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Google App Engine compliant variation of FreeMarker. FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 freemarker.core;

import freemarker.template.TemplateException;
import freemarker.template.TemplateHashModel;
import freemarker.template.TemplateModel;

/**
 * The dot operator. Used to reference items inside a
 * TemplateHashModel.
 */
class Dot extends Expression {
    private final Expression target;
    protected final String key;

    Dot(Expression target, String key) {
        this.target = target;
        this.key = key;
    }

    /**
     * Shallow copy constructor
     */
    Dot(Dot dot) {
        this(dot.target, dot.key);
        this.constantValue = dot.constantValue; // Probably always will be null here
        copyFieldsFrom(dot);
    }

    @Override
    TemplateModel _eval(Environment env) throws TemplateException {
        TemplateModel leftModel = target.eval(env);
        if (leftModel instanceof TemplateHashModel) {
            return evalOnHash((TemplateHashModel) leftModel);
        }
        if (leftModel == null && env.isClassicCompatible()) {
            return null; // ${noSuchVar.foo} has just printed nothing in FM 1.
        }
        throw new NonHashException(target, leftModel, env);
    }

    protected TemplateModel evalOnHash(TemplateHashModel leftModel) throws TemplateException {
        return leftModel.get(key);
    }

    @Override
    public String getCanonicalForm() {
        return target.getCanonicalForm() + getNodeTypeSymbol() + _CoreStringUtils.toFTLIdentifierReferenceAfterDot(key);
    }
    
    @Override
    String getNodeTypeSymbol() {
        return ".";
    }
    
    @Override
    boolean isLiteral() {
        return target.isLiteral();
    }

    @Override
    protected Expression deepCloneWithIdentifierReplaced_inner(
            String replacedIdentifier, Expression replacement, ReplacemenetState replacementState) {
    	return new Dot(
    	        target.deepCloneWithIdentifierReplaced(replacedIdentifier, replacement, replacementState),
    	        key);
    }
    
    @Override
    int getParameterCount() {
        return 2;
    }

    @Override
    Object getParameterValue(int idx) {
        return idx == 0 ? target : key;
    }

    @Override
    ParameterRole getParameterRole(int idx) {
        return ParameterRole.forBinaryOperatorOperand(idx);
    }
    
    String getRHO() {
        return key;
    }

    boolean onlyHasIdentifiers() {
        return (target instanceof Identifier) || ((target instanceof Dot) && ((Dot) target).onlyHasIdentifiers());
    }
}