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/*
* Copyright (C) 2018 Google, Inc.
*
* 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 com.google.escapevelocity;
import com.google.common.collect.ImmutableList;
/**
* A node in the parse tree.
*
* @author emcmanus@google.com (Éamonn McManus)
*/
abstract class Node {
final String resourceName;
final int lineNumber;
Node(String resourceName, int lineNumber) {
this.resourceName = resourceName;
this.lineNumber = lineNumber;
}
/**
* Returns the result of evaluating this node in the given context. This result may be used as
* part of a further operation, for example evaluating {@code 2 + 3} to 5 in order to set
* {@code $x} to 5 in {@code #set ($x = 2 + 3)}. Or it may be used directly as part of the
* template output, for example evaluating replacing {@code name} by {@code Fred} in
* {@code My name is $name.}.
*/
abstract Object evaluate(EvaluationContext context);
private String where() {
String where = "In expression on line " + lineNumber;
if (resourceName != null) {
where += " of " + resourceName;
}
return where;
}
EvaluationException evaluationException(String message) {
return new EvaluationException(where() + ": " + message);
}
EvaluationException evaluationException(Throwable cause) {
return new EvaluationException(where() + ": " + cause, cause);
}
/**
* Returns an empty node in the parse tree. This is used for example to represent the trivial
* "else" part of an {@code #if} that does not have an explicit {@code #else}.
*/
static Node emptyNode(String resourceName, int lineNumber) {
return new Cons(resourceName, lineNumber, ImmutableList.<Node>of());
}
/**
* Create a new parse tree node that is the concatenation of the given ones. Evaluating the
* new node produces the same string as evaluating each of the given nodes and concatenating the
* result.
*/
static Node cons(String resourceName, int lineNumber, ImmutableList<Node> nodes) {
return new Cons(resourceName, lineNumber, nodes);
}
private static final class Cons extends Node {
private final ImmutableList<Node> nodes;
Cons(String resourceName, int lineNumber, ImmutableList<Node> nodes) {
super(resourceName, lineNumber);
this.nodes = nodes;
}
@Override Object evaluate(EvaluationContext context) {
StringBuilder sb = new StringBuilder();
for (Node node : nodes) {
sb.append(node.evaluate(context));
}
return sb.toString();
}
}
}
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