#!/bin/bash
#
# Support script to find the commit from which the given branch was spawned.
# Takes one or two arguments, the first argument is mandatory and specifies
# the child branch while the second argument is optional and specifies the
# parent branch. If omitted, the parent branch defaults to 'master'

CHILD=$1
PARENT=$2

USAGE="Usage: $0 <child branch> <parent branch>"

if [ "$CHILD" == "" ]
then
    echo $USAGE
    exit
fi

if [ "$PARENT" == "" ]
then
    PARENT="master"
fi

PCOMMIT=`diff -u <(git rev-list --first-parent $CHILD) \
    <(git rev-list --first-parent $PARENT) | sed -ne 's/^ //p' | head -1`

git show --pretty="%H %an | %s" $PCOMMIT | head -1