/*
 * ModeShape (http://www.modeshape.org)
 * See the COPYRIGHT.txt file distributed with this work for information
 * regarding copyright ownership.  Some portions may be licensed
 * to Red Hat, Inc. under one or more contributor license agreements.
 * See the AUTHORS.txt file in the distribution for a full listing of 
 * individual contributors. 
 *
 * ModeShape is free software. Unless otherwise indicated, all code in ModeShape
 * is licensed to you under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * ModeShape is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.modeshape.common.util;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.modeshape.common.annotation.Immutable;
import org.modeshape.common.CommonI18n;
import org.modeshape.common.i18n.I18n;

/**
 * A simple utility that determines an appropriate MIME type by matching the extension of the supplied filename against a set of
 * known file extensions.
 * <p>
 * This utility class may be instantiated to create a new instance with its own set of mappings. If desired, the default mappings
 * will be loaded using the current thread's {@link Thread#getContextClassLoader() context class loader}, and will be loaded from
 * the <code>/org/modeshape/mime.types</code> file located on the classpath. The {@link #load(InputStream, Map)} method may be
 * used to load custom mappings (in the standard format) into a {@link Map} instance, which can then be passed to one of the
 * constructors.
 * </p>
 */
@Immutable
public class MimeTypeUtil {

    /**
     * The default location of the properties file containing the extension patterns to MIME types. Value is "{@value} ".
     */
    public static final String MIME_TYPE_EXTENSIONS_RESOURCE_PATH = "org/modeshape/mime.types";

    /**
     * The mapping of extension (which includes the leading '.') to MIME type.
     */
    private final Map<String, String> mimeTypesByExtension;

    /**
     * Create a default instance of the extension-based MIME type detector. The set of extension patterns to MIME-types is loaded
     * from the "org/modeshape/mime.types" classpath resource.
     */
    public MimeTypeUtil() {
        this(null, true);
    }

    /**
     * Create an instance of the extension-based MIME type detector by using the supplied mappings. The set of extension patterns
     * to MIME-types is loaded from the "org/modeshape/mime.types" classpath resource, but the supplied extension mappings
     * override any default mappings.
     * 
     * @param extensionsToMimeTypes the mapping of extension patterns to MIME types, which will override the default mappings; may
     *        be null if the default mappings are to be used
     */
    public MimeTypeUtil( Map<String, String> extensionsToMimeTypes ) {
        this(extensionsToMimeTypes, true);
    }

    /**
     * Create an instance of the extension-based MIME type detector by using the supplied mappings. If requested, the set of
     * extension patterns to MIME-types is loaded from the "org/modeshape/mime.types" classpath resource and any supplied
     * extension mappings override any default mappings.
     * 
     * @param extensionsToMimeTypes the mapping of extension patterns to MIME types, which will override the default mappings; may
     *        be null if the default mappings are to be used
     * @param initWithDefaults true if the default mappings are to be loaded first, or false if the default mappings are not to be
     *        used at all
     */
    public MimeTypeUtil( Map<String, String> extensionsToMimeTypes,
                         boolean initWithDefaults ) {
        Map<String, String> mappings = initWithDefaults ? getDefaultMappings() : new HashMap<String, String>();
        if (extensionsToMimeTypes != null) {
            for (Map.Entry<String, String> entry : extensionsToMimeTypes.entrySet()) {
                String extensionString = entry.getKey();
                if (extensionString == null) continue;
                // Lowercase, trim, and remove all leading '.' characters ...
                extensionString = extensionString.toLowerCase().trim().replaceAll("^[.]+", "");
                if (extensionString.length() == 0) continue;
                String mimeType = entry.getValue();
                if (mimeType == null) continue;
                mimeType = entry.getValue().trim();
                if (mimeType.length() == 0) continue;
                assert extensionString.length() != 0;
                assert mimeType.length() != 0;
                mappings.put(extensionString, mimeType);
            }
        }
        // Now put the mappings into the different maps ...
        Map<String, String> mappingsByAnyCharExtension = new HashMap<String, String>();
        for (Map.Entry<String, String> entry : mappings.entrySet()) {
            String extensionString = entry.getKey();
            String mimeType = entry.getValue();
            assert extensionString != null;
            assert extensionString.length() != 0;
            assert mimeType != null;
            assert mimeType.length() != 0;
            mappingsByAnyCharExtension.put("." + extensionString, mimeType);
        }
        mimeTypesByExtension = Collections.unmodifiableMap(mappingsByAnyCharExtension);
    }

    /**
     * Load the default extensions from {@link #MIME_TYPE_EXTENSIONS_RESOURCE_PATH}, which can either be a property file or a
     * tab-delimited *nix-style MIME types file (common in web servers and libraries). If an extension applies to more than one
     * MIME type, the first one in the file wins.
     * 
     * @return the default mappings; never null
     */
    protected static Map<String, String> getDefaultMappings() {
        Map<String, Set<String>> duplicates = new HashMap<String, Set<String>>();
        ClassLoader contextClassLoader = AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
            @Override
            public ClassLoader run() {
                return Thread.currentThread().getContextClassLoader();
            }
        });
        return load(contextClassLoader.getResourceAsStream(MIME_TYPE_EXTENSIONS_RESOURCE_PATH),
                    duplicates);
    }

    /**
     * Load the extensions from the supplied stream, which may provide the contents in the format of property file or a
     * tab-delimited *nix-style MIME types file (common in web servers and libraries). If an extension applies to more than one
     * MIME type, the first one in the file wins.
     * 
     * @param stream the stream containing the content; may not be null
     * @param duplicateMimeTypesByExtension a map into which any extension should be placed if there are multiple MIME types that
     *        apply; may be null if this information is not required
     * @return the default mappings; never null
     */
    public static Map<String, String> load( InputStream stream,
                                            Map<String, Set<String>> duplicateMimeTypesByExtension ) {
        CheckArg.isNotNull(stream, "stream");
        // Create a Regex pattern that can be used for each line. This pattern looks for a mime type
        // (which may contain no whitespace or '=') followed by an optional whitespace, an optional equals sign,
        // optionally more whitespace, and finally by a string of one or more extensions.
        Pattern linePattern = Pattern.compile("\\s*([^\\s=]+)\\s*=?\\s*(.*)");
        List<String> lines = null;
        try {
            String content = IoUtil.read(stream);
            lines = StringUtil.splitLines(content);
        } catch (IOException e) {
            I18n msg = CommonI18n.unableToAccessResourceFileFromClassLoader;
            Logger.getLogger(MimeTypeUtil.class).warn(e, msg, MIME_TYPE_EXTENSIONS_RESOURCE_PATH);
        }
        Map<String, String> mimeTypesByExtension = new HashMap<String, String>();
        if (lines != null) {
            for (String line : lines) {
                line = line.trim();
                if (line.length() == 0 || line.startsWith("#")) continue;
                // Apply the pattern to each line ...
                Matcher matcher = linePattern.matcher(line);
                if (matcher.matches()) {
                    String mimeType = matcher.group(1).trim().toLowerCase();
                    String extensions = matcher.group(2).trim().toLowerCase();
                    if (extensions.length() != 0) {
                        // A valid mime type with at least one extension was found, so for each extension ...
                        for (String extensionString : extensions.split("\\s+")) {
                            extensionString = extensionString.trim();
                            if (extensionString.length() != 0) {
                                // Register the extension with the MIME type ...
                                String existingMimeType = mimeTypesByExtension.put(extensionString, mimeType);
                                if (existingMimeType != null) {
                                    // A MIME type already had this extension, so use the first one ...
                                    mimeTypesByExtension.put(extensionString, existingMimeType);
                                    if (duplicateMimeTypesByExtension != null) {
                                        // And record the duplicate ...
                                        Set<String> dups = duplicateMimeTypesByExtension.get(extensionString);
                                        if (dups == null) {
                                            dups = new HashSet<String>();
                                            duplicateMimeTypesByExtension.put(extensionString, dups);
                                        }
                                        dups.add(existingMimeType);
                                        dups.add(mimeType);
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        return mimeTypesByExtension;
    }

    /**
     * Returns the MIME-type of a file given the supplied name. If the MIME-type cannot be determined, a <code>null</code> is
     * returned.
     * 
     * @param filename the file name; may be <code>null</code>.
     * @return The MIME-type of the file, or optionally <code>null</code> if the MIME-type could not be determined.
     */
    public String mimeTypeOf( String filename ) {
        if (filename == null || filename.length() == 0) return null;
        String trimmedName = filename.trim();
        if (trimmedName.length() == 0) return null;

        // Find the extension ...
        int indexOfDelimiter = trimmedName.lastIndexOf('.');
        if (indexOfDelimiter < 0) return null;
        String extension = trimmedName.substring(indexOfDelimiter).toLowerCase();

        // Look for a match ...
        return mimeTypesByExtension.get(extension);
    }

    /**
     * Returns the MIME-type of the file using its name. If the MIME-type cannot be determined, a <code>null</code> is returned.
     * 
     * @param file the file; may be <code>null</code>.
     * @return The MIME-type of the file, or optionally <code>null</code> if the MIME-type could not be determined.
     */
    public String mimeTypeOf( File file ) {
        if (file == null) return null;
        return mimeTypeOf(file.getName());
    }
}
