///////////////////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
   // Copyright (C) 2001-2026 the original author or authors.
   //
   // This library is free software; you can redistribute it and/or
   // modify it 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.
   //
  // This library 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 library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.imports;
  
  import java.util.Locale;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.FullIdent;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.UnmodifiableCollectionUtil;
  
  /**
   * <div>
   * Checks the ordering/grouping of imports. Features are:
   * </div>
   * <ul>
   * <li>
   * groups type/static imports: ensures that groups of imports come in a specific order
   * (e.g., java. comes first, javax. comes second, then everything else)
   * </li>
   * <li>
   * adds a separation between type import groups : ensures that a blank line sit between each group
   * </li>
   * <li>
   * type/static import groups aren't separated internally: ensures that each group aren't separated
   * internally by blank line or comment
   * </li>
   * <li>
   * sorts type/static imports inside each group: ensures that imports within each group are in
   * lexicographic order
   * </li>
   * <li>
   * sorts according to case: ensures that the comparison between imports is case-sensitive, in
   * <a href="https://en.wikipedia.org/wiki/ASCII#Order">ASCII sort order</a>
   * </li>
   * <li>
   * arrange static imports: ensures the relative order between type imports and static imports
   * (see
   * <a href="https://checkstyle.org/property-types.html#ImportOrderOption">ImportOrderOption</a>)
   * </li>
   * </ul>
   *
   * @since 3.2
   */
  @FileStatefulCheck
  public class ImportOrderCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_SEPARATION = "import.separation";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_SEPARATED_IN_GROUP = "import.groups.separated.internally";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_ORDERING_LEX = "import.ordering.lex";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_ORDERING_STATIC = "import.ordering.static";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_ORDERING_GROUP = "import.ordering.group";
 
     /** The special wildcard that catches all remaining groups. */
     private static final String WILDCARD_GROUP_NAME = "*";
 
     /** The Forward slash. */
     private static final String FORWARD_SLASH = "/";
 
     /** Empty array of pattern type needed to initialize check. */
     private static final Pattern[] EMPTY_PATTERN_ARRAY = new Pattern[0];
 
     /**
      * Specify list of <b>type import</b> groups. Every group identified either by a common prefix
      * string, or by a regular expression enclosed in forward slashes (e.g. {@code /regexp/}).
      * If an import matches two or more groups,
      * the best match is selected (closest to the start, and the longest match).
      * All type imports, which does not match any group, falls into an additional group,
      * located at the end. Thus, the empty list of type groups (the default value) means one group
      * for all type imports.
      */
     private String[] groups = CommonUtil.EMPTY_STRING_ARRAY;
 
     /**
      * Specify list of <b>static</b> import groups. Every group identified either by a common prefix
      * string, or by a regular expression enclosed in forward slashes (e.g. {@code /regexp/}).
      * If an import matches two or more groups,
      * the best match is selected (closest to the start, and the longest match).
      * All static imports, which does not match any group, fall into an additional group, located
      * at the end. Thus, the empty list of static groups (the default value) means one group for all
      * static imports. This property has effect only when the property {@code option} is set to
      * {@code top} or {@code bottom}.
      */
     private String[] staticGroups = CommonUtil.EMPTY_STRING_ARRAY;
 
     /**
      * Control whether type import groups should be separated by, at least, one blank
      * line or comment and aren't separated internally. It doesn't affect separations for static
      * imports.
      */
     private boolean separated;
 
     /**
      * Control whether static import groups should be separated by, at least, one blank
      * line or comment and aren't separated internally. When the property {@code option}
      * is set to {@code top} or {@code bottom}, this property requires {@code staticGroups}
      * to be enabled. When the property {@code option} is set to {@code under} or
      * {@code above}, this property allows blank lines between static and non-static
      * imports within the same group.
      */
     private boolean separatedStaticGroups;
 
     /**
      * Control whether type imports within each group should be sorted.
      * It doesn't affect sorting for static imports.
      */
     private boolean ordered = true;
 
     /**
      * Control whether string comparison should be case-sensitive or not. Case-sensitive
      * sorting is in <a href="https://en.wikipedia.org/wiki/ASCII#Order">ASCII sort order</a>.
      * It affects both type imports and static imports.
      */
     private boolean caseSensitive = true;
 
     /** Last imported group. */
     private int lastGroup;
     /** Line number of last import. */
     private int lastImportLine;
     /** Name of last import. */
     private String lastImport;
     /** If last import was static. */
     private boolean lastImportStatic;
     /** Whether there were any imports. */
     private boolean beforeFirstImport;
     /**
      * Whether static and type import groups should be split apart.
      * When the {@code option} property is set to {@code INFLOW}, {@code ABOVE} or {@code UNDER},
      * both the type and static imports use the properties {@code groups} and {@code separated}.
      * When the {@code option} property is set to {@code TOP} or {@code BOTTOM}, static imports
      * uses the properties {@code staticGroups} and {@code separatedStaticGroups}.
      */
     private boolean staticImportsApart;
 
     /**
      * Control whether <b>static imports</b> located at <b>top</b> or <b>bottom</b> are
      * sorted within the group.
      */
     private boolean sortStaticImportsAlphabetically;
 
     /**
      * Control whether to use container ordering (Eclipse IDE term) for static imports
      * or not.
      */
     private boolean useContainerOrderingForStatic;
 
     /**
      * Specify policy on the relative order between type imports and static imports.
      */
     private ImportOrderOption option = ImportOrderOption.UNDER;
 
     /**
      * Complied array of patterns for property {@code groups}.
      */
     private Pattern[] groupsReg = EMPTY_PATTERN_ARRAY;
 
     /**
      * Complied array of patterns for property {@code staticGroups}.
      */
     private Pattern[] staticGroupsReg = EMPTY_PATTERN_ARRAY;
 
     /**
      * Creates a new {@code ImportOrderCheck} instance.
      */
     public ImportOrderCheck() {
         // no code by default
     }
 
     /**
      * Setter to specify policy on the relative order between type imports and static imports.
      *
      * @param optionStr string to decode option from
      * @throws IllegalArgumentException if unable to decode
      * @since 5.0
      */
     public void setOption(String optionStr) {
         option = ImportOrderOption.valueOf(optionStr.trim().toUpperCase(Locale.ENGLISH));
     }
 
     /**
      * Setter to specify list of <b>type import</b> groups. Every group identified either by a
      * common prefix string, or by a regular expression enclosed in forward slashes
      * (e.g. {@code /regexp/}). If an import matches two or more groups,
      * the best match is selected (closest to the start, and the longest match).
      * All type imports, which does not match any group, falls into an
      * additional group, located at the end. Thus, the empty list of type groups (the default value)
      * means one group for all type imports.
      *
      * @param packageGroups a comma-separated list of package names/prefixes.
      * @since 3.2
      */
     public void setGroups(String... packageGroups) {
         groups = UnmodifiableCollectionUtil.copyOfArray(packageGroups, packageGroups.length);
         groupsReg = compilePatterns(packageGroups);
     }
 
     /**
      * Setter to specify list of <b>static</b> import groups. Every group identified either by a
      * common prefix string, or by a regular expression enclosed in forward slashes
      * (e.g. {@code /regexp/}). If an import matches two or more groups,
      * the best match is selected (closest to the start, and the longest match).
      * All static imports, which does not match any group, fall into an
      * additional group, located at the end. Thus, the empty list of static groups (the default
      * value) means one group for all static imports. This property has effect only when
      * the property {@code option} is set to {@code top} or {@code bottom}.
      *
      * @param packageGroups a comma-separated list of package names/prefixes.
      * @since 8.12
      */
     public void setStaticGroups(String... packageGroups) {
         staticGroups = UnmodifiableCollectionUtil.copyOfArray(packageGroups, packageGroups.length);
         staticGroupsReg = compilePatterns(packageGroups);
     }
 
     /**
      * Setter to control whether type imports within each group should be sorted.
      * It doesn't affect sorting for static imports.
      *
      * @param ordered
      *            whether lexicographic ordering of imports within a group
      *            required or not.
      * @since 3.2
      */
     public void setOrdered(boolean ordered) {
         this.ordered = ordered;
     }
 
     /**
      * Setter to control whether type import groups should be separated by, at least,
      * one blank line or comment and aren't separated internally.
      * It doesn't affect separations for static imports.
      *
      * @param separated
      *            whether groups should be separated by one blank line or comment.
      * @since 3.2
      */
     public void setSeparated(boolean separated) {
         this.separated = separated;
     }
 
     /**
      * Setter to control whether static import groups should be separated by, at least,
      * one blank line or comment and aren't separated internally.
      * When the property {@code option} is set to {@code top} or {@code bottom},
      * this property requires {@code staticGroups} to be enabled.
      * When the property {@code option} is set to {@code under} or {@code above},
      * this property allows blank lines between static and non-static imports
      * within the same group.
      *
      * @param separatedStaticGroups
      *            whether groups should be separated by one blank line or comment.
      * @since 8.12
      */
     public void setSeparatedStaticGroups(boolean separatedStaticGroups) {
         this.separatedStaticGroups = separatedStaticGroups;
     }
 
     /**
      * Setter to control whether string comparison should be case-sensitive or not.
      * Case-sensitive sorting is in
      * <a href="https://en.wikipedia.org/wiki/ASCII#Order">ASCII sort order</a>.
      * It affects both type imports and static imports.
      *
      * @param caseSensitive
      *            whether string comparison should be case-sensitive.
      * @since 3.3
      */
     public void setCaseSensitive(boolean caseSensitive) {
         this.caseSensitive = caseSensitive;
     }
 
     /**
      * Setter to control whether <b>static imports</b> located at <b>top</b> or
      * <b>bottom</b> are sorted within the group.
      *
      * @param sortAlphabetically true or false.
      * @since 6.5
      */
     public void setSortStaticImportsAlphabetically(boolean sortAlphabetically) {
         sortStaticImportsAlphabetically = sortAlphabetically;
     }
 
     /**
      * Setter to control whether to use container ordering (Eclipse IDE term) for static
      * imports or not.
      *
      * @param useContainerOrdering whether to use container ordering for static imports or not.
      * @since 7.1
      */
     public void setUseContainerOrderingForStatic(boolean useContainerOrdering) {
         useContainerOrderingForStatic = useContainerOrdering;
     }
 
     @Override
     public int[] getDefaultTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getAcceptableTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getRequiredTokens() {
         return new int[] {TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT};
     }
 
     @Override
     public void beginTree(DetailAST rootAST) {
         lastGroup = Integer.MIN_VALUE;
         lastImportLine = Integer.MIN_VALUE;
         lastImportStatic = false;
         beforeFirstImport = true;
         staticImportsApart =
             option == ImportOrderOption.TOP || option == ImportOrderOption.BOTTOM;
     }
 
     // -@cs[CyclomaticComplexity] SWITCH was transformed into IF-ELSE.
     @Override
     public void visitToken(DetailAST ast) {
         final FullIdent ident;
         final boolean isStatic;
 
         if (ast.getType() == TokenTypes.IMPORT) {
             ident = FullIdent.createFullIdentBelow(ast);
             isStatic = false;
         }
         else {
             ident = FullIdent.createFullIdent(ast.getFirstChild()
                     .getNextSibling());
             isStatic = true;
         }
 
         // using set of IF instead of SWITCH to analyze Enum options to satisfy coverage.
         // https://github.com/checkstyle/checkstyle/issues/1387
         if (option == ImportOrderOption.TOP || option == ImportOrderOption.ABOVE) {
             final boolean isStaticAndNotLastImport = isStatic && !lastImportStatic;
             doVisitToken(ident, isStatic, isStaticAndNotLastImport, ast);
         }
         else if (option == ImportOrderOption.BOTTOM || option == ImportOrderOption.UNDER) {
             final boolean isLastImportAndNonStatic = lastImportStatic && !isStatic;
             doVisitToken(ident, isStatic, isLastImportAndNonStatic, ast);
         }
         else if (option == ImportOrderOption.INFLOW) {
             // "previous" argument is useless here
             doVisitToken(ident, isStatic, true, ast);
         }
         else {
             throw new IllegalStateException(
                     String.format(Locale.ROOT, "Unexpected option for static imports: %s", option));
         }
 
         lastImportLine = ast.findFirstToken(TokenTypes.SEMI).getLineNo();
         lastImportStatic = isStatic;
         beforeFirstImport = false;
     }
 
     /**
      * Shares processing...
      *
      * @param ident the import to process.
      * @param isStatic whether the token is static or not.
      * @param previous previous non-static but current is static (above), or
      *                  previous static but current is non-static (under).
      * @param ast node of the AST.
      */
     private void doVisitToken(FullIdent ident, boolean isStatic, boolean previous, DetailAST ast) {
         final String name = ident.getText();
         final int groupIdx = getGroupNumber(isStatic && staticImportsApart, name);
 
         if (groupIdx > lastGroup) {
             handleGreaterGroup(isStatic, ast, name);
         }
         else if (groupIdx == lastGroup) {
             doVisitTokenInSameGroup(isStatic, previous, name, ast);
 
             if (separatedStaticGroups
                     && isStatic != lastImportStatic
                     && !isSeparatorBeforeImport(ast.getLineNo())) {
                 log(ast, MSG_SEPARATION, name);
             }
         }
         else {
             handleLowerGroup(previous, ast, name);
         }
         if (isSeparatorInGroup(groupIdx, isStatic, ast.getLineNo())) {
             log(ast, MSG_SEPARATED_IN_GROUP, name);
         }
 
         lastGroup = groupIdx;
         lastImport = name;
     }
 
     /**
      * Handles the case when the current import belongs to a group
      * that comes after the previous group. Verifies whether a
      * separator between groups is required.
      *
      * @param isStatic whether the current import is static
      * @param ast the AST node of the current import
      * @param name the fully qualified name of the current import
      */
     private void handleGreaterGroup(boolean isStatic, DetailAST ast, String name) {
         if (!beforeFirstImport
             && ast.getLineNo() - lastImportLine < 2
             && needSeparator(isStatic)) {
             log(ast, MSG_SEPARATION, name);
         }
     }
 
     /**
      * Handles the case when the current import belongs to a group
      * that should appear before the previous group. Logs either
      * a static-order violation or a group-order violation.
      *
      * @param previous indicates a static/non-static ordering transition
      * @param ast the AST node of the current import
      * @param name the fully qualified name of the current import
      */
     private void handleLowerGroup(boolean previous, DetailAST ast, String name) {
         if (previous
                 && (option == ImportOrderOption.TOP || option == ImportOrderOption.BOTTOM)) {
             log(ast, MSG_ORDERING_STATIC, name);
         }
         else {
             log(ast, MSG_ORDERING_GROUP, name);
         }
     }
 
     /**
      * Checks whether import groups should be separated.
      *
      * @param isStatic whether the token is static or not.
      * @return true if imports groups should be separated.
      */
     private boolean needSeparator(boolean isStatic) {
         final boolean typeImportSeparator = !isStatic && separated;
         final boolean staticImportSeparator;
         if (staticImportsApart) {
             staticImportSeparator = isStatic && separatedStaticGroups;
         }
         else {
             staticImportSeparator = separated;
         }
         final boolean separatorBetween = isStatic != lastImportStatic
             && (separated || separatedStaticGroups);
 
         return typeImportSeparator || staticImportSeparator || separatorBetween;
     }
 
     /**
      * Checks whether imports group separated internally.
      *
      * @param groupIdx group number.
      * @param isStatic whether the token is static or not.
      * @param line the line of the current import.
      * @return true if imports group are separated internally.
      */
     private boolean isSeparatorInGroup(int groupIdx, boolean isStatic, int line) {
         final boolean inSameGroup = groupIdx == lastGroup;
         final boolean result;
         if (inSameGroup) {
             result = (isStatic == lastImportStatic || !separatedStaticGroups)
                     && isSeparatorBeforeImport(line);
         }
         else {
             result = !needSeparator(isStatic) && isSeparatorBeforeImport(line);
         }
         return result;
     }
 
     /**
      * Checks whether there is any separator before current import.
      *
      * @param line the line of the current import.
      * @return true if there is separator before current import which isn't the first import.
      */
     private boolean isSeparatorBeforeImport(int line) {
         return line - lastImportLine > 1;
     }
 
     /**
      * Shares processing...
      *
      * @param isStatic whether the token is static or not.
      * @param previous previous non-static but current is static (above), or
      *     previous static but current is non-static (under).
      * @param name the name of the current import.
      * @param ast node of the AST.
      */
     private void doVisitTokenInSameGroup(boolean isStatic,
             boolean previous, String name, DetailAST ast) {
         if (ordered) {
             if (option == ImportOrderOption.INFLOW) {
                 if (isWrongOrder(name, isStatic)) {
                     log(ast, MSG_ORDERING_LEX, name, lastImport);
                 }
             }
             else {
                 if (previous) {
                     // static vs non-static placement violation
                     log(ast, MSG_ORDERING_STATIC, name);
                 }
                 else if (lastImportStatic == isStatic && isWrongOrder(name, isStatic)) {
                     // lexicographical violation
                     log(ast, MSG_ORDERING_LEX, name, lastImport);
                 }
             }
         }
     }
 
     /**
      * Checks whether import name is in wrong order.
      *
      * @param name import name.
      * @param isStatic whether it is a static import name.
      * @return true if import name is in wrong order.
      */
     private boolean isWrongOrder(String name, boolean isStatic) {
         final boolean result;
         if (isStatic) {
             if (useContainerOrderingForStatic) {
                 result = compareContainerOrder(lastImport, name, caseSensitive) > 0;
             }
             else if (staticImportsApart) {
                 result = sortStaticImportsAlphabetically
                     && compare(lastImport, name, caseSensitive) > 0;
             }
             else {
                 result = compare(lastImport, name, caseSensitive) > 0;
             }
         }
         else {
             // out of lexicographic order
             result = compare(lastImport, name, caseSensitive) > 0;
         }
         return result;
     }
 
     /**
      * Compares two import strings.
      * We first compare the container of the static import, container being the type enclosing
      * the static element being imported. When this returns 0, we compare the qualified
      * import name. For e.g. this is what is considered to be container names:
      * {@snippet lang="text" :
      * import static HttpConstants.COLON     => HttpConstants
      * import static HttpHeaders.addHeader   => HttpHeaders
      * import static HttpHeaders.setHeader   => HttpHeaders
      * import static HttpHeaders.Names.DATE  => HttpHeaders.Names
      * }
      *
      * <p>
      * According to this logic, HttpHeaders.Names would come after HttpHeaders.
      * For more details, see <a href="https://bugs.eclipse.org/bugs/show_bug.cgi?id=473629#c3">
      * static imports comparison method</a> in Eclipse.
      * </p>
      *
      * @param importName1 first import name
      * @param importName2 second import name
      * @param caseSensitive whether the comparison of fully qualified import names is
      *                      case-sensitive
      * @return the value {@code 0} if str1 is equal to str2; a value
      *         less than {@code 0} if str is less than the str2 (container order
      *         or lexicographical); and a value greater than {@code 0} if str1 is greater than str2
      *         (container order or lexicographically)
      */
     private static int compareContainerOrder(String importName1, String importName2,
                                              boolean caseSensitive) {
         final String container1 = getImportContainer(importName1);
         final String container2 = getImportContainer(importName2);
         final int compareContainersOrderResult;
         if (caseSensitive) {
             compareContainersOrderResult = container1.compareTo(container2);
         }
         else {
             compareContainersOrderResult = container1.compareToIgnoreCase(container2);
         }
         final int result;
         if (compareContainersOrderResult == 0) {
             result = compare(importName1, importName2, caseSensitive);
         }
         else {
             result = compareContainersOrderResult;
         }
         return result;
     }
 
     /**
      * Extracts import container name from fully qualified import name.
      * An import container name is the type which encloses the static element being imported.
      * For example, HttpConstants, HttpHeaders, HttpHeaders.Names are import container names:
      * {@snippet lang="text" :
      * import static HttpConstants.COLON     => HttpConstants
      * import static HttpHeaders.addHeader   => HttpHeaders
      * import static HttpHeaders.setHeader   => HttpHeaders
      * import static HttpHeaders.Names.DATE  => HttpHeaders.Names
      * }
      *
      * @param qualifiedImportName fully qualified import name.
      * @return import container name.
      */
     private static String getImportContainer(String qualifiedImportName) {
         final int lastDotIndex = qualifiedImportName.lastIndexOf('.');
         return qualifiedImportName.substring(0, lastDotIndex);
     }
 
     /**
      * Finds out what group the specified import belongs to.
      *
      * @param isStatic whether the token is static or not.
      * @param name the import name to find.
      * @return group number for given import name.
      */
     private int getGroupNumber(boolean isStatic, String name) {
         final Pattern[] patterns;
         if (isStatic) {
             patterns = staticGroupsReg;
         }
         else {
             patterns = groupsReg;
         }
 
         int number = getGroupNumber(patterns, name);
 
         if (isStatic && option == ImportOrderOption.BOTTOM) {
             number += groups.length + 1;
         }
         else if (!isStatic && option == ImportOrderOption.TOP) {
             number += staticGroups.length + 1;
         }
         return number;
     }
 
     /**
      * Finds out what group the specified import belongs to.
      *
      * @param patterns groups to check.
      * @param name the import name to find.
      * @return group number for given import name.
      */
     private static int getGroupNumber(Pattern[] patterns, String name) {
         int bestIndex = patterns.length;
         int bestEnd = -1;
         int bestPos = Integer.MAX_VALUE;
 
         // find out what group this belongs in
         // loop over patterns and get index
         for (int i = 0; i < patterns.length; i++) {
             final Matcher matcher = patterns[i].matcher(name);
             if (matcher.find()) {
                 if (matcher.start() < bestPos) {
                     bestIndex = i;
                     bestEnd = matcher.end();
                     bestPos = matcher.start();
                 }
                 else if (matcher.start() == bestPos && matcher.end() > bestEnd) {
                     bestIndex = i;
                     bestEnd = matcher.end();
                 }
             }
         }
         return bestIndex;
     }
 
     /**
      * Compares two strings.
      *
      * @param string1
      *            the first string
      * @param string2
      *            the second string
      * @param caseSensitive
      *            whether the comparison is case-sensitive
      * @return the value {@code 0} if string1 is equal to string2; a value
      *         less than {@code 0} if string1 is lexicographically less
      *         than the string2; and a value greater than {@code 0} if
      *         string1 is lexicographically greater than string2
      */
     private static int compare(String string1, String string2,
             boolean caseSensitive) {
         final int result;
         if (caseSensitive) {
             result = string1.compareTo(string2);
         }
         else {
             result = string1.compareToIgnoreCase(string2);
         }
 
         return result;
     }
 
     /**
      * Compiles the list of package groups and the order they should occur in the file.
      *
      * @param packageGroups a comma-separated list of package names/prefixes.
      * @return array of compiled patterns.
      * @throws IllegalArgumentException if any of the package groups are not valid.
      */
     private static Pattern[] compilePatterns(String... packageGroups) {
         final Pattern[] patterns = new Pattern[packageGroups.length];
         for (int i = 0; i < packageGroups.length; i++) {
             String pkg = packageGroups[i];
             final Pattern grp;
 
             // if the pkg name is the wildcard, make it match zero chars
             // from any name, so it will always be used as last resort.
             if (WILDCARD_GROUP_NAME.equals(pkg)) {
                 // matches any package
                 grp = Pattern.compile("");
             }
             else if (pkg.startsWith(FORWARD_SLASH)) {
                 if (!pkg.endsWith(FORWARD_SLASH)) {
                     throw new IllegalArgumentException("Invalid group: " + pkg);
                 }
                 pkg = pkg.substring(1, pkg.length() - 1);
                 grp = Pattern.compile(pkg);
             }
             else {
                 final StringBuilder pkgBuilder = new StringBuilder(pkg);
                 if (!pkg.endsWith(".")) {
                     pkgBuilder.append('.');
                 }
                 grp = Pattern.compile("^" + Pattern.quote(pkgBuilder.toString()));
             }
 
             patterns[i] = grp;
         }
         return patterns;
     }
 
 }