#!/bin/sh

# Older first!
old_maint='maint-1.6.0 maint-1.6.1'

_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
LF='
'

# disable pager
GIT_PAGER=cat
export GIT_PAGER

find_last_tip () {
	topic="$(git rev-parse --verify "$1")" integrate="$2"
	git rev-list --first-parent --parents "$2" |
	sed -n -e "
		/^$_x40 $_x40 $topic$/{
			s/^\($_x40\) $_x40 $topic$/\1/p
			q
		}
	"
}


tmp=/tmp/GR.$$

trap 'rm -f "$tmp".*' 0

git branch --merged master | sed -n -e '/\//s/^. //p' | sort >"$tmp.master"

>"$tmp.known"
for m in $old_maint maint
do
	git branch --merged $m | sed -n -e '/\//s/^. //p' | sort >"$tmp.$m"
	comm -12 "$tmp.$m" "$tmp.master" >"$tmp.both0"
	comm -23 "$tmp.both0" "$tmp.known" >"$tmp.both"
	if test -s "$tmp.both"
	then
		echo "# Graduated to both $m and master"
		while read branch
		do
			echo "$(git show -s --format='%ct' "$branch") $branch"
		done <"$tmp.both" |
		sort -r -n |
		sed -e 's/^[0-9]* //' \
		    -e 's/^/git branch -d /'
		echo
		cat "$tmp.known" "$tmp.both" | sort >"$tmp.next"
		mv "$tmp.next" "$tmp.known"
	fi
done

comm -13 "$tmp.maint" "$tmp.master" |
{
	while read topic
	do
		t=$(find_last_tip $topic master) &&
		test -n "$t" &&
		m=$(git rev-parse --verify "$t^1") &&
		test -n "$m" || continue

		# NEEDSWORK: this misses repeated merges
		#
		#        o---o---maint
		#       /
		#      .---o---o topic
		#     /     \   \
		# ---o---o---*---*---master

		tsize=$(git rev-list "$m..$topic" | wc -l)
		rsize=$(git rev-list "maint..$topic" | wc -l)

		if test $tsize -eq $rsize
		then
			s=$(git show -s --pretty="tformat:%ct %H" $t)
			echo "$s $topic"
		else
			s=$(git show -s --pretty="tformat:%ct %H" $t)
			echo >&3 "$s $topic"
		fi
	done 3>"$tmp.unmergeable" >"$tmp.mergeable"

	if test -s "$tmp.unmergeable"
	then
		echo "# Graduated to master; unmergeable to maint"
		sort -n "$tmp.unmergeable" |
		while read timestamp merge topic
		do
			git show -s --pretty="format:# %h %cd" $merge
			echo "git branch -d $topic"
		done
		echo
	fi
	if test -s "$tmp.mergeable"
	then
		sort -n  "$tmp.mergeable" |
		while read timestamp merge topic
		do
			{
				git show -s --pretty="format:%h %cd" $merge
				git log --pretty=oneline --abbrev-commit maint..$topic 
			} |
			sed -e 's/^/# /'
			echo "git checkout maint && git merge $topic"
			echo
		done
	fi
}