#!/bin/sh
# Give this a commit-ID specification.  It will edit the associated comment.
# Usual caveats apply; the edited one and all commits after will change IDs,
# and pushing them to a repo with the old commits will wreak havoc.
# Note also that this cavalierly overwrites refs/original.
#
# This script by Eric S. Raymond, March 2010, all rites perverted. It's based 
# on an idea by thiago from #git, but debugged and with a safety check.
# It contains porcelain and porcelain byproducts.

topdir=`git rev-parse --show-cdup`
test -n "$topdir" && cd "$topdir"

my_commit=`git rev-parse $1` || exit $?

# Run a safety check before edits that could hose remotes.
if test -n "`git branch -r --contains $mycommit`"
then
    echo -n "Commit has been pushed.  Really edit? "
    read yn
    if test "$yn" != 'y'
    then
	exit 0
    fi
fi

my_file=COMMIT_EDITMSG
test -d .git && myfile=.git/COMMIT_EDITMSG

# This effort to invoke the user's normal editor fails.
# the problem is that anything the editor writes to stdout on the
# controlling terminal becomes part of the commit message.  So
# the editor needs to actually run inside another window.
#test -z "$GIT_EDITOR" && GIT_EDITOR=$EDITOR
#test -z "$GIT_EDITOR" && GIT_EDITOR=vi
#my_editor=$GIT_EDITOR

# xterm -e vi should also work.
my_editor=emacsclient

export my_file my_commit my_editor

exec git filter-branch -f --tag-name-filter cat --msg-filter '
if test "$GIT_COMMIT" = "$my_commit"; then
    cat > $my_file;
    $my_editor $my_file >/dev/null;
    cat $my_file
else
    cat
fi' "$1~.."

# End