terom@120: """
terom@120:     The various Exif backends that we have
terom@120: """
terom@120: 
terom@120: from __future__ import with_statement
terom@120: 
terom@120: import utils
terom@120: 
terom@120: class ExifHandler (object) :
terom@120:     """
terom@120:         Our generic interface for Exif data
terom@120:     """
terom@120: 
terom@120:     def __init__ (self, file) :
terom@120:         """
terom@120:             Load Exif data from the given File.
terom@120:         """
terom@120: 
terom@120:         self.file = file
terom@120:     
terom@120:     def image_tag (self, tag, default=None) :
terom@120:         """
terom@120:             Load and return the human-readable unicode-safe value for the given main image tag.
terom@120:         """
terom@120: 
terom@120:         abstract
terom@120: 
terom@120:     def image_tags (self, tags) :
terom@120:         """
terom@120:             Load and return the given tags for the main image as a sequence of (tag, value) tuples , following the same
terom@120:             rules as image_tag, except there should mainly be only one call to this function, encompassing all the
terom@120:             relevant tags.
terom@120: 
terom@120:             The returned list should omit those values which were not found.
terom@120:         """
terom@120:     
terom@120:         for tag in tags :
terom@120:             # try and fetch value
terom@120:             value = self.image_tag(tag)
terom@120: 
terom@120:             # filter out default not-found
terom@120:             if value is not None :
terom@120:                 yield tag, value
terom@120: 
terom@120: try :
terom@120:     import pyexiv2
terom@120: 
terom@120: except ImportError :
terom@120:     PyExiv2_Handler = None
terom@120: 
terom@120: else :
terom@120:     class PyExiv2_Handler (ExifHandler) :
terom@120:         NAME = 'pyexiv2'
terom@120: 
terom@120:         def __init__ (self, file) :
terom@120:             """
terom@120:                 Load as pyexiv2.Image
terom@120:             """
terom@120:             
terom@120:             # create
terom@120:             self.image = pyexiv2.Image(file.path)
terom@120: 
terom@120:             # load
terom@120:             self.image.readMetadata()
terom@120:         
terom@120:         def image_tag (self, tag, default=None) :
terom@120:             try :
terom@120:                 # XXX: this is wrong
terom@120:                 return self.image.interpretedExifValue("Exif.Photo.%s" % tag)
terom@120:             
terom@120:             except (IndexError, KeyError) :
terom@120:                 return default
terom@120:     
terom@120: try :
terom@120:     from lib import EXIF
terom@120: 
terom@120: except ImportError :
terom@120:     EXIF_Handler = None
terom@120: 
terom@120: else :
terom@120:     class EXIF_Handler (ExifHandler) :
terom@120:         NAME = 'EXIFpy'
terom@120: 
terom@120:         def __init__ (self, file) :
terom@120:             """
terom@120:                 Load using EXIF.process_file
terom@120:             """
terom@120:             
terom@120:             with file.open('rb') as fh :
terom@120:                 self.tags = EXIF.process_file(fh)
terom@120:         
terom@120:         def image_tag (self, tag, default=None) :
terom@120:             # XXX: this is wrong
terom@120:             return self.tags.get('Image %s' % (tag, ), default)
terom@120: 
terom@120: # ExifHandler implementations to use, in preference order
terom@120: EXIF_HANDLERS = [
terom@120:     # reasonably fast, but requires the native library and extension module
terom@120:     PyExiv2_Handler,
terom@120: 
terom@120:     # pure-python, but very, very slow
terom@120:     EXIF_Handler,
terom@120: ]
terom@120: 
terom@120: # default ExifHandler to use
terom@120: EXIF_HANDLER = utils.first(EXIF_HANDLERS)
terom@120: 
terom@120: # ExifHandler implementations by name
terom@120: EXIF_HANDLERS_BY_NAME = dict((h.NAME, h) for h in EXIF_HANDLERS)
terom@120: 
terom@120: def load (config, file) :
terom@120:     """
terom@120:         Load Exif data using the configured Exif handler, and return the instance.
terom@120: 
terom@120:         Returns None if there wasn't any Exif handler available for use.
terom@120:     """
terom@120: 
terom@120:     if config.exif_handler :
terom@120:         # explicit
terom@120:         exif_handler = config.exif_handler
terom@120: 
terom@120:     elif config.exif_handler_name :
terom@120:         # by name
terom@120:         exif_handler = EXIF_HANDLERS_BY_NAME[config.exif_handler_name]
terom@120: 
terom@120:     else :
terom@120:         # default
terom@120:         exif_handler = EXIF_HANDLER
terom@120:     
terom@120:     if exif_handler :
terom@120:         # found one, use it
terom@120:         return exif_handler(file)
terom@120: 
terom@120:     else :
terom@120:         # nothing :(
terom@120:         return None
terom@120: