package liquibase.change.core;
   
   import liquibase.change.AbstractChange;
   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.core.SybaseASADatabase;
  import liquibase.database.structure.Index;
  import liquibase.statement.SqlStatement;
  import liquibase.statement.core.DropUniqueConstraintStatement;
  import liquibase.util.StringUtils;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Removes an existing unique constraint.
   */
  public class DropUniqueConstraintChange extends AbstractChange {
      private String schemaName;
      private String tableName;
      private String constraintName;
      /**
       * Sybase ASA does drop unique constraint not by name, but using list of the columns in unique clause.
       */
      private String uniqueColumns;
  
      public DropUniqueConstraintChange() {
          super("dropUniqueConstraint", "Drop Unique 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 getConstraintName() {
          return constraintName;
      }
  
      public void setConstraintName(String constraintName) {
          this.constraintName = constraintName;
      }
  
      public String getUniqueColumns() {
          return uniqueColumns;
      }
  
      public void setUniqueColumns(String uniqueColumns) {
          this.uniqueColumns = uniqueColumns;
      }
  
      public SqlStatement[] generateStatements(Database database) {
  
          // todo if (database instanceof SQLiteDatabase) {
          // // return special statements for SQLite databases
          // return generateStatementsForSQLiteDatabase(database);
          // }
          DropUniqueConstraintStatement statement = new DropUniqueConstraintStatement(
                  getSchemaName() == null ? database.getDefaultSchemaName() : getSchemaName(), getTableName(),
                  getConstraintName());
          if (database instanceof SybaseASADatabase) {
              statement.setUniqueColumns(uniqueColumns);
          }
          return new SqlStatement[] { statement };
      }
  
      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...
  
          // Note: The attribute "constraintName" is used to pass the column
          // name instead of the constraint name.
  
          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(getConstraintName())) {
                     column.getConstraints().setUnique(false);
                 }
                 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()]);
     }
 
     public String getConfirmationMessage() {
         return "Unique constraint " + getConstraintName() + " dropped from " + getTableName();
     }
 }