Move ActiveRecord::Type to ActiveModel

The first step of bringing typecasting to ActiveModel

23 files changed, 987 insertions, 0 deletions

diff --git a/activemodel/lib/active_model/type.rb b/activemodel/lib/active_model/type.rb
new file mode 100644
index 0000000000..64346bcab2
--- /dev/null
+++ b/activemodel/lib/active_model/type.rb
@@ -0,0 +1,59 @@
+require 'active_model/type/helpers'
+require 'active_model/type/value'
+
+require 'active_model/type/big_integer'
+require 'active_model/type/binary'
+require 'active_model/type/boolean'
+require 'active_model/type/date'
+require 'active_model/type/date_time'
+require 'active_model/type/decimal'
+require 'active_model/type/decimal_without_scale'
+require 'active_model/type/float'
+require 'active_model/type/integer'
+require 'active_model/type/string'
+require 'active_model/type/text'
+require 'active_model/type/time'
+require 'active_model/type/unsigned_integer'
+
+require 'active_model/type/registry'
+require 'active_model/type/type_map'
+require 'active_model/type/hash_lookup_type_map'
+
+module ActiveModel
+  module Type
+    @registry = Registry.new
+
+    class << self
+      attr_accessor :registry # :nodoc:
+      delegate :add_modifier, to: :registry
+
+      # Add a new type to the registry, allowing it to be referenced as a
+      # symbol by ActiveModel::Attributes::ClassMethods#attribute.  If your
+      # type is only meant to be used with a specific database adapter, you can
+      # do so by passing +adapter: :postgresql+. If your type has the same
+      # name as a native type for the current adapter, an exception will be
+      # raised unless you specify an +:override+ option. +override: true+ will
+      # cause your type to be used instead of the native type. +override:
+      # false+ will cause the native type to be used over yours if one exists.
+      def register(type_name, klass = nil, **options, &block)
+        registry.register(type_name, klass, **options, &block)
+      end
+
+      def lookup(*args, **kwargs) # :nodoc:
+        registry.lookup(*args, **kwargs)
+      end
+    end
+
+    register(:big_integer, Type::BigInteger, override: false)
+    register(:binary, Type::Binary, override: false)
+    register(:boolean, Type::Boolean, override: false)
+    register(:date, Type::Date, override: false)
+    register(:date_time, Type::DateTime, override: false)
+    register(:decimal, Type::Decimal, override: false)
+    register(:float, Type::Float, override: false)
+    register(:integer, Type::Integer, override: false)
+    register(:string, Type::String, override: false)
+    register(:text, Type::Text, override: false)
+    register(:time, Type::Time, override: false)
+  end
+end
diff --git a/activemodel/lib/active_model/type/big_integer.rb b/activemodel/lib/active_model/type/big_integer.rb
new file mode 100644
index 0000000000..4168cbfce7
--- /dev/null
+++ b/activemodel/lib/active_model/type/big_integer.rb
@@ -0,0 +1,13 @@
+require 'active_model/type/integer'
+
+module ActiveModel
+  module Type
+    class BigInteger < Integer # :nodoc:
+      private
+
+      def max_value
+        ::Float::INFINITY
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/binary.rb b/activemodel/lib/active_model/type/binary.rb
new file mode 100644
index 0000000000..a0cc45b4c3
--- /dev/null
+++ b/activemodel/lib/active_model/type/binary.rb
@@ -0,0 +1,50 @@
+module ActiveModel
+  module Type
+    class Binary < Value # :nodoc:
+      def type
+        :binary
+      end
+
+      def binary?
+        true
+      end
+
+      def cast(value)
+        if value.is_a?(Data)
+          value.to_s
+        else
+          super
+        end
+      end
+
+      def serialize(value)
+        return if value.nil?
+        Data.new(super)
+      end
+
+      def changed_in_place?(raw_old_value, value)
+        old_value = deserialize(raw_old_value)
+        old_value != value
+      end
+
+      class Data # :nodoc:
+        def initialize(value)
+          @value = value.to_s
+        end
+
+        def to_s
+          @value
+        end
+        alias_method :to_str, :to_s
+
+        def hex
+          @value.unpack('H*')[0]
+        end
+
+        def ==(other)
+          other == to_s || super
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/boolean.rb b/activemodel/lib/active_model/type/boolean.rb
new file mode 100644
index 0000000000..c1bce98c87
--- /dev/null
+++ b/activemodel/lib/active_model/type/boolean.rb
@@ -0,0 +1,21 @@
+module ActiveModel
+  module Type
+    class Boolean < Value # :nodoc:
+      FALSE_VALUES = [false, 0, '0', 'f', 'F', 'false', 'FALSE', 'off', 'OFF'].to_set
+
+      def type
+        :boolean
+      end
+
+      private
+
+      def cast_value(value)
+        if value == ''
+          nil
+        else
+          !FALSE_VALUES.include?(value)
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/date.rb b/activemodel/lib/active_model/type/date.rb
new file mode 100644
index 0000000000..f74243a22c
--- /dev/null
+++ b/activemodel/lib/active_model/type/date.rb
@@ -0,0 +1,50 @@
+module ActiveModel
+  module Type
+    class Date < Value # :nodoc:
+      include Helpers::AcceptsMultiparameterTime.new
+
+      def type
+        :date
+      end
+
+      def type_cast_for_schema(value)
+        "'#{value.to_s(:db)}'"
+      end
+
+      private
+
+      def cast_value(value)
+        if value.is_a?(::String)
+          return if value.empty?
+          fast_string_to_date(value) || fallback_string_to_date(value)
+        elsif value.respond_to?(:to_date)
+          value.to_date
+        else
+          value
+        end
+      end
+
+      ISO_DATE = /\A(\d{4})-(\d\d)-(\d\d)\z/
+      def fast_string_to_date(string)
+        if string =~ ISO_DATE
+          new_date $1.to_i, $2.to_i, $3.to_i
+        end
+      end
+
+      def fallback_string_to_date(string)
+        new_date(*::Date._parse(string, false).values_at(:year, :mon, :mday))
+      end
+
+      def new_date(year, mon, mday)
+        if year && year != 0
+          ::Date.new(year, mon, mday) rescue nil
+        end
+      end
+
+      def value_from_multiparameter_assignment(*)
+        time = super
+        time && time.to_date
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/date_time.rb b/activemodel/lib/active_model/type/date_time.rb
new file mode 100644
index 0000000000..b068cfc672
--- /dev/null
+++ b/activemodel/lib/active_model/type/date_time.rb
@@ -0,0 +1,44 @@
+module ActiveModel
+  module Type
+    class DateTime < Value # :nodoc:
+      include Helpers::TimeValue
+      include Helpers::AcceptsMultiparameterTime.new(
+        defaults: { 4 => 0, 5 => 0 }
+      )
+
+      def type
+        :datetime
+      end
+
+      private
+
+      def cast_value(string)
+        return string unless string.is_a?(::String)
+        return if string.empty?
+
+        fast_string_to_time(string) || fallback_string_to_time(string)
+      end
+
+      # '0.123456' -> 123456
+      # '1.123456' -> 123456
+      def microseconds(time)
+        time[:sec_fraction] ? (time[:sec_fraction] * 1_000_000).to_i : 0
+      end
+
+      def fallback_string_to_time(string)
+        time_hash = ::Date._parse(string)
+        time_hash[:sec_fraction] = microseconds(time_hash)
+
+        new_time(*time_hash.values_at(:year, :mon, :mday, :hour, :min, :sec, :sec_fraction, :offset))
+      end
+
+      def value_from_multiparameter_assignment(values_hash)
+        missing_parameter = (1..3).detect { |key| !values_hash.key?(key) }
+        if missing_parameter
+          raise ArgumentError, missing_parameter
+        end
+        super
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/decimal.rb b/activemodel/lib/active_model/type/decimal.rb
new file mode 100644
index 0000000000..83a16018ea
--- /dev/null
+++ b/activemodel/lib/active_model/type/decimal.rb
@@ -0,0 +1,50 @@
+module ActiveModel
+  module Type
+    class Decimal < Value # :nodoc:
+      include Helpers::Numeric
+
+      def type
+        :decimal
+      end
+
+      def type_cast_for_schema(value)
+        value.to_s.inspect
+      end
+
+      private
+
+      def cast_value(value)
+        casted_value = case value
+        when ::Float
+          convert_float_to_big_decimal(value)
+        when ::Numeric, ::String
+          BigDecimal(value, precision.to_i)
+        else
+          if value.respond_to?(:to_d)
+            value.to_d
+          else
+            cast_value(value.to_s)
+          end
+        end
+
+        scale ? casted_value.round(scale) : casted_value
+      end
+
+      def convert_float_to_big_decimal(value)
+        if precision
+          BigDecimal(value, float_precision)
+        else
+          value.to_d
+        end
+      end
+
+      def float_precision
+        if precision.to_i > ::Float::DIG + 1
+          ::Float::DIG + 1
+        else
+          precision.to_i
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/decimal_without_scale.rb b/activemodel/lib/active_model/type/decimal_without_scale.rb
new file mode 100644
index 0000000000..129baa0c10
--- /dev/null
+++ b/activemodel/lib/active_model/type/decimal_without_scale.rb
@@ -0,0 +1,11 @@
+require 'active_model/type/big_integer'
+
+module ActiveModel
+  module Type
+    class DecimalWithoutScale < BigInteger # :nodoc:
+      def type
+        :decimal
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/float.rb b/activemodel/lib/active_model/type/float.rb
new file mode 100644
index 0000000000..0f925bc7e1
--- /dev/null
+++ b/activemodel/lib/active_model/type/float.rb
@@ -0,0 +1,25 @@
+module ActiveModel
+  module Type
+    class Float < Value # :nodoc:
+      include Helpers::Numeric
+
+      def type
+        :float
+      end
+
+      alias serialize cast
+
+      private
+
+      def cast_value(value)
+        case value
+        when ::Float then value
+        when "Infinity" then ::Float::INFINITY
+        when "-Infinity" then -::Float::INFINITY
+        when "NaN" then ::Float::NAN
+        else value.to_f
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/hash_lookup_type_map.rb b/activemodel/lib/active_model/type/hash_lookup_type_map.rb
new file mode 100644
index 0000000000..45d3515aad
--- /dev/null
+++ b/activemodel/lib/active_model/type/hash_lookup_type_map.rb
@@ -0,0 +1,23 @@
+module ActiveModel
+  module Type
+    class HashLookupTypeMap < TypeMap # :nodoc:
+      def alias_type(type, alias_type)
+        register_type(type) { |_, *args| lookup(alias_type, *args) }
+      end
+
+      def key?(key)
+        @mapping.key?(key)
+      end
+
+      def keys
+        @mapping.keys
+      end
+
+      private
+
+      def perform_fetch(type, *args, &block)
+        @mapping.fetch(type, block).call(type, *args)
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/helpers.rb b/activemodel/lib/active_model/type/helpers.rb
new file mode 100644
index 0000000000..a805a359ab
--- /dev/null
+++ b/activemodel/lib/active_model/type/helpers.rb
@@ -0,0 +1,4 @@
+require 'active_model/type/helpers/accepts_multiparameter_time'
+require 'active_model/type/helpers/numeric'
+require 'active_model/type/helpers/mutable'
+require 'active_model/type/helpers/time_value'
diff --git a/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb b/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb
new file mode 100644
index 0000000000..fa1ccd057e
--- /dev/null
+++ b/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb
@@ -0,0 +1,27 @@
+module ActiveModel
+  module Type
+    module Helpers
+      class AcceptsMultiparameterTime < Module # :nodoc:
+        def initialize(defaults: {})
+          define_method(:cast) do |value|
+            if value.is_a?(Hash)
+              value_from_multiparameter_assignment(value)
+            else
+              super(value)
+            end
+          end
+
+          define_method(:value_from_multiparameter_assignment) do |values_hash|
+            defaults.each do |k, v|
+              values_hash[k] ||= v
+            end
+            return unless values_hash[1] && values_hash[2] && values_hash[3]
+            values = values_hash.sort.map(&:last)
+            ::Time.send(default_timezone, *values)
+          end
+          private :value_from_multiparameter_assignment
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/helpers/mutable.rb b/activemodel/lib/active_model/type/helpers/mutable.rb
new file mode 100644
index 0000000000..4dddbe4e5e
--- /dev/null
+++ b/activemodel/lib/active_model/type/helpers/mutable.rb
@@ -0,0 +1,18 @@
+module ActiveModel
+  module Type
+    module Helpers
+      module Mutable # :nodoc:
+        def cast(value)
+          deserialize(serialize(value))
+        end
+
+        # +raw_old_value+ will be the `_before_type_cast` version of the
+        # value (likely a string). +new_value+ will be the current, type
+        # cast value.
+        def changed_in_place?(raw_old_value, new_value)
+          raw_old_value != serialize(new_value)
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/helpers/numeric.rb b/activemodel/lib/active_model/type/helpers/numeric.rb
new file mode 100644
index 0000000000..c883010506
--- /dev/null
+++ b/activemodel/lib/active_model/type/helpers/numeric.rb
@@ -0,0 +1,34 @@
+module ActiveModel
+  module Type
+    module Helpers
+      module Numeric # :nodoc:
+        def cast(value)
+          value = case value
+                  when true then 1
+                  when false then 0
+                  when ::String then value.presence
+                  else value
+                  end
+          super(value)
+        end
+
+        def changed?(old_value, _new_value, new_value_before_type_cast) # :nodoc:
+          super || number_to_non_number?(old_value, new_value_before_type_cast)
+        end
+
+        private
+
+        def number_to_non_number?(old_value, new_value_before_type_cast)
+          old_value != nil && non_numeric_string?(new_value_before_type_cast)
+        end
+
+        def non_numeric_string?(value)
+          # 'wibble'.to_i will give zero, we want to make sure
+          # that we aren't marking int zero to string zero as
+          # changed.
+          value.to_s !~ /\A-?\d+\.?\d*\z/
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/helpers/time_value.rb b/activemodel/lib/active_model/type/helpers/time_value.rb
new file mode 100644
index 0000000000..5a899d43ec
--- /dev/null
+++ b/activemodel/lib/active_model/type/helpers/time_value.rb
@@ -0,0 +1,69 @@
+module ActiveModel
+  module Type
+    module Helpers
+      module TimeValue # :nodoc:
+        def serialize(value)
+          if precision && value.respond_to?(:usec)
+            number_of_insignificant_digits = 6 - precision
+            round_power = 10 ** number_of_insignificant_digits
+            value = value.change(usec: value.usec / round_power * round_power)
+          end
+
+          if value.acts_like?(:time)
+            zone_conversion_method = is_utc? ? :getutc : :getlocal
+
+            if value.respond_to?(zone_conversion_method)
+              value = value.send(zone_conversion_method)
+            end
+          end
+
+          value
+        end
+        
+        def is_utc?
+          ::Time.zone_default =~ 'UTC'
+        end
+        
+        def default_timezone
+          ::Time.zone_default
+        end
+
+        def type_cast_for_schema(value)
+          "'#{value.to_s(:db)}'"
+        end
+
+        def user_input_in_time_zone(value)
+          value.in_time_zone
+        end
+
+        private
+
+        def new_time(year, mon, mday, hour, min, sec, microsec, offset = nil)
+          # Treat 0000-00-00 00:00:00 as nil.
+          return if year.nil? || (year == 0 && mon == 0 && mday == 0)
+          
+
+          if offset
+            time = ::Time.utc(year, mon, mday, hour, min, sec, microsec) rescue nil
+            return unless time
+
+            time -= offset
+            is_utc? ? time : time.getlocal
+          else
+            ::Time.public_send(default_timezone, year, mon, mday, hour, min, sec, microsec) rescue nil
+          end
+        end
+        
+        ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
+
+        # Doesn't handle time zones.
+        def fast_string_to_time(string)
+          if string =~ ISO_DATETIME
+            microsec = ($7.to_r * 1_000_000).to_i
+            new_time $1.to_i, $2.to_i, $3.to_i, $4.to_i, $5.to_i, $6.to_i, microsec
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/integer.rb b/activemodel/lib/active_model/type/integer.rb
new file mode 100644
index 0000000000..2f73ede009
--- /dev/null
+++ b/activemodel/lib/active_model/type/integer.rb
@@ -0,0 +1,66 @@
+module ActiveModel
+  module Type
+    class Integer < Value # :nodoc:
+      include Helpers::Numeric
+
+      # Column storage size in bytes.
+      # 4 bytes means a MySQL int or Postgres integer as opposed to smallint etc.
+      DEFAULT_LIMIT = 4
+
+      def initialize(*)
+        super
+        @range = min_value...max_value
+      end
+
+      def type
+        :integer
+      end
+
+      def deserialize(value)
+        return if value.nil?
+        value.to_i
+      end
+
+      def serialize(value)
+        result = cast(value)
+        if result
+          ensure_in_range(result)
+        end
+        result
+      end
+
+      protected
+
+      attr_reader :range
+
+      private
+
+      def cast_value(value)
+        case value
+        when true then 1
+        when false then 0
+        else
+          value.to_i rescue nil
+        end
+      end
+
+      def ensure_in_range(value)
+        unless range.cover?(value)
+          raise RangeError, "#{value} is out of range for #{self.class} with limit #{_limit}"
+        end
+      end
+
+      def max_value
+        1 << (_limit * 8 - 1) # 8 bits per byte with one bit for sign
+      end
+
+      def min_value
+        -max_value
+      end
+
+      def _limit
+        self.limit || DEFAULT_LIMIT
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/registry.rb b/activemodel/lib/active_model/type/registry.rb
new file mode 100644
index 0000000000..8070a4bd38
--- /dev/null
+++ b/activemodel/lib/active_model/type/registry.rb
@@ -0,0 +1,151 @@
+module ActiveModel
+  # :stopdoc:
+  module Type
+    class Registry
+      def initialize
+        @registrations = []
+      end
+
+      def register(type_name, klass = nil, **options, &block)
+        block ||= proc { |_, *args| klass.new(*args) }
+        registrations << registration_klass.new(type_name, block, **options)
+      end
+
+      def lookup(symbol, *args)
+        registration = registrations
+          .select { |r| r.matches?(symbol, *args) }
+          .max
+
+        if registration
+          registration.call(self, symbol, *args)
+        else
+          raise ArgumentError, "Unknown type #{symbol.inspect}"
+        end
+      end
+
+      def add_modifier(options, klass, **args)
+        registrations << decoration_registration_klass.new(options, klass, **args)
+      end
+
+      protected
+
+      attr_reader :registrations
+      
+      private
+      
+      def registration_klass
+        Registration
+      end
+      
+      def decoration_registration_klass
+        DecorationRegistration
+      end
+    end
+
+    class Registration
+      def initialize(name, block, override: nil)
+        @name = name
+        @block = block
+        @override = override
+      end
+
+      def call(_registry, *args, **kwargs)
+        if kwargs.any? # https://bugs.ruby-lang.org/issues/10856
+          block.call(*args, **kwargs)
+        else
+          block.call(*args)
+        end
+      end
+
+      def matches?(type_name, *args, **kwargs)
+        type_name == name# && matches_adapter?(**kwargs)
+      end
+
+      def <=>(other)
+        # if conflicts_with?(other)
+        #   raise TypeConflictError.new("Type #{name} was registered for all
+        #                               adapters, but shadows a native type with
+        #                               the same name for #{other.adapter}".squish)
+        # end
+        priority <=> other.priority
+      end
+
+      protected
+
+      attr_reader :name, :block, :override
+
+      def priority
+        result = 0
+        # if adapter
+        #   result |= 1
+        # end
+        if override
+          result |= 2
+        end
+        result
+      end
+
+      # def priority_except_adapter
+      #   priority & 0b111111100
+      # end
+
+      private
+
+      # def matches_adapter?(adapter: nil, **)
+      #   (self.adapter.nil? || adapter == self.adapter)
+      # end
+
+      # def conflicts_with?(other)
+      #   same_priority_except_adapter?(other) &&
+      #     has_adapter_conflict?(other)
+      # end
+
+      # def same_priority_except_adapter?(other)
+      #   priority_except_adapter == other.priority_except_adapter
+      # end
+
+      # def has_adapter_conflict?(other)
+      #   (override.nil? && other.adapter) ||
+      #     (adapter && other.override.nil?)
+      # end
+    end
+
+    class DecorationRegistration < Registration
+      def initialize(options, klass)
+        @options = options
+        @klass = klass
+        # @adapter = adapter
+      end
+
+      def call(registry, *args, **kwargs)
+        subtype = registry.lookup(*args, **kwargs.except(*options.keys))
+        klass.new(subtype)
+      end
+
+      def matches?(*args, **kwargs)
+        matches_options?(**kwargs)
+      end
+
+      def priority
+        super | 4
+      end
+
+      protected
+
+      attr_reader :options, :klass
+
+      private
+
+      def matches_options?(**kwargs)
+        options.all? do |key, value|
+          kwargs[key] == value
+        end
+      end
+    end
+  end
+
+  class TypeConflictError < StandardError
+  end
+
+  # :startdoc:
+end
diff --git a/activemodel/lib/active_model/type/string.rb b/activemodel/lib/active_model/type/string.rb
new file mode 100644
index 0000000000..fd1630c751
--- /dev/null
+++ b/activemodel/lib/active_model/type/string.rb
@@ -0,0 +1,36 @@
+module ActiveModel
+  module Type
+    class String < Value # :nodoc:
+      def type
+        :string
+      end
+
+      def changed_in_place?(raw_old_value, new_value)
+        if new_value.is_a?(::String)
+          raw_old_value != new_value
+        end
+      end
+
+      def serialize(value)
+        case value
+        when ::Numeric, ActiveSupport::Duration then value.to_s
+        when ::String then ::String.new(value)
+        when true then "t"
+        when false then "f"
+        else super
+        end
+      end
+
+      private
+
+      def cast_value(value)
+        case value
+        when true then "t"
+        when false then "f"
+        # String.new is slightly faster than dup
+        else ::String.new(value.to_s)
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/text.rb b/activemodel/lib/active_model/type/text.rb
new file mode 100644
index 0000000000..1ad04daba4
--- /dev/null
+++ b/activemodel/lib/active_model/type/text.rb
@@ -0,0 +1,11 @@
+require 'active_model/type/string'
+
+module ActiveModel
+  module Type
+    class Text < String # :nodoc:
+      def type
+        :text
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/time.rb b/activemodel/lib/active_model/type/time.rb
new file mode 100644
index 0000000000..7101bad566
--- /dev/null
+++ b/activemodel/lib/active_model/type/time.rb
@@ -0,0 +1,42 @@
+module ActiveModel
+  module Type
+    class Time < Value # :nodoc:
+      include Helpers::TimeValue
+      include Helpers::AcceptsMultiparameterTime.new(
+        defaults: { 1 => 1970, 2 => 1, 3 => 1, 4 => 0, 5 => 0 }
+      )
+
+      def type
+        :time
+      end
+
+      def user_input_in_time_zone(value)
+        return unless value.present?
+
+        case value
+        when ::String
+          value = "2000-01-01 #{value}"
+        when ::Time
+          value = value.change(year: 2000, day: 1, month: 1)
+        end
+
+        super(value)
+      end
+
+      private
+
+      def cast_value(value)
+        return value unless value.is_a?(::String)
+        return if value.empty?
+
+        dummy_time_value = "2000-01-01 #{value}"
+
+        fast_string_to_time(dummy_time_value) || begin
+          time_hash = ::Date._parse(dummy_time_value)
+          return if time_hash[:hour].nil?
+          new_time(*time_hash.values_at(:year, :mon, :mday, :hour, :min, :sec, :sec_fraction))
+        end
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/type_map.rb b/activemodel/lib/active_model/type/type_map.rb
new file mode 100644
index 0000000000..402b660a71
--- /dev/null
+++ b/activemodel/lib/active_model/type/type_map.rb
@@ -0,0 +1,64 @@
+require 'concurrent'
+
+module ActiveModel
+  module Type
+    class TypeMap # :nodoc:
+      def initialize
+        @mapping = {}
+        @cache = Concurrent::Map.new do |h, key|
+          h.fetch_or_store(key, Concurrent::Map.new)
+        end
+      end
+
+      def lookup(lookup_key, *args)
+        fetch(lookup_key, *args) { default_value }
+      end
+
+      def fetch(lookup_key, *args, &block)
+        @cache[lookup_key].fetch_or_store(args) do
+          perform_fetch(lookup_key, *args, &block)
+        end
+      end
+
+      def register_type(key, value = nil, &block)
+        raise ::ArgumentError unless value || block
+        @cache.clear
+
+        if block
+          @mapping[key] = block
+        else
+          @mapping[key] = proc { value }
+        end
+      end
+
+      def alias_type(key, target_key)
+        register_type(key) do |sql_type, *args|
+          metadata = sql_type[/\(.*\)/, 0]
+          lookup("#{target_key}#{metadata}", *args)
+        end
+      end
+
+      def clear
+        @mapping.clear
+      end
+
+      private
+
+      def perform_fetch(lookup_key, *args)
+        matching_pair = @mapping.reverse_each.detect do |key, _|
+          key === lookup_key
+        end
+
+        if matching_pair
+          matching_pair.last.call(lookup_key, *args)
+        else
+          yield lookup_key, *args
+        end
+      end
+
+      def default_value
+        @default_value ||= Value.new
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/unsigned_integer.rb b/activemodel/lib/active_model/type/unsigned_integer.rb
new file mode 100644
index 0000000000..3f49f9f5f7
--- /dev/null
+++ b/activemodel/lib/active_model/type/unsigned_integer.rb
@@ -0,0 +1,15 @@
+module ActiveModel
+  module Type
+    class UnsignedInteger < Integer # :nodoc:
+      private
+
+      def max_value
+        super * 2
+      end
+
+      def min_value
+        0
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/type/value.rb b/activemodel/lib/active_model/type/value.rb
new file mode 100644
index 0000000000..c7d1197d69
--- /dev/null
+++ b/activemodel/lib/active_model/type/value.rb
@@ -0,0 +1,104 @@
+module ActiveModel
+  module Type
+    class Value
+      attr_reader :precision, :scale, :limit
+
+      def initialize(precision: nil, limit: nil, scale: nil)
+        @precision = precision
+        @scale = scale
+        @limit = limit
+      end
+
+      def type # :nodoc:
+      end
+
+      # Converts a value from database input to the appropriate ruby type. The
+      # return value of this method will be returned from
+      # ActiveRecord::AttributeMethods::Read#read_attribute. The default
+      # implementation just calls Value#cast.
+      #
+      # +value+ The raw input, as provided from the database.
+      def deserialize(value)
+        cast(value)
+      end
+
+      # Type casts a value from user input (e.g. from a setter). This value may
+      # be a string from the form builder, or a ruby object passed to a setter.
+      # There is currently no way to differentiate between which source it came
+      # from.
+      #
+      # The return value of this method will be returned from
+      # ActiveRecord::AttributeMethods::Read#read_attribute. See also:
+      # Value#cast_value.
+      #
+      # +value+ The raw input, as provided to the attribute setter.
+      def cast(value)
+        cast_value(value) unless value.nil?
+      end
+
+      # Casts a value from the ruby type to a type that the database knows how
+      # to understand. The returned value from this method should be a
+      # +String+, +Numeric+, +Date+, +Time+, +Symbol+, +true+, +false+, or
+      # +nil+.
+      def serialize(value)
+        value
+      end
+
+      # Type casts a value for schema dumping. This method is private, as we are
+      # hoping to remove it entirely.
+      def type_cast_for_schema(value) # :nodoc:
+        value.inspect
+      end
+
+      # These predicates are not documented, as I need to look further into
+      # their use, and see if they can be removed entirely.
+      def binary? # :nodoc:
+        false
+      end
+
+      # Determines whether a value has changed for dirty checking. +old_value+
+      # and +new_value+ will always be type-cast. Types should not need to
+      # override this method.
+      def changed?(old_value, new_value, _new_value_before_type_cast)
+        old_value != new_value
+      end
+
+      # Determines whether the mutable value has been modified since it was
+      # read. Returns +false+ by default. If your type returns an object
+      # which could be mutated, you should override this method. You will need
+      # to either:
+      #
+      # - pass +new_value+ to Value#serialize and compare it to
+      #   +raw_old_value+
+      #
+      # or
+      #
+      # - pass +raw_old_value+ to Value#deserialize and compare it to
+      #   +new_value+
+      #
+      # +raw_old_value+ The original value, before being passed to
+      # +deserialize+.
+      #
+      # +new_value+ The current value, after type casting.
+      def changed_in_place?(raw_old_value, new_value)
+        false
+      end
+
+      def ==(other)
+        self.class == other.class &&
+          precision == other.precision &&
+          scale == other.scale &&
+          limit == other.limit
+      end
+
+      private
+
+      # Convenience method for types which do not need separate type casting
+      # behavior for user and database inputs. Called by Value#cast for
+      # values except +nil+.
+      def cast_value(value) # :doc:
+        value
+      end
+    end
+  end
+end