/*
 * algorithm.cpp, part of VCMI engine
 *
 * Authors: listed in file AUTHORS in main folder
 *
 * License: GNU General Public License v2.0 or later
 * Full text of license available in license.txt file, in main folder
 *
 */
#include "StdInc.h"

#include "algorithm.h"

double Algorithm::distance(double x1, double y1, double x2, double y2)
{
    return std::sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2)) + 1e-9;
}

bool Algorithm::edgesIntersect(const Node& a, const Node& b, const Node& c, const Node& d)
{
    auto cross = [](double x1, double y1, double x2, double y2) {
        return x1 * y2 - y1 * x2;
    };

    double dx1 = b.x - a.x, dy1 = b.y - a.y;
    double dx2 = d.x - c.x, dy2 = d.y - c.y;

    double delta = cross(dx1, dy1, dx2, dy2);
    if (std::abs(delta) < 1e-10) return false; // Parallel

    // Compute intersection
    double s = cross(c.x - a.x, c.y - a.y, dx2, dy2) / delta;
    double t = cross(c.x - a.x, c.y - a.y, dx1, dy1) / delta;

    return s > 0 && s < 1 && t > 0 && t < 1;
}

void Algorithm::forceDirectedLayout(std::vector<Node> & nodes, const std::vector<Edge> & edges, int iterations, double width, double height)
{
    const double area = width * height;
    const double k = std::sqrt(area / nodes.size());

    for (int it = 0; it < iterations; ++it)
    {
        // Reset forces
        for (auto& node : nodes)
            node.dx = node.dy = 0;

        // Repulsive forces
        for (size_t i = 0; i < nodes.size(); ++i)
        {
            for (size_t j = i + 1; j < nodes.size(); ++j)
            {
                double dx = nodes[i].x - nodes[j].x;
                double dy = nodes[i].y - nodes[j].y;
                double dist = distance(nodes[i].x, nodes[i].y, nodes[j].x, nodes[j].y);
                double force = (k * k) / dist;

                nodes[i].dx += (dx / dist) * force;
                nodes[i].dy += (dy / dist) * force;
                nodes[j].dx -= (dx / dist) * force;
                nodes[j].dy -= (dy / dist) * force;
            }
        }

        // Attractive forces
        for (const auto& edge : edges)
        {
            Node& u = nodes[edge.from];
            Node& v = nodes[edge.to];
            double dx = u.x - v.x;
            double dy = u.y - v.y;
            double dist = distance(u.x, u.y, v.x, v.y);
            double force = (dist * dist) / k;

            double fx = (dx / dist) * force;
            double fy = (dy / dist) * force;

            u.dx -= fx;
            u.dy -= fy;
            v.dx += fx;
            v.dy += fy;
        }

        // Edge crossing penalty
        for (size_t i = 0; i < edges.size(); ++i) {
            for (size_t j = i + 1; j < edges.size(); ++j) {
                const Edge& e1 = edges[i];
                const Edge& e2 = edges[j];

                if (e1.from == e2.from || e1.from == e2.to ||
                    e1.to == e2.from || e1.to == e2.to)
                    continue; // Skip if they share nodes

                Node& a = nodes[e1.from];
                Node& b = nodes[e1.to];
                Node& c = nodes[e2.from];
                Node& d = nodes[e2.to];

                if (edgesIntersect(a, b, c, d)) {
                    double strength = 0.05;

                    a.dx += strength * (a.x - c.x);
                    a.dy += strength * (a.y - c.y);
                    b.dx += strength * (b.x - d.x);
                    b.dy += strength * (b.y - d.y);
                    c.dx += strength * (c.x - a.x);
                    c.dy += strength * (c.y - a.y);
                    d.dx += strength * (d.x - b.x);
                    d.dy += strength * (d.y - b.y);
                }
            }
        }

        // Apply displacement
        for (auto& node : nodes)
        {
            node.x += std::max(-5.0, std::min(5.0, node.dx));
            node.y += std::max(-5.0, std::min(5.0, node.dy));

            // Keep within bounds
            node.x = std::min(width, std::max(0.0, node.x));
            node.y = std::min(height, std::max(0.0, node.y));
        }
    }

    for (auto& node : nodes)
    {
        // Center around 0
        node.x -= width / 2;
        node.y -= height / 2;
    }
}