/*
 * 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.commons.io;

import java.io.File;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Stack;

/**
 * General filename and filepath manipulation utilities.
 * <p>
 * When dealing with filenames you can hit problems when moving from a Windows
 * based development machine to a Unix based production machine.
 * This class aims to help avoid those problems.
 * <p>
 * <b>NOTE</b>: You may be able to avoid using this class entirely simply by
 * using JDK {@link java.io.File File} objects and the two argument constructor
 * {@link java.io.File#File(java.io.File, java.lang.String) File(File,String)}.
 * <p>
 * Most methods on this class are designed to work the same on both Unix and Windows.
 * Those that don't include 'System', 'Unix' or 'Windows' in their name.
 * <p>
 * Most methods recognise both separators (forward and back), and both
 * sets of prefixes. See the javadoc of each method for details.
 * <p>
 * This class defines six components within a filename
 * (example C:\dev\project\file.txt):
 * <ul>
 * <li>the prefix - C:\</li>
 * <li>the path - dev\project\</li>
 * <li>the full path - C:\dev\project\</li>
 * <li>the name - file.txt</li>
 * <li>the base name - file</li>
 * <li>the extension - txt</li>
 * </ul>
 * Note that this class works best if directory filenames end with a separator.
 * If you omit the last separator, it is impossible to determine if the filename
 * corresponds to a file or a directory. As a result, we have chosen to say
 * it corresponds to a file.
 * <p>
 * This class only supports Unix and Windows style names.
 * Prefixes are matched as follows:
 * <pre>
 * Windows:
 * a\b\c.txt           --> ""          --> relative
 * \a\b\c.txt          --> "\"         --> current drive absolute
 * C:a\b\c.txt         --> "C:"        --> drive relative
 * C:\a\b\c.txt        --> "C:\"       --> absolute
 * \\server\a\b\c.txt  --> "\\server\" --> UNC
 *
 * Unix:
 * a/b/c.txt           --> ""          --> relative
 * /a/b/c.txt          --> "/"         --> absolute
 * ~/a/b/c.txt         --> "~/"        --> current user
 * ~                   --> "~/"        --> current user (slash added)
 * ~user/a/b/c.txt     --> "~user/"    --> named user
 * ~user               --> "~user/"    --> named user (slash added)
 * </pre>
 * Both prefix styles are matched always, irrespective of the machine that you are
 * currently running on.
 * <p>
 * Origin of code: Excalibur, Alexandria, Tomcat, Commons-Utils.
 *
 * @author <a href="mailto:burton@relativity.yi.org">Kevin A. Burton</A>
 * @author <a href="mailto:sanders@apache.org">Scott Sanders</a>
 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
 * @author <a href="mailto:Christoph.Reck@dlr.de">Christoph.Reck</a>
 * @author <a href="mailto:peter@apache.org">Peter Donald</a>
 * @author <a href="mailto:jefft@apache.org">Jeff Turner</a>
 * @author Matthew Hawthorne
 * @author Martin Cooper
 * @author <a href="mailto:jeremias@apache.org">Jeremias Maerki</a>
 * @author Stephen Colebourne
 * @version $Id: FilenameUtils.java 1004077 2010-10-04 00:58:42Z niallp $
 * @since Commons IO 1.1
 */
public class FilenameUtils {

    /**
     * The extension separator character.
     * @since Commons IO 1.4
     */
    public static final char EXTENSION_SEPARATOR = '.';

    /**
     * The extension separator String.
     * @since Commons IO 1.4
     */
    public static final String EXTENSION_SEPARATOR_STR = Character.toString(EXTENSION_SEPARATOR);

    /**
     * The Unix separator character.
     */
    private static final char UNIX_SEPARATOR = '/';

    /**
     * The Windows separator character.
     */
    private static final char WINDOWS_SEPARATOR = '\\';

    /**
     * The system separator character.
     */
    private static final char SYSTEM_SEPARATOR = File.separatorChar;

    /**
     * The separator character that is the opposite of the system separator.
     */
    private static final char OTHER_SEPARATOR;
    static {
        if (isSystemWindows()) {
            OTHER_SEPARATOR = UNIX_SEPARATOR;
        } else {
            OTHER_SEPARATOR = WINDOWS_SEPARATOR;
        }
    }

    /**
     * Instances should NOT be constructed in standard programming.
     */
    public FilenameUtils() {
        super();
    }

    //-----------------------------------------------------------------------
    /**
     * Determines if Windows file system is in use.
     * 
     * @return true if the system is Windows
     */
    static boolean isSystemWindows() {
        return SYSTEM_SEPARATOR == WINDOWS_SEPARATOR;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks if the character is a separator.
     * 
     * @param ch  the character to check
     * @return true if it is a separator character
     */
    private static boolean isSeparator(char ch) {
        return (ch == UNIX_SEPARATOR) || (ch == WINDOWS_SEPARATOR);
    }

    //-----------------------------------------------------------------------
    /**
     * Normalizes a path, removing double and single dot path steps.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format of the system.
     * <p>
     * A trailing slash will be retained.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null</code>
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo/
     * /foo/./              -->   /foo/
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar/
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo/
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar/
     * ~/../bar             -->   null
     * </pre>
     * (Note the file separator returned will be correct for Windows/Unix)
     *
     * @param filename  the filename to normalize, null returns null
     * @return the normalized filename, or null if invalid
     */
    public static String normalize(String filename) {
        return doNormalize(filename, SYSTEM_SEPARATOR, true);
    }
    /**
     * Normalizes a path, removing double and single dot path steps.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format specified.
     * <p>
     * A trailing slash will be retained.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null</code>
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo/
     * /foo/./              -->   /foo/
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar/
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo/
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar/
     * ~/../bar             -->   null
     * </pre>
     * The output will be the same on both Unix and Windows including
     * the separator character.
     *
     * @param filename  the filename to normalize, null returns null
     * @param unixSeparator <code>true</code> if a unix separator should
     * be used or <code>false</code> if a windows separator should be used.
     * @return the normalized filename, or null if invalid
     * @since Commons IO 2.0
     */
    public static String normalize(String filename, boolean unixSeparator) {
        char separator = (unixSeparator ? UNIX_SEPARATOR : WINDOWS_SEPARATOR);
        return doNormalize(filename, separator, true);
    }

    //-----------------------------------------------------------------------
    /**
     * Normalizes a path, removing double and single dot path steps,
     * and removing any final directory separator.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format of the system.
     * <p>
     * A trailing slash will be removed.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null</code>
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo
     * /foo/./              -->   /foo
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar
     * ~/../bar             -->   null
     * </pre>
     * (Note the file separator returned will be correct for Windows/Unix)
     *
     * @param filename  the filename to normalize, null returns null
     * @return the normalized filename, or null if invalid
     */
    public static String normalizeNoEndSeparator(String filename) {
        return doNormalize(filename, SYSTEM_SEPARATOR, false);
    }

    /**
     * Normalizes a path, removing double and single dot path steps,
     * and removing any final directory separator.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format specified.
     * <p>
     * A trailing slash will be removed.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null</code>
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows including
     * the separator character.
     * <pre>
     * /foo//               -->   /foo
     * /foo/./              -->   /foo
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar
     * ~/../bar             -->   null
     * </pre>
     *
     * @param filename  the filename to normalize, null returns null
     * @param unixSeparator <code>true</code> if a unix separator should
     * be used or <code>false</code> if a windows separtor should be used.
     * @return the normalized filename, or null if invalid
     * @since Commons IO 2.0
     */
    public static String normalizeNoEndSeparator(String filename, boolean unixSeparator) {
         char separator = (unixSeparator ? UNIX_SEPARATOR : WINDOWS_SEPARATOR);
        return doNormalize(filename, separator, false);
    }

    /**
     * Internal method to perform the normalization.
     *
     * @param filename  the filename
     * @param separator The separator character to use
     * @param keepSeparator  true to keep the final separator
     * @return the normalized filename
     */
    private static String doNormalize(String filename, char separator, boolean keepSeparator) {
        if (filename == null) {
            return null;
        }
        int size = filename.length();
        if (size == 0) {
            return filename;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        
        char[] array = new char[size + 2];  // +1 for possible extra slash, +2 for arraycopy
        filename.getChars(0, filename.length(), array, 0);
        
        // fix separators throughout
        char otherSeparator = (separator == SYSTEM_SEPARATOR ? OTHER_SEPARATOR : SYSTEM_SEPARATOR);
        for (int i = 0; i < array.length; i++) {
            if (array[i] == otherSeparator) {
                array[i] = separator;
            }
        }
        
        // add extra separator on the end to simplify code below
        boolean lastIsDirectory = true;
        if (array[size - 1] != separator) {
            array[size++] = separator;
            lastIsDirectory = false;
        }
        
        // adjoining slashes
        for (int i = prefix + 1; i < size; i++) {
            if (array[i] == separator && array[i - 1] == separator) {
                System.arraycopy(array, i, array, i - 1, size - i);
                size--;
                i--;
            }
        }
        
        // dot slash
        for (int i = prefix + 1; i < size; i++) {
            if (array[i] == separator && array[i - 1] == '.' &&
                    (i == prefix + 1 || array[i - 2] == separator)) {
                if (i == size - 1) {
                    lastIsDirectory = true;
                }
                System.arraycopy(array, i + 1, array, i - 1, size - i);
                size -=2;
                i--;
            }
        }
        
        // double dot slash
        outer:
        for (int i = prefix + 2; i < size; i++) {
            if (array[i] == separator && array[i - 1] == '.' && array[i - 2] == '.' &&
                    (i == prefix + 2 || array[i - 3] == separator)) {
                if (i == prefix + 2) {
                    return null;
                }
                if (i == size - 1) {
                    lastIsDirectory = true;
                }
                int j;
                for (j = i - 4 ; j >= prefix; j--) {
                    if (array[j] == separator) {
                        // remove b/../ from a/b/../c
                        System.arraycopy(array, i + 1, array, j + 1, size - i);
                        size -= (i - j);
                        i = j + 1;
                        continue outer;
                    }
                }
                // remove a/../ from a/../c
                System.arraycopy(array, i + 1, array, prefix, size - i);
                size -= (i + 1 - prefix);
                i = prefix + 1;
            }
        }
        
        if (size <= 0) {  // should never be less than 0
            return "";
        }
        if (size <= prefix) {  // should never be less than prefix
            return new String(array, 0, size);
        }
        if (lastIsDirectory && keepSeparator) {
            return new String(array, 0, size);  // keep trailing separator
        }
        return new String(array, 0, size - 1);  // lose trailing separator
    }

    //-----------------------------------------------------------------------
    /**
     * Concatenates a filename to a base path using normal command line style rules.
     * <p>
     * The effect is equivalent to resultant directory after changing
     * directory to the first argument, followed by changing directory to
     * the second argument.
     * <p>
     * The first argument is the base path, the second is the path to concatenate.
     * The returned path is always normalized via {@link #normalize(String)},
     * thus <code>..</code> is handled.
     * <p>
     * If <code>pathToAdd</code> is absolute (has an absolute prefix), then
     * it will be normalized and returned.
     * Otherwise, the paths will be joined, normalized and returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo/ + bar          -->   /foo/bar
     * /foo + bar           -->   /foo/bar
     * /foo + /bar          -->   /bar
     * /foo + C:/bar        -->   C:/bar
     * /foo + C:bar         -->   C:bar (*)
     * /foo/a/ + ../bar     -->   foo/bar
     * /foo/ + ../../bar    -->   null
     * /foo/ + /bar         -->   /bar
     * /foo/.. + /bar       -->   /bar
     * /foo + bar/c.txt     -->   /foo/bar/c.txt
     * /foo/c.txt + bar     -->   /foo/c.txt/bar (!)
     * </pre>
     * (*) Note that the Windows relative drive prefix is unreliable when
     * used with this method.
     * (!) Note that the first parameter must be a path. If it ends with a name, then
     * the name will be built into the concatenated path. If this might be a problem,
     * use {@link #getFullPath(String)} on the base path argument.
     *
     * @param basePath  the base path to attach to, always treated as a path
     * @param fullFilenameToAdd  the filename (or path) to attach to the base
     * @return the concatenated path, or null if invalid
     */
    public static String concat(String basePath, String fullFilenameToAdd) {
        int prefix = getPrefixLength(fullFilenameToAdd);
        if (prefix < 0) {
            return null;
        }
        if (prefix > 0) {
            return normalize(fullFilenameToAdd);
        }
        if (basePath == null) {
            return null;
        }
        int len = basePath.length();
        if (len == 0) {
            return normalize(fullFilenameToAdd);
        }
        char ch = basePath.charAt(len - 1);
        if (isSeparator(ch)) {
            return normalize(basePath + fullFilenameToAdd);
        } else {
            return normalize(basePath + '/' + fullFilenameToAdd);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Converts all separators to the Unix separator of forward slash.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToUnix(String path) {
        if (path == null || path.indexOf(WINDOWS_SEPARATOR) == -1) {
            return path;
        }
        return path.replace(WINDOWS_SEPARATOR, UNIX_SEPARATOR);
    }

    /**
     * Converts all separators to the Windows separator of backslash.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToWindows(String path) {
        if (path == null || path.indexOf(UNIX_SEPARATOR) == -1) {
            return path;
        }
        return path.replace(UNIX_SEPARATOR, WINDOWS_SEPARATOR);
    }

    /**
     * Converts all separators to the system separator.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToSystem(String path) {
        if (path == null) {
            return null;
        }
        if (isSystemWindows()) {
            return separatorsToWindows(path);
        } else {
            return separatorsToUnix(path);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the length of the filename prefix, such as <code>C:/</code> or <code>~/</code>.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * <p>
     * The prefix length includes the first slash in the full filename
     * if applicable. Thus, it is possible that the length returned is greater
     * than the length of the input string.
     * <pre>
     * Windows:
     * a\b\c.txt           --> ""          --> relative
     * \a\b\c.txt          --> "\"         --> current drive absolute
     * C:a\b\c.txt         --> "C:"        --> drive relative
     * C:\a\b\c.txt        --> "C:\"       --> absolute
     * \\server\a\b\c.txt  --> "\\server\" --> UNC
     *
     * Unix:
     * a/b/c.txt           --> ""          --> relative
     * /a/b/c.txt          --> "/"         --> absolute
     * ~/a/b/c.txt         --> "~/"        --> current user
     * ~                   --> "~/"        --> current user (slash added)
     * ~user/a/b/c.txt     --> "~user/"    --> named user
     * ~user               --> "~user/"    --> named user (slash added)
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * ie. both Unix and Windows prefixes are matched regardless.
     *
     * @param filename  the filename to find the prefix in, null returns -1
     * @return the length of the prefix, -1 if invalid or null
     */
    public static int getPrefixLength(String filename) {
        if (filename == null) {
            return -1;
        }
        int len = filename.length();
        if (len == 0) {
            return 0;
        }
        char ch0 = filename.charAt(0);
        if (ch0 == ':') {
            return -1;
        }
        if (len == 1) {
            if (ch0 == '~') {
                return 2;  // return a length greater than the input
            }
            return (isSeparator(ch0) ? 1 : 0);
        } else {
            if (ch0 == '~') {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 1);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 1);
                if (posUnix == -1 && posWin == -1) {
                    return len + 1;  // return a length greater than the input
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            }
            char ch1 = filename.charAt(1);
            if (ch1 == ':') {
                ch0 = Character.toUpperCase(ch0);
                if (ch0 >= 'A' && ch0 <= 'Z') {
                    if (len == 2 || isSeparator(filename.charAt(2)) == false) {
                        return 2;
                    }
                    return 3;
                }
                return -1;
                
            } else if (isSeparator(ch0) && isSeparator(ch1)) {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 2);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 2);
                if ((posUnix == -1 && posWin == -1) || posUnix == 2 || posWin == 2) {
                    return -1;
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            } else {
                return (isSeparator(ch0) ? 1 : 0);
            }
        }
    }

    /**
     * Returns the index of the last directory separator character.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The position of the last forward or backslash is returned.
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * 
     * @param filename  the filename to find the last path separator in, null returns -1
     * @return the index of the last separator character, or -1 if there
     * is no such character
     */
    public static int indexOfLastSeparator(String filename) {
        if (filename == null) {
            return -1;
        }
        int lastUnixPos = filename.lastIndexOf(UNIX_SEPARATOR);
        int lastWindowsPos = filename.lastIndexOf(WINDOWS_SEPARATOR);
        return Math.max(lastUnixPos, lastWindowsPos);
    }

    /**
     * Returns the index of the last extension separator character, which is a dot.
     * <p>
     * This method also checks that there is no directory separator after the last dot.
     * To do this it uses {@link #indexOfLastSeparator(String)} which will
     * handle a file in either Unix or Windows format.
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * 
     * @param filename  the filename to find the last path separator in, null returns -1
     * @return the index of the last separator character, or -1 if there
     * is no such character
     */
    public static int indexOfExtension(String filename) {
        if (filename == null) {
            return -1;
        }
        int extensionPos = filename.lastIndexOf(EXTENSION_SEPARATOR);
        int lastSeparator = indexOfLastSeparator(filename);
        return (lastSeparator > extensionPos ? -1 : extensionPos);
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the prefix from a full filename, such as <code>C:/</code>
     * or <code>~/</code>.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The prefix includes the first slash in the full filename where applicable.
     * <pre>
     * Windows:
     * a\b\c.txt           --> ""          --> relative
     * \a\b\c.txt          --> "\"         --> current drive absolute
     * C:a\b\c.txt         --> "C:"        --> drive relative
     * C:\a\b\c.txt        --> "C:\"       --> absolute
     * \\server\a\b\c.txt  --> "\\server\" --> UNC
     *
     * Unix:
     * a/b/c.txt           --> ""          --> relative
     * /a/b/c.txt          --> "/"         --> absolute
     * ~/a/b/c.txt         --> "~/"        --> current user
     * ~                   --> "~/"        --> current user (slash added)
     * ~user/a/b/c.txt     --> "~user/"    --> named user
     * ~user               --> "~user/"    --> named user (slash added)
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * ie. both Unix and Windows prefixes are matched regardless.
     *
     * @param filename  the filename to query, null returns null
     * @return the prefix of the file, null if invalid
     */
    public static String getPrefix(String filename) {
        if (filename == null) {
            return null;
        }
        int len = getPrefixLength(filename);
        if (len < 0) {
            return null;
        }
        if (len > filename.length()) {
            return filename + UNIX_SEPARATOR;  // we know this only happens for unix
        }
        return filename.substring(0, len);
    }

    /**
     * Gets the path from a full filename, which excludes the prefix.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before and
     * including the last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> a\b\
     * ~/a/b/c.txt  --> a/b/
     * a.txt        --> ""
     * a/b/c        --> a/b/
     * a/b/c/       --> a/b/c/
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * <p>
     * This method drops the prefix from the result.
     * See {@link #getFullPath(String)} for the method that retains the prefix.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getPath(String filename) {
        return doGetPath(filename, 1);
    }

    /**
     * Gets the path from a full filename, which excludes the prefix, and
     * also excluding the final directory separator.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before the
     * last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> a\b
     * ~/a/b/c.txt  --> a/b
     * a.txt        --> ""
     * a/b/c        --> a/b
     * a/b/c/       --> a/b/c
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * <p>
     * This method drops the prefix from the result.
     * See {@link #getFullPathNoEndSeparator(String)} for the method that retains the prefix.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getPathNoEndSeparator(String filename) {
        return doGetPath(filename, 0);
    }

    /**
     * Does the work of getting the path.
     * 
     * @param filename  the filename
     * @param separatorAdd  0 to omit the end separator, 1 to return it
     * @return the path
     */
    private static String doGetPath(String filename, int separatorAdd) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        int index = indexOfLastSeparator(filename);
        int endIndex = index+separatorAdd;
        if (prefix >= filename.length() || index < 0 || prefix >= endIndex) {
            return "";
        }
        return filename.substring(prefix, endIndex);
    }

    /**
     * Gets the full path from a full filename, which is the prefix + path.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before and
     * including the last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> C:\a\b\
     * ~/a/b/c.txt  --> ~/a/b/
     * a.txt        --> ""
     * a/b/c        --> a/b/
     * a/b/c/       --> a/b/c/
     * C:           --> C:
     * C:\          --> C:\
     * ~            --> ~/
     * ~/           --> ~/
     * ~user        --> ~user/
     * ~user/       --> ~user/
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getFullPath(String filename) {
        return doGetFullPath(filename, true);
    }

    /**
     * Gets the full path from a full filename, which is the prefix + path,
     * and also excluding the final directory separator.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before the
     * last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> C:\a\b
     * ~/a/b/c.txt  --> ~/a/b
     * a.txt        --> ""
     * a/b/c        --> a/b
     * a/b/c/       --> a/b/c
     * C:           --> C:
     * C:\          --> C:\
     * ~            --> ~
     * ~/           --> ~
     * ~user        --> ~user
     * ~user/       --> ~user
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getFullPathNoEndSeparator(String filename) {
        return doGetFullPath(filename, false);
    }

    /**
     * Does the work of getting the path.
     * 
     * @param filename  the filename
     * @param includeSeparator  true to include the end separator
     * @return the path
     */
    private static String doGetFullPath(String filename, boolean includeSeparator) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        if (prefix >= filename.length()) {
            if (includeSeparator) {
                return getPrefix(filename);  // add end slash if necessary
            } else {
                return filename;
            }
        }
        int index = indexOfLastSeparator(filename);
        if (index < 0) {
            return filename.substring(0, prefix);
        }
        int end = index + (includeSeparator ?  1 : 0);
        if (end == 0) {
            end++;
        }
        return filename.substring(0, end);
    }

    /**
     * Gets the name minus the path from a full filename.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The text after the last forward or backslash is returned.
     * <pre>
     * a/b/c.txt --> c.txt
     * a.txt     --> a.txt
     * a/b/c     --> c
     * a/b/c/    --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the name of the file without the path, or an empty string if none exists
     */
    public static String getName(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfLastSeparator(filename);
        return filename.substring(index + 1);
    }

    /**
     * Gets the base name, minus the full path and extension, from a full filename.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The text after the last forward or backslash and before the last dot is returned.
     * <pre>
     * a/b/c.txt --> c
     * a.txt     --> a
     * a/b/c     --> c
     * a/b/c/    --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the name of the file without the path, or an empty string if none exists
     */
    public static String getBaseName(String filename) {
        return removeExtension(getName(filename));
    }

    /**
     * Gets the extension of a filename.
     * <p>
     * This method returns the textual part of the filename after the last dot.
     * There must be no directory separator after the dot.
     * <pre>
     * foo.txt      --> "txt"
     * a/b/c.jpg    --> "jpg"
     * a/b.txt/c    --> ""
     * a/b/c        --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename the filename to retrieve the extension of.
     * @return the extension of the file or an empty string if none exists or <code>null</code>
     * if the filename is <code>null</code>.
     */
    public static String getExtension(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfExtension(filename);
        if (index == -1) {
            return "";
        } else {
            return filename.substring(index + 1);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Removes the extension from a filename.
     * <p>
     * This method returns the textual part of the filename before the last dot.
     * There must be no directory separator after the dot.
     * <pre>
     * foo.txt    --> foo
     * a\b\c.jpg  --> a\b\c
     * a\b\c      --> a\b\c
     * a.b\c      --> a.b\c
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the filename minus the extension
     */
    public static String removeExtension(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfExtension(filename);
        if (index == -1) {
            return filename;
        } else {
            return filename.substring(0, index);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether two filenames are equal exactly.
     * <p>
     * No processing is performed on the filenames other than comparison,
     * thus this is merely a null-safe case-sensitive equals.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SENSITIVE
     */
    public static boolean equals(String filename1, String filename2) {
        return equals(filename1, filename2, false, IOCase.SENSITIVE);
    }

    /**
     * Checks whether two filenames are equal using the case rules of the system.
     * <p>
     * No processing is performed on the filenames other than comparison.
     * The check is case-sensitive on Unix and case-insensitive on Windows.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SYSTEM
     */
    public static boolean equalsOnSystem(String filename1, String filename2) {
        return equals(filename1, filename2, false, IOCase.SYSTEM);
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether two filenames are equal after both have been normalized.
     * <p>
     * Both filenames are first passed to {@link #normalize(String)}.
     * The check is then performed in a case-sensitive manner.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SENSITIVE
     */
    public static boolean equalsNormalized(String filename1, String filename2) {
        return equals(filename1, filename2, true, IOCase.SENSITIVE);
    }

    /**
     * Checks whether two filenames are equal after both have been normalized
     * and using the case rules of the system.
     * <p>
     * Both filenames are first passed to {@link #normalize(String)}.
     * The check is then performed case-sensitive on Unix and
     * case-insensitive on Windows.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SYSTEM
     */
    public static boolean equalsNormalizedOnSystem(String filename1, String filename2) {
        return equals(filename1, filename2, true, IOCase.SYSTEM);
    }

    /**
     * Checks whether two filenames are equal, optionally normalizing and providing
     * control over the case-sensitivity.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @param normalized  whether to normalize the filenames
     * @param caseSensitivity  what case sensitivity rule to use, null means case-sensitive
     * @return true if the filenames are equal, null equals null
     * @since Commons IO 1.3
     */
    public static boolean equals(
            String filename1, String filename2,
            boolean normalized, IOCase caseSensitivity) {
        
        if (filename1 == null || filename2 == null) {
            return (filename1 == null && filename2 == null);
        }
        if (normalized) {
            filename1 = normalize(filename1);
            filename2 = normalize(filename2);
            if (filename1 == null || filename2 == null) {
                throw new NullPointerException(
                    "Error normalizing one or both of the file names");
            }
        }
        if (caseSensitivity == null) {
            caseSensitivity = IOCase.SENSITIVE;
        }
        return caseSensitivity.checkEquals(filename1, filename2);
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether the extension of the filename is that specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extension  the extension to check for, null or empty checks for no extension
     * @return true if the filename has the specified extension
     */
    public static boolean isExtension(String filename, String extension) {
        if (filename == null) {
            return false;
        }
        if (extension == null || extension.length() == 0) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        return fileExt.equals(extension);
    }

    /**
     * Checks whether the extension of the filename is one of those specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extensions  the extensions to check for, null checks for no extension
     * @return true if the filename is one of the extensions
     */
    public static boolean isExtension(String filename, String[] extensions) {
        if (filename == null) {
            return false;
        }
        if (extensions == null || extensions.length == 0) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        for (String extension : extensions) {
            if (fileExt.equals(extension)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Checks whether the extension of the filename is one of those specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extensions  the extensions to check for, null checks for no extension
     * @return true if the filename is one of the extensions
     */
    public static boolean isExtension(String filename, Collection<String> extensions) {
        if (filename == null) {
            return false;
        }
        if (extensions == null || extensions.isEmpty()) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        for (String extension : extensions) {
            if (fileExt.equals(extension)) {
                return true;
            }
        }
        return false;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks a filename to see if it matches the specified wildcard matcher,
     * always testing case-sensitive.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * This is the same as often found on Dos/Unix command lines.
     * The check is case-sensitive always.
     * <pre>
     * wildcardMatch("c.txt", "*.txt")      --> true
     * wildcardMatch("c.txt", "*.jpg")      --> false
     * wildcardMatch("a/b/c.txt", "a/b/*")  --> true
     * wildcardMatch("c.txt", "*.???")      --> true
     * wildcardMatch("c.txt", "*.????")     --> false
     * </pre>
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @return true if the filename matches the wilcard string
     * @see IOCase#SENSITIVE
     */
    public static boolean wildcardMatch(String filename, String wildcardMatcher) {
        return wildcardMatch(filename, wildcardMatcher, IOCase.SENSITIVE);
    }

    /**
     * Checks a filename to see if it matches the specified wildcard matcher
     * using the case rules of the system.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * This is the same as often found on Dos/Unix command lines.
     * The check is case-sensitive on Unix and case-insensitive on Windows.
     * <pre>
     * wildcardMatch("c.txt", "*.txt")      --> true
     * wildcardMatch("c.txt", "*.jpg")      --> false
     * wildcardMatch("a/b/c.txt", "a/b/*")  --> true
     * wildcardMatch("c.txt", "*.???")      --> true
     * wildcardMatch("c.txt", "*.????")     --> false
     * </pre>
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @return true if the filename matches the wilcard string
     * @see IOCase#SYSTEM
     */
    public static boolean wildcardMatchOnSystem(String filename, String wildcardMatcher) {
        return wildcardMatch(filename, wildcardMatcher, IOCase.SYSTEM);
    }

    /**
     * Checks a filename to see if it matches the specified wildcard matcher
     * allowing control over case-sensitivity.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @param caseSensitivity  what case sensitivity rule to use, null means case-sensitive
     * @return true if the filename matches the wilcard string
     * @since Commons IO 1.3
     */
    public static boolean wildcardMatch(String filename, String wildcardMatcher, IOCase caseSensitivity) {
        if (filename == null && wildcardMatcher == null) {
            return true;
        }
        if (filename == null || wildcardMatcher == null) {
            return false;
        }
        if (caseSensitivity == null) {
            caseSensitivity = IOCase.SENSITIVE;
        }
        String[] wcs = splitOnTokens(wildcardMatcher);
        boolean anyChars = false;
        int textIdx = 0;
        int wcsIdx = 0;
        Stack<int[]> backtrack = new Stack<int[]>();
        
        // loop around a backtrack stack, to handle complex * matching
        do {
            if (backtrack.size() > 0) {
                int[] array = backtrack.pop();
                wcsIdx = array[0];
                textIdx = array[1];
                anyChars = true;
            }
            
            // loop whilst tokens and text left to process
            while (wcsIdx < wcs.length) {
      
                if (wcs[wcsIdx].equals("?")) {
                    // ? so move to next text char
                    textIdx++;
                    if (textIdx > filename.length()) {
                        break;
                    }
                    anyChars = false;
                    
                } else if (wcs[wcsIdx].equals("*")) {
                    // set any chars status
                    anyChars = true;
                    if (wcsIdx == wcs.length - 1) {
                        textIdx = filename.length();
                    }
                    
                } else {
                    // matching text token
                    if (anyChars) {
                        // any chars then try to locate text token
                        textIdx = caseSensitivity.checkIndexOf(filename, textIdx, wcs[wcsIdx]);
                        if (textIdx == -1) {
                            // token not found
                            break;
                        }
                        int repeat = caseSensitivity.checkIndexOf(filename, textIdx + 1, wcs[wcsIdx]);
                        if (repeat >= 0) {
                            backtrack.push(new int[] {wcsIdx, repeat});
                        }
                    } else {
                        // matching from current position
                        if (!caseSensitivity.checkRegionMatches(filename, textIdx, wcs[wcsIdx])) {
                            // couldnt match token
                            break;
                        }
                    }
      
                    // matched text token, move text index to end of matched token
                    textIdx += wcs[wcsIdx].length();
                    anyChars = false;
                }
      
                wcsIdx++;
            }
            
            // full match
            if (wcsIdx == wcs.length && textIdx == filename.length()) {
                return true;
            }
            
        } while (backtrack.size() > 0);
  
        return false;
    }

    /**
     * Splits a string into a number of tokens.
     * The text is split by '?' and '*'.
     * Where multiple '*' occur consecutively they are collapsed into a single '*'.
     * 
     * @param text  the text to split
     * @return the array of tokens, never null
     */
    static String[] splitOnTokens(String text) {
        // used by wildcardMatch
        // package level so a unit test may run on this
        
        if (text.indexOf('?') == -1 && text.indexOf('*') == -1) {
            return new String[] { text };
        }

        char[] array = text.toCharArray();
        ArrayList<String> list = new ArrayList<String>();
        StringBuilder buffer = new StringBuilder();
        for (int i = 0; i < array.length; i++) {
            if (array[i] == '?' || array[i] == '*') {
                if (buffer.length() != 0) {
                    list.add(buffer.toString());
                    buffer.setLength(0);
                }
                if (array[i] == '?') {
                    list.add("?");
                } else if (list.size() == 0 ||
                        (i > 0 && list.get(list.size() - 1).equals("*") == false)) {
                    list.add("*");
                }
            } else {
                buffer.append(array[i]);
            }
        }
        if (buffer.length() != 0) {
            list.add(buffer.toString());
        }

        return list.toArray( new String[ list.size() ] );
    }

}
