module Tackle

# File lib/tackle.rb, line 43
def self.check_for_instrumentation(klass, method_name)
  method = "_#{method_name}".to_sym
  raise ArgumentError, "#{method} already instrumented on #{klass}" if klass.instance_methods.include?(method)
  method
end

# File lib/tackle.rb, line 37
def self.check_method(klass, method_name)
  method = method_name.to_sym
  raise ArgumentError, "#{method} not defined on #{klass}" unless klass.instance_methods.include?(method)
  method
end

# File lib/tackle.rb, line 5
def self.decorate(class_name, method_name, &block)
  klass = Kernel.const_get(class_name)
  method = check_method(klass, method_name)
  old_method = check_for_instrumentation(klass, method_name)

  klass.class_eval do
    alias_method old_method, method

    define_method(method) do |*args|
      send(old_method, *args)
      instance_eval(&block)
    end
  end
end

# File lib/tackle.rb, line 20
def self.time(class_name, method_name, &block)
  klass = Kernel.const_get(class_name)
  method = check_method(klass, method_name)
  old_method = check_for_instrumentation(klass, method_name)

  klass.class_eval do
    alias_method old_method, method

    define_method(method) do |*args|
      time = Benchmark.realtime do
        send(old_method, *args)
      end
      block.call(time)
    end
  end
end