/layers/models.py

from django.db import models
from django.dispatch import receiver
from django.conf import settings
from django.contrib.gis.gdal import DataSource
from django.template.defaultfilters import slugify
import zipfile
import os, errno
import glob

class Layer(models.Model):
    name = models.CharField(max_length=255)
    description = models.TextField(null=True, blank=True)
    slug = models.SlugField(editable=False)
    bbox = models.CharField(max_length=255, null=True, blank=True)
    original = models.FileField(upload_to='uploads', null=True, blank=True,
                                help_text="""Zip file with either geotiff and
                                        projection or shapefiles and friends""")
#    type = models.CharField(max_length=255)
    style = models.TextField(null=True, blank=True)

    def __unicode__(self):
        return self.name

    def save(self, force_insert=False, force_update=False):
        self.slug = slugify(self.name)
        super(Layer, self).save(force_insert, force_update)

def create_folder(path):
    try:
        os.makedirs(path)
    except OSError as exc: # Python >2.5
        if exc.errno == errno.EEXIST and os.path.isdir(path):
            pass
        else: raise

@receiver(models.signals.pre_save, sender=Layer)
def layer_handler(sender, instance, *args, **kwargs):
    """
    Post process the uploaded layer
    Get the bounding box information and save it with the model
    """

    instance.slug = slugify(instance.name)

    # Make a folder with the slug name
    # and create a 'raw' subdirectory to hold the files
    layer_folder = os.path.join(settings.MEDIA_ROOT, 'layers', instance.slug)
    create_folder(layer_folder)
    zip_out = os.path.join(layer_folder, 'raw')
    create_folder(zip_out)

    # Iterate over the files in the zip and create them in the raw folder.
    z = zipfile.ZipFile(instance.original)
    for name in z.namelist():
        outfile = open(os.path.join(zip_out, name), 'wb')
        outfile.write(z.read(name))
        outfile.close()

    # Check if it is vector or raster
    # if it has a .shp file, it is vector :)
    os.chdir(zip_out)
    shapefiles = glob.glob('*.shp')

    if len(shapefiles) > 0:
        # this means it is a vector

        # FIXME(This is a very weak way to get the shapefile)
        shapefile = shapefiles[0]

        # Use ogr to inspect the file and get the bounding box
        ds = DataSource(shapefile)
        layer = ds[0]
        extent = layer.extent.tuple
        instance.bbox = ",".join(["%s" % x for x in extent])

    # Render the tiles (if possible)