module AbAdmin
  module Utils
    # Provides a set of helper methods for evaluating methods within the context
    # of an object.
    module EvalHelpers
      # Evaluates one of several different types of methods within the context
      # of the given object.  Methods can be one of the following types:
      # * Symbol
      # * Method / Proc
      # * String
      # 
      # == Examples
      # 
      # Below are examples of the various ways that a method can be evaluated
      # on an object:
      # 
      #   class Person
      #     def initialize(name)
      #       @name = name
      #     end
      #     
      #     def name
      #       @name
      #     end
      #   end
      #   
      #   class PersonCallback
      #     def self.run(person)
      #       person.name
      #     end
      #   end
      # 
      #   person = Person.new('John Smith')
      #   
      #   evaluate_method(person, :name)                            # => "John Smith"
      #   evaluate_method(person, PersonCallback.method(:run))      # => "John Smith"
      #   evaluate_method(person, Proc.new {|person| person.name})  # => "John Smith"
      #   evaluate_method(person, lambda {|person| person.name})    # => "John Smith"
      #   evaluate_method(person, '@name')                          # => "John Smith"
      # 
      # == Additional arguments
      # 
      # Additional arguments can be passed to the methods being evaluated.  If
      # the method defines additional arguments other than the object context,
      # then all arguments are required.
      # 
      # For example,
      # 
      #   person = Person.new('John Smith')
      #   
      #   evaluate_method(person, lambda {|person| person.name}, 21)                              # => "John Smith"
      #   evaluate_method(person, lambda {|person, age| "#{person.name} is #{age}"}, 21)          # => "John Smith is 21"
      #   evaluate_method(person, lambda {|person, age| "#{person.name} is #{age}"}, 21, 'male')  # => ArgumentError: wrong number of arguments (3 for 2)
      def evaluate_method(object, method, *args, &block)
        case method
          when Symbol
            object.method(method).arity == 0 ? object.send(method, &block) : object.send(method, *args, &block)
          when Proc, Method
            args.unshift(object)
            arity = method.arity
            limit = [0, 1].include?(arity) ? arity : args.length
            
            # Procs don't support blocks in < Ruby 1.8.6, so it's tacked on as an
            # argument for consistency across versions of Ruby (even though 1.9
            # supports yielding within blocks)
            if block_given? && Proc === method && arity != 0
              if [1, 2].include?(arity)
                # Force the block to be either the only argument or the 2nd one
                # after the object (may mean additional arguments get discarded)
                limit = arity
                args.insert(limit - 1, block)
              else
                # Tack the block to the end of the args
                limit += 1 unless limit < 0
                args.push(block)
              end
            end
            
            method.call(*args[0, limit], &block)
          when String
            eval(method, object.instance_eval {binding}, &block)
          else
            raise ArgumentError, 'Methods must be a symbol denoting the method to call, a block to be invoked, or a string to be evaluated'
          end
      end

      def call_method_or_proc_on(obj, symbol_or_proc, options = {})
        exec = options[:exec].nil? ? true : options[:exec]
        case symbol_or_proc
          when Symbol, String
            obj.send(symbol_or_proc.to_sym, *options[:attrs])
          when Proc
            exec ? obj.instance_exec(&symbol_or_proc) : symbol_or_proc.call(obj)
        end
      end

    end
  end
end