package org.codehaus.plexus.util.introspection;

/*
 * Copyright The 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.lang.ref.WeakReference;
import java.lang.reflect.Array;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Map;
import java.util.WeakHashMap;

import org.codehaus.plexus.util.StringUtils;

/**
 * <p>
 * Using simple dotted expressions to extract the values from an Object instance, For example we might want to extract a
 * value like: <code>project.build.sourceDirectory</code>
 * </p>
 * <p>
 * The implementation supports indexed, nested and mapped properties similar to the JSP way.
 * </p>
 *
 * @author <a href="mailto:jason@maven.org">Jason van Zyl </a>
 * @author <a href="mailto:vincent.siveton@gmail.com">Vincent Siveton</a>
 *
 * @see <a href=
 *      "http://struts.apache.org/1.x/struts-taglib/indexedprops.html">http://struts.apache.org/1.x/struts-taglib/indexedprops.html</a>
 */
public class ReflectionValueExtractor {
    private static final Class<?>[] CLASS_ARGS = new Class[0];

    private static final Object[] OBJECT_ARGS = new Object[0];

    /**
     * Use a WeakHashMap here, so the keys (Class objects) can be garbage collected. This approach prevents permgen
     * space overflows due to retention of discarded classloaders.
     */
    private static final Map<Class<?>, WeakReference<ClassMap>> classMaps =
            new WeakHashMap<Class<?>, WeakReference<ClassMap>>();

    static final int EOF = -1;

    static final char PROPERTY_START = '.';

    static final char INDEXED_START = '[';

    static final char INDEXED_END = ']';

    static final char MAPPED_START = '(';

    static final char MAPPED_END = ')';

    static class Tokenizer {
        final String expression;

        int idx;

        public Tokenizer(String expression) {
            this.expression = expression;
        }

        public int peekChar() {
            return idx < expression.length() ? expression.charAt(idx) : EOF;
        }

        public int skipChar() {
            return idx < expression.length() ? expression.charAt(idx++) : EOF;
        }

        public String nextToken(char delimiter) {
            int start = idx;

            while (idx < expression.length() && delimiter != expression.charAt(idx)) {
                idx++;
            }

            // delimiter MUST be present
            if (idx <= start || idx >= expression.length()) {
                return null;
            }

            return expression.substring(start, idx++);
        }

        public String nextPropertyName() {
            final int start = idx;

            while (idx < expression.length() && Character.isJavaIdentifierPart(expression.charAt(idx))) {
                idx++;
            }

            // property name does not require delimiter
            if (idx <= start || idx > expression.length()) {
                return null;
            }

            return expression.substring(start, idx);
        }

        public int getPosition() {
            return idx < expression.length() ? idx : EOF;
        }

        // to make tokenizer look pretty in debugger
        @Override
        public String toString() {
            return idx < expression.length() ? expression.substring(idx) : "<EOF>";
        }
    }

    private ReflectionValueExtractor() {}

    /**
     * <p>The implementation supports indexed, nested and mapped properties.</p>
     *
     * <ul>
     * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li>
     * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code>
     * pattern, i.e. "user.addresses[1].street"</li>
     * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e.
     * "user.addresses(myAddress).street"</li>
     * </ul>
     *
     * @param expression not null expression
     * @param root not null object
     * @return the object defined by the expression
     * @throws Exception if any
     */
    public static Object evaluate(String expression, Object root) throws Exception {
        return evaluate(expression, root, true);
    }

    /**
     * <p>The implementation supports indexed, nested and mapped properties.</p>
     *
     * <ul>
     * <li>nested properties should be defined by a dot, i.e. "user.address.street"</li>
     * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code>
     * pattern, i.e. "user.addresses[1].street"</li>
     * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern, i.e.
     * "user.addresses(myAddress).street"</li>
     * </ul>
     *
     * @param expression not null expression
     * @param root not null object
     * @param trimRootToken  root start
     * @return the object defined by the expression
     * @throws Exception if any
     */
    // TODO: don't throw Exception
    public static Object evaluate(String expression, final Object root, final boolean trimRootToken) throws Exception {
        Object value = root;

        // ----------------------------------------------------------------------
        // Walk the dots and retrieve the ultimate value desired from the
        // MavenProject instance.
        // ----------------------------------------------------------------------

        if (StringUtils.isEmpty(expression) || !Character.isJavaIdentifierStart(expression.charAt(0))) {
            return null;
        }

        boolean hasDots = expression.indexOf(PROPERTY_START) >= 0;

        final Tokenizer tokenizer;
        if (trimRootToken && hasDots) {
            tokenizer = new Tokenizer(expression);
            tokenizer.nextPropertyName();
            if (tokenizer.getPosition() == EOF) {
                return null;
            }
        } else {
            tokenizer = new Tokenizer("." + expression);
        }

        int propertyPosition = tokenizer.getPosition();
        while (value != null && tokenizer.peekChar() != EOF) {
            switch (tokenizer.skipChar()) {
                case INDEXED_START:
                    value = getIndexedValue(
                            expression,
                            propertyPosition,
                            tokenizer.getPosition(),
                            value,
                            tokenizer.nextToken(INDEXED_END));
                    break;
                case MAPPED_START:
                    value = getMappedValue(
                            expression,
                            propertyPosition,
                            tokenizer.getPosition(),
                            value,
                            tokenizer.nextToken(MAPPED_END));
                    break;
                case PROPERTY_START:
                    propertyPosition = tokenizer.getPosition();
                    value = getPropertyValue(value, tokenizer.nextPropertyName());
                    break;
                default:
                    // could not parse expression
                    return null;
            }
        }

        return value;
    }

    private static Object getMappedValue(
            final String expression, final int from, final int to, final Object value, final String key)
            throws Exception {
        if (value == null || key == null) {
            return null;
        }

        if (value instanceof Map) {
            Object[] localParams = new Object[] {key};
            ClassMap classMap = getClassMap(value.getClass());
            Method method = classMap.findMethod("get", localParams);
            return method.invoke(value, localParams);
        }

        final String message = String.format(
                "The token '%s' at position '%d' refers to a java.util.Map, but the value seems is an instance of '%s'",
                expression.subSequence(from, to), from, value.getClass());

        throw new Exception(message);
    }

    private static Object getIndexedValue(
            final String expression, final int from, final int to, final Object value, final String indexStr)
            throws Exception {
        try {
            int index = Integer.parseInt(indexStr);

            if (value.getClass().isArray()) {
                return Array.get(value, index);
            }

            if (value instanceof List) {
                ClassMap classMap = getClassMap(value.getClass());
                // use get method on List interface
                Object[] localParams = new Object[] {index};
                Method method = classMap.findMethod("get", localParams);
                return method.invoke(value, localParams);
            }
        } catch (NumberFormatException e) {
            return null;
        } catch (InvocationTargetException e) {
            // catch array index issues gracefully, otherwise release
            if (e.getCause() instanceof IndexOutOfBoundsException) {
                return null;
            }

            throw e;
        }

        final String message = String.format(
                "The token '%s' at position '%d' refers to a java.util.List or an array, but the value seems is an instance of '%s'",
                expression.subSequence(from, to), from, value.getClass());

        throw new Exception(message);
    }

    private static Object getPropertyValue(Object value, String property) throws Exception {
        if (value == null || property == null) {
            return null;
        }

        ClassMap classMap = getClassMap(value.getClass());
        String methodBase = StringUtils.capitalizeFirstLetter(property);
        String methodName = "get" + methodBase;
        Method method = classMap.findMethod(methodName, CLASS_ARGS);

        if (method == null) {
            // perhaps this is a boolean property??
            methodName = "is" + methodBase;

            method = classMap.findMethod(methodName, CLASS_ARGS);
        }

        if (method == null) {
            return null;
        }

        try {
            return method.invoke(value, OBJECT_ARGS);
        } catch (InvocationTargetException e) {
            throw e;
        }
    }

    private static ClassMap getClassMap(Class<?> clazz) {

        WeakReference<ClassMap> softRef = classMaps.get(clazz);

        ClassMap classMap;

        if (softRef == null || (classMap = softRef.get()) == null) {
            classMap = new ClassMap(clazz);

            classMaps.put(clazz, new WeakReference<ClassMap>(classMap));
        }

        return classMap;
    }
}
