// ==========================================================================
//                 SeqAn - The Library for Sequence Analysis
// ==========================================================================
// Copyright (c) 2006-2024, Knut Reinert, FU Berlin
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// ==========================================================================
// Author: Tobias Raussch <rausch@embl.de>
// ==========================================================================
// Implementation of Topological-Sort algorithm.
// ==========================================================================

#ifndef INCLUDE_SEQAN_GRAPH_ALGORITHMS_TOPOLOGICAL_SORT_H_
#define INCLUDE_SEQAN_GRAPH_ALGORITHMS_TOPOLOGICAL_SORT_H_

namespace seqan2 {

// ============================================================================
// Forwards
// ============================================================================

// ============================================================================
// Tags, Classes, Enums
// ============================================================================

// ============================================================================
// Metafunctions
// ============================================================================

// ============================================================================
// Functions
// ============================================================================

// ----------------------------------------------------------------------------
// Function topologicalSort()
// ----------------------------------------------------------------------------

/*!
 * @fn topologicalSort
 * @headerfile <seqan/graph_algorithms.h>
 * @brief Performs a topological sort on a directed acyclic graph (DAG).
 *
 * @signature void topologicalSort(topSort, g);
 *
 * @param[out] topSort A topological ordering of the vertices. Types: String.
 * @param[in]  g       A directed acyclic graph. Types: Directed Graph
 *
 * A topological sort is a linear ordering of all its vertices such that if the graph contains an edge (u,v) then u
 * appears before v in the ordering.
 *
 * @section Example
 *
 * @include demos/dox/graph_algorithms/topological_sort.cpp
 *
 * @include demos/dox/graph_algorithms/topological_sort.cpp.stdout
 */
template <typename TSpec, typename TVertexDescriptor>
void topologicalSort(String<TVertexDescriptor> & topSort,
                     Graph<TSpec> const & g)
{
    typedef typename Size<Graph<TSpec> >::Type TSize;

    // Variable definition.
    String<TSize> predMap;
    String<TSize> discoveryTimeMap;
    String<TSize> finishingTimeMap;

    // Perform DFS.
    depthFirstSearch(predMap, discoveryTimeMap, finishingTimeMap, g);
    SEQAN_ASSERT_EQ(numVertices(g), length(predMap));
    SEQAN_ASSERT_EQ(numVertices(g), length(discoveryTimeMap));
    SEQAN_ASSERT_EQ(numVertices(g), length(finishingTimeMap));

    // Order vertices.
    typedef std::pair<TSize, TVertexDescriptor> TTimeVertexPair;
    std::priority_queue<TTimeVertexPair> q;
    typedef typename Iterator<Graph<TSpec>, VertexIterator>::Type TVertexIterator;
    TVertexIterator it(g);
    for (; !atEnd(it); goNext(it))
        q.push(std::make_pair(getProperty(finishingTimeMap, getValue(it)), getValue(it)));

    // Create topological order.
    resize(topSort, numVertices(g));
    TSize count = 0;
    while (!q.empty())
    {
        assignValue(topSort, count, q.top().second);
        q.pop();
        ++count;
    }
    SEQAN_ASSERT_EQ(length(topSort), numVertices(g));
}

}  // namespace seqan2

#endif  // #ifndef INCLUDE_SEQAN_GRAPH_ALGORITHMS_TOPOLOGICAL_SORT_H_
