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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   *
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   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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  package jdkx.annotation.processing;
  
  import jdkx.tools.JavaFileManager;
  import jdkx.tools.*;
  import jdkx.lang.model.element.Element;
  import jdkx.lang.model.util.Elements;
  import java.io.IOException;
  
  /**
   * This interface supports the creation of new files by an annotation
   * processor.  Files created in this way will be known to the
   * annotation processing tool implementing this interface, better
   * enabling the tool to manage them.  Source and class files so
   * created will be {@linkplain RoundEnvironment#getRootElements
   * considered for processing} by the tool in a subsequent {@linkplain
   * RoundEnvironment round of processing} after the {@code close}
   * method has been called on the {@code Writer} or {@code
   * OutputStream} used to write the contents of the file.
   *
   * Three kinds of files are distinguished: source files, class files,
   * and auxiliary resource files.
   *
   * <p> There are two distinguished supported locations (subtrees
   * within the logical file system) where newly created files are
   * placed: one for {@linkplain
   * jdkx.tools.StandardLocation#SOURCE_OUTPUT new source files}, and
   * one for {@linkplain jdkx.tools.StandardLocation#CLASS_OUTPUT new
   * class files}.  (These might be specified on a tool's command line,
   * for example, using flags such as {@code -s} and {@code -d}.)  The
   * actual locations for new source files and new class files may or
   * may not be distinct on a particular run of the tool.  Resource
   * files may be created in either location.  The methods for reading
   * and writing resources take a relative name argument.  A relative
   * name is a non-null, non-empty sequence of path segments separated
   * by {@code '/'}; {@code '.'} and {@code '..'} are invalid path
   * segments.  A valid relative name must match the
   * &quot;path-rootless&quot; rule of <a
   * href="http://www.ietf.org/rfc/rfc3986.txt">RFC&nbsp;3986</a>, section
   * 3.3.
   *
   * <p>The file creation methods take a variable number of arguments to
   * allow the <em>originating elements</em> to be provided as hints to
   * the tool infrastructure to better manage dependencies.  The
   * originating elements are the classes or interfaces or packages
   * (representing {@code package-info} files) or modules (representing
   * {@code module-info} files) which caused an annotation processor to
   * attempt to create a new file.  For example, if an annotation
   * processor tries to create a source file, {@code
   * GeneratedFromUserSource}, in response to processing
   *
   * <blockquote><pre>
   *  &#64;Generate
   *  public class UserSource {}
   * </pre></blockquote>
   *
   * the type element for {@code UserSource} should be passed as part of
   * the creation method call as in:
   *
   * <blockquote><pre>
   *      filer.createSourceFile("GeneratedFromUserSource",
   *                             eltUtils.getTypeElement("UserSource"));
   * </pre></blockquote>
   *
   * If there are no originating elements, none need to be passed.  This
   * information may be used in an incremental environment to determine
   * the need to rerun processors or remove generated files.
   * Non-incremental environments may ignore the originating element
   * information.
   *
   * <p> During each run of an annotation processing tool, a file with a
   * given pathname may be created only once.  If that file already
   * exists before the first attempt to create it, the old contents will
   * be deleted.  Any subsequent attempt to create the same file during
   * a run will throw a {@link FilerException}, as will attempting to
   * create both a class file and source file for the same type name or
   * same package name.  The {@linkplain Processor initial inputs} to
   * the tool are considered to be created by the zeroth round;
   * therefore, attempting to create a source or class file
   * corresponding to one of those inputs will result in a {@link
   * FilerException}.
   *
   * <p> In general, processors must not knowingly attempt to overwrite
   * existing files that were not generated by some processor.  A {@code
   * Filer} may reject attempts to open a file corresponding to an
   * existing class or interface, like {@code java.lang.Object}.  Likewise, the
   * invoker of the annotation processing tool must not knowingly
   * configure the tool such that the discovered processors will attempt
   * to overwrite existing files that were not generated.
   *
   * <p> Processors can indicate a source or class file is generated by
   * including a {@link jdkx.annotation.processing.Generated}
   * annotation if the environment is configured so that that class or
   * interface is accessible.
   *
   * @apiNote Some of the effect of overwriting a file can be
   * achieved by using a <i>decorator</i>-style pattern.  Instead of
   * modifying a class directly, the class is designed so that either
   * its superclass is generated by annotation processing or subclasses
   * of the class are generated by annotation processing.  If the
   * subclasses are generated, the parent class may be designed to use
   * factories instead of public constructors so that only subclass
   * instances would be presented to clients of the parent class.
   *
   * @author Joseph D. Darcy
   * @author Scott Seligman
   * @author Peter von der Ah&eacute;
   * @since 1.6
   */
  public interface Filer {
      /**
       * Creates a new source file and returns an object to allow
       * writing to it. A source file for a class, interface, or a
       * package can be created.
       *
       * The file's name and path (relative to the {@linkplain
       * StandardLocation#SOURCE_OUTPUT root output location for source
       * files}) are based on the name of the item to be declared in
       * that file as well as the specified module for the item (if
       * any).
       *
       * If more than one class or interface is being declared in a single file (that
       * is, a single compilation unit), the name of the file should
       * correspond to the name of the principal top-level class or interface (the
       * public one, for example).
       *
       * <p>A source file can also be created to hold information about
       * a package, including package annotations.  To create a source
       * file for a named package, have the {@code name} argument be the
       * package's name followed by {@code ".package-info"}; to create a
       * source file for an unnamed package, use {@code "package-info"}.
       *
       * <p>The optional module name is prefixed to the type name or
       * package name and separated using a "{@code /}" character. For
       * example, to create a source file for class {@code a.B} in module
       * {@code foo}, use a {@code name} argument of {@code "foo/a.B"}.
       *
       * <p>If no explicit module prefix is given and modules are supported
       * in the environment, a suitable module is inferred. If a suitable
       * module cannot be inferred {@link FilerException} is thrown.
       * An implementation may use information about the configuration of
       * the annotation processing tool as part of the inference.
       *
       * <p>Creating a source file in or for an <em>unnamed</em> package in a <em>named</em>
       * module is <em>not</em> supported.
       *
       * @apiNote To use a particular {@linkplain
       * java.nio.charset.Charset charset} to encode the contents of the
       * file, an {@code OutputStreamWriter} with the chosen charset can
       * be created from the {@code OutputStream} from the returned
       * object. If the {@code Writer} from the returned object is
       * directly used for writing, its charset is determined by the
       * implementation.  An annotation processing tool may have an
       * {@code -encoding} flag or analogous option for specifying this;
       * otherwise, it will typically be the platform's default
       * encoding.
       *
       * <p>To avoid subsequent errors, the contents of the source file
       * should be compatible with the {@linkplain
       * ProcessingEnvironment#getSourceVersion source version} being used
       * for this run.
       *
       * @implNote In the reference implementation, if the annotation
       * processing tool is processing a single module <i>M</i>,
       * then <i>M</i> is used as the module for files created without
       * an explicit module prefix. If the tool is processing multiple
       * modules, and {@link
       * Elements#getPackageElement(java.lang.CharSequence)
       * Elements.getPackageElement(package-of(name))}
       * returns a package, the module that owns the returned package is used
       * as the target module. A separate option may be used to provide the target
       * module if it cannot be determined using the above rules.
       *
       * @param name  canonical (fully qualified) name of the principal class or interface
       *          being declared in this file or a package name followed by
       *          {@code ".package-info"} for a package information file
       * @param originatingElements class, interface, package, or module
       * elements causally associated with the creation of this file,
       * may be elided or {@code null}
       * @return a {@code JavaFileObject} to write the new source file
       * @throws FilerException if the same pathname has already been
       * created, the same class or interface has already been created, the name is
       * otherwise not valid for the entity requested to being created,
       * if the target module cannot be determined, if the target
       * module is not writable, or a module is specified when the environment
       * doesn't support modules.
       * @throws IOException if the file cannot be created
       * @jls 7.3 Compilation Units
       */
      JavaFileObject createSourceFile(CharSequence name,
                                      Element... originatingElements) throws IOException;
  
      /**
       * Creates a new class file, and returns an object to allow
       * writing to it. A class file for a class, interface, or a package can
       * be created.
       *
       * The file's name and path (relative to the {@linkplain
       * StandardLocation#CLASS_OUTPUT root output location for class
       * files}) are based on the name of the item to be declared as
       * well as the specified module for the item (if any).
       *
       * <p>A class file can also be created to hold information about a
       * package, including package annotations. To create a class file
       * for a named package, have the {@code name} argument be the
       * package's name followed by {@code ".package-info"}; creating a
       * class file for an unnamed package is not supported.
       *
       * <p>The optional module name is prefixed to the type name or
       * package name and separated using a "{@code /}" character. For
       * example, to create a class file for class {@code a.B} in module
       * {@code foo}, use a {@code name} argument of {@code "foo/a.B"}.
       *
       * <p>If no explicit module prefix is given and modules are supported
       * in the environment, a suitable module is inferred. If a suitable
       * module cannot be inferred {@link FilerException} is thrown.
       * An implementation may use information about the configuration of
       * the annotation processing tool as part of the inference.
       *
       * <p>Creating a class file in or for an <em>unnamed</em> package in a <em>named</em>
       * module is <em>not</em> supported.
       *
       * @apiNote To avoid subsequent errors, the contents of the class
       * file should be compatible with the {@linkplain
       * ProcessingEnvironment#getSourceVersion source version} being
       * used for this run.
       *
       * @implNote In the reference implementation, if the annotation
       * processing tool is processing a single module <i>M</i>,
       * then <i>M</i> is used as the module for files created without
       * an explicit module prefix. If the tool is processing multiple
       * modules, and {@link
       * Elements#getPackageElement(java.lang.CharSequence)
       * Elements.getPackageElement(package-of(name))}
       * returns a package, the module that owns the returned package is used
       * as the target module. A separate option may be used to provide the target
       * module if it cannot be determined using the above rules.
       *
       * @param name binary name of the class or interface being written
       * or a package name followed by {@code ".package-info"} for a
       * package information file
       * @param originatingElements class or interface or package or
       * module elements causally associated with the creation of this
       * file, may be elided or {@code null}
       * @return a {@code JavaFileObject} to write the new class file
       * @throws FilerException if the same pathname has already been
       * created, the same class or interface has already been created, the name is
       * not valid for a class or interface, if the target module cannot be determined,
       * if the target module is not writable, or a module is specified when
       * the environment doesn't support modules.
       * @throws IOException if the file cannot be created
       */
      JavaFileObject createClassFile(CharSequence name,
                                     Element... originatingElements) throws IOException;
  
      /**
       * Creates a new auxiliary resource file for writing and returns a
       * file object for it.  The file may be located along with the
       * newly created source files, newly created binary files, or
       * other supported location.  The locations {@link
       * StandardLocation#CLASS_OUTPUT CLASS_OUTPUT} and {@link
       * StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must be
       * supported. The resource may be named relative to some module
       * and/or package (as are source and class files), and from there
       * by a relative pathname.  In a loose sense, the full pathname of
       * the new file will be the concatenation of {@code location},
       * {@code moduleAndPkg}, and {@code relativeName}.
       *
       * If {@code moduleAndPkg} contains a "{@code /}" character, the
       * prefix before the "{@code /}" character is the module name and
       * the suffix after the "{@code /}" character is the package
       * name. The package suffix may be empty. If {@code moduleAndPkg}
       * does not contain a "{@code /}" character, the entire argument
       * is interpreted as a package name.
       *
       * <p>If the given location is neither a {@linkplain
       * JavaFileManager.Location#isModuleOrientedLocation()
       * module oriented location}, nor an {@linkplain
       * JavaFileManager.Location#isOutputLocation()
       * output location containing multiple modules}, and the explicit
       * module prefix is given, {@link FilerException} is thrown.
       *
       * <p>If the given location is either a module oriented location,
       * or an output location containing multiple modules, and no explicit
       * modules prefix is given, a suitable module is
       * inferred. If a suitable module cannot be inferred {@link
       * FilerException} is thrown. An implementation may use information
       * about the configuration of the annotation processing tool
       * as part of the inference.
       *
       * <p>Files created via this method are <em>not</em> registered for
       * annotation processing, even if the full pathname of the file
       * would correspond to the full pathname of a new source file
       * or new class file.
       *
       * @implNote In the reference implementation, if the annotation
       * processing tool is processing a single module <i>M</i>,
       * then <i>M</i> is used as the module for files created without
       * an explicit module prefix. If the tool is processing multiple
       * modules, and {@link
       * Elements#getPackageElement(java.lang.CharSequence)
       * Elements.getPackageElement(package-of(name))}
       * returns a package, the module that owns the returned package is used
       * as the target module. A separate option may be used to provide the target
       * module if it cannot be determined using the above rules.
       *
       * @param location location of the new file
       * @param moduleAndPkg module and/or package relative to which the file
       *           should be named, or the empty string if none
       * @param relativeName final pathname components of the file
       * @param originatingElements class or interface or package or
       * module elements causally associated with the creation of this
       * file, may be elided or
       * {@code null}
       * @return a {@code FileObject} to write the new resource
       * @throws IOException if the file cannot be created
       * @throws FilerException if the same pathname has already been
       * created, if the target module cannot be determined,
       * or if the target module is not writable, or if an explicit
       * target module is specified and the location does not support it.
       * @throws IllegalArgumentException for an unsupported location
       * @throws IllegalArgumentException if {@code moduleAndPkg} is ill-formed
       * @throws IllegalArgumentException if {@code relativeName} is not relative
       */
     FileObject createResource(JavaFileManager.Location location,
                               CharSequence moduleAndPkg,
                               CharSequence relativeName,
                               Element... originatingElements) throws IOException;
  
      /**
       * Returns an object for reading an existing resource.  The
       * locations {@link StandardLocation#CLASS_OUTPUT CLASS_OUTPUT}
       * and {@link StandardLocation#SOURCE_OUTPUT SOURCE_OUTPUT} must
       * be supported.
       *
       * <p>If {@code moduleAndPkg} contains a "{@code /}" character, the
       * prefix before the "{@code /}" character is the module name and
       * the suffix after the "{@code /}" character is the package
       * name. The package suffix may be empty; however, if a module
       * name is present, it must be nonempty. If {@code moduleAndPkg}
       * does not contain a "{@code /}" character, the entire argument
       * is interpreted as a package name.
       *
       * <p>If the given location is neither a {@linkplain
       * JavaFileManager.Location#isModuleOrientedLocation()
       * module oriented location}, nor an {@linkplain
       * JavaFileManager.Location#isOutputLocation()
       * output location containing multiple modules}, and the explicit
       * module prefix is given, {@link FilerException} is thrown.
       *
       * <p>If the given location is either a module oriented location,
       * or an output location containing multiple modules, and no explicit
       * modules prefix is given, a suitable module is
       * inferred. If a suitable module cannot be inferred {@link
       * FilerException} is thrown. An implementation may use information
       * about the configuration of the annotation processing tool
       * as part of the inference.
       *
       * @implNote In the reference implementation, if the annotation
       * processing tool is processing a single module <i>M</i>,
       * then <i>M</i> is used as the module for files read without
       * an explicit module prefix. If the tool is processing multiple
       * modules, and {@link
       * Elements#getPackageElement(java.lang.CharSequence)
       * Elements.getPackageElement(package-of(name))}
       * returns a package, the module that owns the returned package is used
       * as the source module. A separate option may be used to provide the target
       * module if it cannot be determined using the above rules.
       *
       * @param location location of the file
       * @param moduleAndPkg module and/or package relative to which the file
       *          should be searched for, or the empty string if none
       * @param relativeName final pathname components of the file
       * @return an object to read the file
       * @throws FilerException if the same pathname has already been
       * opened for writing, if the source module cannot be determined,
       * or if the target module is not writable, or if an explicit target
       * module is specified and the location does not support it.
       * @throws IOException if the file cannot be opened
       * @throws IllegalArgumentException for an unsupported location
       * @throws IllegalArgumentException if {@code moduleAndPkg} is ill-formed
       * @throws IllegalArgumentException if {@code relativeName} is not relative
       */
      FileObject getResource(JavaFileManager.Location location,
                             CharSequence moduleAndPkg,
                             CharSequence relativeName) throws IOException;
  }
  