Grape: Use case for value coercion after or between running other validators

clamp_validator.rb

class ClampValidator < Grape::Validations::SingleOptionValidator
  def validate_param!(attr_name, params)
    params[attr_name] = clamp(params[attr_name], @option.min, @option.max)
  end

  def clamp (value, min, max)
    [[value, max].min, min].max
  end
end

companies.rb

class Companies < Grape::API
  SEPARATOR_REGEXP = /,/
  INTEGER_REGEXP   = /\A(0|[1-9][0-9]*)\z/
  ID_REGEXP        = /\A([1-9][0-9]*)\z/
  IDS_REGEXP       = /\A([1-9][0-9]*)(,([1-9][0-9]*))*\z/
  
  helpers do
    params :filters do
      # Example of coercing after RegExp validation for a non-zero Integer
      optional :location,
               regexp:  ID_REGEXP,
               convert: Integer
      # Example of using coercion after RegExp validation and splitting a String into an Array
      optional :services,
               regexp:  IDS_REGEXP,
               split:   SEPARATOR_REGEXP,
               convert: Set[Integer]
    end
    params :pagination do
      # Examples of using coercion after RegExp validation, but before clamping the value between a Range 
      optional :limit,
               regexp:  INTEGER_REGEXP,
               convert: Integer,
               clamp:   [0..100],
               default: 25
      optional :offset,
               regexp:  INTEGER_REGEXP,
               convert: Integer,
               clamp:   [0..-1],
               default: 0
    end
  end
  
  resource :companies do
    params do
      use :filters, :pagination
    end
    get do
      location, services, offset, limit = params[:location], params[:services], params[:offset], params[:limit]
      Company.where(location: location, services: services).offset(offset * limit).limit(limit).all
    end
  end
end

convert_validator.rb

# Modified from https://github.com/intridea/grape/blob/master/lib/grape/validations/coerce.rb
# Set inclusion suggested at https://github.com/intridea/grape/pull/642
class ConvertValidator < Grape::Validations::SingleOptionValidator
  def validate_param!(attr_name, params)
    unless params.is_a? Hash
      raise Grape::Exceptions::Validation,
            param: @scope.full_name(attr_name), message_key: :convert
    end
    new_value = convert_value(@option, params[attr_name])
    if valid_type?(new_value)
      params[attr_name] = new_value
    else
      raise Grape::Exceptions::Validation,
            param: @scope.full_name(attr_name), message_key: :convert
    end
  end

  class InvalidValue
  end

  private

  def _valid_array_type?(type, values)
    values.all? do |val|
      _valid_single_type?(type, val)
    end
  end

  def _valid_single_type?(klass, val)
    # allow nil, to ignore when a parameter is absent
    return true if val.nil?
    if klass == Virtus::Attribute::Boolean
      val.is_a?(TrueClass) || val.is_a?(FalseClass)
    elsif klass == Rack::Multipart::UploadedFile
      val.is_a?(Hashie::Mash) && val.key?(:tempfile)
    else
      val.is_a?(klass)
    end
  end

  def valid_type?(val)
    if @option.is_a?(Array) || @option.is_a?(Set)
      _valid_array_type?(@option.first, val)
    else
      _valid_single_type?(@option, val)
    end
  end

  def convert_value(type, val)
    # Don't coerce things other than nil to Arrays, Hashes, or Sets
    return val || [] if type == Array
    return val || Set.new if type == Set
    return val || {} if type == Hash

    converter = Virtus::Attribute.build(type)
    converter.coerce(val)

    # not the prettiest but some invalid coercion can currently trigger
    # errors in Virtus (see coerce_spec.rb:75)
  rescue
    InvalidValue.new
  end
end

split_validator.rb

class SplitValidator < Grape::Validations::SingleOptionValidator
  def validate_param!(attr_name, params)
    params[attr_name] = params[attr_name].split(@option)
  end
end