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from werkzeug import Request, Response, exceptions

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from werkzeug.utils import html

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import pypngtile

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import os.path

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class BaseApplication (object):

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    def __init__ (self, image_root):

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        if not os.path.isdir(image_root) :

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            raise Exception("Given image_root does not exist: {image_root}".format(image_root=image_root))

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        self.image_root = os.path.abspath(image_root)

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        self.image_cache = { }

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    def lookup_image (self, url):

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        """

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            Lookup image by request path.

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            Returns image_name, image_path.

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        """

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        if not os.path.isdir(self.image_root):

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            raise exceptions.InternalServerError("Server image_root has gone missing")

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        # path to image

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        name = url.lstrip('/')

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        # build absolute path

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        path = os.path.abspath(os.path.join(self.image_root, name))

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        # ensure the path points inside the data root

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        if not path.startswith(self.image_root):

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            raise exceptions.NotFound(name)

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        if not os.path.exists(path):

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            raise exceptions.NotFound(name)

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        if os.path.isdir(path):

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            raise exceptions.BadRequest("Is a directory: {name}".format(name=name))

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        if not path.endswith('.png'):

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            raise exceptions.BadRequest("Not a PNG image: {name}".format(name=name))

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        return name, path

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    def get_image (self, url):

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        """

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            Return Image object.

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        """

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        name, path = self.lookup_image(url)

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        # get Image object

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        image = self.image_cache.get(path)

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        if not image:

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            # open

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            image = pypngtile.Image(path)

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            # check

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            if image.status() not in (pypngtile.CACHE_FRESH, pypngtile.CACHE_STALE):

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                raise exceptions.InternalServerError("Image cache not available: {name}".format(name=name))

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            # load

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            image.open()

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            # cache

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            self.image_cache[path] = image

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        return image, name

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    def handle (self, request):

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        """

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            Handle request for an image

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        """

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        raise NotImplementedError()

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    @Request.application

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    def __call__ (self, request):

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        """

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            WSGI entry point.

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        """

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        try:

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            return self.handle(request)

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        except exceptions.HTTPException as error:

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            return error

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    STYLESHEETS = ( )

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    SCRIPTS = ( )

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        if stylesheets is None:

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            stylesheets = self.STYLESHEETS

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        if scripts is None:

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            scripts = self.SCRIPTS

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        return html.html(lang='en', *[

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            html.head(

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                html.title(title),

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                *[

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                    html.link(rel='stylesheet', href=href) for href in stylesheets

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                ]

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            ),

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            html.body(

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                *(body + tuple(

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                    html.script(src=src) for src in scripts

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            ),

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        ])

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