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  package org.apache.cayenne.dba.oracle;
  
  import org.apache.cayenne.CayenneRuntimeException;
  import org.apache.cayenne.access.DataNode;
  import org.apache.cayenne.dba.JdbcAdapter;
  import org.apache.cayenne.dba.JdbcPkGenerator;
  import org.apache.cayenne.map.DataMap;
  import org.apache.cayenne.map.DbEntity;
  import org.apache.cayenne.map.DbKeyGenerator;
  
  import java.sql.Connection;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import java.sql.Statement;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Sequence-based primary key generator implementation for Oracle. Uses Oracle
   * sequences to generate primary key values. This approach is at least 50%
   * faster when tested with Oracle compared to the lookup table approach.
   * <p>
   * When using Cayenne key caching mechanism, make sure that sequences in the
   * database have "INCREMENT BY" greater or equal to OraclePkGenerator
   * "pkCacheSize" property value. If this is not the case, you will need to
   * adjust PkGenerator value accordingly. For example when sequence is
   * incremented by 1 each time, use the following code:
   * </p>
   *
   * <pre>
   * dataNode.getAdapter().getPkGenerator().setPkCacheSize(1);
   * </pre>
   */
  public class OraclePkGenerator extends JdbcPkGenerator {
  
      /**
       * Used by DI
       * @since 4.1
       */
      public OraclePkGenerator() {
          super();
      }
  
      protected OraclePkGenerator(JdbcAdapter adapter) {
          super(adapter);
      }
  
      private static final String _SEQUENCE_PREFIX = "pk_";
  
      @Override
      public void createAutoPk(DataNode node, List<DbEntity> dbEntities) throws Exception {
          List<String> sequences = getExistingSequences(node);
          // create needed sequences
          for (DbEntity dbEntity : dbEntities) {
              if (!sequences.contains(sequenceName(dbEntity))) {
                  runUpdate(node, createSequenceString(dbEntity));
              }
          }
      }
  
      /**
       * Creates a list of CREATE SEQUENCE statements for the list of DbEntities.
       */
      @Override
      public List<String> createAutoPkStatements(List<DbEntity> dbEntities) {
          List<String> list = new ArrayList<>(dbEntities.size());
          for (DbEntity dbEntity : dbEntities) {
              list.add(createSequenceString(dbEntity));
          }
  
          return list;
      }
  
      /**
       * Drops PK sequences for all specified DbEntities.
       */
      @Override
      public void dropAutoPk(DataNode node, List<DbEntity> dbEntities) throws Exception {
          List<String> sequences = getExistingSequences(node);
  
          // drop obsolete sequences
          for (DbEntity dbEntity : dbEntities) {
              String name;
              if (dbEntity.getDataMap().isQuotingSQLIdentifiers()) {
                  DbEntity tempEnt = new DbEntity();
                  DataMap dm = new DataMap();
                  dm.setQuotingSQLIdentifiers(false);
                  tempEnt.setDataMap(dm);
                  tempEnt.setName(dbEntity.getName());
                  name = stripSchemaName(sequenceName(tempEnt));
              } else {
                  name = stripSchemaName(sequenceName(dbEntity));
              }
              if (sequences.contains(name)) {
                  runUpdate(node, dropSequenceString(dbEntity));
              }
          }
      }
  
      /**
       * Creates a list of DROP SEQUENCE statements for the list of DbEntities.
       */
      @Override
      public List<String> dropAutoPkStatements(List<DbEntity> dbEntities) {
          List<String> list = new ArrayList<>(dbEntities.size());
          for (DbEntity dbEntity : dbEntities) {
              list.add(dropSequenceString(dbEntity));
          }
  
          return list;
      }
  
      protected String createSequenceString(DbEntity ent) {
          return "CREATE SEQUENCE " + sequenceName(ent) + " START WITH " + pkStartValue + " INCREMENT BY " + pkCacheSize(ent);
      }
  
      /**
       * Returns a SQL string needed to drop any database objects associated with
       * automatic primary key generation process for a specific DbEntity.
       */
      protected String dropSequenceString(DbEntity ent) {
          return "DROP SEQUENCE " + sequenceName(ent);
      }
  
      protected String selectNextValQuery(String pkGeneratingSequenceName) {
          return "SELECT " + pkGeneratingSequenceName + ".nextval FROM DUAL";
      }
  
      protected String selectAllSequencesQuery() {
          return "SELECT LOWER(SEQUENCE_NAME) FROM ALL_SEQUENCES";
      }
  
      /**
       * Generates primary key by calling Oracle sequence corresponding to the
       * <code>dbEntity</code>. Executed SQL looks like this:
       *
       * <pre>
       *   SELECT pk_table_name.nextval FROM DUAL
       * </pre>
       *
       * @since 3.0
       */
      @Override
      protected long longPkFromDatabase(DataNode node, DbEntity entity) throws Exception {
  
          DbKeyGenerator pkGenerator = entity.getPrimaryKeyGenerator();
          String pkGeneratingSequenceName;
          if (pkGenerator != null && DbKeyGenerator.ORACLE_TYPE.equals(pkGenerator.getGeneratorType())
                  && pkGenerator.getGeneratorName() != null) {
              pkGeneratingSequenceName = pkGenerator.getGeneratorName();
          } else {
              pkGeneratingSequenceName = sequenceName(entity);
          }
  
          try (Connection con = node.getDataSource().getConnection()) {
              try (Statement st = con.createStatement()) {
                  String sql = selectNextValQuery(pkGeneratingSequenceName);
                  adapter.getJdbcEventLogger().log(sql);
  
                  try (ResultSet rs = st.executeQuery(sql)) {
                      if (!rs.next()) {
                          throw new CayenneRuntimeException("Error generating pk for DbEntity %s", entity.getName());
                      }
                      return rs.getLong(1);
                  }
              }
          }
      }
  
      protected int pkCacheSize(DbEntity entity) {
          // use custom generator if possible
          DbKeyGenerator keyGenerator = entity.getPrimaryKeyGenerator();
          if (keyGenerator != null && DbKeyGenerator.ORACLE_TYPE.equals(keyGenerator.getGeneratorType())
                  && keyGenerator.getGeneratorName() != null) {
  
              Integer size = keyGenerator.getKeyCacheSize();
              return (size != null && size >= 1) ? size : super.getPkCacheSize();
          } else {
              return super.getPkCacheSize();
          }
      }
  
      /**
       * Returns expected primary key sequence name for a DbEntity.
       */
      protected String sequenceName(DbEntity entity) {
  
          // use custom generator if possible
          DbKeyGenerator keyGenerator = entity.getPrimaryKeyGenerator();
          if (keyGenerator != null && DbKeyGenerator.ORACLE_TYPE.equals(keyGenerator.getGeneratorType())
                  && keyGenerator.getGeneratorName() != null) {
  
              return keyGenerator.getGeneratorName().toLowerCase();
          } else {
              String seqName = getSequencePrefix() + entity.getName().toLowerCase();
              return adapter.getQuotingStrategy().quotedIdentifier(entity, entity.getCatalog(), entity.getSchema(), seqName);
          }
      }
  
      protected String getSequencePrefix() {
          return _SEQUENCE_PREFIX;
      }
  
      private String stripSchemaName(String sequenceName) {
          int ind = sequenceName.indexOf('.');
          return ind >= 0 ? sequenceName.substring(ind + 1) : sequenceName;
      }
  
      /**
       * Fetches a list of existing sequences that might match Cayenne generated
       * ones.
       */
      protected List<String> getExistingSequences(DataNode node) throws SQLException {
  
          // check existing sequences
          try (Connection con = node.getDataSource().getConnection()) {
              try (Statement sel = con.createStatement()) {
                  String sql = selectAllSequencesQuery();
                  adapter.getJdbcEventLogger().log(sql);
  
                  try (ResultSet rs = sel.executeQuery(sql)) {
                      List<String> sequenceList = new ArrayList<>();
                      while (rs.next()) {
                          String name = rs.getString(1);
                          if (name != null) {
                              sequenceList.add(name.trim());
                          }
                      }
                      return sequenceList;
                  }
              }
          }
      }
  }
  