/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package gov.nist.secauto.metaschema.core.metapath;
   
   import gov.nist.secauto.metaschema.core.metapath.antlr.FailingErrorListener;
   import gov.nist.secauto.metaschema.core.metapath.antlr.Metapath10;
  import gov.nist.secauto.metaschema.core.metapath.antlr.Metapath10Lexer;
  import gov.nist.secauto.metaschema.core.metapath.antlr.ParseTreePrinter;
  import gov.nist.secauto.metaschema.core.metapath.cst.BuildCSTVisitor;
  import gov.nist.secauto.metaschema.core.metapath.cst.CSTPrinter;
  import gov.nist.secauto.metaschema.core.metapath.cst.path.ContextItem;
  import gov.nist.secauto.metaschema.core.metapath.item.IItem;
  import gov.nist.secauto.metaschema.core.metapath.item.ISequence;
  import gov.nist.secauto.metaschema.core.util.ObjectUtils;
  
  import org.antlr.v4.runtime.CharStreams;
  import org.antlr.v4.runtime.CommonTokenStream;
  import org.antlr.v4.runtime.DefaultErrorStrategy;
  import org.antlr.v4.runtime.Parser;
  import org.antlr.v4.runtime.misc.ParseCancellationException;
  import org.antlr.v4.runtime.tree.ParseTree;
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.PrintStream;
  import java.nio.charset.StandardCharsets;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  
  /**
   * Supports compiling and executing Metapath expressions.
   */
  @SuppressWarnings({
      "PMD.CouplingBetweenObjects" // necessary since this class aggregates functionality
  })
  class MetapathExpression implements IMetapathExpression {
  
    /**
     * The Metapath expression identifying the current context node.
     */
    @NonNull
    public static final MetapathExpression CONTEXT_NODE
        = new MetapathExpression(".", ContextItem.instance(), StaticContext.instance());
    private static final Logger LOGGER = LogManager.getLogger(MetapathExpression.class);
  
    @NonNull
    private final String path;
    @NonNull
    private final IExpression expression;
    @NonNull
    private final StaticContext staticContext;
  
    /**
     * Compiles a Metapath expression string using the provided static context.
     *
     * @param path
     *          the metapath expression
     * @param context
     *          the static evaluation context
     * @return the compiled expression object
     * @throws MetapathException
     *           if an error occurred while compiling the Metapath expression
     */
    @NonNull
    public static MetapathExpression compile(@NonNull String path, @NonNull StaticContext context) {
      @NonNull
      MetapathExpression retval;
      if (".".equals(path)) {
        retval = CONTEXT_NODE;
      } else {
        try {
          Metapath10 parser = newParser(path);
          ParseTree tree = ObjectUtils.notNull(parser.metapath());
          logAst(tree);
          IExpression expr = new BuildCSTVisitor(context).visit(tree);
          logCst(expr);
          retval = new MetapathExpression(path, expr, context);
        } catch (StaticMetapathException ex) {
          String message = ex.getMessageText();
          throw new StaticMetapathException(
              ex.getCode(),
              String.format("Unable to compile path '%s'.%s", path, message == null ? "" : " " + message),
              ex);
        } catch (MetapathException | ParseCancellationException ex) {
          String msg = String.format("Unable to compile Metapath '%s'", path);
          LOGGER.atError().withThrowable(ex).log(msg);
          throw new StaticMetapathException(StaticMetapathException.INVALID_PATH_GRAMMAR, msg, ex);
        }
      }
      return retval;
    }
  
    private static void logCst(@NonNull IExpression expr) {
     if (LOGGER.isDebugEnabled()) {
       LOGGER.atDebug().log(String.format("Metapath CST:%n%s", CSTPrinter.toString(expr)));
     }
   }
 
   private static void logAst(@NonNull ParseTree tree) {
     if (LOGGER.isDebugEnabled()) {
       try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
         try (PrintStream ps = new PrintStream(os, true, StandardCharsets.UTF_8)) {
           ParseTreePrinter printer = new ParseTreePrinter(ps);
           printer.print(tree, Metapath10.ruleNames);
           ps.flush();
         }
         LOGGER.atDebug().log(String.format("Metapath AST:%n%s", os.toString(StandardCharsets.UTF_8)));
       } catch (IOException ex) {
         LOGGER.atError().withThrowable(ex).log("An unexpected error occurred while closing the steam.");
       }
     }
   }
 
   @NonNull
   private static Metapath10 newParser(@NonNull String path) {
     Metapath10Lexer lexer = new Metapath10Lexer(CharStreams.fromString(path));
     lexer.removeErrorListeners();
     lexer.addErrorListener(new FailingErrorListener());
 
     CommonTokenStream tokens = new CommonTokenStream(lexer);
     Metapath10 parser = new Metapath10(tokens);
     parser.removeErrorListeners();
     parser.addErrorListener(new FailingErrorListener());
     parser.setErrorHandler(new DefaultErrorStrategy() {
 
       @Override
       public void sync(Parser recognizer) {
         // disable
       }
     });
     return parser;
   }
 
   /**
    * Construct a new Metapath expression.
    *
    * @param path
    *          the Metapath as a string
    * @param expr
    *          the Metapath as a compiled abstract syntax tree (AST)
    * @param staticContext
    *          the static evaluation context
    */
   protected MetapathExpression(
       @NonNull String path,
       @NonNull IExpression expr,
       @NonNull StaticContext staticContext) {
     this.path = path;
     this.expression = expr;
     this.staticContext = staticContext;
   }
 
   @Override
   public String getPath() {
     return path;
   }
 
   /**
    * Get the compiled compact syntax tree (CST) representation of the Metapath.
    *
    * @return the Metapath CST
    */
   @NonNull
   protected IExpression getCSTNode() {
     return expression;
   }
 
   @Override
   public StaticContext getStaticContext() {
     return staticContext;
   }
 
   @Override
   public String toString() {
     return getPath();
   }
 
   @Override
   @NonNull
   public <T extends IItem> ISequence<T> evaluate(
       @Nullable IItem focus,
       @NonNull DynamicContext dynamicContext) {
     try {
       return ObjectUtils.asType(getCSTNode().accept(dynamicContext, ISequence.of(focus)).reusable());
     } catch (MetapathException ex) {
       throw new MetapathException(
           String.format("An error occurred while evaluating the expression '%s'. %s",
               getPath(),
               ex.getLocalizedMessage()),
           ex);
     }
   }
 
   @FunctionalInterface
   interface ConversionFunction {
     @Nullable
     Object convert(@NonNull ISequence<?> sequence);
   }
 
 }