Software Público Brasileiro

###############################################################################
# Name: histcache.py                                                          #
# Purpose: History Cache                                                      #
# Author: Cody Precord <cprecord@editra.org>                                  #
# Copyright: (c) 2009 Cody Precord <staff@editra.org>                         #
# Licence: wxWindows Licence                                                  #
###############################################################################

"""
Editra Buisness Model Library: HistoryCache

History cache that acts as a stack for managing a history list o

"""

__author__ = "Cody Precord <cprecord@editra.org>"
__cvsid__ = "$Id: histcache.py 67123 2011-03-04 00:02:35Z CJP $"
__revision__ = "$Revision: 67123 $"

__all__ = [ 'HistoryCache', 'HIST_CACHE_UNLIMITED',
            'CycleCache']

#-----------------------------------------------------------------------------#
# Imports

#-----------------------------------------------------------------------------#
# Globals
HIST_CACHE_UNLIMITED = -1

#-----------------------------------------------------------------------------#

class HistoryCache(object):
    """Data management cache.
    Maintains a positional list of objects that remembers the last access 
    position in the cache.

    """
    def __init__(self, max_size=HIST_CACHE_UNLIMITED):
        """@param max_size: size of history cache (int)"""
        super(HistoryCache, self).__init__()

        # Attributes
        self._list = list()
        self.cpos = -1
        self.max_size = max_size

    def _Resize(self):
        """Adjust cache size based on max size setting"""
        if self.max_size != HIST_CACHE_UNLIMITED:
            lsize = len(self._list)
            if lsize:
                adj = self.max_size - lsize 
                if adj < 0:
                    self._list.pop(0)
                    self.cpos = len(self._list) - 1 

    def Clear(self):
        """Clear the history cache"""
        del self._list
        self._list = list()
        self.cpos = -1

    def GetSize(self):
        """Get the current size of the cache
        @return: int (number of items in the cache)

        """
        return len(self._list)

    def GetMaxSize(self):
        """Get the max size of the cache
        @return: int

        """
        return self.max_size

    def GetNextItem(self):
        """Get the next item in the history cache, moving the
        current position towards the end of the cache.
        @return: object or None if at end of list

        """
        item = None
        if self.cpos < len(self._list) - 1:
            self.cpos += 1
            item = self._list[self.cpos]
        return item

    def GetPreviousItem(self):
        """Get the previous item in the history cache, moving the
        current position towards the beginning of the cache.
        @return: object or None if at start of list

        """
        item = None
        if self.cpos >= 0 and len(self._list) > 0:
            if self.cpos == len(self._list):
                self.cpos -= 1
            item = self._list[self.cpos]
            self.cpos -= 1
        return item

    def HasPrevious(self):
        """Are there more items to the left of the current position
        @return: bool

        """
        llen = len(self._list)
        more = ((self.cpos >= 0) and llen and (self.cpos < llen))
        return more

    def HasNext(self):
        """Are there more items to the right of the current position
        @return: bool

        """
        if self.cpos == -1 and len(self._list):
            more = True
        else:
            more = self.cpos >= 0 and self.cpos < (len(self._list) - 1)
        return more

    def PeekNext(self):
        """Return the next item in the cache without modifying the
        currently managed position.
        @return: cache object

        """
        if self.HasNext():
            return self._list[self.cpos+1]
        else:
            return None

    def PeekPrevious(self):
        """Return the previous item in the cache without modifying the
        currently managed position.
        @return: cache object

        """
        if self.HasPrevious():
            return self._list[self.cpos]
        else:
            return None

    def PutItem(self, item):
        """Put an item on the top of the cache
        @param item: object

        """
        if self.cpos != len(self._list) - 1:
            self._list = self._list[:self.cpos]
        self._list.append(item)
        self.cpos += 1
        self._Resize()

    def SetMaxSize(self, max_size):
        """Set the maximum size of the cache
        @param max_size: int (HIST_CACHE_UNLIMITED for unlimited size)

        """
        assert max_size > 0 or max_size == 1, "Invalid max size"
        self.max_size = max_size
        self._Resize()

#-----------------------------------------------------------------------------#

class CycleCache(object):
    """A simple circular cache. All items are added to the end of the cache
    regardless of the current reference position. As items are accessed from
    the cache the cache reference pointer is incremented, if it passes the
    end it will go back to the beginning.

    """
    def __init__(self, size):
        """Initialize the cache.
        @param size: cache size

        """
        super(CycleCache, self).__init__()

        # Attributes
        self._list = list()
        self._cpos = -1
        self._size = size

    def __len__(self):
        return len(self._list)

    def NextIndex(self):
        """Get the next index in the cache
        @return: int

        """
        idx = self._cpos 
        idx -= 1
        if abs(idx) > len(self._list):
            idx = -1
        return idx

    def Clear(self):
        """Clear the cache"""
        del self._list
        self._list = list()

    def GetCurrentSize(self):
        """Get the size of the cache
        @return: int

        """
        return len(self._list)

    def GetNext(self):
        """Get the next item in the cache and increment the
        current position.
        @return: object

        """
        item = None
        if len(self._list): 
            item = self._list[self._cpos]
            self._cpos = self.NextIndex()
        return item

    def PeekNext(self):
        """Look the next item in the cache
        @return: object

        """
        item = None
        if abs(self._cpos) < len(self._list):
            item = self._list[self._cpos]
        return item

    def PeekPrev(self):
        """Look the next item in the cache
        @return: object

        """
        idx = self._cpos + 1
        if idx == 0:
            idx = -1 * len(self._list)

        llen = len(self._list)
        if llen and abs(idx) <= llen:
            item = self._list[idx]
        else:
            item = None
        return item

    def PutItem(self, item):
        """Put an item in the cache
        @param item: object

        """
        llen = len(self._list)
        if llen and (llen == self._size):
            del self._list[0]
        self._list.append(item)

    def Reset(self):
        """Reset the list reference pointer"""
        self._cpos = -1