rescuable.rb

rescuable.rb

#
# Rescuable allows you to lazily wrap methods with a rescue logic outside.
# Example:
#
#   class Foo
#     extend Rescuable
#
#     def kaboom
#       raise RuntimeError, 'This will be rescued and will return 1337'
#       raise 'This, however, will not be rescued'
#     end
#
#     def bam
#       raise RuntimeError, 'This will also be rescued'
#     end
#
#     rescue_method :kaboom, :bam, from: RuntimeError, with: :handle_kaboom
#
#     def handle_kaboom(e)
#       1337
#     end
#   end
#
#   class Bar < Foo
#     def bam
#       raise RuntimeError, 'This will be rescued from Foo and return 1337'
#     end
#   end
#
#   class Baz < Foo
#     rescue_method :bam, from: RuntimeError, return: -1
#   end
#
#   puts Foo.new.bam    # => 1337
#   puts Bar.new.bam    # => 1337
#   puts Baz.new.bam    # => -1
#
# It can also store the error for further inspection:
#
#   class Foo
#     extend Rescuable
#     attr_reader :error
#
#     def kaboom
#       raise RuntimeError, 'This will be rescued and will return 1337'
#     end
#
#     rescue_method :kaboom, from: RuntimeError, return: 1337, ivar: :error
#   end
#
#   foo = Foo.new
#   foo.kaboom      # 1337
#   foo.error       # #<RuntimeError: This will be rescued and will return 1337>
#
module Rescuable
  def rescue_method(*methods)
    options = methods.pop

    raise ArgumentError, 'Missing required key :from' unless options[:from]

    methods.each do |meth|
      rescues[meth] ||= {}

      Array(options[:from]).each do |klass|
        rescues[meth][klass] = {
          with:   options[:with],
          return: options[:return],
          ivar:   options[:ivar] && "@#{options[:ivar].to_s.gsub(/^@/, '')}".to_sym,
        }
      end

      unless self.instance_methods.include?(:"#{meth}_with_rescue")
        define_method(:"#{meth}_with_rescue") do |*args, &block|
          begin
            self.send(:"#{meth}_without_rescue", *args, &block)
          rescue => e
            self.class.rescues[meth].each do |klass, rescue_options|
              if e.is_a?(klass)
                self.instance_variable_set(rescue_options[:ivar], e) if rescue_options[:ivar]
                return rescue_options[:with] ? self.send(rescue_options[:with], e) : rescue_options[:result]
              end
            end

            raise
          end
        end

        alias_method :"#{meth}_without_rescue", meth
        alias_method meth, :"#{meth}_with_rescue"
      end
    end
  end

  def method_added(meth)
    if rescues[meth] && self.instance_method(meth) != self.instance_method(:"#{meth}_with_rescue")
      alias_method :"#{meth}_without_rescue", meth
      alias_method meth, :"#{meth}_with_rescue"
    end
  end

  def rescues
    @_rescues ||= self.ancestors[1..-1].reverse.reduce({}) do |result, klass|
      if klass.is_a?(Class) && klass.instance_variable_defined?('@_rescues')
        result.merge(klass.instance_variable_get('@_rescues').map{ |k, v| [k, v.dup] }.to_h)
      else
        result
      end
    end
  end
end