Added GitRevisionProvider class

- added specialized class as git revision provider
- build step will also update version.py
- in absence of .git dir version and git_revision will be taken
  from package distribution

setup.py

@@ -5,40 +5,49 @@ import os
 from setuptools import find_packages
 from setuptools import setup
 from setuptools.command.install import install
+from setuptools.command.build_py import build_py as build_py
 
 assert sys.version_info[0] == 3 and sys.version_info[1] >= 6, "hive requires Python 3.6 or newer"
 
 VERSION = '0.0.1'
 
-class InstallWrapper(install):
+class GitRevisionProvider(object):
     _GIT_REVISION = None
-    def run(self):
-        self._GIT_REVISION = self._get_git_version()
-        self._save_version_file()
-        install.run(self)
 
-    def _get_git_version(self):
+    @staticmethod
+    def provide_git_revision():
         if os.path.exists(".git"):
             from subprocess import check_output
             command = 'git describe --tags --long --dirty'
             version = check_output(command.split()).decode('utf-8').strip()
             parts = version.split('-')
             _, _, sha = parts[:3]
-            return sha.lstrip('g')
-        return self._get_git_version_from_file()
+            GitRevisionProvider._save_version_file(VERSION, sha.lstrip('g'))
+        else:
+            from pkg_resources import get_distribution
+            try:
+                version, git_revision = get_distribution("hivemind").version.split("+")
+                GitRevisionProvider._save_version_file(version, git_revision)
+            except:
+                GitRevisionProvider._save_version_file(VERSION, "")
 
-    def _get_git_version_from_file(self):
-        with open("hive/version.py", 'r') as version_file:
-            lines = version_file.readlines()
-            _, git_version = lines[-1].split('=')
-            return git_version.strip()
-
-    def _save_version_file(self):
+    @staticmethod
+    def _save_version_file(hivemind_version, git_revision):
         with open("hive/version.py", 'w') as version_file:
             version_file.write("# generated by setup.py\n")
             version_file.write("# contents will be overwritten\n")
-            version_file.write("VERSION = '{}'\n".format(VERSION))
-            version_file.write("GIT_REVISION = '{}'".format(self._GIT_REVISION))
+            version_file.write("VERSION = '{}'\n".format(hivemind_version))
+            version_file.write("GIT_REVISION = '{}'".format(git_revision))
+
+class BuildWrapper(build_py):
+    def run(self):
+        GitRevisionProvider.provide_git_revision()
+        build_py.run(self)
+
+class InstallWrapper(install):
+    def run(self):
+        GitRevisionProvider.provide_git_revision()
+        install.run(self)
 
 # yapf: disable
 setup(
@@ -68,12 +77,14 @@ setup(
         'aiocache',
         'configargparse',
         'pdoc',
-        'diff-match-patch',
+        'diff-match-patch'
     ],
     entry_points={
         'console_scripts': [
             'hive=hive.cli:run',
         ]
     },
-    cmdclass={'install': InstallWrapper}
+    cmdclass={
+        'install': InstallWrapper,
+        'build_py':BuildWrapper}
 )