module Fugit::Nat

def parse_crons(s, a, opts)
  return nil unless a
  h = a
    .reverse
    .inject({}) { |r, e| send("parse_#{e[0]}_elt", e, opts, r); r }
      #
      # the reverse ensure that in "every day at five", the
      # "at five" is placed before the "every day" so that
      # parse_x_elt calls have the right sequence
  if f = h[:_fail]
    #fail ArgumentError.new(f)
    return nil
  end
  hms = h[:hms]
  hours = (hms || [])
    .uniq
    .inject({}) { |r, hm| (r[hm[1]] ||= []) << hm[0]; r }
    .inject({}) { |r, (m, hs)| (r[hs.sort] ||= []) << m; r }
    .to_a
    .sort_by { |hs, ms| -hs.size }
  if hours.empty?
    hours << (h[:dom] ? [ [ '0' ], [ '0' ] ] : [ [ '*' ], [ '*' ] ])
  end
  crons = hours
    .collect { |hm| assemble_cron(h.merge(hms: hm)) }
  fail ArgumentError.new(
    "multiple crons in #{s.inspect} " +
    "(#{crons.collect(&:original).join(' | ')})"
  ) if opts[:multi] == :fail && crons.size > 1
  if opts[:multi] == true || (opts[:multi] && opts[:multi] != :fail)
    crons
  else
    crons.first
  end
end