import xml.etree.ElementTree
import hashdb

class DatImportError(Exception):
    '''This error is raised when a DAT import fails.'''

# TODO: l o g g i n g

# TODO: Consider using a context object to avoid keeping large XML trees in memory.
class Dat:
    '''A Dat object processes DAT files into the data structures defined in hashdb. '''
    def __init__(self, filename):
        '''Open the given DAT file and gather metadata from it.'''

        xml_tree = xml.etree.ElementTree.parse(filename)
        self._xml_root = xml_tree.getroot()

        dat_header = self._xml_root.find('header')
        self.info = hashdb.DatInfo(name=dat_header.find('name').text,
                                   description=dat_header.find('description').text,
                                   platform=None,
                                   version=dat_header.find('version').text)

    def set_platform(self, platform_info):
        '''
        Set a platform for this DAT file.
        DAT files don't include platform metadata, but are all platform-specific.
        '''
        new_info = hashdb.DatInfo(name=self.info.name,
                                  description=self.info.description,
                                  platform=platform_info.shortcode,
                                  version=self.info.version)
        self.info = new_info

    def set_name(self, new_name):
        '''
        Override the DAT file's name.
        DAT files often have less-than-helpful names.
        '''
        new_info = hashdb.DatInfo(name=new_name,
                                  description=self.info.description,
                                  platform=self.info.platform,
                                  version=self.info.version)
        self.info = new_info

    def read_all_hashes(self):
        '''Read every hash in the DAT file and return it as a large list of RomInfo tuples.'''
        if self.info.platform is None:
            raise DatImportError('DAT platform not set.')

        rom_info_list = []
        all_rom_entries = self._xml_root.findall('.//rom')

        for rom in all_rom_entries:
            rom_info = hashdb.RomInfo(sha1sum=rom.get('sha1'),
                                      filename=rom.get('name'),
                                      platform=self.info.platform,
                                      datorigin=self.info.name)

            rom_info_list.append(rom_info)

        return rom_info_list