Dynamic Pundit Policies per user type

final_controller_calls.rb

class FoosController < ApplicationController
  include Pundit
  #...

  # record policy
  def set_record_policy
    policy(PolicyContext.new(record, current_user)
  end

  # scope policy
  def set_policy_scope
    policy_scope(PolicyContext.new(RecordClassName, current_user))
  end

  # authorizing controller action
  def authorize_action
    authorize PolicyContext.new(record, user), "#{action_name}?"
  end
end

final_policy_object.rb

class AdminFooPolicy < ApplicationPolicy
  class Scope
    attr_reader :user, :scope

    def initialize(user, context)
      @user = user
      @scope = context.record
    end

    def resolve
      scope.not_cancelled?
    end
  end
	
  def initialize(user, context)
    @user = user
    @record = context.record
  end
	
  def show?
    !record.cancelled?
  end
end

initial_policy_example.rb

class FooPolicy < ApplicationPolicy
  #...
  class Scope
    #...
    def resolve
      if user.roles.include?("admin")
        scope.not_cancelled
      elsif user.roles.include?("official")
        scope.not_draft
      elsif user.roles.include?("provider")
        scope.provided_by(user)
      else
      	scope.none
      end
    end
  end

  def show?
    (provider && !record.cancelled?) ||
    (official || user_is_assigned_provider?(user))
  end
end

policy_context.rb

class PolicyContext
  attr_reader :record

  def initialize(record, user)
    @record = record
    @user = user
  end

  def policy_class
    "#{@user.role}FooPolicy".classify
  end
end

target_code.rb

class AdminFooPolicy < ApplicationPolicy
  # ...
  class Scope
    # ...
    def resolve
      scope.not_cancelled
    end
  end

  def show?
    record.cancelled?
  end
end