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

// Its assumed that u,v are distinct.
// Check if all four vertices are distinct
bool edgeConflicts(const Edge &e1, const Edge &e2) {
    return (e1.u == e2.u || e1.u == e2.v || e1.v == e2.u || e1.v == e2.v);
}

class SwitchChain {
  public:
    SwitchChain() : mt(std::random_device{}()), permutationDistribution(0, 2) {
        // random_device uses hardware entropy if available
        // std::random_device rd;
        // mt.seed(rd());
    }
    ~SwitchChain() {}

    bool initialize(const Graph &gstart) {
        if (gstart.edgeCount() == 0)
            return false;
        g = gstart;
        edgeDistribution.param(
            std::uniform_int_distribution<>::param_type(0, g.edgeCount() - 1));
        return true;
    }

    bool doMove() {
        Edge e1 = g.getEdge(edgeDistribution(mt));
        Edge e2 = g.getEdge(edgeDistribution(mt));
        // Keep regenerating while conflicting edges
        int timeout = 0;
        while (edgeConflicts(e1, e2)) {
            e1 = g.getEdge(edgeDistribution(mt));
            e2 = g.getEdge(edgeDistribution(mt));
            ++timeout;
            if (timeout % 100 == 0) {
                std::cerr << "Warning: sampled " << timeout
                          << " random edges but they keep conflicting.\n";
            }
        }
        // Consider one of the three possible permutations
        // 1) e1.u - e1.v and e2.u - e2.v (original)
        // 2) e1.u - e2.u and e1.v - e2.v
        // 3) e1.u - e2.v and e1.v - e2.u

        // Note that it might be that these new edges already exist
        // in which case we also reject the move
        // This is checked in exchangeEdges

        int perm = permutationDistribution(mt);
        if (perm == 0) // Original permutation
            return false;
        return g.exchangeEdges(e1, e2, perm == 1);
    }

    Graph g;
    std::mt19937 mt;
    std::uniform_int_distribution<> edgeDistribution;
    std::uniform_int_distribution<> permutationDistribution;
};

int main() {
    Graph g;

    // Generate a random degree sequence
    std::mt19937 gen(std::random_device{}());

    // 50 nodes with average degree 12
    DegreeSequence ds(50);
    std::poisson_distribution<> degDist(7);

    // Try at most 10 times to generate a valid sequence
    bool validGraph = false;
    for (int i = 0; i < 10; ++i) {
        std::generate(ds.begin(), ds.end(),
                      [&degDist, &gen] { return degDist(gen); });
        if (g.createFromDegreeSequence(ds)) {
            validGraph = true;
            break;
        }
    }
    if (!validGraph) {
        std::cerr << "Could not create graph from degree sequence.\n";
        return 1;
    }
    std::sort(ds.begin(), ds.end());

    std::cout << "Degree sequence:";
    for (auto i : ds)
        std::cout << ' ' << i;
    std::cout << std::endl;

    SwitchChain chain;
    if (!chain.initialize(g)) {
        std::cerr << "Could not initialize Markov chain.\n";
        return 1;
    }

    std::ofstream outfile("graphdata.m");
    outfile << '{' << g;

    std::cout << "Starting switch Markov chain" << std::endl;
    int movesDone = 0;
    int movesTotal = 100000;
    for (int i = 0; i < movesTotal; ++i) {
        if (chain.doMove())
            ++movesDone;
        if (i % (movesTotal / 50) == (movesTotal / 50 - 1))
            outfile << ',' << chain.g;
    }
    outfile << '}';

    std::cout << movesDone << '/' << movesTotal << " moves succeeded."
              << std::endl;

    return 0;
}