package liquibase.change.core;

 import liquibase.change.AbstractChange;

 import liquibase.change.Change;

 import liquibase.change.ChangeMetaData;

 import liquibase.change.ColumnConfig;

 import liquibase.database.Database;

 import liquibase.database.core.SQLiteDatabase;

 import liquibase.database.core.SQLiteDatabase.AlterTableVisitor;

 import liquibase.database.structure.Index;

 import liquibase.statement.SqlStatement;

 import liquibase.statement.core.SetNullableStatement;

 import liquibase.util.StringUtils;

 import java.util.ArrayList;

 import java.util.List;

 /**

  * Drops a not-null constraint from an existing column.

  */

 public class DropNotNullConstraintChange extends AbstractChange {

     private String schemaName;

     private String tableName;

     private String columnName;

     private String columnDataType;

     public DropNotNullConstraintChange() {

         super("dropNotNullConstraint", "Drop Not-Null Constraint", ChangeMetaData.PRIORITY_DEFAULT);

     }

     public String getSchemaName() {

         return schemaName;

     }

     public void setSchemaName(String schemaName) {

         this.schemaName = StringUtils.trimToNull(schemaName);

     }

     public String getTableName() {

         return tableName;

     }

     public void setTableName(String tableName) {

         this.tableName = tableName;

     }

     public String getColumnName() {

         return columnName;

     }

     public void setColumnName(String columnName) {

         this.columnName = columnName;

     }

     public String getColumnDataType() {

         return columnDataType;

     }

     public void setColumnDataType(String columnDataType) {

         this.columnDataType = columnDataType;

     }

     public SqlStatement[] generateStatements(Database database) {

         // todo if (database instanceof SQLiteDatabase) {

         // // return special statements for SQLite databases

         // return generateStatementsForSQLiteDatabase(database);

         // }

         return new SqlStatement[] { new SetNullableStatement(getSchemaName() == null ? database.getDefaultSchemaName()

                 : getSchemaName(), getTableName(), getColumnName(), getColumnDataType(), true) };

     }

     private SqlStatement[] generateStatementsForSQLiteDatabase(Database database) {

         // SQLite does not support this ALTER TABLE operation until now.

         // For more information see: http://www.sqlite.org/omitted.html.

         // This is a small work around...

         List<SqlStatement> statements = new ArrayList<SqlStatement>();

         // define alter table logic

         AlterTableVisitor rename_alter_visitor = new AlterTableVisitor() {

             public ColumnConfig[] getColumnsToAdd() {

                 return new ColumnConfig[0];

             }

             public boolean copyThisColumn(ColumnConfig column) {

                 return true;

             }

             public boolean createThisColumn(ColumnConfig column) {

                 if (column.getName().equals(getColumnName())) {

                     column.getConstraints().setNullable(true);

                 }

                 return true;

             }

             public boolean createThisIndex(Index index) {

                 return true;

             }

         };

         try {

             // alter table

             statements.addAll(SQLiteDatabase.getAlterTableStatements(rename_alter_visitor, database, getSchemaName(),

                     getTableName()));

         } catch (Exception e) {

             e.printStackTrace();

         }

         return statements.toArray(new SqlStatement[statements.size()]);

     }

     @Override

     protected Change[] createInverses() {

         AddNotNullConstraintChange inverse = new AddNotNullConstraintChange();

         inverse.setColumnName(getColumnName());

         inverse.setSchemaName(getSchemaName());

         inverse.setTableName(getTableName());

         inverse.setColumnDataType(getColumnDataType());

         return new Change[] { inverse };

     }

     public String getConfirmationMessage() {

         return "Null constraint dropped from " + getTableName() + "." + getColumnName();

     }

 }