#include "graph.hpp"
#include <algorithm>
#include <iostream>
#include <random>
#include <vector>

//
// Assumes degree sequence does NOT contain any zeroes!
//
// method2 = true  -> take highest degree and finish its pairing completely
// method2 = false -> take new highest degree after every pairing
template <typename RNG>
bool constrainedConfigurationModel(DegreeSequence& ds, Graph& g, RNG& rng, bool method2) {
    // Similar to Havel-Hakimi but instead of pairing up with the highest ones
    // that remain, simply pair up with random ones
    unsigned int n = ds.size();

    // degree, vertex index
    std::vector<std::pair<unsigned int, unsigned int>> degrees(n);
    for (unsigned int i = 0; i < n; ++i) {
        degrees[i].first = ds[i];
        degrees[i].second = i;
    }

    std::vector<decltype(degrees.begin())> available;
    available.reserve(n);

    // Clear the graph
    g.reset(n);

    while (!degrees.empty()) {
        std::shuffle(degrees.begin(), degrees.end(), rng);
        // Get the highest degree:
        // If there are multiple highest ones, we pick a random one,
        // ensured by the shuffle.
        // The shuffle is needed anyway for the remaining part
        unsigned int dmax = 0;
        auto uIter = degrees.begin();
        for (auto iter = degrees.begin(); iter != degrees.end(); ++iter) {
            if (iter->first >= dmax) {
                dmax = iter->first;
                uIter = iter;
            }
        }

        if (dmax > degrees.size() - 1)
            return false;

        if (dmax == 0) {
            std::cerr << "ERROR 1 in CCM.\n";
        }

        unsigned int u = uIter->second;

        if (method2) {
            // Take the highest degree out of the vector
            degrees.erase(uIter);

            // Now assign randomly to the remaining vertices
            // Since its shuffled, we can pick the first 'dmax' ones
            auto vIter = degrees.begin();
            while (dmax--) {
                if (vIter->first == 0)
                    std::cerr << "ERROR in CCM2.\n";
                if (!g.addEdge({u, vIter->second}))
                    std::cerr << "ERROR. Could not add edge in CCM2.\n";
                vIter->first--;
                if (vIter->first == 0)
                    vIter = degrees.erase(vIter);
                else
                    vIter++;
            }
        } else {
            // Pair with a random vertex that is not u itself and to which
            // u has not paired yet!
            available.clear();
            for (auto iter = degrees.begin(); iter != degrees.end(); ++iter) {
                if (iter->second != u && !g.hasEdge({u, iter->second}))
                    available.push_back(iter);
            }
            if (available.empty())
                return false;
            std::uniform_int_distribution<> distr(0, available.size() - 1);
            auto vIter = available[distr(rng)];
            // pair u to v
            if (vIter->first == 0)
                std::cerr << "ERROR 2 in CCM1.\n";
            if (!g.addEdge({u, vIter->second}))
                std::cerr << "ERROR. Could not add edge in CCM1.\n";
            // Purge anything with degree zero
            // Be careful with invalidating the other iterator!
            // Degree of u is always greater or equal to the degree of v
            if (dmax == 1) {
                // Remove both
                // Erasure invalidates all iterators AFTER the erased one
                if (vIter > uIter) {
                    degrees.erase(vIter);
                    degrees.erase(uIter);
                } else {
                    degrees.erase(uIter);
                    degrees.erase(vIter);
                }
            } else {
                // Remove only v if it reaches zero
                uIter->first--;
                vIter->first--;
                if (vIter->first == 0)
                    degrees.erase(vIter);
            }
            //degrees.erase(std::remove_if(degrees.begin(), degrees.end(),
            //                             [](auto x) { return x.first == 0; }));
        }
    }
    return true;
}