#!/usr/bin/env python
import sys
import os
import subprocess

# This server-side pre-receive hook is to be put and activated in all modules
# that depend on the common submodule.
#
# It will check whether any modifications to the common 'submodule file' has a
# a valid commit SHA1 that exists in the common module.

def commit_exists(sha1, gitdir):
    """Returns True if the sha1 is a valid commit in the given
    git directory"""
    # FIXME: We're using 'git show' for the time being, but there's a small
    # risk that there might be a valid SHA1 for a non-commit object.
    env = os.environ.copy()
    env["GIT_DIR"] = gitdir
    sub = subprocess.Popen(["git", "show", sha1], env=env,
                           stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE)
    while True:
        res = sub.poll()
        if res != None:
            return res == 0

# location of the common git module
COMMON_GIT_DIR = "/git/gstreamer/common.git"

pushvalid = True
error_badcommon = False
error_badcommit = False

print "=> Checking for integrity of common submodule changes"
print

for line in sys.stdin.readlines():
    # ref is the ref to be modified
    # old is the old commit it was pointing to
    # new is the new commit it was pointing to
    old, new, ref = line.split(' ', 2)

    # 1. Get the latest change to common (if there was any changes)
    sub = subprocess.Popen(["git", "diff", "%s..%s" % (old, new, ), "--", "common"],
                           stdout=subprocess.PIPE)
    stdout, stderr = sub.communicate()
    if stdout != "":
        # Format of submodule special files
        # Subproject commit <SHA1>

        # we get a diff, therefore only grab the last line
        lastline = stdout.strip().rsplit('\n',1)[-1]
        if not lastline.startswith("+Subproject commit"):
            # this is bad, it means the diff has changed to something completely
            # different
            continue
        subsha1 = lastline.rsplit(' ', 1)[-1]
        print "   Pack wants common to point to", subsha1
        if not commit_exists(subsha1, COMMON_GIT_DIR):
            print "   /!\\ Commit does not exist in common git module /!\\"
            print "   /!\\ for ref", ref
            pushvalid = False
            break

        # 2. Figure out if that commit exists in the common submodule
        # (use GIT_DIR to execute commands in that directory)

    # Get the commit message
    sub = subprocess.Popen(["git", "log", "--format=%s",
	    "%s..%s" % (old, new, )], stdout=subprocess.PIPE)
    stdout, stderr = sub.communicate()
    if stdout != "":
	for line in stdout.strip().rsplit('\n',1):
	    if line.startswith("!"):
	        error_badcommit = True
		pushvalid = False
		break

if pushvalid:
    print "   Incoming packet valid, proceeding to actual commit"
    sys.exit(0)
else:
    if error_badcommit:
        print "   Attempting to push commits with commit messages that start"
        print "   with '!'.  Commit messages starting with '!' are reserved"
	print "   for private branches to prevent the commits from accidentally"
	print "   getting to the main repository."
    if error_badcommon:
        print "   Attempting to push commits containing modifications to common"
        print "   that have not been commited to the actuall common module."
        print
        print "   First push your changes to common/ before pushing the changes"
        print "   to the module using it."
    sys.exit(-1)