package BackendManagers;

import BackendManagers.Interfaces.WorldBuildingUtilInterface;
import CommonUtils.MST;
import CommonUtils.UsefulContainers.iPair;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;

/**
 * Contains helpful functions for dealing with our world building. Will not be integrated with
 *   production classes, as it is a tool for helping us with content creation.
 *
 * <bold>251 students: you may use any of the data structures you have previously created, but may not use
 *   any Java util library except List/ArrayList and java.util.stream.* .</bold>
 */
public class WorldBuildingUtil implements WorldBuildingUtilInterface {
    private static double euclideanDistance(iPair p, iPair q) {
        return Math.sqrt(Math.pow(p.a - q.a, 2) + Math.pow(p.b - q.b, 2));
    }

    /**
     * Selects roads per the specifications (minimum cost to connect all cities).
     *
     * @param filename file to read input from
     * @return list of roads, per the specifications
     */
    @Override
    public List<CityEdge> getMinimumConnectingRoads(String filename) {
        try {
            BufferedReader bf = new BufferedReader(new FileReader(filename));

            int C = Integer.parseInt(bf.readLine());
            double[][] weights = new double[C][C];
            iPair[] coords = new iPair[C];

            // Read in city coordinates
            for (int i = 0; i < C; i++) {
                String[] in = bf.readLine().split(" ");
                int a = Integer.parseInt(in[0]);
                int b = Integer.parseInt(in[1]);

                iPair coord = new iPair(a, b);
                coords[i] = coord;

                // Update distances to all previous cities
                for (int j = 0; j < i; j++) {
                    double dist = euclideanDistance(coords[i], coords[j]);
                    weights[i][j] = dist;
                    weights[j][i] = dist;
                }
            }

            return MST.denseMST(weights)
                .stream()
                .map(p -> new CityEdge(coords[p.a], coords[p.b]))
                .toList();

        } catch (IOException e) {
            //This should never happen... uh oh o.o
            System.err.println("ATTENTION TAs: Couldn't find test file: \"" + filename + "\":: " + e.getMessage());
            System.exit(1);
        }
        return null;
    }
}