#compdef strftime

local expl two='epoch time'

if (( words[(I)-r] )); then
  two='date string'
fi

_arguments -S -A '-*' -s \
  '-n[omit trailing newline]' \
  '-q[run quietly]' \
  '(3)-r[reverse lookup using strptime]' \
  '-s+[assign result to parameter]:param:_parameters' \
  '1:format: _date_formats zsh' \
  "2:$two" \
  '3:nanoseconds' \