"""
interfaces to get information from a package
"""

import imp
import os
import subprocess
import sys

from subprocess import check_call as call

class PackageInfo(object):
    """abstract base class of package info"""
    def __init__(self, path):
        """
        - path : path to setup.py or its directory
        """
        if os.path.isdir(path):
            path = os.path.join(path, 'setup.py')
        assert os.path.exists(path), "'%s' not found" % path
        self.setup_py = os.path.abspath(path)

    def __call__(self):
        """returns dictionary of package info"""
        raise NotImplementedError("abstract base class")

class SetupOverridePackageInfo(PackageInfo):
    """
    gather setup.py information by overriding the function
    """

    def __call__(self):
        setuptools = sys.modules.get('setuptools')
        sys.modules['setuptools'] = sys.modules[__name__]
        globals()['setup'] = self._setup
        try:
            module = imp.load_source('setup', self.setup_py)
        finally:
            sys.modules.pop('setuptools')
            if setuptools:
                sys.modules['setuptools'] = setuptools
            globals().pop('setup')
        return self.__dict__.pop('_info')

    def _setup(self, **kwargs):
        self._info = kwargs

class EggInfo(PackageInfo):
    """
    use `python setup.py egg_info` to gather package information
    """

    def __call__(self):

        info = self.read_pkg_info(self._pkg_info())
        # TODO: install_requires
        return info

    @classmethod
    def read_pkg_info(cls, path):
        """reads PKG-INFO and returns a dict"""

        # read the package information
        info_dict = {}
        for line in file(path).readlines():
            if not line or line[0].isspace():
                continue # XXX neglects description
            assert ':' in line
            key, value = [i.strip() for i in line.split(':', 1)]
            info_dict[key] = value

        # return the information
        return info_dict

    def _egg_info(self):
        """build the egg_info directory"""

        if self._egg_info_path:
            return self._egg_info_path

        directory = os.path.dirname(self.setup_py)

        # setup the egg info
        try:
            call([sys.executable, 'setup.py', 'egg_info'], cwd=directory, stdout=subprocess.PIPE)
        except Exception:
            print "Failure to generate egg_info: %s" % self.setup_py
            raise

        # get the .egg-info directory
        egg_info = [i for i in os.listdir(directory)
                    if i.endswith('.egg-info')]
        assert len(egg_info) == 1, 'Expected one .egg-info directory in %s, got: %s' % (directory, egg_info)
        egg_info = os.path.join(directory, egg_info[0])
        assert os.path.isdir(egg_info), "%s is not a directory" % egg_info

        # cache it
        self._egg_info_path = egg_info
        return self._egg_info_path

    def _pkg_info(self):
        """returns path to PKG-INFO file"""

        if getattr(self, '_pkg_info_path', None):
            # return cached value
            return self._pkg_info_path

        try:
            egg_info = self._egg_info()
        except Exception, exception:
            # try to get the package info from a file
            path = os.path.dirname(self.setup_py)
            pkg_info = os.path.join(path, 'PKG-INFO')
            if os.path.exists(pkg_info):
                self._pkg_info_path = pkg_info
                return self._pkg_info_path
            raise Exception("Cannot find or generate PKG-INFO")

        pkg_info = os.path.join(egg_info, 'PKG-INFO')
        assert os.path.exists(pkg_info)
        self._pkg_info_path = pkg_info
        return self._pkg_info_path