import os

try:
    from osgeo import gdal
    from osgeo import gdalconst
except:
    grass.fatal(_("Unable to load GDAL Python bindings"))

import xml.etree.ElementTree as etree

import grass.script as grass

from wms_base import WMSBase

class NullDevice():
    def write(self, s):
        pass

class WMSGdalDrv(WMSBase):
    def _createXML(self):
        """!Create XML for GDAL WMS driver
        
        @return path to XML file
        """
        self._debug("_createXML", "started")
        
        gdal_wms = etree.Element("GDAL_WMS")
        service = etree.SubElement(gdal_wms, "Service")
        name = etree.Element("name")
        service.set("name","WMS")
        
        version = etree.SubElement(service, "Version")
        version.text =self.o_wms_version
        
        server_url = etree.SubElement(service, "ServerUrl")
        server_url.text =self.o_mapserver_url
        
        srs = etree.SubElement(service, self.projection_name)   
        srs.text = 'EPSG:' + str(self.o_srs)
        
        image_format = etree.SubElement(service, "ImageFormat")
        image_format.text = self.mime_format
        
        image_format = etree.SubElement(service, "Transparent")
        image_format.text = self.transparent
        
        layers = etree.SubElement(service, "Layers")
        layers.text = self.o_layers
        
        styles = etree.SubElement(service, "Styles")
        styles.text = self.o_styles
        
        data_window = etree.SubElement(gdal_wms, "DataWindow")
        
        upper_left_x = etree.SubElement(data_window, "UpperLeftX")
        upper_left_x.text = str(self.bbox['minx']) 
        
        upper_left_y = etree.SubElement(data_window, "UpperLeftY")
        upper_left_y.text = str(self.bbox['maxy']) 
        
        lower_right_x = etree.SubElement(data_window, "LowerRightX")
        lower_right_x.text = str(self.bbox['maxx']) 
        
        lower_right_y = etree.SubElement(data_window, "LowerRightY")
        lower_right_y.text = str(self.bbox['miny'])
        
        size_x = etree.SubElement(data_window, "SizeX")
        size_x.text = str(self.region['cols']) 
        
        size_y = etree.SubElement(data_window, "SizeY")
        size_y.text = str(self.region['rows']) 
        
        # RGB + alpha
        self.temp_map_bands_num = 4
        block_size_x = etree.SubElement(gdal_wms, "BandsCount")
        block_size_x.text = str(self.temp_map_bands_num)
        
        block_size_x = etree.SubElement(gdal_wms, "BlockSizeX")
        block_size_x.text = str(self.tile_cols) 
        
        block_size_y = etree.SubElement(gdal_wms, "BlockSizeY")
        block_size_y.text = str(self.tile_rows)
        
        xml_file = self._tempfile()
        
        etree.ElementTree(gdal_wms).write(xml_file)
        
        self._debug("_createXML", "finished -> %s" % xml_file)
        
        return xml_file
    
    def _download(self):
        """!Downloads data from WMS server using GDAL WMS driver
        
        @return temp_map with stored downloaded data
        """
        grass.message("Downloading data from WMS server...")

        # GDAL WMS driver does not flip geographic coordinates 
        # according to WMS standard 1.3.0.
        if self.flip_coords and self.o_wms_version == "1.3.0":
            grass.warning(_("If module will not be able to fetch the data in this\
                           geographic projection, \n try flag -d or use WMS version 1.1.1."))

        self._debug("_download", "started")
        
        temp_map = self._tempfile()        

        xml_file = self._createXML()
        wms_dataset = gdal.Open(xml_file, gdal.GA_ReadOnly)
        grass.try_remove(xml_file)
        if wms_dataset is None:
            grass.fatal(_("Unable to open GDAL WMS driver"))
        
        self._debug("_download", "GDAL dataset created")
        
        driver = gdal.GetDriverByName(self.gdal_drv_format)
        if driver is None:
            grass.fatal(_("Unable to find %s driver" % format))
        
        metadata = driver.GetMetadata()
        if not metadata.has_key(gdal.DCAP_CREATECOPY) or \
           metadata[gdal.DCAP_CREATECOPY] == 'NO':
            grass.fatal(_('Driver %s supports CreateCopy() method.') % self.gdal_drv_name)
        
        self._debug("_download", "calling GDAL CreateCopy...")
        
        temp_map_dataset = driver.CreateCopy(temp_map, wms_dataset, 0)
        
        if temp_map_dataset is None:
            grass.fatal(_("Incorrect WMS query"))
        
        temp_map_dataset  = None
        wms_dataset = None
        
        self._debug("_download", "finished")
        
        return temp_map