# URITemplateParser.java

    /*
    *  Copyright (c) 2005-2010, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
    *
    *  WSO2 Inc. 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 org.apache.synapse.commons.templates.uri.parser;

    import org.apache.synapse.commons.templates.uri.URITemplateException;

    public class URITemplateParser {

        private static final char[] operators = new char[] { '+', '.', '/', ';', '?', '&', '#' };

        private Node syntaxTree;
        private Node currentNode;

        public Node parse(String template) throws URITemplateException {
            if (!"/".equals(template) && template.endsWith("/")) {
                template = template.substring(0, template.length() - 1);
            }

            boolean expression = false;
            int startIndex = 0;
            int maxIndex = template.length() - 1;

            for (int pointerIndex = 0; pointerIndex < template.length(); pointerIndex++) {
                char ch = template.charAt(pointerIndex);

                switch (ch) {
                    case '{':
                        if (!expression) {
                            if (pointerIndex + 1 >= maxIndex) {
                                throw new URITemplateException("Illegal open brace character");
                            }

                            expression = true;
                            if (pointerIndex > startIndex) {
                                addNode(new Literal(template.substring(startIndex, pointerIndex)));
                                startIndex = pointerIndex + 1;
                            } else if (template.charAt(pointerIndex - 1) != '}') {
                                throw new URITemplateException("Illegal empty literal");
                            } else {
                                startIndex++;
                            }
                        } else {
                            throw new URITemplateException("Already in expression");
                        }
                        break;

                    case '}':
                        if (expression) {
                            expression = false;
                            if (pointerIndex > startIndex) {
                                createExpressionNode(template.substring(startIndex, pointerIndex));
                                startIndex = pointerIndex + 1;
                            } else {
                                throw new URITemplateException("Illegal empty expression");
                            }
                        } else {
                            throw new URITemplateException("Illegal closing brace detected");
                        }
                        break;

                    default:
                        if (pointerIndex == maxIndex) {
                            String token = template.substring(startIndex);
                            if (expression) {
                                createExpressionNode(token);
                            } else {
                                addNode(new Literal(token));
                            }
                        }
                }
            }
            return syntaxTree;
        }

        private void addNode(Node node) {
            if (syntaxTree == null) {
                syntaxTree = node;
                currentNode = syntaxTree;
            } else {
                currentNode.setNext(node);
                currentNode = node;
            }
        }

        private void createExpressionNode(String expression) throws URITemplateException {
            Node node = null;
            if (isSimpleString(expression)) {
                node = new SimpleStringExpression(expression);
            }

            if (expression.length() < 1) {
                throw new URITemplateException("Invalid template expression: {" + expression + "}");
            }

            if (expression.startsWith("#")) {
                node = new FragmentExpression(expression.substring(1));
            } else if (expression.startsWith("+")) {
                node = new ReservedStringExpression(expression.substring(1));
            } else if (expression.startsWith(".")) {
                node = new LabelExpression(expression.substring(1));
            } else if (expression.startsWith("/")) {
                node = new PathSegmentExpression(expression.substring(1));
            }

            if (node != null) {
                addNode(node);
            } else {
                throw new URITemplateException("Unsupported template expression: {" + expression + "}");
            }
        }

        private boolean isSimpleString(String expression) {
            for (char op : operators) {
                if (expression.indexOf(op) == 0) {
                    return false;
                }
            }
            return true;
        }
    }