/*
 * Copyright 2003-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.codehaus.groovy.transform.sc.transformers;

import groovyjarjarasm.asm.Label;
import groovyjarjarasm.asm.MethodVisitor;
import groovyjarjarasm.asm.Opcodes;

import org.codehaus.groovy.ast.ClassHelper;
import org.codehaus.groovy.ast.ClassNode;
import org.codehaus.groovy.ast.GroovyCodeVisitor;
import org.codehaus.groovy.ast.expr.BinaryExpression;
import org.codehaus.groovy.ast.expr.ConstantExpression;
import org.codehaus.groovy.ast.expr.Expression;
import org.codehaus.groovy.ast.expr.ExpressionTransformer;
import org.codehaus.groovy.classgen.AsmClassGenerator;
import org.codehaus.groovy.classgen.asm.WriterController;
import org.codehaus.groovy.syntax.Token;
import org.codehaus.groovy.syntax.Types;

public class CompareToNullExpression extends BinaryExpression implements Opcodes {
    private final boolean equalsNull;
    private final Expression objectExpression;

    public CompareToNullExpression(final Expression objectExpression, final boolean compareToNull) {
        super(objectExpression, new Token(Types.COMPARE_TO, compareToNull ? "==" : "!=", -1, -1), ConstantExpression.NULL);
        this.objectExpression = objectExpression;
        this.equalsNull = compareToNull;
    }

    public Expression getObjectExpression() {
        return objectExpression;
    }

    @Override
    public Expression transformExpression(final ExpressionTransformer transformer) {
        return this;
    }

    @Override
    public void visit(final GroovyCodeVisitor visitor) {
        if (visitor instanceof AsmClassGenerator) {
            AsmClassGenerator acg = (AsmClassGenerator) visitor;
            WriterController controller = acg.getController();
            ClassNode objectType = controller.getTypeChooser().resolveType(objectExpression, controller.getClassNode());
            MethodVisitor mv = controller.getMethodVisitor();
            if (ClassHelper.isPrimitiveType(objectType)) {
                // we're in a primitive == null comparison, which *always* return false
                mv.visitInsn(ICONST_0);
                controller.getOperandStack().push(ClassHelper.boolean_TYPE);
            } else {
                objectExpression.visit(acg);
                Label zero = new Label();
                mv.visitJumpInsn(equalsNull?IFNONNULL:IFNULL, zero);
                mv.visitInsn(ICONST_1);
                Label end = new Label();
                mv.visitJumpInsn(GOTO, end);
                mv.visitLabel(zero);
                mv.visitInsn(ICONST_0);
                mv.visitLabel(end);
                controller.getOperandStack().replace(ClassHelper.boolean_TYPE);
            }
        } else {
            super.visit(visitor);
        }
    }
}