/*!
  @header FTPersistentSet
  @abstract Module of FT
 
  @availability OS X, GNUstep
  @copyright 2004, 2005, 2006 Free Software Foundation, Inc.
  
  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA

  <pre>
  -------------------------------------------------------------------------
  Modification history

  30.03.06 ola     initial version
  23.08.06 ola     license changed
  -------------------------------------------------------------------------
  </pre>
*/

#if !defined(__FTPersistentSetImpl_H)
#define __FTPersistentSetImpl_H

#include <Foundation/Foundation.h>
#include <Encore/Encore.h>
#include <FT/FTObject.h>
#include <FT/FTPersistentSet.h>
#include <FT/FTTransactionContext.h>
#include <FT/FTTransactionStep.h>
#include <BDB/BDB.h>

@class _FTPersistentSetChunk;


/*!
 * @class FTPersistentSetImpl
 * @abstract Utility class which uses a BDB database in order to manage a
 *   set of objects in the database
 * @description TODO:The currently implemented version works without any caching
 *   althought this might be <b>very</b> helpful here. <p/>
 *   So operations evaluating all entries within a set may require
 *   iteration over all database records thus they are very expensive
 *   at present. Examples of such operations: count, member
 */
@interface FTPersistentSetImpl : FTObject <FTPersistentSet> {
  @private
    BDBDatabase *recordNrToObject;
    
    /* current chunk to be used for insertion */
    _FTPersistentSetChunk *currentInsertionChunk;
    unsigned maxEntriesPerChunk;
    
    NSLock *lock;
}

- init;

- createDBUsingDataFile: (NSString *) aFilename;
- openDBUsingDataFile: (NSString *) aFilename;
- (void) closeDB;

- (void) dealloc;


/*!
 * @method addObject
 * @abstract Adds a object to the set. This object must implement
 * NSCoding.
 * @result self
 */
- addObject: (id) anObject;


/*!
 * @method chunkAtRecordNumber
 * @abstract Tries to read a chunk from the specified record.
 * @param recNr record number to read from
 * @result related chunk or nil if not existent at the given record number
 */
- (_FTPersistentSetChunk *) chunkAtRecordNumber: (unsigned) recNr;


/*!
 * @method chunkContainingObject
 * @param anObject object to look for
 * @result returns the chunk which contains the specified object or nil if not
 *   existent
 */
- (_FTPersistentSetChunk *) chunkContainingObject: (id) anObject;


/*!
 * @method chunkIterator 
 * @abstract Note that iterating over chunks is an expensive operation at 
 *   present
 * @result iterator of all chunks
 */
- (id <ECIterator>) chunkIterator;


/*!
 * @method containsObject
 * @abstract This is an expensive operation at present
 * @result YES if the specified object is to be found in the set.
 */
- (BOOL) containsObject: (id) anObject;


/*!
 * @method count
 * @abstract Expensive operation used to determine the number of elements
 *   in this set
 * @description TODO: optimize this operation
 * @result number of elements in the current set
 */
- (unsigned) count;


/*!
 * @method dbConfig
 * @result configuration settings for the underlying database
 */
- (BDBDatabaseConfig *) dbConfig;


/*!
 * @method iterator
 * @abstract Returns an iterator over all members of this set. This is an
 *   expensive operation at present
 * @result iterator over all elements of the set
 */
- (id <ECIterator>) iterator;



/*!
 * @method newChunk
 * @abstract Examines new available chunk and sets up corresponding internal
 *   fields appropriately
 * @result self
 */
- newChunk;


/*!
 * @method removeObject
 * @abstract removes the specified object from the set. Operation is ignored
 *   the object could no be found within the set.
 * @result self
 */
- removeObject: (id) anObject;


/*!
 * @method validateDBIsOpen
 * @abstract throws an exception if the database is not opened since this marks
 *   an illegal state
 */
- (void) validateDBIsOpen;

@end

/* ----------------------------------------- _FTPersistentSetChunk */
@interface _FTPersistentSetChunk : FTObject {
  @private
    BDBDatabase *database;
    NSMutableArray *objects;
    unsigned bdb_record_nr;
    BOOL isModified;
    BOOL chunkInTransaction;
    NSLock *lock;
}


/*!
 * @method createForDatabase
 * @abstract Creates a chunk and stores its initial content in the database.
 * @param aDatabase database to use
 * @param a_record_nr record number at which to store the chunk
 * @result created chunk
 */
+ (_FTPersistentSetChunk *) createForDatabase: (BDBDatabase *) aDatabase
  atRecordNumber: (unsigned) a_record_nr;
  
  
/*!
 * @method readFromDatabase
 * @abstract reads the specified chunk from the database
 * @param aDatabase database to use
 * @param a_record_nr record number at which to store the chunk
 * @result loaded chunk or nil if not existent
 */
+ (_FTPersistentSetChunk *) readFromDatabase: (BDBDatabase *) aDatabase 
  atRecordNumber: (unsigned) record_nr;


/*!
 * @method initForDatabase
 * @abstract internal method call
 * @param aDatabase database to use
 * @param a_record_nr record number to use
 * @param givenObjects used as the initial set of data for this chunk.
 *   if nil then an empty set will be created and loadedFromDatabase
 *   may only equal NO
 * @result self
 */
- initForDatabase: (BDBDatabase *) aDatabase 
  atRecordNumber: (unsigned) a_record_nr
  usingObjects: (NSArray *) givenObjects;
  
- (void) dealloc;


/*!
 * @method addObject
 * @abstract adds an object to this chunk. Does *not* store the result in the
 *   database! Call storeChunk for this purpose
 * @param anObject given object must implement NSCoding
 * @result self
 */
- addObject: (id) anObject;


/*!
 * @method count
 * @result number of objects in this chunk
 */
- (unsigned) count;


/*!
 * @method containsObject
 * @result YES if the given object is to be found in the chunk
 */
- (BOOL) containsObject: (id) anObject;


/*!
 * @method isChunkInTransaction 
 * @result YES if this chunk is already been placed in a transaction
 */
- (BOOL) isChunkInTransaction; 


/*!
 * @method loadChunk
 * @abstract Loads the chunk from the database
 * @result self
 */
- loadChunk;


/*!
 * @method objects
 * @abstract get all objects stored in this chunk
 * lresult all objects stored in this chunk
 */
- (NSArray *) objects;


/*!
 * @method recordNumber
 * @result number of BDB record used for storing the chunk
 */
- (unsigned) recordNumber;


/*!
 * @method remove
 * @abstract removes the chunk from the database
 */
- (void) remove;


/*!
 * @method removeObject
 * @abstract removes the specified objects. Operation is ignored if given
 *   object is not to be found in the chunk
 * @result self
 */
- removeObject: (id) anObject;


/*!
 * @method setChunkInTransaction
 * @param itIs set to YES if the chunk is placed within a transaction
 * @result self
 */
- setChunkInTransaction: (BOOL) itIs;


/*!
 * @method store
 * @abstract this method is used to store the content of the chunk into the
 *   database
 * @result self
 */
- store;


/*!
 * @method update
 * @abstract either stores the chunk or deletes it. The latter is done if the
 *   chunk contains no more data.
 *   This method should only called by transaction steps since it directly
 *   writes the content to the database
 * @result self
 */
- (void) update;
@end


/* ----------------------------------------- _FTPersistentSetChunkIterator */
/*!
 * @class _FTPersistentSetChunkIterator
 * @abstract Used to iterate over all chunks of a persistent set
 */
@interface _FTPersistentSetChunkIterator : FTObject <ECIterator> {
  @private
    unsigned current_rec_number;
    FTPersistentSetImpl *persistentSet;
    _FTPersistentSetChunk *fetchedChunk;
    BOOL fetchedBefore;
}

- initWithPersistentSet: (FTPersistentSetImpl *) aPersistentSet;
- (void) dealloc;

- (BOOL) hasNext;
- next;

- fetchChunk;
@end


/* ----------------------------------------- _FTPersistentSetIterator */
/*!
 * @class _FTPersistentSetIterator
 * @abstract Used to iterate over all elements of a persistent set
 * @description TODO: Expensive operation at present
 */
@interface _FTPersistentSetIterator : FTObject <ECIterator> {
  @private 
    id <ECIterator> chunkIterator;
    NSEnumerator *chunkElements;
    BOOL elementFetched;
    id nextObject;
}

- initWithPersistentSet: (FTPersistentSetImpl *) aPersistentSet;
- (void) dealloc;


/*!
 * @method fetchNextChunkElements
 * @abstract fetch enumeration of elements of the next chunk and set up internal
 *   fields appropriately
 * @result self
 */
- fetchNextChunkElements;


/*!
 * @nethod currentElement
 * @abstract Reads the current element of the current enumeration of the current
 *   selected chunk. It stores a reference to this object so that subsequent
 *   calls to this method will return the same object until the flag
 *   elementFetched is set to NO
 * @result the current object
 */
- currentElement;


/*!
 * @method hasNext
 * @result YES if there is an element to return via "next"
 */
- (BOOL) hasNext;


/*!
 * @method next
 * @result next element of the current iteration or nil, if not existent.
 */
- next;
@end


/* ----------------------------------------- _FTPersistentSetTransactionSetp */
/*!
 * @class _FTPersistentSetTransactionStep
 * @abstract Internal method used to perform the database updates
 */
@interface _FTPersistentSetTransactionStep : FTObject <FTTransactionStep> 

+ (void) initialze;

/*!
 * @method addTransactionStepForChunk
 * @abstract Adds a transaction step to the current transaction in order
 *   to update the given chunk for the given set. Does nothing if there already
 *   exists a transaction for this chunk
 * @param aChunk chunk to update
 * @param aSet set the chunk belongs to
 */
+ (void) addTransactionStepForChunk: (_FTPersistentSetChunk *) aChunk
  forSet: (FTPersistentSetImpl *) aSet;


/*!
 * @method initWithChunk
 * @param chunk to update
 * @param aContext underlying transaction context
 * @result self
 */
- initWithChunk: (_FTPersistentSetChunk *) chunk 
  forContext: (FTTransactionContext *) aContext;


/*!
 * @method performAction 
 * @abstract Called by the transaction controll in order to run the 
 * transaction
 * @result return information about the success of this operation
 */
- (BOOL) performAction: (FTTransactionContext *) transactionContext;


/*!
 * @method undoAction
 * @abstract removes all modifications previously been done by 
 *   {@link #performAction}
 * @result return YES if done successfully
 */
- (BOOL) undoAction: (FTTransactionContext *) transactionContext;
@end

#endif