package liquibase.ext.spatial.sqlgenerator;
   
   import java.util.ArrayList;
   import java.util.Arrays;
   import java.util.List;
   
   import liquibase.database.Database;
   import liquibase.database.core.DerbyDatabase;
   import liquibase.database.core.H2Database;
  import liquibase.exception.ValidationErrors;
  import liquibase.ext.spatial.statement.DropSpatialIndexStatement;
  import liquibase.ext.spatial.utils.GeometryColumnsUtils;
  import liquibase.sql.Sql;
  import liquibase.sql.UnparsedSql;
  import liquibase.sqlgenerator.SqlGeneratorChain;
  import liquibase.sqlgenerator.core.DropColumnGenerator;
  import liquibase.statement.core.DropColumnStatement;
  import liquibase.structure.core.Column;
  
  /**
   * <code>DropGeometryColumnGeneratorGeoDB</code> is a {@link DropColumnGenerator} that specializes
   * in GeoDB. If there exists an index on the column, <code>DropSpatialIndex</code> is invoked first.
   * If the column to be dropped is the geometry column, the <code>DropGeometryColumn</code> procedure
   * is invoked instead of performing the typical <code>ALTER TABLE</code> statement. Otherwise, the
   * next SQL generator in the chain is invoked to handle the request.
   */
  public class DropGeometryColumnGeneratorGeoDB extends DropColumnGenerator {
     /**
      * @see liquibase.sqlgenerator.core.AbstractSqlGenerator#supports(liquibase.statement.SqlStatement,
      *      liquibase.database.Database)
      */
     @Override
     public boolean supports(final DropColumnStatement statement, final Database database) {
        return database instanceof DerbyDatabase || database instanceof H2Database;
     }
  
     /**
      * @see liquibase.sqlgenerator.core.AbstractSqlGenerator#getPriority()
      */
     @Override
     public int getPriority() {
        return super.getPriority() + 1;
     }
  
     @Override
     public ValidationErrors validate(final DropColumnStatement statement, final Database database,
           final SqlGeneratorChain sqlGeneratorChain) {
        return sqlGeneratorChain.validate(statement, database);
     }
  
     @Override
     public Sql[] generateSql(final DropColumnStatement statement, final Database database,
           final SqlGeneratorChain sqlGeneratorChain) {
  
        String schemaName = statement.getSchemaName();
        if (schemaName == null) {
           schemaName = database.getDefaultSchemaName();
        }
        final String tableName = statement.getTableName();
        final String columnName = statement.getColumnName();
        final boolean isGeometryColumn = GeometryColumnsUtils.isGeometryColumn(database, schemaName,
              tableName, columnName);
        final List<Sql> list = new ArrayList<Sql>();
        if (isGeometryColumn) {
           dropSpatialIndexIfExists(statement.getCatalogName(), schemaName, tableName, database, list);
           final String sql = "CALL DropGeometryColumn('" + schemaName + "', '" + tableName + "', '"
                 + columnName + "')";
           final Column column = getAffectedColumn(statement);
           final Sql dropGeometryColumn = new UnparsedSql(sql, column);
           list.add(dropGeometryColumn);
        } else {
           list.addAll(Arrays.asList(sqlGeneratorChain.generateSql(statement, database)));
        }
        return list.toArray(new Sql[list.size()]);
     }
  
     /**
      * Adds the SQL statement to drop the spatial index if it is present.
      * 
      * @param catalogName
      *           the catalog name.
      * @param schemaName
      *           the schema name.
      * @param tableName
      *           the table name.
      * @param database
      *           the database.
      * @param list
      *           the list of SQL statements to execute.
      */
     protected void dropSpatialIndexIfExists(final String catalogName, final String schemaName,
           final String tableName, final Database database, final List<Sql> list) {
        final DropSpatialIndexGeneratorGeoDB generator = new DropSpatialIndexGeneratorGeoDB();
        final DropSpatialIndexStatement statement = new DropSpatialIndexStatement(null, catalogName,
              schemaName, tableName);
        list.addAll(Arrays.asList(generator.generateSqlIfExists(statement, database)));
     }
  }