import org.gnu.glpk.*;

public class Gmpl implements GlpkCallbackListener, GlpkTerminalListener {
  private boolean hookUsed = false;

  public static void main(String[] arg) {
    if (1 != arg.length) {
      System.out.println("Usage: java Gmpl model.mod");
      return;
    }
    GLPK.glp_java_set_numeric_locale("C");
    new Gmpl().solve(arg);
  }

  public void solve(String[] arg) {
    glp_prob lp = null;
    glp_tran tran = null;
    glp_iocp iocp;

    String fname;
    int skip = 0;
    int ret;

    // listen to callbacks
    GlpkCallback.addListener(this);

    // listen to terminal output
    GlpkTerminal.addListener(this);

    try {

      // create problem
      lp = GLPK.glp_create_prob();

      // allocate workspace
      tran = GLPK.glp_mpl_alloc_wksp();

      // read model
      fname = arg[0];
      ret = GLPK.glp_mpl_read_model(tran, fname, skip);
      if (ret != 0) {
        GLPK.glp_mpl_free_wksp(tran);
        GLPK.glp_delete_prob(lp);
        throw new RuntimeException("Model file not valid: "
                                   + fname);
      }

      // generate model
      ret = GLPK.glp_mpl_generate(tran, null);
      if (ret != 0) {
        GLPK.glp_mpl_free_wksp(tran);
        GLPK.glp_delete_prob(lp);
        throw new RuntimeException("Cannot generate model: "
                                   + fname);
      }

      // build model
      GLPK.glp_mpl_build_prob(tran, lp);

      // set solver parameters
      iocp = new glp_iocp();
      GLPK.glp_init_iocp(iocp);
      iocp.setPresolve(GLPKConstants.GLP_ON);

      // do not listen to output anymore
      GlpkTerminal.removeListener(this);

      // solve model
      ret = GLPK.glp_intopt(lp, iocp);

      // postsolve model
      if (ret == 0) {
        GLPK.glp_mpl_postsolve(tran, lp,
                               GLPKConstants.GLP_MIP);
      }

      // free memory
      GLPK.glp_mpl_free_wksp(tran);
      GLPK.glp_delete_prob(lp);
    } catch (RuntimeException e) {
      System.err.println("An exeption of class "
                         + e.getClass() + " occured.");
      System.err.println(e.getMessage());
    }

    // do not listen for callbacks anymore
    GlpkCallback.removeListener(this);

    // check that the terinal hook function has been used
    if (!hookUsed) {
      throw new RuntimeException(
        "The terminal output hook was not used.");
    }
  }

  @Override
  public boolean output(String str) {
    hookUsed = true;
    System.out.print(str);
    return false;
  }

  @Override
  public void callback(glp_tree tree) {
    int reason = GLPK.glp_ios_reason(tree);
    if (reason == GLPKConstants.GLP_IBINGO) {
      System.out.println("Better solution found");
    }
  }
}