/*
    * 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.IExpression;
  import gov.nist.secauto.metaschema.core.metapath.cst.path.ContextItem;
  import gov.nist.secauto.metaschema.core.metapath.function.FunctionUtils;
  import gov.nist.secauto.metaschema.core.metapath.function.library.FnBoolean;
  import gov.nist.secauto.metaschema.core.metapath.function.library.FnData;
  import gov.nist.secauto.metaschema.core.metapath.item.IItem;
  import gov.nist.secauto.metaschema.core.metapath.item.atomic.IAnyAtomicItem;
  import gov.nist.secauto.metaschema.core.metapath.item.atomic.IDecimalItem;
  import gov.nist.secauto.metaschema.core.metapath.item.atomic.INumericItem;
  import gov.nist.secauto.metaschema.core.metapath.item.node.INodeItem;
  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.math.BigDecimal;
  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
  })
  public class MetapathExpression {
  
    public enum ResultType {
      /**
       * The result is expected to be a {@link BigDecimal} value.
       */
      NUMBER,
      /**
       * The result is expected to be a {@link String} value.
       */
      STRING,
      /**
       * The result is expected to be a {@link Boolean} value.
       */
      BOOLEAN,
      /**
       * The result is expected to be an {@link ISequence} value.
       */
      SEQUENCE,
      /**
       * The result is expected to be an {@link INodeItem} value.
       */
      // TODO: audit use of this value, replace with ITEM where appropriate
      NODE,
      /**
       * The result is expected to be an {@link IItem} value.
       */
      ITEM;
    }
  
    private static final Logger LOGGER = LogManager.getLogger(MetapathExpression.class);
  
    @NonNull
    public static final MetapathExpression CONTEXT_NODE
        = new MetapathExpression(".", ContextItem.instance(), StaticContext.instance());
  
    @NonNull
    private final String path;
    @NonNull
    private final IExpression expression;
    @NonNull
    private final StaticContext staticContext;
  
    /**
     * Compiles a Metapath expression string.
     *
     * @param path
     *          the metapath expression
     * @return the compiled expression object
     * @throws MetapathException
    *           if an error occurred while compiling the Metapath expression
    */
   @NonNull
   public static MetapathExpression compile(@NonNull String path) {
     return compile(path, StaticContext.instance());
   }
 
   /**
    * 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 {
         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
           }
         });
 
         ParseTree tree = ObjectUtils.notNull(parser.expr());
 
         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.");
           }
         }
 
         IExpression expr = new BuildCSTVisitor(context).visit(tree);
 
         if (LOGGER.isDebugEnabled()) {
           LOGGER.atDebug().log(String.format("Metapath CST:%n%s", CSTPrinter.toString(expr)));
         }
         retval = new MetapathExpression(path, expr, context);
       } 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;
   }
 
   /**
    * 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;
   }
 
   /**
    * Get the original Metapath expression as a string.
    *
    * @return the expression
    */
   @NonNull
   public String getPath() {
     return path;
   }
 
   /**
    * Get the compiled abstract syntax tree (AST) representation of the Metapath.
    *
    * @return the Metapath AST
    */
   @NonNull
   protected IExpression getASTNode() {
     return expression;
   }
 
   /**
    * Get the static context used to compile this Metapath.
    *
    * @return the static context
    */
   @NonNull
   protected StaticContext getStaticContext() {
     return staticContext;
   }
 
   @Override
   public String toString() {
     return CSTPrinter.toString(getASTNode());
   }
 
   /**
    * Evaluate this Metapath expression without a specific focus. The required
    * result type will be determined by the {@code resultType} argument.
    *
    * @param <T>
    *          the expected result type
    * @param resultType
    *          the type of result to produce
    * @return the converted result
    * @throws TypeMetapathException
    *           if the provided sequence is incompatible with the requested result
    *           type
    * @throws MetapathException
    *           if an error occurred during evaluation
    * @see #toResultType(ISequence, ResultType)
    */
   @Nullable
   public <T> T evaluateAs(@NonNull ResultType resultType) {
     return evaluateAs(null, resultType);
   }
 
   /**
    * Evaluate this Metapath expression using the provided {@code focus} as the
    * initial evaluation context. The required result type will be determined by
    * the {@code resultType} argument.
    *
    * @param <T>
    *          the expected result type
    * @param focus
    *          the outer focus of the expression
    * @param resultType
    *          the type of result to produce
    * @return the converted result
    * @throws TypeMetapathException
    *           if the provided sequence is incompatible with the requested result
    *           type
    * @throws MetapathException
    *           if an error occurred during evaluation
    * @see #toResultType(ISequence, ResultType)
    */
   @Nullable
   public <T> T evaluateAs(
       @Nullable IItem focus,
       @NonNull ResultType resultType) {
     ISequence<?> result = evaluate(focus);
     return toResultType(result, resultType);
   }
 
   /**
    * Evaluate this Metapath expression using the provided {@code focus} as the
    * initial evaluation context. The specific result type will be determined by
    * the {@code resultType} argument.
    * <p>
    * This variant allow for reuse of a provided {@code dynamicContext}.
    *
    * @param <T>
    *          the expected result type
    * @param focus
    *          the outer focus of the expression
    * @param resultType
    *          the type of result to produce
    * @param dynamicContext
    *          the dynamic context to use for evaluation
    * @return the converted result
    * @throws TypeMetapathException
    *           if the provided sequence is incompatible with the requested result
    *           type
    * @throws MetapathException
    *           if an error occurred during evaluation
    * @see #toResultType(ISequence, ResultType)
    */
   @Nullable
   public <T> T evaluateAs(
       @Nullable IItem focus,
       @NonNull ResultType resultType,
       @NonNull DynamicContext dynamicContext) {
     ISequence<?> result = evaluate(focus, dynamicContext);
     return toResultType(result, resultType);
   }
 
   /**
    * Converts the provided {@code sequence} to the requested {@code resultType}.
    * <p>
    * The {@code resultType} determines the returned result, which is derived from
    * the evaluation result sequence, as follows:
    * <ul>
    * <li>BOOLEAN - the effective boolean result is produced using
    * {@link FnBoolean#fnBoolean(ISequence)}.</li>
    * <li>NODE - the first result item in the sequence is returned.</li>
    * <li>NUMBER - the sequence is cast to a number using
    * {@link IDecimalItem#cast(IAnyAtomicItem)}.</li>
    * <li>SEQUENCE - the evaluation result sequence.</li>
    * <li>STRING - the string value of the first result item in the sequence.</li>
    * </ul>
    *
    * @param <T>
    *          the requested return value
    * @param sequence
    *          the sequence to convert
    * @param resultType
    *          the type of result to produce
    * @return the converted result
    * @throws TypeMetapathException
    *           if the provided sequence is incompatible with the requested result
    *           type
    */
   @SuppressWarnings({ "PMD.NullAssignment", "PMD.CyclomaticComplexity" }) // for readability
   @Nullable
   protected <T> T toResultType(@NonNull ISequence<?> sequence, @NonNull ResultType resultType) {
     Object result;
     switch (resultType) {
     case BOOLEAN:
       result = FnBoolean.fnBoolean(sequence).toBoolean();
       break;
     case ITEM:
     case NODE:
       result = sequence.getFirstItem(true);
       break;
     case NUMBER:
       INumericItem numeric = FunctionUtils.toNumeric(sequence, true);
       result = numeric == null ? null : numeric.asDecimal();
       break;
     case SEQUENCE:
       result = sequence;
       break;
     case STRING:
       IAnyAtomicItem item = FnData.fnData(sequence).getFirstItem(true);
       result = item == null ? "" : item.asString();
       break;
     default:
       throw new InvalidTypeMetapathException(null, String.format("unsupported result type '%s'", resultType.name()));
     }
 
     @SuppressWarnings("unchecked") T retval = (T) result;
     return retval;
   }
 
   /**
    * Evaluate this Metapath expression without a specific focus.
    *
    * @param <T>
    *          the type of items contained in the resulting sequence
    * @return a sequence of Metapath items representing the result of the
    *         evaluation
    * @throws MetapathException
    *           if an error occurred during evaluation
    */
   @NonNull
   public <T extends IItem> ISequence<T> evaluate() {
     return evaluate((IItem) null);
   }
 
   /**
    * Evaluate this Metapath expression using the provided {@code focus} as the
    * initial evaluation context.
    *
    * @param <T>
    *          the type of items contained in the resulting sequence
    * @param focus
    *          the outer focus of the expression
    * @return a sequence of Metapath items representing the result of the
    *         evaluation
    * @throws MetapathException
    *           if an error occurred during evaluation
    */
   @SuppressWarnings("unchecked")
   @NonNull
   public <T extends IItem> ISequence<T> evaluate(
       @Nullable IItem focus) {
     return (ISequence<T>) evaluate(focus, new DynamicContext(getStaticContext()));
   }
 
   /**
    * Evaluate this Metapath expression using the provided {@code focus} as the
    * initial evaluation context.
    * <p>
    * This variant allow for reuse of a provided {@code dynamicContext}.
    *
    * @param <T>
    *          the type of items contained in the resulting sequence
    * @param focus
    *          the outer focus of the expression
    * @param dynamicContext
    *          the dynamic context to use for evaluation
    * @return a sequence of Metapath items representing the result of the
    *         evaluation
    * @throws MetapathException
    *           if an error occurred during evaluation
    */
   @SuppressWarnings("unchecked")
   @NonNull
   public <T extends IItem> ISequence<T> evaluate(
       @Nullable IItem focus,
       @NonNull DynamicContext dynamicContext) {
     try {
       return (ISequence<T>) getASTNode().accept(dynamicContext, ISequence.of(focus));
     } catch (MetapathException ex) { // NOPMD - intentional
       throw new MetapathException(
           String.format("An error occurred while evaluating the expression '%s'.", getPath()), ex);
     }
   }
 }