def createhistory(graph, rrddef, rrdline, historycount, colors, historystep = None, hidedetails = False):
    '''Multiplies rrddef and rrdline to create a set of history views.
    Colors is a list of color values, first is the latest.
    Returns list of the new lines for eg. changing description.'''
    
    import copy
    
    r = []
    
    if historystep is None:
        historystep = graph.end - graph.start
    
    for i in range(historycount):
        offset = historycount * historystep
        
        newdef = copy.copy(rrddef)
        newdef.start -= offset
        newdef.end -= offset
        newdef.history += offset
        graph.defs.append(newdef)
        
        newline = copy.copy(rrdline)
        newline.rrddef = newdef
        newline.color = colors[i]
        
        if hidedetails:
            newline.description = None
            newline.writeinfo = False
        
        graph.lines.append(newline)
        r.append(newline)
    
    return r




timeunits = {'m' : 60,
             'h' : 3600,
             'd' : 86400,
             'w' : 604800}

def parsetime(timedesc):
    '''Parses a time description, it can be either unix timestamp,
    time & date in format YYYY-MM-DDTHH-MM or relative time as a negative number'''
    
    import re, datetime, time
    
    timedesc = timedesc.strip()
    
    results = re.findall('^(\d\d\d\d)-(\d\d)-(\d\d)T(\d\d)-(\d\d)', timedesc)
    
    if results:
        year, month, day, hours, minutes = results[0]
        d = datetime.datetime(int(year), int(month), int(day), int(hours), int(minutes))
        return int(d.strftime("%s"))
    
    else:
        if timeunits.has_key(timedesc[-1]):
            timestamp = int(timedesc[:-1]) * timeunits[timedesc[-1]]
        else:
            timestamp = int(timedesc)
        
        if timestamp <= 0:
            return time.time() + timestamp
        else:
            return timestamp