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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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/*
 * Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
 * 
 * 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 freemarker.core;

import freemarker.ext.beans.BeanModel;
import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateBooleanModel;
import freemarker.template.TemplateCollectionModel;
import freemarker.template.TemplateDateModel;
import freemarker.template.TemplateException;
import freemarker.template.TemplateHashModel;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateNumberModel;
import freemarker.template.TemplateScalarModel;
import freemarker.template.TemplateSequenceModel;

/**
 * An abstract class for nodes in the parse tree 
 * that represent a FreeMarker expression.
 */
abstract public class Expression extends TemplateObject {

    /**
     * @param env might be {@code null}, if this kind of expression can be evaluated during parsing (as opposed to
     *     during template execution).
     */
    abstract TemplateModel _eval(Environment env) throws TemplateException;
    
    abstract boolean isLiteral();

    // Used to store a constant return value for this expression. Only if it
    // is possible, of course.
    
    TemplateModel constantValue;

    // Hook in here to set the constant value if possible.
    
    void setLocation(Template template, int beginColumn, int beginLine, int endColumn, int endLine)
    throws
        ParseException
    {
        super.setLocation(template, beginColumn, beginLine, endColumn, endLine);
        if (isLiteral()) {
            try {
                constantValue = _eval(null);
            } catch (Exception e) {
            // deliberately ignore.
            }
        }
    }

    /**
     * @deprecated At the moment FreeMarker has no API for this with backward-compatibility promises.
     */
    public final TemplateModel getAsTemplateModel(Environment env) throws TemplateException {
        return eval(env);
    }
    
    final TemplateModel eval(Environment env) throws TemplateException {
        return constantValue != null ? constantValue : _eval(env);
    }
    
    String evalAndCoerceToString(Environment env) throws TemplateException {
        return EvalUtil.coerceModelToString(eval(env), this, null, env);
    }

    /**
     * @param seqTip Tip to display if the value type is not coercable, but it's sequence or collection.
     */
    String evalAndCoerceToString(Environment env, String seqTip) throws TemplateException {
        return EvalUtil.coerceModelToString(eval(env), this, seqTip, env);
    }
    
    static String coerceModelToString(TemplateModel tm, Expression exp, Environment env) throws TemplateException {
        return EvalUtil.coerceModelToString(tm, exp, null, env);
    }
    
    Number evalToNumber(Environment env) throws TemplateException {
        TemplateModel model = eval(env);
        return modelToNumber(model, env);
    }

    Number modelToNumber(TemplateModel model, Environment env) throws TemplateException {
        if(model instanceof TemplateNumberModel) {
            return EvalUtil.modelToNumber((TemplateNumberModel) model, this);
        } else {
            throw new NonNumericalException(this, model, env);
        }
    }
    
    boolean evalToBoolean(Environment env) throws TemplateException {
        return evalToBoolean(env, null);
    }

    boolean evalToBoolean(Configuration cfg) throws TemplateException {
        return evalToBoolean(null, cfg);
    }
    
    private boolean evalToBoolean(Environment env, Configuration cfg) throws TemplateException {
        TemplateModel model = eval(env);
        return modelToBoolean(model, env, cfg);
    }
    
    boolean modelToBoolean(TemplateModel model, Environment env) throws TemplateException {
        return modelToBoolean(model, env, null);
    }

    boolean modelToBoolean(TemplateModel model, Configuration cfg) throws TemplateException {
        return modelToBoolean(model, null, cfg);
    }
    
    private boolean modelToBoolean(TemplateModel model, Environment env, Configuration cfg) throws TemplateException {
        if (model instanceof TemplateBooleanModel) {
            return ((TemplateBooleanModel) model).getAsBoolean();
        } else if (env != null ? env.isClassicCompatible() : cfg.isClassicCompatible()) {
            return model != null && !isEmpty(model);
        } else {
            throw new NonBooleanException(this, model, env);
        }
    }
    
    final Expression deepCloneWithIdentifierReplaced(
            String replacedIdentifier, Expression replacement, ReplacemenetState replacementState) {
        Expression clone = deepCloneWithIdentifierReplaced_inner(replacedIdentifier, replacement, replacementState);
        if (clone.beginLine == 0) {
            clone.copyLocationFrom(this);
        }
        return clone;
    }
    
    static class ReplacemenetState {
        /**
         * If the replacement expression is not in use yet, we don't have to clone it.
         */
        boolean replacementAlreadyInUse; 
    }

    /**
     * This should return an equivalent new expression object (or an identifier replacement expression).
     * The position need not be filled, unless it will be different from the position of what were cloning. 
     */
    protected abstract Expression deepCloneWithIdentifierReplaced_inner(
            String replacedIdentifier, Expression replacement, ReplacemenetState replacementState);

    static boolean isEmpty(TemplateModel model) throws TemplateModelException
    {
        if (model instanceof BeanModel) {
            return ((BeanModel) model).isEmpty();
        } else if (model instanceof TemplateSequenceModel) {
            return ((TemplateSequenceModel) model).size() == 0;
        } else if (model instanceof TemplateScalarModel) {
            String s = ((TemplateScalarModel) model).getAsString();
            return (s == null || s.length() == 0);
        } else if (model == null) {
            return true;
        } else if (model instanceof TemplateCollectionModel) {
            return !((TemplateCollectionModel) model).iterator().hasNext();
        } else if (model instanceof TemplateHashModel) {
            return ((TemplateHashModel) model).isEmpty();
        } else if (model instanceof TemplateNumberModel
                || model instanceof TemplateDateModel
                || model instanceof TemplateBooleanModel) {
            return false;
        } else {
            return true;
        }
    }
    
    void assertNonNull(TemplateModel model, Environment env) throws InvalidReferenceException {
        if (model == null) throw InvalidReferenceException.getInstance(this, env);
    }
    
}