	#!/usr/bin/env python
	import os, shutil, subprocess, time
	from optparse import OptionParser

	USAGE = """%prog [options] name

	Converts a bzr repository into a git repository and preps it for git-flow"""

	def run(*cmds):
	output = []
	for cmd in cmds:
	try:
	p = subprocess.Popen(cmd, shell = True, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
	stdout, stderr = p.communicate()
	if p.returncode is not 0:
	raise Exception(stderr)
	output.append(stdout.strip())
	except Exception, e:
	raise Exception("error executing the command: %s\n\n%s" % (cmd, e))
	return output[0] if len(output) == 1 else output

	def Main():
	parser = OptionParser(usage = USAGE)
	parser.add_option("-k", "--keep", dest = "keep", action = "store_true", default = False, help = "keep a copy of the original bzr repo on disk")
	parser.add_option("-r", "--repo", dest = "repo", type = "string", help = "url of the repository to convert; if not specified, assumes that 'name' is a local or checked out bzr repository")
	parser.add_option("-t", "--tree-only", dest = "tree", type = "string", help = "subdirectory to create as new project root; other history will be discarded")
	parser.add_option("-T", "--tree-exclude", dest = "tree_exclude", type = "string", help = "subdirectory to discarded, along with its history")
	parser.add_option("-c", "--cripple", dest = "cripple", action = "store_true", default = False, help = "cripple the BZR repo when done (remove all files, add a README saying it was migrated)")
	options, args = parser.parse_args()

	# raise errors on weird conditions
	if len(args) not in (1,2):
	parser.error("Incorrect number of arguments")
	if options.tree and options.tree_exclude:
	parser.error("tree and tree-exclude are mutually exclusive options")
	if (options.tree or options.tree_exclude) and options.cripple:
	parser.error("cripple and tree are (currently) mutually exclusive options")

	name = args.pop(0).rstrip("/")
	gitname = ("%s.git" % args.pop(0)).replace(".git.git", ".git") if len(args) else "%s.git" % name
	if not options.repo and not os.path.isdir(os.path.join(name, ".bzr")):
	parser.error("No bzr repo found at %s" % name)
	elif os.path.isdir(gitname):
	parser.error("%s already exists; have you migrated this repo already?" % gitname)
	elif options.repo and os.path.isdir(name):
	parser.error("%s already exists; are you sure you want to checkout another copy?" % name)

	gitpath = os.path.abspath(os.path.join(os.getcwd(), gitname))

	print "Migrating %s to git" % name

	# make a backup in case something goes wrong
	BACKUP_DIR = "%s.__backup__" % name
	if os.path.isdir(name):
	shutil.copytree(name, BACKUP_DIR, symlinks = True)

	cwd = os.getcwd()
	try:
	if options.repo:
	print " * Checking out repository at %s" % options.repo
	run("bzr checkout %s %s" % (options.repo, name))
	os.chdir(name)

	# things go south if the repo has no commit history
	if run("bzr revno") == "0":
	print " * bzr revno is 0; performing initial commit"
	run('bzr commit --unchanged -m "Initial commit"')

	# quick convert
	print " * Migrating commit history from bzr to git"
	run("git init", "bzr fast-export `pwd` \| git fast-import")
	if options.cripple:
	print " * Crippling the BZR repo"
	for node in [n for n in os.listdir(".") if n != ".git" and n != ".bzr"]:
	if os.path.isfile(node):
	os.remove(node)
	elif os.path.isdir(node):
	shutil.rmtree(node)
	open("README", "wb").write("This repository has been migrated to Git.\nLook in the Git repo for the appropriate version of this project.")
	run("bzr add README")
	try:
	i = 5
	while i:
	print " Committing dead BZR repo to server in %s seconds... (ctrl-c to skip)" % i
	time.sleep(1)
	i -= 1
	print " - Committing..."
	run('bzr commit -m "Crippled the repo; it has been migrated to git"')
	except KeyboardInterrupt:
	print " - Skipped commit of dead BZR repo"

	run("rm -rf .bzr", "git reset --hard HEAD")
	ignore = None
	if os.path.exists(".bzrignore"):
	ignore = open(".bzrignore").read()
	run("git mv .bzrignore .gitignore", "git add .gitignore", 'git commit -m "Migrate .bzrignore to .gitignore"')

	MIGRATE_ALL = True
	if options.tree or options.tree_exclude:
	tree = options.tree if options.tree else options.tree_exclude
	if options.tree:
	if os.path.isdir(tree):
	MIGRATE_ALL = False
	# promote the tree and prune all history not pertinent to it
	print " * Pruning out everything except the %s tree (this may take a while)" % tree
	run("git filter-branch --subdirectory-filter %s HEAD -- --all" % tree, "git reset --hard")
	else:
	print " ! Specified tree not found; migrating the whole repo"
	else:
	MIGRATE_ALL = False
	# destroy the tree(s) and historical references
	print " * Destroying the specified tree(s) and all historical commit references (this may take a while)"
	run('git filter-branch --index-filter "git rm -r -f --cached --ignore-unmatch %s" --prune-empty HEAD' % tree, "git reset --hard")

	if MIGRATE_ALL:
	# create the shared bare repo
	print " * Creating a bare git clone at %s" % gitname
	run("git clone --bare %s %s" % (os.getcwd(), gitpath))
	else:
	if ignore:
	open(".gitignore", "wb").write(ignore)
	run("git add .gitignore", 'git commit -m "Migrate old .bzrignore to .gitignore"')
	# create the destination bare repo and push to it; doing this
	# will free up disk space used by commits we just ignored
	print " * Creating a bate git clone at %s" % gitname
	run("git init --bare %s" % gitpath, "git push %s HEAD" % gitpath)

	os.chdir(gitpath)
	# set up git-flow branches
	print " * Prepping branches for git-flow"
	run("git branch -m master develop", "git branch production")

	# pack the new repo
	print " * Aggressively packing the new repo"
	run("git gc --aggressive")

	# set up git-daemon and web ui hooks
	open("git-daemon-export-ok", "wb").write('')
	shutil.move(os.path.join("hooks", "post-update.sample"), os.path.join("hooks", "post-update"))

	# set some config options
	run("git config core.sharedrepository true")
	run("git config core.ignorecase false")
	run("git config receive.denyNonFastForwards true")

	# verify correct file permissions
	run("find objects -type d -exec chmod 02775 {} \;")

	# clean up
	print " * Cleaning up working directories"
	os.chdir(cwd)
	if os.path.isdir(name):
	shutil.rmtree(name)
	if os.path.isdir(BACKUP_DIR):
	if options.keep:
	shutil.move(BACKUP_DIR, name)
	else:
	shutil.rmtree(BACKUP_DIR)
	print "Success! Place the bare git repo in the desired location."
	except Exception, e:
	os.chdir(cwd)
	if os.path.isdir(name):
	shutil.rmtree(name)
	if os.path.isdir(BACKUP_DIR):
	shutil.move(BACKUP_DIR, name)
	print "\nError:", e

	if __name__ == "__main__":
	Main()