import java.util.LinkedList;
import java.util.Vector;
import java.util.Scanner;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
/**
 * AdjListsDiGraph.java
 * Implements the DiGraph Interface.
 * Uses a Vector of LinkedLists to keep track of the adjacent vertices.
 *
 * @author (SK)
 * @version 2022.11.15  
 * SK: fixed removeVertex() ConcurrentModificationEception 
 * 
 */

public class AdjListsDiGraph<T> //implements DiGraph<T>
{
    private Vector<T> vertices; //Vector to hold the vertices in the graph
    private Vector<LinkedList<T>> arcs;   // Lists of adjacent vertices

    /**
     * Constructor. Creates an empty graph.
     *
     */
    public AdjListsDiGraph() {
        this.arcs = new Vector<LinkedList<T>>();
        this.vertices = new Vector<T>();
    }

    /**
     * Creates and returns a new graph of Strings using the data found
     * in the input tgf file.
     * If the file does not exist, a message is printed.
     *
     * @param String The name of the tgf file to read the graph from
     * @return AdjListsDiGraph<String> the graph of Strings created
     */
    public static AdjListsDiGraph<String> AdjListsGraphFromFile(String tgf_fName) {
        //create an empty graph of Strings
        AdjListsDiGraph<String> g = new AdjListsDiGraph<String>();

        try{
            Scanner scanner = new Scanner(new File(tgf_fName));

            //read vertices
            while (!scanner.next().equals("#")){ //discard special symbol (#)
                String token = scanner.next(); //read next String
                g.vertices.add(token); //add it a vertex to the vertices
                g.arcs.add(new LinkedList<String>());
            }

            //read arcs
            while (scanner.hasNext()){
                int sourceIndex = scanner.nextInt() -1; //correct to start at 0
                int destinationIndex = scanner.nextInt() - 1;
                
                //locate the LinkedList corresponding to the source
                LinkedList<String> list = g.arcs.get(sourceIndex);
                //find the destination that corresponds to the destinationIndex
                String destination = g.vertices.get(destinationIndex);
                //add destination to the list
                list.add(destination);
            }
            scanner.close();
        } catch (IOException ex) {
            System.out.println(" ***ERROR***  " +  tgf_fName + " file could not be read. ");
        }
        return g;
    }



    /**
     * Saves the current graph into a .tgf file.
     * @param the name of the file to write to
     */
    public void saveToTGF(String fName) {
        try {
            PrintWriter writer = new PrintWriter(new File(fName));
            //notice that indexing in the tgf format starts at 1 (not 0)

            //write vertices by iterating through vector "vertices"
            for (int i = 0; i < vertices.size(); i++) {
                writer.print((i+1) + " " + vertices.get(i));
                writer.println("");
            }
            writer.println("#"); // # symbol separates the vertices from the arcs

            //write arcs by iterating through arcs vector
            for (int i = 0; i < arcs.size(); i++){ //for each adjacent list
                for (T destinationVertex :arcs.get(i)) { //for each destination vertex in that list
                    int destinationIndex = vertices.indexOf(destinationVertex); //find the index of that vertex
                    writer.println((i+1) + " " + (destinationIndex+1));
                }
            }
            writer.close();
        } catch (IOException ex) {
            System.out.println("***ERROR***" +  fName + " could not be written");
        }
    }


    /**
     *  Basic Driver program.
     */

    public static void main (String args[]){
        System.out.println("TESTING METHODS");
        System.out.println("_________________");
        AdjListsDiGraph<String> g = new AdjListsDiGraph<String>();
        System.out.println("New graph created.");

        g.saveToTGF("out.tgf");
    }
}