package liquibase.sqlgenerator.ext;
   
   import liquibase.database.Database;
   import liquibase.database.core.*;
   import liquibase.exception.ValidationErrors;
   import liquibase.sql.Sql;
   import liquibase.sql.UnparsedSql;
   import liquibase.sqlgenerator.SqlGenerator;
   import liquibase.sqlgenerator.SqlGeneratorChain;
  import liquibase.statement.core.AddUniqueConstraintStatement;
  import liquibase.util.StringUtils;
  
  import static liquibase.ext.Constants.EXTENSION_PRIORITY;
  
  public class AddUniqueConstraintGenerator extends liquibase.sqlgenerator.core.AddUniqueConstraintGenerator {
  
      @Override
      public int getPriority() {
          return EXTENSION_PRIORITY;
      }
  
      public Sql[] generateSql(AddUniqueConstraintStatement statement, Database database, SqlGeneratorChain sqlGeneratorChain) {
  
  		String sql = null;
  		if (statement.getConstraintName() == null) {
  			sql = String.format("ALTER TABLE %s ADD UNIQUE (%s)"
  					, database.escapeTableName(null, statement.getTableName())
  					, database.escapeColumnNameList(statement.getColumnNames())
  			);
  		} else {
  			sql = String.format("ALTER TABLE %s ADD CONSTRAINT %s UNIQUE (%s)"
  					, database.escapeTableName(null, statement.getTableName())
  					, database.escapeConstraintName(statement.getConstraintName())
  					, database.escapeColumnNameList(statement.getColumnNames())
  			);
  		}
  		if(database instanceof OracleDatabase) {
  	        if (statement.isDeferrable() || statement.isInitiallyDeferred()) {
  	            if (statement.isDeferrable()) {
  	            	sql += " DEFERRABLE";
  	            }
  
  	            if (statement.isInitiallyDeferred()) {
  	            	sql +=" INITIALLY DEFERRED";
  	            }
  	        }
              if (statement.isDisabled()) {
                  sql +=" DISABLE";
              }
  		}
  
          if (StringUtils.trimToNull(statement.getTablespace()) != null && database.supportsTablespaces()) {
              if (database instanceof MSSQLDatabase) {
                  sql += " ON " + statement.getTablespace();
              } else if (database instanceof DB2Database
                  || database instanceof SybaseASADatabase
                  || database instanceof InformixDatabase) {
                  ; //not supported
              } else {
                  sql += " USING INDEX TABLESPACE " + statement.getTablespace();
              }
          }
  
          return new Sql[] {
                  new UnparsedSql(sql)
          };
  
      }
  }