serene-simple/src/main/java/serene/simple/builtin/NewFn.java

/**
 * Serene (simple) - A PoC lisp to collect data on Serenes concepts
 * Copyright (C) 2019-2020 Sameer Rahmani <lxsameer@gnu.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA  02110-1301, USA.
 */
package serene.simple.builtin;

import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import serene.simple.BaseScope;
import serene.simple.SereneException;
import static serene.simple.Utils.getClassOf;

public class NewFn extends AFn {
  public String fnName() {
    return "new";
  };

  public Object eval(BaseScope scope) throws SereneException {
    List<Object> args = this.arguments();

    if (args.size() == 0) {
      throw new SereneException("Needs a class to instantiate.");
    }
    else if(args.size() == 1) {
      return this.createObject((Class<?>) args.get(0));
    }

    return this.createObject((Class<?>) args.get(0), args.subList(1, args.size()));
  }

  private Object createObject(Class<?> c) {
    return this.createObject(c, (List<Object>) new ArrayList<Object>());
  }


  private Object createObject(Class c, List<Object> args) {
    Constructor<?> constructor = this.getConstructor(c, args);
    //Object[] argvals = new Object[args.size()];
    Object[] argvals = (Object[]) args.toArray();

    for(int i = 0; i < args.size(); i++)

      if(constructor != null) {
        try {
          return constructor.newInstance(
            Reflector.boxArgs(constructor.getParameterTypes(), argvals));
        }
        catch(Exception e) {
          throw new SereneException(
            String.format("Can't instantiate class '%s' because: %s", c.getName(), e.getMessage()));

        }
      }
    return Reflector.invokeConstructor(c, argvals);
  }

  private Constructor<?> getConstructor(Class<?> c, List<Object> args) {
    ArrayList<Constructor<?>> possibleInitFns = new ArrayList<Constructor<?>>();
    Constructor<?>[] inits = c.getConstructors();
    ArrayList<Class<?>[]> params = new ArrayList<Class<?>[]>();
    ArrayList<Class<?>> rets = new ArrayList<Class<?>>();
    // Constructor index on the possibleInitFns List
    int id = 0;

    for (int i = 0; i < inits.length; i++){
      Constructor<?> initFn = inits[i];
      if(initFn.getParameterTypes().length == args.size())
        {
          possibleInitFns.add(initFn);
          params.add(initFn.getParameterTypes());
          rets.add(c);
        }
    }

    if (possibleInitFns.isEmpty()) {
      throw new IllegalArgumentException("No matching constructor found for " + c);
    }

    if (possibleInitFns.size() > 1) {
      id = findMatchingConstructor(c.getName(), params, args, rets);
    }

    return id == 0 ? null : (Constructor<?>) possibleInitFns.get(id);
  }

  public int findMatchingConstructor(String methodName,
                                     ArrayList<Class<?>[]> paramlists,
                                     List<Object> args,
                                     List<Class<?>> rets) {
    // presumes matching lengths
    int matchIdx = -1;
    boolean tied = false;
    boolean foundExact = false;

    for (int i = 0; i < paramlists.size(); i++) {
      boolean match = true;
      int exact = 0;

      for (int p = 0; match && p < args.size(); ++p) {
        Object arg = args.get(p);
        Class<?> aclass = getClassOf(arg);
        Class<?> pclass = paramlists.get(i)[p];

        // TODO: handle null aclass here here
        if (aclass == pclass)
          exact++;
        else
          match = Reflector.paramArgTypeMatch(pclass, aclass);
      }

      if (exact == args.size()) {
        if (!foundExact || matchIdx == -1 || rets.get(matchIdx).isAssignableFrom(rets.get(i)))
          matchIdx = i;

        tied = false;
        foundExact = true;

      }
      else if (match && !foundExact) {
        if (matchIdx == -1)
          matchIdx = i;
        else {
          if (subsumes(paramlists.get(i), paramlists.get(matchIdx))) {
            matchIdx = i;
            tied = false;
          }
          else if (Arrays.equals(paramlists.get(matchIdx), paramlists.get(i))) {
            if (rets.get(matchIdx).isAssignableFrom(rets.get(i)))
              matchIdx = i;
          }
          else if (!(subsumes(paramlists.get(matchIdx), paramlists.get(i))))
            tied = true;
        }
      }
    }
    if (tied)
      throw new IllegalArgumentException(
        "More than one matching method found: " + methodName);

    return matchIdx;
  }

  static public boolean subsumes(Class<?>[] c1, Class<?>[] c2){
    //Presumes matching lengths
    Boolean better = false;

    for(int i = 0; i < c1.length; i++) {
      if(c1[i] != c2[i]) {
        if(!c1[i].isPrimitive() && c2[i].isPrimitive()
           ||
           c2[i].isAssignableFrom(c1[i]))
          better = true;
        else
          return false;
      }
    }
    return better;
  }
}