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"""

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    State for thumbnails; derivates of Images

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"""

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import filesystem

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import PIL.Image

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class Thumbnail (filesystem.File) :

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    """

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        A Thumbnail is a derivate of an Image, usually resized to some other size.

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    """

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    def __init__ (self, image, subdir, target_size) :

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        """

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            Initialize to link against the given `image`.

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            `subdir` specifies the directory to store this thumbnail in.

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            `target_size` determines the target resolution of the output thumbnail.

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        """

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        # our file path, image name inside of the given subdir

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        super(Thumbnail, self).__init__(subdir, image.fsname)

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        # store

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        self.image = image

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        self.target_size = target_size

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    def stale (self) :

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        """

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            Tests if this thumbnail is stale

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        """

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        if self.image.older_than(self) :

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            # both exist and this is newer

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            return False

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        else :

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            # this thumb doesn't exist or is older

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            return True

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    @property

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    def size (self) :

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        """

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            Compute the *real* size of this thumbnail, from the image's actual size and our target size.

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            Preserves the aspect ratio etc.

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        """

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        # real image size

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        img_width, img_height = self.image.img_size

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        # target size

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        thumb_width, thumb_height = self.target_size

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        # calc new size, preserving aspect ratio

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        if img_width > thumb_width : 

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            height = max(img_height * thumb_width / img_width, 1)

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            width = thumb_width

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            width = max(img_width * thumb_height / img_height, 1)

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            height = thumb_height

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        return width, height 

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    def update (self) :

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        """

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            Render new output thumbnail.

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        """

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        # create resized copy of main image, using our size

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        thumb = self.image.img.resize(self.size, resample=PIL.Image.ANTIALIAS)

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        # write it out

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        thumb.save(self.path)

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