module SuperGrouper

# File lib/super_grouper.rb, line 30
def _recursively_group(things, extractors)
  return things if extractors.empty?

  x = extractors.first
  groupings = things.group_by(&x)

  retval = {}
  groupings.each do |k, v|
    next_extractors = extractors[1..-1]
    retval[k] = _recursively_group(v, next_extractors)
  end

  retval
end

# File lib/super_grouper.rb, line 11
def coerce_extractors(extractors)
  extractors.map do |x|
    if x.respond_to? :call
      x
    else
      key_retriever_for(x)
    end
  end
end

# File lib/super_grouper.rb, line 21
def group(things, extractors)
  if extractors.any?
    _recursively_group(things, coerce_extractors(extractors))
  else
    raise ArgumentError.new("Expected at least 1 item in grouping extractors")
  end
end

# File lib/super_grouper.rb, line 6
def key_retriever_for(key)
  ->(thing) { thing[key] }
end