/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package dev.metaschema.core.model.validation;
   
   import org.everit.json.schema.Schema;
   import org.everit.json.schema.ValidationException;
  import org.everit.json.schema.loader.SchemaLoader;
  import org.json.JSONException;
  import org.json.JSONObject;
  import org.json.JSONTokener;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.Reader;
  import java.net.URI;
  import java.util.Collections;
  import java.util.List;
  import java.util.Objects;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  
  import dev.metaschema.core.model.IResourceLocation;
  import dev.metaschema.core.model.constraint.IConstraint;
  import dev.metaschema.core.util.ObjectUtils;
  import edu.umd.cs.findbugs.annotations.NonNull;
  
  /**
   * Validates JSON content against a JSON schema.
   */
  public class JsonSchemaContentValidator
      extends AbstractContentValidator {
    @NonNull
    private final Schema schema;
  
    /**
     * Construct a new JSON schema validator using the provided reader to load the
     * JSON schema.
     *
     * @param reader
     *          the JSON schema reader
     */
    public JsonSchemaContentValidator(@NonNull Reader reader) {
      this(new JSONTokener(reader));
    }
  
    /**
     * Construct a new JSON schema validator using the provided input stream to load
     * the JSON schema.
     *
     * @param is
     *          the JSON schema input source
     */
    public JsonSchemaContentValidator(@NonNull InputStream is) {
      this(new JSONTokener(is));
    }
  
    /**
     * Construct a new JSON schema validator using the provided JSON object for the
     * JSON schema.
     *
     * @param jsonSchema
     *          the JSON schema
     */
    public JsonSchemaContentValidator(@NonNull JSONObject jsonSchema) {
      this(ObjectUtils.notNull(SchemaLoader.load(jsonSchema)));
    }
  
    /**
     * Construct a new JSON schema validator using the provided JSON tokenizer to
     * load the schema.
     *
     * @param tokenizer
     *          the JSON schema token stream
     */
    protected JsonSchemaContentValidator(@NonNull JSONTokener tokenizer) {
      this(new JSONObject(tokenizer));
    }
  
    /**
     * Construct a new JSON schema validator using the preloaded JSON schema.
     *
     * @param schema
     *          the preloaded JSON schema
     */
    protected JsonSchemaContentValidator(@NonNull Schema schema) {
      this.schema = ObjectUtils.requireNonNull(schema, "schema");
    }
  
    @Override
    public IValidationResult validate(InputStream is, URI resourceUri) throws IOException {
      JSONObject json;
      try {
        json = new JSONObject(new JSONTokener(is));
      } catch (JSONException ex) {
        throw new IOException(String.format("Unable to parse JSON from '%s'", resourceUri), ex);
      }
     return validate(json, resourceUri);
   }
 
   /**
    * Validate the provided JSON.
    *
    * @param json
    *          the JSON to validate
    * @param resourceUri
    *          the source URI for the JSON to validate
    * @return the validation results
    */
   @SuppressWarnings("null")
   @NonNull
   public IValidationResult validate(@NonNull JSONObject json, @NonNull URI resourceUri) {
     IValidationResult retval;
     try {
       schema.validate(json);
       retval = IValidationResult.PASSING_RESULT;
     } catch (ValidationException ex) {
       retval = new JsonValidationResult(handleValidationException(ex, resourceUri).collect(Collectors.toList()));
     }
 
     return retval;
   }
 
   /**
    * Build validation findings from a validation exception.
    *
    * @param exception
    *          the JSON schema validation exception generated during schema
    *          validation representing the issue
    * @param resourceUri
    *          the resource the issue was found in
    * @return the stream of findings
    */
   @SuppressWarnings("null")
   @NonNull
   protected Stream<JsonValidationFinding> handleValidationException(
       @NonNull ValidationException exception,
       @NonNull URI resourceUri) {
     JsonValidationFinding finding = new JsonValidationFinding(exception, resourceUri);
     Stream<JsonValidationFinding> childFindings = exception.getCausingExceptions().stream()
         .flatMap(ex -> handleValidationException(ex, resourceUri));
     return Stream.concat(Stream.of(finding), childFindings);
   }
 
   /**
    * Records an identified individual validation result found during JSON schema
    * validation.
    */
   public static class JsonValidationFinding implements IValidationFinding {
     @NonNull
     private final ValidationException exception;
     @NonNull
     private final URI documentUri;
 
     /**
      * Construct a new XML schema validation finding, which represents an issue
      * identified during XML schema validation.
      *
      * @param exception
      *          the JSON schema validation exception generated during schema
      *          validation representing the issue
      * @param resourceUri
      *          the resource the issue was found in
      */
     public JsonValidationFinding(
         @NonNull ValidationException exception,
         @NonNull URI resourceUri) {
       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 IValidationFinding.Kind.FAIL;
     }
 
     @Override
     public IConstraint.Level getSeverity() {
       return IConstraint.Level.CRITICAL;
     }
 
     @Override
     public URI getDocumentUri() {
       return documentUri;
     }
 
     @Override
     public IResourceLocation getLocation() {
       // not known
       return null;
     }
 
     @Override
     public String getPathKind() {
       return "JSON-pointer";
     }
 
     @Override
     public String getPath() {
       return getCause().getPointerToViolation();
     }
 
     @Override
     public String getMessage() {
       return getCause().getLocalizedMessage();
     }
 
     @NonNull
     @Override
     public ValidationException getCause() {
       return exception;
     }
   }
 
   private static class JsonValidationResult implements IValidationResult {
     @NonNull
     private final List<JsonValidationFinding> findings;
 
     @SuppressWarnings("null")
     public JsonValidationResult(@NonNull List<JsonValidationFinding> findings) {
       this.findings = Collections.unmodifiableList(Objects.requireNonNull(findings, "findings"));
     }
 
     @Override
     public IConstraint.Level getHighestSeverity() {
       return findings.isEmpty() ? IConstraint.Level.INFORMATIONAL : IConstraint.Level.ERROR;
     }
 
     @Override
     public List<? extends IValidationFinding> getFindings() {
       return findings;
     }
 
   }
 }