SparqlTransformer.scala

/*
 * Copyright © 2015-2018 the contributors (see Contributors.md).
 *
 *  This file is part of Knora.
 *
 *  Knora is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published
 *  by the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  Knora is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public
 *  License along with Knora.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.knora.webapi.messages.util.search

import org.knora.webapi._
import org.knora.webapi.exceptions.{AssertionException, GravsearchException}
import org.knora.webapi.messages.IriConversions._
import org.knora.webapi.messages.{OntologyConstants, SmartIri, StringFormatter}

/**
  * Methods and classes for transforming generated SPARQL.
  */
object SparqlTransformer {

  /**
    * Transforms a non-triplestore-specific SELECT query for GraphDB.
    *
    * @param useInference `true` if the triplestore's inference should be used.
    */
  class GraphDBSelectToSelectTransformer(useInference: Boolean) extends SelectToSelectTransformer {
    private implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    override def transformStatementInSelect(statementPattern: StatementPattern): Seq[StatementPattern] =
      Seq(statementPattern)

    override def transformStatementInWhere(statementPattern: StatementPattern,
                                           inputOrderBy: Seq[OrderCriterion]): Seq[StatementPattern] = {
      transformKnoraExplicitToGraphDBExplicit(statement = statementPattern, useInference = useInference)
    }

    override def transformFilter(filterPattern: FilterPattern): Seq[QueryPattern] = Seq(filterPattern)

    override def optimiseQueryPatterns(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
      moveBindToBeginning(moveResourceIrisToBeginning(moveLuceneToBeginning(patterns)))
    }

    override def transformLuceneQueryPattern(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] = {
      transformLuceneQueryPatternForGraphDB(luceneQueryPattern)
    }

    override def getFromClause: Option[FromClause] = {
      if (useInference) {
        None
      } else {
        // To turn off inference, add FROM <http://www.ontotext.com/explicit>.
        Some(FromClause(IriRef(OntologyConstants.NamedGraphs.GraphDBExplicitNamedGraph.toSmartIri)))
      }
    }

    override def enteringUnionBlock(): Unit = {}

    override def leavingUnionBlock(): Unit = {}
  }

  /**
    * Transforms a non-triplestore-specific SELECT for a triplestore that does not have inference enabled (e.g., Fuseki).
    *
    * @param simulateInference `true` if RDFS inference should be simulated using property path syntax.
    */
  class NoInferenceSelectToSelectTransformer(simulateInference: Boolean) extends SelectToSelectTransformer {
    private implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    override def transformStatementInSelect(statementPattern: StatementPattern): Seq[StatementPattern] =
      Seq(statementPattern)

    override def transformStatementInWhere(statementPattern: StatementPattern,
                                           inputOrderBy: Seq[OrderCriterion]): Seq[StatementPattern] =
      transformStatementInWhereForNoInference(statementPattern = statementPattern,
                                              simulateInference = simulateInference)

    override def transformFilter(filterPattern: FilterPattern): Seq[QueryPattern] = Seq(filterPattern)

    override def optimiseQueryPatterns(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
      moveBindToBeginning(optimiseIsDeletedWithFilter(moveResourceIrisToBeginning(moveLuceneToBeginning(patterns))))
    }

    override def transformLuceneQueryPattern(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] =
      transformLuceneQueryPatternForFuseki(luceneQueryPattern)

    override def getFromClause: Option[FromClause] = None

    override def enteringUnionBlock(): Unit = {}

    override def leavingUnionBlock(): Unit = {}
  }

  /**
    * Transforms a non-triplestore-specific CONSTRUCT query for GraphDB.
    */
  class GraphDBConstructToConstructTransformer extends ConstructToConstructTransformer {
    private implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    override def transformStatementInConstruct(statementPattern: StatementPattern): Seq[StatementPattern] =
      Seq(statementPattern)

    override def transformStatementInWhere(statementPattern: StatementPattern,
                                           inputOrderBy: Seq[OrderCriterion]): Seq[StatementPattern] = {
      transformKnoraExplicitToGraphDBExplicit(statement = statementPattern, useInference = true)
    }

    override def transformFilter(filterPattern: FilterPattern): Seq[QueryPattern] = Seq(filterPattern)

    override def optimiseQueryPatterns(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
      moveBindToBeginning(moveResourceIrisToBeginning(moveLuceneToBeginning(patterns)))
    }

    override def transformLuceneQueryPattern(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] =
      transformLuceneQueryPatternForGraphDB(luceneQueryPattern)

    override def enteringUnionBlock(): Unit = {}

    override def leavingUnionBlock(): Unit = {}
  }

  /**
    * Transforms a non-triplestore-specific CONSTRUCT query for a triplestore that does not have inference enabled (e.g., Fuseki).
    */
  class NoInferenceConstructToConstructTransformer extends ConstructToConstructTransformer {
    private implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    override def transformStatementInConstruct(statementPattern: StatementPattern): Seq[StatementPattern] =
      Seq(statementPattern)

    override def transformStatementInWhere(statementPattern: StatementPattern,
                                           inputOrderBy: Seq[OrderCriterion]): Seq[StatementPattern] =
      transformStatementInWhereForNoInference(statementPattern = statementPattern, simulateInference = true)

    override def transformFilter(filterPattern: FilterPattern): Seq[QueryPattern] = Seq(filterPattern)

    override def optimiseQueryPatterns(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
      moveBindToBeginning(optimiseIsDeletedWithFilter(moveResourceIrisToBeginning(moveLuceneToBeginning(patterns))))
    }

    override def transformLuceneQueryPattern(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] =
      transformLuceneQueryPatternForFuseki(luceneQueryPattern)

    override def enteringUnionBlock(): Unit = {}

    override def leavingUnionBlock(): Unit = {}
  }

  /**
    * Creates a syntactically valid variable base name, based on the given entity.
    *
    * @param entity the entity to be used to create a base name for a variable.
    * @return a base name for a variable.
    */
  def escapeEntityForVariable(entity: Entity): String = {
    val entityStr = entity match {
      case QueryVariable(varName)       => varName
      case IriRef(iriLiteral, _)        => iriLiteral.toOntologySchema(InternalSchema).toString
      case XsdLiteral(stringLiteral, _) => stringLiteral
      case _                            => throw GravsearchException(s"A unique variable name could not be made for ${entity.toSparql}")
    }

    entityStr
      .replaceAll("[:/.#-]", "")
      .replaceAll("\\s", "") // TODO: check if this is complete and if it could lead to collision of variable names
  }

  /**
    * Creates a unique variable name from the given entity and the local part of a property IRI.
    *
    * @param base        the entity to use to create the variable base name.
    * @param propertyIri the IRI of the property whose local part will be used to form the unique name.
    * @return a unique variable.
    */
  def createUniqueVariableNameFromEntityAndProperty(base: Entity, propertyIri: IRI): QueryVariable = {
    val propertyHashIndex = propertyIri.lastIndexOf('#')

    if (propertyHashIndex > 0) {
      val propertyName = propertyIri.substring(propertyHashIndex + 1)
      QueryVariable(escapeEntityForVariable(base) + "__" + escapeEntityForVariable(QueryVariable(propertyName)))
    } else {
      throw AssertionException(s"Invalid property IRI: $propertyIri")
    }
  }

  /**
    * Creates a unique variable name representing the `rdf:type` of an entity with a given base class.
    *
    * @param base         the entity to use to create the variable base name.
    * @param baseClassIri a base class of the entity's type.
    * @return a unique variable.
    */
  def createUniqueVariableNameForEntityAndBaseClass(base: Entity, baseClassIri: IriRef): QueryVariable = {
    QueryVariable(escapeEntityForVariable(base) + "__subClassOf__" + escapeEntityForVariable(baseClassIri))
  }

  /**
    * Create a unique variable from a whole statement.
    *
    * @param baseStatement the statement to be used to create the variable base name.
    * @param suffix        the suffix to be appended to the base name.
    * @return a unique variable.
    */
  def createUniqueVariableFromStatement(baseStatement: StatementPattern, suffix: String): QueryVariable = {
    QueryVariable(
      escapeEntityForVariable(baseStatement.subj) + "__" + escapeEntityForVariable(baseStatement.pred) + "__" + escapeEntityForVariable(
        baseStatement.obj) + "__" + suffix)
  }

  /**
    * Create a unique variable name from a whole statement for a link value.
    *
    * @param baseStatement the statement to be used to create the variable base name.
    * @return a unique variable for a link value.
    */
  def createUniqueVariableFromStatementForLinkValue(baseStatement: StatementPattern): QueryVariable = {
    createUniqueVariableFromStatement(baseStatement, "LinkValue")
  }

  /**
    * Optimises a query by replacing `knora-base:isDeleted false` with a `FILTER NOT EXISTS` pattern
    * placed at the end of the block.
    *
    * @param patterns the block of patterns to be optimised.
    * @return the result of the optimisation.
    */
  def optimiseIsDeletedWithFilter(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
    implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    // Separate the knora-base:isDeleted statements from the rest of the block.
    val (isDeletedPatterns: Seq[QueryPattern], otherPatterns: Seq[QueryPattern]) = patterns.partition {
      case StatementPattern(_,
                            IriRef(SmartIri(OntologyConstants.KnoraBase.IsDeleted), _),
                            XsdLiteral("false", SmartIri(OntologyConstants.Xsd.Boolean)),
                            _) =>
        true
      case _ => false
    }

    // Replace the knora-base:isDeleted statements with FILTER NOT EXISTS patterns.
    val filterPatterns: Seq[FilterNotExistsPattern] = isDeletedPatterns.collect {
      case statementPattern: StatementPattern =>
        FilterNotExistsPattern(
          Seq(
            StatementPattern.makeExplicit(
              subj = statementPattern.subj,
              pred = IriRef(OntologyConstants.KnoraBase.IsDeleted.toSmartIri),
              obj = XsdLiteral(value = "true", datatype = OntologyConstants.Xsd.Boolean.toSmartIri)
            )
          )
        )
    }

    otherPatterns ++ filterPatterns
  }

  /**
    * Optimises a query by moving BIND patterns to the beginning of a block.
    *
    * @param patterns the block of patterns to be optimised.
    * @return the result of the optimisation.
    */
  def moveBindToBeginning(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
    val (bindQueryPatterns: Seq[QueryPattern], otherPatterns: Seq[QueryPattern]) = patterns.partition {
      case _: BindPattern => true
      case _              => false
    }

    bindQueryPatterns ++ otherPatterns
  }

  /**
    * Optimises a query by moving Lucene query patterns to the beginning of a block.
    *
    * @param patterns the block of patterns to be optimised.
    * @return the result of the optimisation.
    */
  def moveLuceneToBeginning(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
    val (luceneQueryPatterns: Seq[QueryPattern], otherPatterns: Seq[QueryPattern]) = patterns.partition {
      case _: LuceneQueryPattern => true
      case _                     => false
    }

    luceneQueryPatterns ++ otherPatterns
  }

  /**
    * Optimises a query by moving statement patterns containing resource IRIs to the beginning of a block.
    *
    * @param patterns the query patterns to be optimised.
    * @return the optimised query patterns.
    */
  def moveResourceIrisToBeginning(patterns: Seq[QueryPattern]): Seq[QueryPattern] = {
    val (patternsWithResourceIris: Seq[QueryPattern], otherPatterns: Seq[QueryPattern]) = patterns.partition {
      case statementPattern: StatementPattern =>
        val subjIsResourceIri = statementPattern.subj match {
          case iriRef: IriRef if iriRef.iri.isKnoraResourceIri => true
          case _                                               => false
        }

        // Don't move statements whose predicate is rdf:subject or rdf:object: their subject
        // is a link value that needs to be defined first.
        val statementIsInLinkValue = statementPattern.pred match {
          case iriRef: IriRef =>
            iriRef.iri.toString match {
              case OntologyConstants.Rdf.Subject | OntologyConstants.Rdf.Object => true
              case _                                                            => false
            }

          case _ => false
        }

        val objIsResourceIri = statementPattern.obj match {
          case iriRef: IriRef if iriRef.iri.isKnoraResourceIri => true
          case _                                               => false
        }

        !statementIsInLinkValue && (subjIsResourceIri || objIsResourceIri)

      case _ => false
    }

    patternsWithResourceIris ++ otherPatterns
  }

  /**
    * Transforms a statement in a WHERE clause for a triplestore that does not provide inference.
    *
    * @param statementPattern  the statement pattern.
    * @param simulateInference `true` if RDFS inference should be simulated using property path syntax.
    * @return the statement pattern as expanded to work without inference.
    */
  def transformStatementInWhereForNoInference(statementPattern: StatementPattern,
                                              simulateInference: Boolean): Seq[StatementPattern] = {
    implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    statementPattern.pred match {
      case iriRef: IriRef if iriRef.iri.toString == OntologyConstants.KnoraBase.StandoffTagHasStartAncestor =>
        // Simulate knora-api:standoffTagHasStartAncestor, using knora-api:standoffTagHasStartParent.
        Seq(
          statementPattern.copy(
            pred = IriRef(OntologyConstants.KnoraBase.StandoffTagHasStartParent.toSmartIri, Some('*'))
          )
        )

      case _ =>
        // Is the statement in KnoraExplicitNamedGraph?
        statementPattern.namedGraph match {
          case Some(graphIri: IriRef)
              if graphIri.iri.toString == OntologyConstants.NamedGraphs.KnoraExplicitNamedGraph =>
            // Yes. No expansion needed. Just remove KnoraExplicitNamedGraph.
            Seq(statementPattern.copy(namedGraph = None))

          case _ =>
            // Is inference enabled?
            if (simulateInference) {
              // Yes. The statement might need to be expanded. Is the predicate a property IRI?
              statementPattern.pred match {
                case iriRef: IriRef =>
                  // Yes.
                  val propertyIri = iriRef.iri.toString

                  // Is the property rdf:type?
                  if (propertyIri == OntologyConstants.Rdf.Type) {
                    // Yes. Expand using rdfs:subClassOf*.

                    val baseClassIri: IriRef = statementPattern.obj match {
                      case iriRef: IriRef => iriRef
                      case other =>
                        throw GravsearchException(s"The object of rdf:type must be an IRI, but $other was used")
                    }

                    val rdfTypeVariable: QueryVariable = createUniqueVariableNameForEntityAndBaseClass(
                      base = statementPattern.subj,
                      baseClassIri = baseClassIri)

                    Seq(
                      StatementPattern(
                        subj = rdfTypeVariable,
                        pred = IriRef(
                          iri = OntologyConstants.Rdfs.SubClassOf.toSmartIri,
                          propertyPathOperator = Some('*')
                        ),
                        obj = statementPattern.obj
                      ),
                      StatementPattern(
                        subj = statementPattern.subj,
                        pred = statementPattern.pred,
                        obj = rdfTypeVariable
                      )
                    )
                  } else {
                    // No. Expand using rdfs:subPropertyOf*.

                    val propertyVariable: QueryVariable = createUniqueVariableNameFromEntityAndProperty(
                      base = statementPattern.pred,
                      propertyIri = OntologyConstants.Rdfs.SubPropertyOf)

                    Seq(
                      StatementPattern(
                        subj = propertyVariable,
                        pred = IriRef(
                          iri = OntologyConstants.Rdfs.SubPropertyOf.toSmartIri,
                          propertyPathOperator = Some('*')
                        ),
                        obj = statementPattern.pred
                      ),
                      StatementPattern(
                        subj = statementPattern.subj,
                        pred = propertyVariable,
                        obj = statementPattern.obj
                      )
                    )
                  }

                case _ =>
                  // The predicate isn't a property IRI, so no expansion needed.
                  Seq(statementPattern)
              }
            } else {
              // Inference is disabled. Just return the statement as is.
              Seq(statementPattern)
            }
        }
    }
  }

  /**
    * Transforms the the Knora explicit graph name to GraphDB explicit graph name.
    *
    * @param statement    the given statement whose graph name has to be renamed.
    * @param useInference `true` if the triplestore's inference should be used.
    * @return the statement with the renamed graph, if given.
    */
  private def transformKnoraExplicitToGraphDBExplicit(statement: StatementPattern,
                                                      useInference: Boolean): Seq[StatementPattern] = {
    implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    val transformedPattern = statement.copy(
      pred = statement.pred,
      namedGraph = statement.namedGraph match {
        case Some(IriRef(SmartIri(OntologyConstants.NamedGraphs.KnoraExplicitNamedGraph), _)) =>
          if (useInference) {
            Some(IriRef(OntologyConstants.NamedGraphs.GraphDBExplicitNamedGraph.toSmartIri))
          } else {
            // Inference will be turned off in a FROM clause, so there's no need to specify a named graph here.
            None
          }

        case Some(IriRef(_, _)) =>
          throw AssertionException(
            s"Named graphs other than ${OntologyConstants.NamedGraphs.KnoraExplicitNamedGraph} cannot occur in non-triplestore-specific generated search query SPARQL")

        case None => None
      }
    )

    Seq(transformedPattern)
  }

  /**
    * Transforms a [[LuceneQueryPattern]] for GraphDB.
    *
    * @param luceneQueryPattern the query pattern.
    * @return GraphDB-specific statements implementing the query.
    */
  private def transformLuceneQueryPatternForGraphDB(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] = {
    implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    Seq(
      StatementPattern(
        subj = luceneQueryPattern.obj, // In GraphDB, an index entry is associated with a literal.
        pred = IriRef("http://www.ontotext.com/owlim/lucene#fullTextSearchIndex".toSmartIri),
        obj = XsdLiteral(
          value = luceneQueryPattern.queryString.getQueryString,
          datatype = OntologyConstants.Xsd.String.toSmartIri
        )
      )
    ) ++ luceneQueryPattern.literalStatement
  }

  /**
    * Transforms a [[LuceneQueryPattern]] for Fuseki.
    *
    * @param luceneQueryPattern the query pattern.
    * @return Fuseki-specific statements implementing the query.
    */
  private def transformLuceneQueryPatternForFuseki(luceneQueryPattern: LuceneQueryPattern): Seq[QueryPattern] = {
    implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance

    Seq(
      StatementPattern(
        subj = luceneQueryPattern.subj, // In Fuseki, an index entry is associated with an entity that has a literal.
        pred = IriRef("http://jena.apache.org/text#query".toSmartIri),
        obj = XsdLiteral(
          value = luceneQueryPattern.queryString.getQueryString,
          datatype = OntologyConstants.Xsd.String.toSmartIri
        )
      )
    )
  }
}