fakefiletime

#!/bin/bash

ERROR=false
[[ -z ${DEBUG+X} ]] && DEBUG=false
unset -v FRFILE FRDATE TOFILE TODATE BTFILE BTDATE ADJUST

read -r -d '' HLPMSG <<'HEREDOC'
fakefiletime --from [file] --to [file] --adjust [time-adjustment]'
fakefiletime --from [file] --to [file] --between [file]'
HEREDOC

while test $# -gt 0; do

  case "${1}" in
    --from)    shift; FRFILE="${1}"; shift  ;;
    --to)      shift; TOFILE="${1}"; shift  ;;
    --between) shift; BTFILE="${1}"; shift  ;;
    --adjust)  shift; ADJUST="${1}"; shift  ;;
    --help)    echo "${HLPMSG}";     exit 0 ;;
    *) echo -e "Argument '${1}' is unknown.\n${HLPMSG}"; exit 1 ;;
  esac

done

if ${DEBUG}; then
  echo "FRFILE=${FRFILE}"
  echo "TOFILE=${TOFILE}"
  echo "BTFILE=${BTFILE}"
  echo "ADJUST=${ADJUST}"
fi

[[ -z ${FRFILE} ]] && ERROR=true && echo 'No file to copy time from.'
[[ -z ${TOFILE} ]] && ERROR=true && echo 'No file to copy time to.'
[[ -z ${BTFILE} ]] && [[ -z ${ADJUST} ]] && ERROR=true && \
  echo 'Neither --adjust or --between was specified.'

[[ ! -f "${FRFILE}" ]] && ERROR=true && echo 'The --from file does not exist.'
[[ ! -f "${TOFILE}" ]] && ERROR=true && echo 'The --to file does not exist.'
[[ ! -f "${BTFILE}" ]] && [[ -z ${ADJUST} ]] && ERROR=true && \
  echo 'The --between file does not exist.'

${ERROR} && "${0}" --help && exit 1

[ "${ADJUST}" == none ] && ADJUST="+0 seconds"

FRDATE="$(stat -c %Y "${FRFILE}")"
TODATE="$(stat -c %Y "${TOFILE}")"

if [[ -z ${BTFILE} ]]; then
  NWDATE="$(date -d "$(date -r "${FRFILE}") ${ADJUST}" +%s)"
else
  BTDATE="$(stat -c %Y "${BTFILE}")"
  NWDATE="$(awk "BEGIN {a=${BTDATE};b=${FRDATE};c=b-a;d=int(c/2);print d+a }")"
fi

if ${DEBUG}; then
  echo "FRDATE=${FRDATE}="$(date -R -d @"${FRDATE}" 2> /dev/null)""
  echo "TODATE=${TODATE}="$(date -R -d @"${TODATE}" 2> /dev/null)""
  [[ ! -z ${BTFILE} ]] && echo "BTDATE=${BTDATE}="$(date -R -d @"${BTDATE}" 2> /dev/null)""
  echo "NWDATE=${NWDATE}="$(date -R -d @"${NWDATE}" 2> /dev/null)""
fi

echo "Changing date of '${TOFILE}' from '$(date -d @${TODATE})' to '$(date -d @${NWDATE})'"

touch -d "$(date -R -d @"${NWDATE}")" "${TOFILE}"

exit 0