#!/bin/bash
#
# Three-way merge driver for PO files, runs on multiple CPUs where possible
#
# Copyright 2015-2016 Marco Ciampa
# Copyright 2021 Mikko Rantalainen <mikko.rantalainen@iki.fi>
# License: MIT (https://opensource.org/licenses/MIT)
#
# Original source:
# https://stackoverflow.com/a/29535676/334451
# https://github.com/mezis/git-whistles/blob/master/libexec/git-merge-po.sh
#
# Install with
# git config merge.merge-po-files.driver "./bin/merge-po-files %A %O %B %P"
#
# Note that you also need file `.gitattributes` with following lines:
# (for debian-reference)
#
# po/*.po merge=merge-po-files
# po/*.pot merge=merge-po-files
#
##########################################################################
# CONFIG:

# Formatting flags to be be used to produce merged .po files
# This can be set to match project needs for the .po files.
# NOTE: $MSGCAT_FINAL_FLAGS will be passed to msgcat without quotation
MSGCAT_FINAL_FLAGS="--no-wrap --sort-output"

# Verbosity level:
# 0: Silent except for real errors
# 1: Show simple header for each file processed
# 2: Also show all conflicts in merge result (both new and existing)
# 3: Also show all status messages with timestamps
VERBOSITY="${VERBOSITY:=2}"

##########################################################################
# Implementation:

# Use logical names for arguments:
LOCAL="$1"
BASE="$2"
OTHER="$3"
FILENAME="$4"
OUTPUT="$LOCAL"

# The temporary directory for all files we need - note that most files are
# created without extensions to emit nicer conflict messages where gettext
# likes to embed the basename of the file in the conflict message so we
# use names like "local" and "other" instead of e.g. "local.G2wZ.po".
TEMP="$(mktemp -d /tmp/merge-po.XXXXXX)"

# abort on any error and report the details if possible
set -E
set -e
on_error() {
  local parent_lineno="$1"
  local message="$3"
  local code="$2"
  if [[ -n $message ]]; then
    printf "### $0: error near line %d: status %d: %s\n" "${parent_lineno}" "${code}" "${message}" 1>&2
  else
    printf "### $0: error near line %d: status %d\n" "${parent_lineno}" "${code}" 1>&2
  fi
  exit 255
}
trap 'on_error ${LINENO} $?' ERR

# Maybe print message(s) to stdout with timestamps
function status() {
  if test "$VERBOSITY" -ge 3; then
    printf "%s %s\n" "$(date '+%Y-%m-%d %H:%M:%S.%3N')" "$@"
  fi
}

# Quietly take translations from $1 and apply those according to template $2
# (and do not use fuzzy-matching, always generate output)
# also supports all flags to msgmerge
function apply_po_template() {
  msgmerge --force-po --quiet --no-fuzzy-matching "$@"
}

# Take stdin, remove the "graveyard strings" and emit the result to stdout
function strip_graveyard() {
  msgattrib --no-obsolete
}

# Take stdin, keep only confict lines and emit the result to stdout
function only_conflicts() {
  msggrep --msgstr -F -e '#-#-#-#-#' -
  # alternative slightly worse implementation: msgattrib --only-fuzzy
}

# Take stdin, discard confict lines and emit the result to stdout
function without_conflicts() {
  msggrep -v --msgstr -F -e '#-#-#-#-#' -
  # alternative slightly worse implementation: msgattrib --no-fuzzy
}

# Select messages from $1 that are also in $2 but whose contents have changed
# and emit results to stdout
function extract_changes() {
  # Extract conflicting changes and discard any changes to graveyard area only
  msgcat -o - "$1" "$2" |
    only_conflicts |
    apply_po_template -o - "$1" - |
    strip_graveyard
}

# Emit only the header of $1, supports flags of msggrep
function extract_header() {
  # Unfortunately gettext really doesn't support extracting just header
  # so we have to get creative: extract only strings that originate
  # from file called "//" which should result to header only
  msggrep --force-po -N // "$@"

  # Logically msggrep --force-po -v -K -E -e '.' should return the header
  # only but msggrep seems be buggy with msgids with line feeds and output
  # those, too
}

# Take file in $1 and show conflicts with colors in the file to stdout
function show_conflicts() {
  OUTPUT="$1"
  shift
  # Count number of lines to remove from the output and output conflict lines without the header
  CONFLICT_HEADER_LINES=$(cat "$OUTPUT" | msggrep --force-po --color=never --msgstr -F -e '#-#-#-#-#' - | extract_header - | wc -l)
  # tail wants line number of the first displayed line so we want +1 here:
  CONFLICTS=$(cat "$OUTPUT" | msggrep --force-po --color --msgstr -F -e '#-#-#-#-#' - | tail -n "+$((CONFLICT_HEADER_LINES + 1))")
  if test -n "$CONFLICTS"; then
    #echo "----------------------------"
    #echo "Conflicts after merge:"
    echo "----------------------------"
    printf "%s\n" "$CONFLICTS"
    echo "----------------------------"
  fi
}

# Sanity check that we have a sensible temporary directory
test -n "$TEMP" || exit 125
test -d "$TEMP" || exit 126
test -w "$TEMP" || exit 127

if test "$VERBOSITY" -ge 1; then
  printf "Using gettext .PO merge driver: %s ...\n" "$FILENAME"
fi

# Extract the PO header from the current branch (top of file until first empty line)
extract_header -o "${TEMP}/header" "$LOCAL"

##########################################################################
# Following parts can be run partially parallel and "wait" is used to syncronize processing

# Clean input files and use logical filenames for possible conflict markers:
status "Canonicalizing input files ..."
msguniq --force-po -o "${TEMP}/base" --unique "${BASE}" &
msguniq --force-po -o "${TEMP}/local" --unique "${LOCAL}" &
msguniq --force-po -o "${TEMP}/other" --unique "${OTHER}" &
wait

status "Computing local-changes, other-changes and unchanged ..."
msgcat --force-po -o - "${TEMP}/base" "${TEMP}/local" "${TEMP}/other" | without_conflicts >"${TEMP}/unchanged" &
extract_changes "${TEMP}/local" "${TEMP}/base" >"${TEMP}/local-changes" &
extract_changes "${TEMP}/other" "${TEMP}/base" >"${TEMP}/other-changes" &
wait

# Messages changed on both local and other (conflicts):
status "Computing conflicts ..."
msgcat --force-po -o - "${TEMP}/other-changes" "${TEMP}/local-changes" | only_conflicts >"${TEMP}/conflicts"

# Messages changed on local, not on other; and vice-versa:
status "Computing local-only and other-only changes ..."
msgcat --force-po -o "${TEMP}/local-only" --unique "${TEMP}/local-changes" "${TEMP}/conflicts" &
msgcat --force-po -o "${TEMP}/other-only" --unique "${TEMP}/other-changes" "${TEMP}/conflicts" &
wait

# Note: following steps require sequential processing and cannot be run in parallel

status "Computing initial merge without template ..."
# Note that we may end up with some extra so we have to apply template later
msgcat --force-po -o "${TEMP}/merge1" "${TEMP}/unchanged" "${TEMP}/conflicts" "${TEMP}/local-only" "${TEMP}/other-only"

# Create a template to only output messages that are actually needed (union of messages on local and other create the template!)
status "Computing template and applying it to merge result ..."
msgcat --force-po -o - "${TEMP}/local" "${TEMP}/other" | apply_po_template -o "${TEMP}/merge2" "${TEMP}/merge1" -

# Final merge result is merge2 with original header
status "Fixing the header after merge ..."
msgcat --force-po $MSGCAT_FINAL_FLAGS -o "${TEMP}/merge3" --use-first "${TEMP}/header" "${TEMP}/merge2"

# Produce output file (overwrites input LOCAL file because git expects that for the results)
status "Saving output ..."
mv "${TEMP}/merge3" "$OUTPUT"

status "Cleaning up ..."

rm "${TEMP}"/*
rmdir "${TEMP}"

status "Checking for conflicts in the result ..."

# Check for conflicts in the final merge
if grep -q '#-#-#-#-#' "$OUTPUT"; then
  if test "$VERBOSITY" -ge 1; then
    printf "### Conflict(s) detected ###\n"
  fi

  if test "$VERBOSITY" -ge 2; then
    # Verbose diagnostics
    show_conflicts "$OUTPUT"
  fi

  status "Automatic merge failed, exiting with status 1."
  exit 1
fi

status "Automatic merge completed successfully, exiting with status 0."
exit 0