#!/usr/bin/env bash
#
# Change files modification time to their last commit date
#
if [ "$1" = "--touch" ]; then
  # Internal use option only just to parallelize things.
  newer_flag=""
  [ "$2" = "--newer" ] && newer_flag="true"
  shift 2
  bsd=$(date -j > /dev/null 2>&1 && echo 'true')
  if [ -n "$bsd" ]; then
    stat_flags="-f %m"
    date_flags="-r"
  else
    stat_flags="-c %Y"
    date_flags="-d@"
  fi
  for f; do
    git_s=$(git --no-pager log --no-renames --pretty=format:%ct -1 @ -- "$f" 2>/dev/null)
    mod_s=$(stat $stat_flags "$f" 2>/dev/null)
    if [ -n "$git_s" ] && [ -n "$mod_s" ] && [ "$mod_s" -ne "$git_s" ]; then
      if [ "$mod_s" -gt "$git_s" ] || [ -z "$newer_flag" ]; then
        t=$(date $date_flags$git_s '+%Y%m%d%H%M.%S')
        echo "+ touch -h -t $t $f" >&2
        touch -h -t "$t" "$f"
      fi
    fi
  done
else
  opt_r=$(xargs -r false < /dev/null > /dev/null 2>&1 && echo '-r')

  # `-n` should be limited or parallelization will not give effect,
  # because all args will go into single worker.
  NPROC=$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null)
  # don't touch files that have been modified in the worktree or index
  #   bsd doesn't have `-z` option for `comm` and `cut`, so use `tr` as work around
  prefix="$(git rev-parse --show-prefix) "
  comm -23 <(git ls-tree -z -r --name-only --full-name @ | tr '\0' '\n' | sort) \
           <(git status -z --porcelain | tr '\0' '\n' | cut -c 4- | sort) \
  | cut -c ${#prefix}- \
  | tr '\n' '\0' \
  | xargs -0 -P${NPROC:-1} -n 24 $opt_r git utimes --touch "$1"
fi
