#!/bin/sh

# Convert git log output to ChangeLog format for GNU Emacs.

# Copyright (C) 2014-2022 Free Software Foundation, Inc.

# Author: Paul Eggert

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

LC_ALL=C
export LC_ALL

# The newest revision that should not appear in the generated ChangeLog.
gen_origin=

force=
output=ChangeLog
nmax=2

while [ $# -gt 0 ]; do
  case "$1" in
      -g|--gen-origin) gen_origin="$2" ; shift ;;
      -f|--force) force=1 ;;
      -n|--nmax) nmax="$2"; shift ;;
      -o|--output) output="$2" ; shift ;;
      *) printf '%s\n' "Unrecognized argument: $1" >&2; exit 1 ;;
  esac
  shift
done

if [ ! -f ChangeLog.$nmax ]; then
    printf '%s\n' "Can't find ChangeLog.$nmax" >&2
    printf '%s\n' "Must be run from the top source directory" >&2
    exit 1
fi

# If not specified in the command line, get gen_origin from the existing
# ChangeLog file.
[ "$gen_origin" ] || {
    gen_origin_line=`
      grep -E '^commit [0-9a-f]+ [(]inclusive[)]' ChangeLog.$nmax
    ` || {
	printf '%s\n' "ChangeLog.$nmax lacks a 'commit ... (inclusive)' line" >&2
	exit 1
    }
    set $gen_origin_line
    gen_origin=$2
}

# Get the new value for gen_origin from the latest version in the repository.
new_origin=`git log --pretty=format:%H 'HEAD^!'` || exit

if [ -f "$output" ]; then
    [ ! "$force" ] && printf '%s\n' "$output exists" >&2 && exit 1
    rm -f "$output" || exit 1
fi

# If this is not a Git repository, just generate an empty ChangeLog.
test -r .git || {
  >"$output"
  exit
}

# Use Gnulib's packaged ChangeLog generator.
# Maybe we should skip all "Merge branch 'master'" messages.
# See eg the cairo-related ones.
./build-aux/gitlog-to-changelog \
    --ignore-matching="^; |^Merge branch '[^']*' of git\.(savannah|sv)\.gnu\.org:/srv/git/emacs|^Merge remote-tracking branch '.*'$" \
  --ignore-line='^; ' --format='%B' \
  "$gen_origin..$new_origin" >"ChangeLog.tmp" || exit

if test -r "ChangeLog.tmp"; then

  # Fix up bug references.
  # This would be better as eg a --transform option to gitlog-to-changelog,
  # but... effort.  FIXME does not handle rare cases like:
  # Fixes: debbugs:19434 debbugs:19519
  sed 's/	Fixes: \(debbugs:\|bug#\)\([0-9][0-9]*\)/	(Bug#\2)/' \
      "ChangeLog.tmp" > "ChangeLog.tmp2"
  mv "ChangeLog.tmp2" "ChangeLog.tmp"

  # Find the years covered by the generated ChangeLog, so that
  # a proper copyright notice can be output.
  years=`
    sed -n 's/^\([0-9][0-9]*\).*/\1/p' "ChangeLog.tmp" |
    sort -nu
  `
  start_year=
  end_year=
  for year in ${years:-`date +%Y`}; do
    : ${start_year:=$year}
    end_year=$year
  done

  if test "$start_year" = "$end_year"; then
    year_range=$start_year
  else
    year_range=$start_year-$end_year
  fi

  # Update gen_origin
  if test "$gen_origin" != "$new_origin"; then
      sed -n '
        1i\

        /^This file records repository revisions/p
        s/^commit [0-9a-f]* (exclusive)/commit '"$gen_origin"' (exclusive)/p
        s/^commit [0-9a-f]* (inclusive)/commit '"$new_origin"' (inclusive)/p
      ' <ChangeLog.$nmax >>"ChangeLog.tmp" || exit
  fi

  # Append a proper copyright notice.
  sed -n '
    /^See ChangeLog.[0-9]* for earlier/,${
       s/ChangeLog\.[0-9]*/ChangeLog.'$nmax'/
       s/\(Copyright[ (C)]*\)[0-9]*-[0-9]*/\1'"$year_range"'/
       p
    }
  ' <ChangeLog.$nmax >>"ChangeLog.tmp" || exit
fi

# Install the generated ChangeLog.
test "$output" = "ChangeLog.tmp" || mv "ChangeLog.tmp" "$output"