#!/bin/sh
#
# Watches for merges that had only local merges (e.g. should have been rebases).
#
# If they are introducing non-merge commits /and/ merge commits, it could
# look like one of two ways. This way:
#
# * --- B --- * --- oldrev
#        \             \
#        new --- new --- newrev
#
# They basically had an un-shared local dev branch (probably by making a
# merge) and instead should have done a rebase. Also, if they did:
#
# * --- B --- * --- oldrev
#        \             \
#        new --- new --- new -- newrev
#
# We should try and catch them--where the merge happened previously to
# them doing more work in the newrev commit.
#
# But if it looks like:
#
# * --- B --- * --- oldrev
#        \              \
#        old --- new --- newrev
#
# Then they had a pre-shared branch that cannot be rebased and so they
# were correct in doing a merge to tie "old" and "oldrev" together.
#
# Also, we obviously have to be okay with:
#
# * --- * --- * --- oldrev --- new --- new --- newrev

refname="$1"
oldrev="$2"
newrev="$3"

if expr "$oldrev" : '0*$' >/dev/null ; then
	exit 0
fi

# Read backwards: all commits from old..new, unless they are already referenced by a branch
git rev-parse --not --branches | git rev-list --stdin $oldrev..$newrev | while read commit ; do
	number_of_parents=$(git rev-list -n 1 --parents $commit | sed 's/ /\n/g' | grep -v $commit | wc -l)
	if [[ $number_of_parents > 1 ]] ; then
		# Hack to not interfer with the update-stable "--no-ff" method
		if [[ "$refname" == "refs/heads/stable" && "$commit" == "$newrev" ]] ; then
			exit 0
		fi

		# Find the original branch point (B)
		parents=$(git rev-list -n 1 --parents $commit | sed 's/ /\n/g' | grep -v $commit)

		# For each baserev
		git merge-base --all $parents | while read baserev ; do
			# For each parent
			git rev-list -n 1 --parents $commit | sed 's/ /\n/g' | grep -v $commit | while read parent ; do
				all_commits=$(git rev-list --first-parent $baserev..$parent | wc -l)
				new_commits=$(git rev-parse --not --branches | git rev-list --stdin $baserev..$parent | wc -l)
				if [[ $all_commits -eq $new_commits ]] ; then
					echo "----------------------------------------------------"
					echo
					echo "It looks like you should rebase instead of merging $commit"
					echo
					echo "----------------------------------------------------"
					exit 1
				fi
			done
			if [ $? -ne 0 ] ; then
				exit 1
			fi
		done
		if [ $? -ne 0 ] ; then
			exit 1
		fi
	fi
done