#!/usr/bin/env sh
#
# Output the difference between a facter command run on two different versions
# of facter. Uses unified diff format.

OPTIONS_SPEC="\
facter-diff [options] <rev1> <rev2> [fact]...

Example:

    ./ext/facter-diff 1.5.7 1.0.2

--
h,help      Display this help"

. "$(git --exec-path)/git-sh-setup"
eval "$(echo "$OPTIONS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
trap 'err=$?; cleanup; exit $err' 0

cleanup() {
  test $origin && git checkout -q "$origin"
}

facter() {
  ruby -Ilib bin/facter "$@"
}

log_facter_run() {
  local ref=$1 && shift
  local tmpfile=$1 && shift

  git checkout -qf "$ref" ||
    die "fatal: unable to checkout $ref"
  facter "$@" > $tmpfile
}

verify_revision() {
  git rev-parse --verify --quiet "$1" > /dev/null ||
    die "fatal: '$1' is not a valid revision"
}

test $1 = "--" && shift # git rev-parse seems to leave the -- in
test $# -eq 0 && usage

test $# -gt 1 ||
  die "fatal: must specify two revisions"

status=$(git status -s)
test -z "$status" ||
  die "fatal: $0 cannot be used with a dirty working copy"

origin=$(git rev-parse --symbolic-full-name HEAD)
test "$origin" = "HEAD" &&
  origin=$(git rev-parse HEAD)

test -x "bin/facter" ||
  die "fatal: $0 must be run from the project root"

ref1="$1" && shift
ref2="$1" && shift

verify_revision $ref1
verify_revision $ref2

tmpfile1="/tmp/$(basename $0).$$.1.tmp"
tmpfile2="/tmp/$(basename $0).$$.2.tmp"

log_facter_run $ref1 $tmpfile1 $@
log_facter_run $ref2 $tmpfile2 $@

git checkout -f "$origin" > /dev/null 2>&1

diff --label "$ref1" --label "$ref2" -u $tmpfile1 $tmpfile2