import sys
try:
    import curses
except ImportError:
    pass

class ProgressMeter(object):
    """An abstract object which prints out progress messages."""

    def newstage(self, title, length):
        """Called when a new part of the scanning has been reached.
        title is a human-readable description of the part, length
        is the estimated length of the part - the total count that
        will be passed to "progress" eventually."""
        
        raise NotImplementedError        
        
    def progress(self, amount):
        """Called when the part has progressed by "amount" units
        (out of "length" that was passed to newstage)."""
        
        raise NotImplementedError
        
    def endstage(self):
        """Called at the end of each stage."""
        
        raise NotImplementedError
        
    def finished(self):
        """Called when there are no more stages."""        
        
        raise NotImplementedError

class ConsoleProgressMeter(object):
    """A text-mode progress bar for the scanner, that
    moves the cursor about to print a percentage and a bar."""

    def __init__(self):
        # Use curses to get the terminal width.
        try:
            curses.setupterm()
            self.width = curses.tigetnum("cols") - 1
        except:
            raise IOError, "curses not available - " + \
                  "try using PlainProgressMeter"
    
    def newstage(self, desc, length):
        print desc
        self.length = length
        self.total = 0
        self.redraw()

    def progress(self, amount):
        self.total += amount
        self.redraw()
    
    def endstage(self):
        print
        print
    
    def finished(self):
        pass

    def redraw(self):
        # The width we can use, excluding room for the percentage
        # (5 characters) and [, ] and >
        mainwidth = self.width - 8
        # Percentage complete
        percentage = self.total * 100 // self.length
        # Number of characters complete
        squares = self.total * mainwidth // self.length
    
        percentage_str = (str(percentage) + "%").ljust(5)
        filled_bar = "=" * squares
        empty_bar = " " * (mainwidth - squares)
    
        print "\r" + percentage_str + "[" + filled_bar + ">" + \
              empty_bar + "]",
        sys.stdout.flush()

class PlainProgressMeter(object):
    """A text-mode progress reporting thingy for the scanner,
    that does nothing very exciting apart from print dots."""
    
    def newstage(self, desc, length):
        sys.stdout.write(desc)
        sys.stdout.write("..")
        sys.stdout.flush()
        
    def progress(self, amount):
        sys.stdout.write(".")
        sys.stdout.flush()
        
    def endstage(self):
        print
        
    def finished(self):
        pass

def meter():
    """Returns a (hopefully) appropriate meter."""
    
    try:
        return ConsoleProgressMeter()
    except IOError:
        return PlainProgressMeter()