#compdef tail gtail

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

if _pick_variant gnu=GNU unix --version; then
  args=(
    '(-n --lines -c --bytes)'{-c+,--bytes=}'[print the last specified bytes; with +, start at the specified byte]:number of bytes:->number'
    '(-n --lines -c --bytes)'{-n+,--lines=}'[print the last specified lines; with +, start at the specified line]:number of lines:->number'
    '(-F -f)--follow=-[output appended data as the file grows]::how:(name descriptor)'
    '(-F --follow)-f[same as --follow=descriptor]'
    '(-f --follow --retry)-F[same as --follow=name --retry]'
    '--max-unchanged-stats=[with --follow=name, check file rename after the specified number of iterations]:number of iterations'
    '(-s --sleep-interval)'{-s+,--sleep-interval=}'[with -f, sleep the specified seconds between iterations]:seconds'
    '--pid=[with -f, terminate after the specified process dies]:pid:_pids'
    '(-q --quiet --silent -v --verbose)'{-q,--quiet,--silent}'[never output headers giving file names]'
    '(-q --quiet --silent -v --verbose)'{-v,--verbose}'[always output headers giving file names]'
    '--retry[keep trying to open a file even when it becomes inaccessible]'
    '(- *)--help[display help and exit]'
    '(- *)--version[output version information and exit]'
  )
else
  opts=(-A '-*')
  args=(
    '(-b -n)-c+[start at the specified byte]:bytes relative to the end (with +, beginning) of file'
    '(-b -c)-n+[start at the specified line]:lines relative to the end (with +, beginning) of file'
    '(-F -r)-f[wait for new data to be appended to the file]'
  )
  case $OSTYPE in
    (freebsd*|darwin*|dragonfly*|netbsd*|openbsd*|solaris*)
      args+=(
	'(-f -F)-r[display the file in reverse order]'
      )
    ;|
    (freebsd*|darwin*|dragonfly*|netbsd*|openbsd*)
      args+=(
	'(-c -n)-b+[start at the specified block (512-byte)]:blocks relative to the end (with +, beginning) of file'
      )
      ;|
    (freebsd*|darwin*|dragonfly*|netbsd*)
      args+=( '(-f -r)-F[implies -f, but also detect file rename]' )
      ;|
    (freebsd*|darwin*|dragonfly*)
      args+=( '-q[suppress the headers when displaying multiple files]' )
      ;;
  esac
fi

_arguments -C -s -S $opts : $args '*:file:_files' && return

case $state in
  (number)
    local mlt sign digit
    mlt='multipliers:multiplier:((b\:512 K\:1024 KB\:1000 M\:1024\^2'
    mlt+=' MB\:1000\^2 G\:1024\^3 GB\:1000\^3 T\:1024\^4 TB\:1000\^4))'
    sign='signs:sign:((+\:"start at the specified byte/line"'
    sign+=' -\:"output the last specified bytes/lines (default)"))'
    digit='digits:digit:(0 1 2 3 4 5 6 7 8 9)'
    if compset -P '(-|+|)[0-9]##'; then
      _alternative $mlt $digit && ret=0
    elif [[ -z $PREFIX ]]; then
      _alternative $sign $digit && ret=0
    elif compset -P '(+|-)'; then
      _alternative $digit && ret=0
    fi
    ;;
esac

return ret