 *        as \c metapath, indicating the probability to terminate after transition.
 * \return A pair of
 *         1. One 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *            paths that terminated early are padded with -1.
 *         2. One 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *            paths that terminated early are padded with -1.
 *         3. One 1D array of shape (len(metapath) + 1) with node type IDs.
 */
std::tuple<IdArray, IdArray, TypeArray> RandomWalkWithStepwiseRestart(
    const HeteroGraphPtr hg,
    const IdArray seeds,
    const TypeArray metapath,
    const std::vector<FloatArray> &prob,
    FloatArray restart_prob);

};  // namespace sampling

};  // namespace dgl

#endif  // DGL_SAMPLING_RANDOMWALKS_H_
