StringSearchInterpolator.java

package org.codehaus.plexus.interpolation;

/*
 * Copyright 2001-2008 Codehaus Foundation.
 *
 * 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.
 */

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class StringSearchInterpolator implements Interpolator {

    private Map<String, Object> existingAnswers = new HashMap<String, Object>();

    private List<ValueSource> valueSources = new ArrayList<ValueSource>();

    private List<InterpolationPostProcessor> postProcessors = new ArrayList<InterpolationPostProcessor>();

    private boolean cacheAnswers = false;

    public static final String DEFAULT_START_EXPR = "${";

    public static final String DEFAULT_END_EXPR = "}";

    private String startExpr;

    private String endExpr;

    private String escapeString;

    public StringSearchInterpolator() {
        this.startExpr = DEFAULT_START_EXPR;
        this.endExpr = DEFAULT_END_EXPR;
    }

    public StringSearchInterpolator(String startExpr, String endExpr) {
        this.startExpr = startExpr;
        this.endExpr = endExpr;
    }

    /**
     * {@inheritDoc}
     */
    public void addValueSource(ValueSource valueSource) {
        valueSources.add(valueSource);
    }

    /**
     * {@inheritDoc}
     */
    public void removeValuesSource(ValueSource valueSource) {
        valueSources.remove(valueSource);
    }

    /**
     * {@inheritDoc}
     */
    public void addPostProcessor(InterpolationPostProcessor postProcessor) {
        postProcessors.add(postProcessor);
    }

    /**
     * {@inheritDoc}
     */
    public void removePostProcessor(InterpolationPostProcessor postProcessor) {
        postProcessors.remove(postProcessor);
    }

    public String interpolate(String input, String thisPrefixPattern) throws InterpolationException {
        return interpolate(input, new SimpleRecursionInterceptor());
    }

    public String interpolate(String input, String thisPrefixPattern, RecursionInterceptor recursionInterceptor)
            throws InterpolationException {
        return interpolate(input, recursionInterceptor);
    }

    public String interpolate(String input) throws InterpolationException {
        return interpolate(input, new SimpleRecursionInterceptor());
    }

    /**
     * Entry point for recursive resolution of an expression and all of its
     * nested expressions.
     *
     * TODO: Ensure unresolvable expressions don't trigger infinite recursion.
     */
    public String interpolate(String input, RecursionInterceptor recursionInterceptor) throws InterpolationException {
        try {
            return interpolate(input, recursionInterceptor, new HashSet<String>());
        } finally {
            if (!cacheAnswers) {
                existingAnswers.clear();
            }
        }
    }

    private String interpolate(String input, RecursionInterceptor recursionInterceptor, Set<String> unresolvable)
            throws InterpolationException {
        if (input == null) {
            // return empty String to prevent NPE too
            return "";
        }

        int startIdx;
        int endIdx = -1;
        if ((startIdx = input.indexOf(startExpr, endIdx + 1)) > -1) {
            StringBuilder result = new StringBuilder(input.length() * 2);
            do {
                result.append(input, endIdx + 1, startIdx);

                endIdx = input.indexOf(endExpr, startIdx + 1);
                if (endIdx < 0) {
                    break;
                }

                final String wholeExpr = input.substring(startIdx, endIdx + endExpr.length());
                String realExpr = wholeExpr.substring(startExpr.length(), wholeExpr.length() - endExpr.length());

                if (startIdx >= 0 && escapeString != null && escapeString.length() > 0) {
                    int startEscapeIdx = startIdx == 0 ? 0 : startIdx - escapeString.length();
                    if (startEscapeIdx >= 0) {
                        String escape = input.substring(startEscapeIdx, startIdx);
                        if (escapeString.equals(escape)) {
                            result.append(wholeExpr);
                            result.replace(startEscapeIdx, startEscapeIdx + escapeString.length(), "");
                            continue;
                        }
                    }
                }

                boolean resolved = false;
                if (!unresolvable.contains(wholeExpr)) {
                    if (realExpr.startsWith(".")) {
                        realExpr = realExpr.substring(1);
                    }

                    if (recursionInterceptor.hasRecursiveExpression(realExpr)) {
                        throw new InterpolationCycleException(recursionInterceptor, realExpr, wholeExpr);
                    }

                    recursionInterceptor.expressionResolutionStarted(realExpr);
                    try {
                        Object value = getExistingAnswer(realExpr);
                        Object bestAnswer = null;

                        for (ValueSource valueSource : valueSources) {
                            if (value != null) {
                                break;
                            }
                            value = valueSource.getValue(realExpr);

                            if (value != null && value.toString().contains(wholeExpr)) {
                                bestAnswer = value;
                                value = null;
                            }
                        }

                        // this is the simplest recursion check to catch exact recursion
                        // (non synonym), and avoid the extra effort of more string
                        // searching.
                        if (value == null && bestAnswer != null) {
                            throw new InterpolationCycleException(recursionInterceptor, realExpr, wholeExpr);
                        }

                        if (value != null) {
                            value = interpolate(String.valueOf(value), recursionInterceptor, unresolvable);

                            if (postProcessors != null && !postProcessors.isEmpty()) {
                                for (InterpolationPostProcessor postProcessor : postProcessors) {
                                    Object newVal = postProcessor.execute(realExpr, value);
                                    if (newVal != null) {
                                        value = newVal;
                                        break;
                                    }
                                }
                            }

                            // could use:
                            // result = matcher.replaceFirst( stringValue );
                            // but this could result in multiple lookups of stringValue, and replaceAll is not correct
                            // behaviour
                            result.append(String.valueOf(value));
                            resolved = true;

                            if (cacheAnswers) {
                                existingAnswers.put(realExpr, value);
                            }
                        } else {
                            unresolvable.add(wholeExpr);
                        }
                    } finally {
                        recursionInterceptor.expressionResolutionFinished(realExpr);
                    }
                }

                if (!resolved) {
                    result.append(wholeExpr);
                }

                if (endIdx > -1) {
                    endIdx += endExpr.length() - 1;
                }
            } while ((startIdx = input.indexOf(startExpr, endIdx + 1)) > -1);

            if (endIdx == -1 && startIdx > -1) {
                result.append(input, startIdx, input.length());
            } else if (endIdx < input.length()) {
                result.append(input, endIdx + 1, input.length());
            }

            return result.toString();
        } else {
            return input;
        }
    }

    /**
     * Return any feedback messages and errors that were generated - but
     * suppressed - during the interpolation process. Since unresolvable
     * expressions will be left in the source string as-is, this feedback is
     * optional, and will only be useful for debugging interpolation problems.
     *
     * @return a {@link List} that may be interspersed with {@link String} and
     *         {@link Throwable} instances.
     */
    public List getFeedback() {
        List<?> messages = new ArrayList();
        for (ValueSource vs : valueSources) {
            List feedback = vs.getFeedback();
            if (feedback != null && !feedback.isEmpty()) {
                messages.addAll(feedback);
            }
        }

        return messages;
    }

    /**
     * Clear the feedback messages from previous interpolate(..) calls.
     */
    public void clearFeedback() {
        for (ValueSource vs : valueSources) {
            vs.clearFeedback();
        }
    }

    public boolean isCacheAnswers() {
        return cacheAnswers;
    }

    public void setCacheAnswers(boolean cacheAnswers) {
        this.cacheAnswers = cacheAnswers;
    }

    public void clearAnswers() {
        existingAnswers.clear();
    }

    public String getEscapeString() {
        return escapeString;
    }

    public void setEscapeString(String escapeString) {
        this.escapeString = escapeString;
    }

    /**
     * For testing purposes only. Not part of the public API.
     * @param key the key of a possible existing answer.
     * @return the associated interpolated object, or null if there is none.
     */
    protected Object getExistingAnswer(String key) {
        return existingAnswers.get(key);
    }
}