/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package dev.metaschema.core.model.validation;
   
   import org.eclipse.jdt.annotation.Owning;
   import org.xml.sax.ErrorHandler;
  import org.xml.sax.SAXException;
  import org.xml.sax.SAXParseException;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URI;
  import java.util.Collections;
  import java.util.LinkedList;
  import java.util.List;
  
  import javax.xml.XMLConstants;
  import javax.xml.transform.Source;
  import javax.xml.transform.stream.StreamSource;
  import javax.xml.validation.Schema;
  import javax.xml.validation.SchemaFactory;
  import javax.xml.validation.Validator;
  
  import dev.metaschema.core.model.IResourceLocation;
  import dev.metaschema.core.model.constraint.IConstraint.Level;
  import dev.metaschema.core.util.ObjectUtils;
  import edu.umd.cs.findbugs.annotations.NonNull;
  
  /**
   * Supports validating an XML resource using an XML schema.
   */
  public class XmlSchemaContentValidator
      extends AbstractContentValidator {
    private final Schema schema;
  
    @SuppressWarnings({ "resource", "PMD.UseTryWithResources" })
    @NonNull
    private static Schema toSchema(@NonNull List<? extends Source> schemaSources) throws IOException {
      SchemaFactory schemafactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
      // schemafactory.setResourceResolver(new ClasspathResourceResolver());
      // TODO verify source input streams are closed
      try {
        return ObjectUtils.notNull(schemaSources.isEmpty()
            ? schemafactory.newSchema()
            : schemafactory.newSchema(schemaSources.toArray(new Source[0])));
      } catch (SAXException ex) {
        throw new IOException(ex);
      } finally {
        // Close all source input streams
        for (Source source : schemaSources) {
          if (source instanceof StreamSource) {
            StreamSource streamSource = (StreamSource) source;
            if (streamSource.getInputStream() != null) {
              streamSource.getInputStream().close();
            }
          }
        }
      }
    }
  
    /**
     * Construct a new XML schema validator using the provided XML schema sources.
     * <p>
     * This constructor takes ownership of the provided schema sources and is
     * responsible for closing any associated input streams.
     *
     * @param schemaSources
     *          the XML schemas to use for validation. Ownership of these sources is
     *          transferred to this constructor, which will close any associated
     *          input streams.
     * @throws IOException
     *           if an error occurred while parsing the provided XML schemas
     */
    public XmlSchemaContentValidator(@Owning @NonNull List<? extends Source> schemaSources) throws IOException {
      this(toSchema(ObjectUtils.requireNonNull(schemaSources, "schemaSources")));
    }
  
    /**
     * Construct a new XML schema validator using the provided pre-parsed XML
     * schema(s).
     *
     * @param schema
     *          the pre-parsed XML schema(s) to use for validation
     */
    protected XmlSchemaContentValidator(@NonNull Schema schema) {
      this.schema = ObjectUtils.requireNonNull(schema, "schema");
    }
  
    private Schema getSchema() {
      return schema;
    }
  
    @Override
    public IValidationResult validate(InputStream is, URI documentUri) throws IOException {
      Source xmlSource = new StreamSource(is, documentUri.toASCIIString());
  
     Validator validator = getSchema().newValidator();
     XmlValidationErrorHandler errorHandler = new XmlValidationErrorHandler(documentUri);
     validator.setErrorHandler(errorHandler);
     try {
       validator.validate(xmlSource);
     } catch (SAXParseException ex) {
       String location = ex.getLineNumber() > -1 && ex.getColumnNumber() > -1
           ? String.format("at %d:%d", ex.getLineNumber(), ex.getColumnNumber())
           : "";
       throw new IOException(
           String.format("Unexpected failure during validation of '%s'%s. %s",
               documentUri,
               location,
               ex.getLocalizedMessage()),
           ex);
     } catch (SAXException ex) {
       throw new IOException(
           String.format("Unexpected failure during validation of '%s'. %s",
               documentUri,
               ex.getLocalizedMessage()),
           ex);
     }
     return errorHandler;
   }
 
   /**
    * Records an identified individual validation result found during XML schema
    * validation.
    */
   public static class XmlValidationFinding implements IValidationFinding, IResourceLocation {
     @NonNull
     private final URI documentUri;
     @NonNull
     private final SAXParseException exception;
     @NonNull
     private final Level severity;
 
     /**
      * Construct a new XML schema validation finding, which represents an issue
      * identified during XML schema validation.
      *
      * @param severity
      *          the finding significance
      * @param exception
      *          the XML schema validation exception generated during schema
      *          validation representing the issue
      * @param resourceUri
      *          the resource the issue was found in
      */
     public XmlValidationFinding(
         @NonNull Level severity,
         @NonNull SAXParseException exception,
         @NonNull URI resourceUri) {
       this.severity = ObjectUtils.requireNonNull(severity, "severity");
       this.exception = ObjectUtils.requireNonNull(exception, "exception");
       this.documentUri = ObjectUtils.requireNonNull(resourceUri, "documentUri");
     }
 
     @Override
     public String getIdentifier() {
       // always null
       return null;
     }
 
     @Override
     public Kind getKind() {
       return getSeverity() == Level.WARNING ? Kind.PASS : Kind.FAIL;
     }
 
     @Override
     public Level getSeverity() {
       return severity;
     }
 
     @Override
     public URI getDocumentUri() {
       String systemId = getCause().getSystemId();
       return systemId == null ? documentUri : URI.create(systemId);
     }
 
     @Override
     public int getLine() {
       return getCause().getLineNumber();
     }
 
     @Override
     public int getColumn() {
       return getCause().getColumnNumber();
     }
 
     @Override
     public long getCharOffset() {
       // not known
       return -1;
     }
 
     @Override
     public long getByteOffset() {
       // not known
       return -1;
     }
 
     @Override
     public IResourceLocation getLocation() {
       return this;
     }
 
     @Override
     public String getPathKind() {
       // not known
       return null;
     }
 
     @Override
     public String getPath() {
       // not known
       return null;
     }
 
     @Override
     public String getMessage() {
       return getCause().getLocalizedMessage();
     }
 
     @NonNull
     @Override
     public SAXParseException getCause() {
       return exception;
     }
   }
 
   private static class XmlValidationErrorHandler implements ErrorHandler, IValidationResult {
     @NonNull
     private final URI documentUri;
     @NonNull
     private final List<XmlValidationFinding> findings = new LinkedList<>();
     @NonNull
     private Level highestSeverity = Level.INFORMATIONAL;
 
     public XmlValidationErrorHandler(@NonNull URI documentUri) {
       this.documentUri = ObjectUtils.requireNonNull(documentUri, "documentUri");
     }
 
     @NonNull
     public URI getDocumentUri() {
       return documentUri;
     }
 
     private void adjustHighestSeverity(@NonNull Level severity) {
       if (highestSeverity.ordinal() < severity.ordinal()) {
         highestSeverity = severity;
       }
     }
 
     @SuppressWarnings("null")
     @Override
     public void warning(SAXParseException ex) throws SAXException {
       findings.add(new XmlValidationFinding(Level.WARNING, ex, getDocumentUri()));
       adjustHighestSeverity(Level.WARNING);
     }
 
     @SuppressWarnings("null")
     @Override
     public void error(SAXParseException ex) throws SAXException {
       findings.add(new XmlValidationFinding(Level.ERROR, ex, getDocumentUri()));
       adjustHighestSeverity(Level.CRITICAL);
     }
 
     @SuppressWarnings("null")
     @Override
     public void fatalError(SAXParseException ex) throws SAXException {
       findings.add(new XmlValidationFinding(Level.CRITICAL, ex, getDocumentUri()));
       adjustHighestSeverity(Level.CRITICAL);
     }
 
     @SuppressWarnings("null")
     @Override
     @NonNull
     public List<XmlValidationFinding> getFindings() {
       return Collections.unmodifiableList(findings);
     }
 
     @Override
     public Level getHighestSeverity() {
       return highestSeverity;
     }
   }
 }