package liquibase.precondition.core;

 import liquibase.changelog.ChangeSet;

 import liquibase.changelog.DatabaseChangeLog;

 import liquibase.database.Database;

 import liquibase.exception.DatabaseException;

 import liquibase.exception.PreconditionErrorException;

 import liquibase.exception.PreconditionFailedException;

 import liquibase.exception.ValidationErrors;

 import liquibase.exception.Warnings;

 import liquibase.precondition.Precondition;

 import liquibase.snapshot.DatabaseSnapshot;

 import liquibase.snapshot.DatabaseSnapshotGeneratorFactory;

 import liquibase.util.StringUtils;

 public class SequenceExistsPrecondition implements Precondition {

     private String schemaName;

     private String sequenceName;

     public String getSchemaName() {

         return schemaName;

     }

     public void setSchemaName(String schemaName) {

         this.schemaName = StringUtils.trimToNull(schemaName);

     }

     public String getSequenceName() {

         return sequenceName;

     }

     public void setSequenceName(String sequenceName) {

         this.sequenceName = sequenceName;

     }

     @Override

     public Warnings warn(Database database) {

         return new Warnings();

     }

     @Override

     public ValidationErrors validate(Database database) {

         return new ValidationErrors();

     }

     @Override

     public void check(Database database, DatabaseChangeLog changeLog, ChangeSet changeSet)

             throws PreconditionFailedException, PreconditionErrorException {

         DatabaseSnapshot snapshot;

         try {

             snapshot = DatabaseSnapshotGeneratorFactory.getInstance().createSnapshot(database, getSchemaName(), null);

         } catch (DatabaseException e) {

             throw new PreconditionErrorException(e, changeLog, this);

         }

         if (snapshot.getSequence(getSequenceName()) == null) {

             throw new PreconditionFailedException("Sequence "

                     + database.escapeSequenceName(getSchemaName(), getSequenceName()) + " does not exist", changeLog,

                     this);

         }

     }

     @Override

     public String getName() {

         return "sequenceExists";

     }

 }