require 'delegate'

module DissociatedIntrospection
  module Try
    module Core
      def try(*a, &b)
        if a.empty? || respond_to?(a.first)
          if a.empty? && block_given?
            if b.arity.zero?
              instance_eval(&b)
            else
              yield self
            end
          else
            public_send(*a, &b)
          end
        end
      end
    end

    refine Object do
      include Core
    end

    refine Delegator do
      include Core
    end

    refine NilClass do
      def try(*args)
        nil
      end
    end
  end

# class Object
##
# :method: try
#
# :call-seq:
#   try(*a, &b)
#
# Invokes the public method whose name goes as first argument just like
# +public_send+ does, except that if the receiver does not respond to it the
# call returns +nil+ rather than raising an exception.
#
# This method is defined to be able to write
#
#   @person.try(:name)
#
# instead of
#
#   @person.name if @person
#
# +try+ calls can be chained:
#
#   @person.try(:spouse).try(:name)
#
# instead of
#
#   @person.spouse.name if @person && @person.spouse
#
# +try+ will also return +nil+ if the receiver does not respond to the method:
#
#   @person.try(:non_existing_method) # => nil
#
# instead of
#
#   @person.non_existing_method if @person.respond_to?(:non_existing_method) # => nil
#
# +try+ returns +nil+ when called on +nil+ regardless of whether it responds
# to the method:
#
#   nil.try(:to_i) # => nil, rather than 0
#
# Arguments and blocks are forwarded to the method if invoked:
#
#   @posts.try(:each_slice, 2) do |a, b|
#     ...
#   end
#
# The number of arguments in the signature must match. If the object responds
# to the method the call is attempted and +ArgumentError+ is still raised
# in case of argument mismatch.
#
# If +try+ is called without arguments it yields the receiver to a given
# block unless it is +nil+:
#
#   @person.try do |p|
#     ...
#   end
#
# You can also call try with a block without accepting an argument, and the block
# will be instance_eval'ed instead:
#
#   @person.try { upcase.truncate(50) }
#
# Please also note that +try+ is defined on +Object+. Therefore, it won't work
# with instances of classes that do not have +Object+ among their ancestors,
# like direct subclasses of +BasicObject+.

##
# :method: try!
#
# :call-seq:
#   try!(*a, &b)
#
# Same as #try, but raises a NoMethodError exception if the receiver is
# not +nil+ and does not implement the tried method.
#
#   "a".try!(:upcase) # => "A"
#   nil.try!(:upcase) # => nil
#   123.try!(:upcase) # => NoMethodError: undefined method `upcase' for 123:Fixnum
# end

# class Delegator
##
# :method: try
#
# :call-seq:
#   try(a*, &b)
#
# See Object#try

##
# :method: try!
#
# :call-seq:
#   try!(a*, &b)
#
# See Object#try!
# end

# class NilClass
# Calling +try+ on +nil+ always returns +nil+.
# It becomes especially helpful when navigating through associations that may return +nil+.
#
#   nil.try(:name) # => nil
#
# Without +try+
#   @person && @person.children.any? && @person.children.first.name
#
# With +try+
#   @person.try(:children).try(:first).try(:name)
# end
end