module Clavatar

# File lib/clavatar.rb, line 5
def self.cast(hash, example)
  klass = example.class
  accessible_attr = []
  example.instance_variables.each do |attr|
    attr = attr.to_s.sub('@', '').to_sym
    if example.respond_to? ("#{attr}=")
      accessible_attr << attr
    end
  end

  key_args = {}
  args = []
  construct_params = example.method(:initialize).parameters
  construct_params.each do |param|
    arg_required, arg_name = param

    case arg_required
      when :req
        args << arg_name
      when :opt
        args << arg_name if hash.key? arg_name
      when :keyreq
        raise "parameter #{arg_name} is mandatory but missing in #{hash}" unless hash.key? arg_name
        key_args[arg_name] = hash[arg_name]
      when :keyrest
        key_args.merge! hash
        break
    end
  end

  args.map! { |val| hash[val] }
  if args.empty? and key_args.empty?
    instance = klass.send(:new)
  elsif args.empty?
    instance = klass.send(:new, key_args)
  elsif key_args.empty?
    instance = klass.send(:new, *args)
  else
    instance = klass.send(:new, *args, **key_args)
  end

  accessible_attr.each do |attr|
    instance.send("#{attr}=", hash[attr])
  end

  instance
end