package com.googlecode.prolog_cafe.builtin;
import com.googlecode.prolog_cafe.exceptions.IllegalTypeException;
import com.googlecode.prolog_cafe.exceptions.PInstantiationException;
import com.googlecode.prolog_cafe.lang.*;
/**
 * <code>atom_concat/3</code><br>
 * @author Mutsunori Banbara (banbara@kobe-u.ac.jp)
 * @author Naoyuki Tamura (tamura@kobe-u.ac.jp)
 * @version 1.0
*/
public class PRED_atom_concat_3 extends Predicate.P3 {
    private static final SymbolTerm AC_2 = SymbolTerm.intern("ac", 2);

    public PRED_atom_concat_3(Term a1, Term a2, Term a3, Operation cont) {
        arg1 = a1;
        arg2 = a2;
        arg3 = a3;
        this.cont = cont;
    }

    public Operation exec(Prolog engine) {
        engine.setB0();
        Term a1, a2, a3;
        a1 = arg1;
        a2 = arg2;
        a3 = arg3;

	a3 = a3.dereference();
	if (a3.isSymbol()) {
	    String str3 = ((SymbolTerm)a3).name();
	    int endIndex = str3.length();
	    Term t = Prolog.Nil;
	    for (int i=0; i<=endIndex; i++) {
		Term[] args = {SymbolTerm.create(str3.substring(0, i)),
			       SymbolTerm.create(str3.substring(i, endIndex))};
		t = new ListTerm(new StructureTerm(AC_2, args), t);
	    }
	    return new PRED_$member_in_reverse_2(new StructureTerm(AC_2, a1, a2), t, cont);
	} else if (! a3.isVariable()) {
	    throw new IllegalTypeException(this, 3, "atom", a3);
	}
	// a3 is a variable
	a1 = a1.dereference();
	a2 = a2.dereference();
	if (a1.isVariable())
	    throw new PInstantiationException(this, 1);
	if (a2.isVariable())
	    throw new PInstantiationException(this, 2);
	if (! a1.isSymbol())
	    throw new IllegalTypeException(this, 1, "integer", a1);
	if (! a2.isSymbol())
	    throw new IllegalTypeException(this, 2, "integer", a2);
	String str3 = ((SymbolTerm) a1).name().concat(((SymbolTerm) a2).name());
	if (! a3.unify(SymbolTerm.create(str3), engine.trail))
	    return engine.fail();
        return cont;
    }
}