/*!
 *  Copyright (c) 2018 by Contributors
 * \file graph/sampling/randomwalks_impl.h
 * \brief DGL sampler - templated implementation definition of random walks
 */

#ifndef DGL_GRAPH_SAMPLING_RANDOMWALKS_RANDOMWALKS_IMPL_H_
#define DGL_GRAPH_SAMPLING_RANDOMWALKS_RANDOMWALKS_IMPL_H_

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

namespace dgl {

using namespace dgl::runtime;
using namespace dgl::aten;

namespace sampling {

namespace impl {

/*!
 * \brief Random walk step function
 */
template<typename IdxType>
using StepFunc = std::function<
  //        ID        Edge ID   terminate?
  std::tuple<dgl_id_t, dgl_id_t, bool>(
      IdxType *,    // node IDs generated so far
      dgl_id_t,     // last node ID
      int64_t)>;    // # of steps

/*!
 * \brief Get the node types traversed by the metapath.
 * \return A 1D array of shape (len(metapath) + 1,) with node type IDs.
 */
template<DGLDeviceType XPU, typename IdxType>
TypeArray GetNodeTypesFromMetapath(
    const HeteroGraphPtr hg,
    const TypeArray metapath);

/*!
 * \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 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *         paths that terminated early are padded with -1.
 *         A 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *         paths that terminated early are padded with -1.
 * \note This function should be called together with GetNodeTypesFromMetapath to
 *       determine the node type of each node in the random walk traces.
 */
template<DGLDeviceType XPU, typename IdxType>
std::pair<IdArray, IdArray> 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 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *         paths that terminated early are padded with -1.
 *         A 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *         paths that terminated early are padded with -1.
 * \note This function should be called together with GetNodeTypesFromMetapath to
 *       determine the node type of each node in the random walk traces.
 */
template<DGLDeviceType XPU, typename IdxType>
std::pair<IdArray, IdArray> 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 2D array of shape (len(seeds), len(metapath) + 1) with node IDs.  The
 *         paths that terminated early are padded with -1.
 *         A 2D array of shape (len(seeds), len(metapath)) with edge IDs.  The
 *         paths that terminated early are padded with -1.
 * \note This function should be called together with GetNodeTypesFromMetapath to
 *       determine the node type of each node in the random walk traces.
 */
template<DGLDeviceType XPU, typename IdxType>
std::pair<IdArray, IdArray> RandomWalkWithStepwiseRestart(
    const HeteroGraphPtr hg,
    const IdArray seeds,
    const TypeArray metapath,
    const std::vector<FloatArray> &prob,
    FloatArray restart_prob);

template<DGLDeviceType XPU, typename IdxType>
std::tuple<IdArray, IdArray, IdArray> SelectPinSageNeighbors(
    const IdArray src,
    const IdArray dst,
    const int64_t num_samples_per_node,
    const int64_t k);

};  // namespace impl

};  // namespace sampling

};  // namespace dgl

#endif  // DGL_GRAPH_SAMPLING_RANDOMWALKS_RANDOMWALKS_IMPL_H_
