#!/bin/sh
#
# Three-way merge driver for PO files
#
set -e
IFS=
# failure handler
on_error() {
  local parent_lineno="$1"
  local message="$3"
  local code="$2"
  if [[ -n "$message" ]] ; then
    echo "Error on or near line ${parent_lineno}: ${message}; Code ${code}"
  else
    echo "Error on or near line ${parent_lineno}; Code ${code}"
  fi
  exit 255
}
trap 'on_error ${LINENO} $?' ERR

# given a file, find the path that matches its contents
show_file() {
  hash=`git hash-object "${1}"`
  git ls-tree -r HEAD | fgrep "$hash" | cut -b54-
}

# wraps msgmerge with default options
function m_msgmerge() {
  msgmerge --force-po --quiet --no-fuzzy-matching $@
}

# wraps msgcat with default options
function m_msgcat() {
  msgcat --force-po $@
}


# removes the "graveyard strings" from the input
function strip_graveyard() {
  sed -e '/^#~/d'
}

# select messages with a conflict marker
# pass -v to inverse selection
function grep_conflicts() {
  msggrep $@ --msgstr -F -e '#-#-#-#-#' -
}

# select messages from $1 that are also in $2 but whose contents have changed
function extract_changes() {
  msgcat -o - $1 $2 \
    | grep_conflicts \
    | m_msgmerge -o - $1 - \
    | strip_graveyard
}


BASE=$1
LOCAL=$2
REMOTE=$3
OUTPUT=$LOCAL
TEMP=`mktemp /tmp/merge-po.XXXX`

echo "Using custom PO merge driver (`show_file ${LOCAL}`; $TEMP)"

# Extract the PO header from the current branch (top of file until first empty line)
sed -e '/^$/q' < $LOCAL > ${TEMP}.header

# clean input files
msguniq --force-po -o ${TEMP}.base   --unique ${BASE}
msguniq --force-po -o ${TEMP}.local  --unique ${LOCAL}
msguniq --force-po -o ${TEMP}.remote --unique ${REMOTE}

# messages changed on local
extract_changes ${TEMP}.local ${TEMP}.base > ${TEMP}.local-changes

# messages changed on remote
extract_changes ${TEMP}.remote ${TEMP}.base > ${TEMP}.remote-changes

# unchanged messages
m_msgcat -o - ${TEMP}.base ${TEMP}.local ${TEMP}.remote \
  | grep_conflicts -v \
  > ${TEMP}.unchanged

# messages changed on both local and remote (conflicts)
m_msgcat -o - ${TEMP}.remote-changes ${TEMP}.local-changes \
  | grep_conflicts \
  > ${TEMP}.conflicts

# messages changed on local, not on remote; and vice-versa
m_msgcat -o ${TEMP}.local-only  --unique ${TEMP}.local-changes  ${TEMP}.conflicts
m_msgcat -o ${TEMP}.remote-only --unique ${TEMP}.remote-changes ${TEMP}.conflicts

# the big merge
m_msgcat -o ${TEMP}.merge1 ${TEMP}.unchanged ${TEMP}.conflicts ${TEMP}.local-only ${TEMP}.remote-only

# create a template to filter messages actually needed (those on local and remote)
m_msgcat -o - ${TEMP}.local ${TEMP}.remote \
  | m_msgmerge -o ${TEMP}.merge2 ${TEMP}.merge1 -

# final merge, adds saved header
m_msgcat -o ${TEMP}.merge3 --use-first ${TEMP}.header ${TEMP}.merge2

# produce output file (overwrites input LOCAL file)
cat ${TEMP}.merge3 > $OUTPUT

# check for conflicts
if grep -q '#-#-#-#-#' $OUTPUT ; then
  echo "Conflict(s) detected"
  echo "   between ${TEMP}.local and ${TEMP}.remote"
  exit 1
fi
rm -f ${TEMP}*
exit 0