isa       = ->(cls, obj) { cls === obj } .curry
is_string = isa[String]
is_email  = ->(x) { %r{^.*@.*\.[a-z]+$}.match x }

address = Obfusk::Data.data do
  field [:street, :number, :postal_code, :town], [is_string]
  field :country, [is_string], optional: true
end

person = Obfusk::Data.data do
  field [:first_name, :last_name, :phone_number], [is_string]
  field :email, [is_string, is_email]
  field :address, [], isa: [address]
end

tree = Obfusk::Data.union :type do |_tree|
  data :empty
  data :leaf do
    field :value, []
  end
  data :node do
    field [:left, :right], [], isa: [_tree]
  end
end

Obfusk::Data.valid? tree,
  { type: :node,
    left: { type: :empty },
    right: { type: :leaf, value: "spam!" } }
# => true

class Foo < Obfusk::Data::ValidHamster
  data { field :foo, [] }
end

x = Foo.new foo: 'ok'

x.put :invalid, 'oops'
# ---> Obfusk::Data::Valid::InvalidError

Foo.new
# ---> Obfusk::Data::Valid::InvalidError

class Bar < Obfusk::Data::ValidHash
  data { field :bar, [] }
end

y = Bar.new bar: 'ok'
y[:bar] = 'also ok'

begin
  y[:invalid] = 'oops'
rescue Obfusk::Data::Valid::InvalidError
  y.valid?    # => true
  y[:invalid] # => nil
end

class Baz < Obfusk::Data::UnsafeValidHash
  data { field :baz, [] }
end

z = Baz.new baz: 'ok'
c = z.dup

begin
  z[:invalid] = 'oops'
rescue Obfusk::Data::Valid::InvalidError
  z.valid?    # => false
  c.valid?    # => true
  z[:invalid] # => 'oops'
  c[:invalid] # => nil
end