/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.maven.usability.plugin;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.maven.usability.plugin.io.xpp3.ParamdocXpp3Reader;
import org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

/**
 * ExpressionDocumenter
 */
public class ExpressionDocumenter {

    private static final String[] EXPRESSION_ROOTS = {"project", "settings", "session", "plugin", "rootless"};

    private static final String EXPRESSION_DOCO_ROOTPATH = "META-INF/maven/plugin-expressions/";

    private static Map<String, Expression> expressionDocumentation;

    public static Map<String, Expression> load() throws ExpressionDocumentationException {
        if (expressionDocumentation == null) {
            expressionDocumentation = new HashMap<>();

            ClassLoader docLoader = initializeDocLoader();

            for (String root : EXPRESSION_ROOTS) {
                try (InputStream docStream =
                        docLoader.getResourceAsStream(EXPRESSION_DOCO_ROOTPATH + root + ".paramdoc.xml")) {
                    if (docStream != null) {
                        Map<String, Expression> doco = parseExpressionDocumentation(docStream);

                        expressionDocumentation.putAll(doco);
                    }
                } catch (IOException e) {
                    throw new ExpressionDocumentationException(
                            "Failed to read documentation for expression root: " + root, e);
                } catch (XmlPullParserException e) {
                    throw new ExpressionDocumentationException(
                            "Failed to parse documentation for expression root: " + root, e);
                }
            }
        }

        return expressionDocumentation;
    }

    /**
     * <expressions>
     * <expression>
     * <syntax>project.distributionManagementArtifactRepository</syntax>
     * <origin><![CDATA[
     * <distributionManagement>
     * <repository>
     * <id>some-repo</id>
     * <url>scp://host/path</url>
     * </repository>
     * <snapshotRepository>
     * <id>some-snap-repo</id>
     * <url>scp://host/snapshot-path</url>
     * </snapshotRepository>
     * </distributionManagement>
     * ]]></origin>
     * <usage><![CDATA[
     * The repositories onto which artifacts should be deployed.
     * One is for releases, the other for snapshots.
     * ]]></usage>
     * </expression>
     * <expressions>
     *
     * @throws IOException
     * @throws XmlPullParserException
     */
    private static Map<String, Expression> parseExpressionDocumentation(InputStream docStream)
            throws IOException, XmlPullParserException {
        Reader reader = new BufferedReader(ReaderFactory.newXmlReader(docStream));

        ParamdocXpp3Reader paramdocReader = new ParamdocXpp3Reader();

        ExpressionDocumentation documentation = paramdocReader.read(reader, true);

        List<Expression> expressions = documentation.getExpressions();

        Map<String, Expression> bySyntax = new HashMap<>();

        if (expressions != null && !expressions.isEmpty()) {
            for (Expression expression : expressions) {
                bySyntax.put(expression.getSyntax(), expression);
            }
        }

        return bySyntax;
    }

    private static ClassLoader initializeDocLoader() throws ExpressionDocumentationException {
        String myResourcePath = ExpressionDocumenter.class.getName().replace('.', '/') + ".class";

        URL myResource = ExpressionDocumenter.class.getClassLoader().getResource(myResourcePath);

        assert myResource != null : "The resource is this class itself loaded by its own classloader and must exist";

        String myClasspathEntry = myResource.getPath();

        myClasspathEntry = myClasspathEntry.substring(0, myClasspathEntry.length() - (myResourcePath.length() + 2));

        if (myClasspathEntry.startsWith("file:")) {
            myClasspathEntry = myClasspathEntry.substring("file:".length());
        }

        URL docResource;
        try {
            docResource = new File(myClasspathEntry).toURL();
        } catch (MalformedURLException e) {
            throw new ExpressionDocumentationException(
                    "Cannot construct expression documentation classpath" + " resource base.", e);
        }

        return new URLClassLoader(new URL[] {docResource});
    }
}
