Pattern matching for old Rubies

pattern_matching.rb

def on(arg, spec)
  track, result = arg.to_a[0]
  type, data = result.to_a[0]

  hook = spec.fetch(track, {})[type]

  return unless hook

  keys = hook.parameters.map(&:last)

  keys.empty? ? hook.call : hook.call(*data.values_at(*keys))
end

result = { success: { print_name: { first: 'Rodrigo', last: 'Serradura' } } }

on(
  result,
  success: { 
    greet: -> (first, last) { puts "Hi #{first} #{last}!" },
    print_name: -> (last, first) { puts "#{last}, #{first}!" }
  }
)