#!/bin/sh

TEMP_D=""
error() { echo "$@" 1>&2; }
fail() { [ $# -eq 0 ] || error "$@"; exit 1; }
Usage() {
cat <<EOF
${0##*/} [branch]
    update current branch with trunk branch.
    branch defaults to 'master'
EOF
}

print_commit() {
    local subject="$1" author="$2" bugs="$3" aname=""
    aname=${author% <*}
    echo "    - $subject [${aname}]${bugs:+ (LP: ${bugs})}"
}

git_log_to_dch() {
    local line="" commit="" lcommit="" bugs=""
    while :; do
        read line || break
        case "$line" in
            commit\ *)
                if [ -n "$commit" ]; then
                    print_commit "$subject" "$author" "$bugs"
                fi
                commit=${line#*: }
                bugs=""
                author=""
                subject=""
                ;;
            Author:*) author="${line#Author: }";;
            LP:*) bugs="${bugs:+${bugs}, }${line#*: }";;
            "") [ -z "$subject" ] && read subject;;
        esac
    done
    if [ -n "$commit" ]; then
        print_commit "$subject" "$author" "$bugs"
    fi
}
cleanup() {
    [ ! -d "${TEMP_D}" ] || rm -Rf "${TEMP_D}"
}

from_ref=${1:-"master"}
cur_branch=$(git rev-parse --abbrev-ref HEAD) ||
   fail "failed to get current branch"

case "$cur_branch" in
    ubuntu/*) :;;
    *) fail "You are on branch '$cur_branch', expect to be on ubuntu/*";;
esac

trap cleanup EXIT

prev_pkg_ver=$(dpkg-parsechangelog --show-field Version) ||
   fail "failed reading package version"
pkg_name=$(dpkg-parsechangelog --show-field Source) ||
   fail "failed to read Source from changelog"

# turn 0.7.7-10-gbc2c326-0ubuntu1 into 'bc2c326'
t=${prev_pkg_ver%-*}
prev_pkg_hash=${t##*-g}

new_pkg_upstream=$(git describe master)
new_pkg_debian="0ubuntu1"
new_upstream_ver=$(git describe "${from_ref}")
new_pkg_ver="${new_upstream_ver}-${new_pkg_debian}"

prev_upstream_ver=${prev_pkg_ver%-*}
if [ "${prev_upstream_ver}" = "${new_upstream_ver}" ]; then
    echo "nothing to commit.  '$from_ref' is at ${new_upstream_ver}."
    exit 0
fi

git merge "${from_ref}" -m "merge from $from_ref at $new_upstream_ver" ||
    fail "failed: git merge ${from_ref} -m 'merge from $from_ref ..'"
TEMP_D=$(mktemp -d) || fail "failed mktemp"
clog="${TEMP_D}/changelog"
gitlog="${TEMP_D}/gitlog"

git log --first-parent --no-decorate --format=full \
   "${prev_pkg_hash}..${from_ref}" >  "$gitlog" ||
   fail "failed git log ${prev_pkg_hash}..${from_ref}"

cat >> "$clog" <<EOF
$pkg_name ($new_pkg_ver) UNRELEASED; urgency=medium

  * New upstream snapshot.
EOF
git_log_to_dch < "$gitlog" >> "$clog" ||
   fail "failed git_log_to_dch"
cat >> "$clog" <<EOF

 -- ${DEBFULLNAME} <$DEBEMAIL>  $(date -R)

EOF

cat "$clog" "debian/changelog" > "$TEMP_D/newlog" &&
   cp "$TEMP_D/newlog" "debian/changelog" ||
   fail "failed replacing debian/changelog"

dch -e || fail "dch -e exited $?"

git diff

echo -n "Commit this change? (Y/n): "
read answer || fail "failed to read answer"
case "$answer" in
   n|[Nn][oO]) exit 1;;
esac

msg="update changelog (new upstream snapshot $new_upstream_ver)."
git commit -m "$msg" debian/changelog ||
   fail "failed to commit '$msg'"