package liquibase.sqlgenerator.core;

 import liquibase.database.Database;

 import liquibase.exception.UnexpectedLiquibaseException;

 import liquibase.exception.ValidationErrors;

 import liquibase.sql.Sql;

 import liquibase.sql.UnparsedSql;

 import liquibase.sqlgenerator.SqlGenerator;

 import liquibase.sqlgenerator.SqlGeneratorChain;

 import liquibase.statement.core.SelectFromDatabaseChangeLogStatement;

 import liquibase.util.StringUtils;

 public class SelectFromDatabaseChangeLogGenerator extends AbstractSqlGenerator<SelectFromDatabaseChangeLogStatement> {

     public ValidationErrors validate(SelectFromDatabaseChangeLogStatement statement, Database database,

             SqlGeneratorChain sqlGeneratorChain) {

         ValidationErrors errors = new ValidationErrors();

         errors.checkRequiredField("columnToSelect", statement.getColumnsToSelect());

         return errors;

     }

     public Sql[] generateSql(SelectFromDatabaseChangeLogStatement statement, Database database,

             SqlGeneratorChain sqlGeneratorChain) {

         String sql = "SELECT " + StringUtils.join(statement.getColumnsToSelect(), ",").toUpperCase() + " FROM "

                 + database.escapeTableName(database.getLiquibaseSchemaName(), database.getDatabaseChangeLogTableName());

         SelectFromDatabaseChangeLogStatement.WhereClause whereClause = statement.getWhereClause();

         if (whereClause != null) {

             if (whereClause instanceof SelectFromDatabaseChangeLogStatement.ByTag) {

                 sql += " WHERE TAG='" + ((SelectFromDatabaseChangeLogStatement.ByTag) whereClause).getTagName() + "'";

             } else if (whereClause instanceof SelectFromDatabaseChangeLogStatement.ByNotNullCheckSum) {

                 sql += " WHERE MD5SUM IS NOT NULL";

             } else {

                 throw new UnexpectedLiquibaseException("Unknown where clause type: " + whereClause.getClass().getName());

             }

         }

         if (statement.getOrderByColumns() != null && statement.getOrderByColumns().length > 0) {

             sql += " ORDER BY " + StringUtils.join(statement.getOrderByColumns(), ", ").toUpperCase();

         }

         return new Sql[] { new UnparsedSql(sql) };

     }

 }