#compdef date gdate

local curcontext="$curcontext" state state_descr line ret=1
local -A opt_args
local -a opts args

opts=( -s -w -C )

if _pick_variant gnu="Free Software Foundation" unix --version; then
  local d='(-d --date -f --file -r --reference -s --set)'
  local f='(-I --iso-8601 -R --rfc-email --rfc-3339)'
  args=(
    $d{-d+,--date=}'[output date specified by string]:time string'
    '--debug[annotate parsed date and warn about questionable usage]'
    $d{-f+,--file=}'[output dates specified in file]:file:_files'
    $d{-r+,--reference=}'[output last modification time of specified file]:file:_files'
    $d{-s+,--set=}'[set time]:time string'
    $f{-I-,--iso-8601=-}'[display in ISO 8601 format]::precision:(date hours minutes seconds ns)'
    $f{-R,--rfc-email}'[display in RFC5322 format]'
    $f'--rfc-3339=-[display in RFC 3339 format]:precision:(date seconds ns)'
    '(-u --utc --universal)'{-u,--utc,--universal}'[display or set time in UTC]'
    '(- :)--help[output help and exit]'
    '(- :)--version[output version info and exit]'
  )
else
  args=( '-u[display or set time in UTC]' )
  case "$OSTYPE" in
    solaris*)
      args+=( '-a:adjustment' )
    ;;
    freebsd*|dragonfly*|darwin*|netbsd*|openbsd*)
      opts+=( -A '-*' )
      args+=(
	'-j[do not try to set date]'
	'2:format or date:->fmt_date'
      )
    ;|
    freebsd*|dragonfly*|darwin*|netbsd*)
      args+=( '-n[only set time on current machine]' )
    ;|
    freebsd*|dragonfly*|darwin*|openbsd*)
      args+=(
	'-d+:daylight saving time value'
	'-t+:minutes west of GMT'
      )
    ;|
    dragonfly*|darwin*|netbsd*|openbsd*)
      args+=(
	'-r+[output date specified by reference time]:seconds since epoch'
      )
    ;|
    freebsd*)
      local -a alts
      alts=(
	'seconds:sec:_guard "(0x[0-9a-fA-F]#|[0-9]#)" "seconds since epoch"'
	'files:file:_files'
      )
      args+=(
	'-r+[reference time: file modification or literal time]:reference: _alternative $alts'
      )
    ;|
    freebsd*|dragonfly*|darwin*)
      args+=(
	'-f+[use specified format for input]:parsing format:_date_formats:new date:'
	'*-v+[adjust and print (but not set) date]:[+-]value[ymwdHMS]:'
      )
    ;;
    freebsd*|dragonfly*)
      args+=( '-R[display in RFC2822 format]' )
    ;|
    openbsd*|netbsd*) args+=( '-a[gradually skew]' )
    ;|
    openbsd*)
      args+=( '-z[specify timezone for output]:time zone:_time_zone')
    ;|
    netbsd*)
      args+=( '-d[output date specified by string]:time string:' )
    ;;
  esac
fi

_arguments $opts : $args \
  '1:format or date:->fmt_date' && ret=0

case $state in
  (fmt_date)
    local expl
    if compset -P '+'; then
      _wanted date-formats expl 'output format' _date_formats && ret=0
    elif [[ $words[CURRENT] != -* ]]; then
      # TODO: in most cases it should be possible to determine which
      # (or both or neither) of the +format and/or date is allowed
      # depending on the options already on the command line
      _message -e date-formats '+format or date' && ret=0
    fi
    ;;
esac

return ret