Restructuredtext directive for photolouge

from photologue.models import Photo, PhotoSize

from docutils import nodes
from docutils.parsers.rst import directives
from docutils.parsers.rst.directives.images import image

OPTIONS = {
    'alt': directives.unchanged,
    'class': directives.class_option
}

def imageblock_directive(name, arguments, options, content, lineno,
                       content_offset, block_text, state, state_machine):
    """
    Directive for inserting images using photolouge in django.
    
    Syntax:
        
        .. imageblock:: photo_title_slug photo_size_name left|right|center
            :class: optionalclassoption
        
            optional description for image, can be multiple lines
    """
    try: 
        slug, attr, pos = arguments[0].split(' ')
    except ValueError:
        error = state_machine.reporter.error(
            'Error in "%s" directive: Too many arguments. '
            'Valid arguments are "title_slug image_size position". '
            % (name,) ,
            nodes.literal_block(block_text, block_text), line=lineno)
        return [error]
        
    if pos not in ('left', 'right', 'center'):
        error = state_machine.reporter.error(
                    'Error in "%s" directive: "%s" is not a valid position for '
                    'images. Valid positions are: "left right center". '
                    % (name, pos) ,
                    nodes.literal_block(block_text, block_text), line=lineno)
        return [error]
        
    img = Photo.objects.get(title_slug=slug)
    
    try:
        imgurl = getattr(img, 'get_%s_url' % attr)()
    except AttributeError:
        error = state_machine.reporter.error(
                    'Error in "%s" directive: "%s" is not a valid size for '
                    'images. Valid sizes are: "%s" '
                    % (name, attr, ", ".join([s.name for s in PhotoSize.objects.all()]) ) ,
                    nodes.literal_block(block_text, block_text), line=lineno)
        return [error]
        
    imgsize = getattr(img, 'get_%s_size' % attr)()
    
    options['width'] = str(imgsize[0])
    options['height'] = str(imgsize[1])
    
    if not 'alt' in options:
        options['alt'] = img.title
        
    text = '\n'.join(content)      
    node = nodes.container(text)
    
    classes = ['imageblock', '%simage' % attr, '%spos' % pos]
    
    if 'class' in options:
        classes.append(''.join(options['class']))
        del options['class']
        
    node['classes'].extend(classes)
    
    imagenode = image(name, [imgurl], options, content, lineno,
          content_offset, block_text, state, state_machine)          
        
    node.insert(0, imagenode)
    
    state.nested_parse(content, content_offset, node)
    
    return [node]

imageblock_directive.arguments = (1, 0, 1)
imageblock_directive.content = 1
imageblock_directive.options = OPTIONS

directives.register_directive('imageblock', imageblock_directive)