package liquibase.sqlgenerator.core;

 import java.util.ArrayList;

 import java.util.List;

 import liquibase.database.Database;

 import liquibase.database.core.DB2Database;

 import liquibase.database.core.DerbyDatabase;

 import liquibase.database.core.FirebirdDatabase;

 import liquibase.database.core.H2Database;

 import liquibase.database.core.HsqlDatabase;

 import liquibase.database.core.InformixDatabase;

 import liquibase.database.core.OracleDatabase;

 import liquibase.database.core.SybaseASADatabase;

 import liquibase.database.core.SybaseDatabase;

 import liquibase.database.structure.Column;

 import liquibase.database.structure.Table;

 import liquibase.database.typeconversion.TypeConverterFactory;

 import liquibase.exception.ValidationErrors;

 import liquibase.sql.Sql;

 import liquibase.sql.UnparsedSql;

 import liquibase.sqlgenerator.SqlGeneratorChain;

 import liquibase.statement.core.AddColumnStatement;

 public class AddColumnGeneratorDefaultClauseBeforeNotNull extends AddColumnGenerator {

     @Override

     public int getPriority() {

         return PRIORITY_DATABASE;

     }

     @Override

     public boolean supports(AddColumnStatement statement, Database database) {

         return database instanceof OracleDatabase || database instanceof HsqlDatabase || database instanceof H2Database

                 || database instanceof DerbyDatabase || database instanceof DB2Database

                 || database instanceof FirebirdDatabase || database instanceof SybaseDatabase

                 || database instanceof SybaseASADatabase || database instanceof InformixDatabase;

     }

     @Override

     public ValidationErrors validate(AddColumnStatement statement, Database database,

             SqlGeneratorChain sqlGeneratorChain) {

         ValidationErrors validationErrors = super.validate(statement, database, sqlGeneratorChain);

         if (database instanceof DerbyDatabase && statement.isAutoIncrement()) {

             validationErrors.addError("Cannot add an identity column to a database");

         }

         return validationErrors;

     }

     @Override

     public Sql[] generateSql(AddColumnStatement statement, Database database, SqlGeneratorChain sqlGeneratorChain) {

         String alterTable = "ALTER TABLE "

                 + database.escapeTableName(statement.getSchemaName(), statement.getTableName())

                 + " ADD "

                 + database.escapeColumnName(statement.getSchemaName(), statement.getTableName(),

                         statement.getColumnName())

                 + " "

                 + TypeConverterFactory.getInstance().findTypeConverter(database)

                         .getDataType(statement.getColumnType(), statement.isAutoIncrement());

         alterTable += getDefaultClause(statement, database);

         if (primaryKeyBeforeNotNull(database)) {

             if (statement.isPrimaryKey()) {

                 alterTable += " PRIMARY KEY";

             }

         }

         if (statement.isAutoIncrement()) {

             alterTable += " " + database.getAutoIncrementClause();

         }

         if (!statement.isNullable()) {

             alterTable += " NOT NULL";

         } else if (database instanceof SybaseDatabase || database instanceof SybaseASADatabase) {

             alterTable += " NULL";

         }

         if (!primaryKeyBeforeNotNull(database)) {

             if (statement.isPrimaryKey()) {

                 alterTable += " PRIMARY KEY";

             }

         }

         if (statement.isUnique()) {

             alterTable += " UNIQUE ";

         }

         List<Sql> returnSql = new ArrayList<Sql>();

         returnSql.add(new UnparsedSql(alterTable, new Column().setTable(

                 new Table(statement.getTableName()).setSchema(statement.getSchemaName())).setName(

                 statement.getColumnName())));

         addForeignKeyStatements(statement, database, returnSql);

         return returnSql.toArray(new Sql[returnSql.size()]);

     }

     private String getDefaultClause(AddColumnStatement statement, Database database) {

         String clause = "";

         Object defaultValue = statement.getDefaultValue();

         if (defaultValue != null) {

             clause += " DEFAULT "

                     + TypeConverterFactory.getInstance().findTypeConverter(database).getDataType(defaultValue)

                             .convertObjectToString(defaultValue, database);

         }

         return clause;

     }

     private boolean primaryKeyBeforeNotNull(Database database) {

         return !(database instanceof HsqlDatabase || database instanceof H2Database);

     }

 }