#!/bin/sh

TEMP_D=""
CR='
'
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="$3" aname="" buf="" abugs=""
    local indent="    - " indent2="      " ll=79
    aname=${author% <*}
    [ "${aname}" = "Scott Moser" ] && aname=""
    abugs="${aname:+ [${aname}]}${bugs:+ (LP: ${bugs})}"
    if [ $((${#subject}+${#abugs})) -le $(($ll-${#indent})) ]; then
        echo "${indent}${subject}${abugs}"
    elif [ ${#subject} -ge $(($ll-${#indent})) ]; then
        echo "${subject}${abugs}" |
            fmt --width=$(($ll-${#indent})) |
            sed -e "1s/^/${indent}/; 1n;" \
                -e 's/^[ ]*//' \
                -e '/^[ ]*$/d' -e "s/^/$indent2/" -e 's/[ ]\+$//'

    else
        ( echo "${subject}"; echo "${abugs}" ) |
            fmt --width=$(($ll-${#indent})) |
            sed -e "1s/^/${indent}/; 1n;" \
                -e 's/^[ ]*//' \
                -e '/^[ ]*$/d' -e "s/^/$indent2/" -e 's/[ ]\+$//'
    fi
}

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

TEMP_D=$(mktemp -d) || fail "failed mktemp"
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_debian="0ubuntu1"
new_upstream_ver=$(git describe --abbrev=8 "${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

dpseries="debian/patches/series"
if [ -e $dpseries ]; then
   drops=""
   while read bname extra; do
      case "$bname" in
         cpick-*)
            commit=${bname#cpick-}
            commit=${commit%%-*}
            echo "bname=$bname commit=${commit}" 1>&2
            if git merge-base --is-ancestor "$commit" "$from_ref"; then
               drops="${drops} debian/patches/$bname"
            fi
            ;;
         *) echo "$bname${extra:+ ${extra}}";;
      esac
   done < $dpseries > "${TEMP_D}/series"
   drops=${drops# }
   if [ -n "$drops" ]; then
      cp "${TEMP_D}/series" "$dpseries" ||
         fail "failed copying to $dpseries"
      if [ ! -s $dpseries ]; then
         git rm --force "$dpseries" ||
            fail "failed removing empty $dpseries: git rm $dpseries"
      fi
      msg="drop cherry picks before merge from ${from_ref} at $new_upstream_ver"
      msg="$msg${CR}${CR}drop the following cherry picks:"
      for file in $drops; do
         git rm "$file" || fail "failed to git rm $file"
         msg="${msg}$CR  $file"
      done
      git commit -m "$msg" "$dpseries" $drops
   fi
fi

git merge "${from_ref}" -m "merge from $from_ref at $new_upstream_ver" ||
    fail "failed: git merge ${from_ref} -m 'merge from $from_ref ..'"
clog="${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'"