From 6a79f48541cd3afb232de207d3e113ddbe6e3427 Mon Sep 17 00:00:00 2001
From: Malte Rohde <malte@bitcrowd.net>
Date: Fri, 1 Dec 2023 15:11:47 +0100
Subject: [PATCH] Add BitcrowdEcto.FixedWidthInteger

---
 lib/bitcrowd_ecto/fixed_width_integer.ex      | 66 +++++++++++++++++++
 .../fixed_width_integer_test.exs              | 50 ++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 lib/bitcrowd_ecto/fixed_width_integer.ex
 create mode 100644 test/bitcrowd_ecto/fixed_width_integer_test.exs

diff --git a/lib/bitcrowd_ecto/fixed_width_integer.ex b/lib/bitcrowd_ecto/fixed_width_integer.ex
new file mode 100644
index 0000000..6ccf200
--- /dev/null
+++ b/lib/bitcrowd_ecto/fixed_width_integer.ex
@@ -0,0 +1,66 @@
+defmodule BitcrowdEcto.FixedWidthInteger do
+  @moduledoc """
+  An Ecto type that automatically validates that the given integer fits the underlying DB type.
+
+  This turns the ugly Postgrex errors into neat `validation: :cast` changeset errors without
+  having to manually `validate_number` all `:integer` fields.
+
+  Named widths are based on Postgres' integer types.
+
+  https://www.postgresql.org/docs/current/datatype-numeric.html
+  """
+
+  use Ecto.ParameterizedType
+
+  @postgres_type_ranges %{
+    smallint: -32_768..32_767,
+    integer: -2_147_483_648..2_147_483_647,
+    bigint: -9_223_372_036_854_775_808..9_223_372_036_854_775_807,
+    smallserial: 1..32_767,
+    serial: 1..2_147_483_647,
+    bigserial: 1..9_223_372_036_854_775_807
+  }
+
+  @generic_byte_size_ranges %{
+    2 => -32_768..32_767,
+    4 => -2_147_483_648..2_147_483_647,
+    8 => -9_223_372_036_854_775_808..9_223_372_036_854_775_807
+  }
+
+  @impl true
+  def init(opts) do
+    opts
+    |> Keyword.get(:width, 4)
+    |> width_to_range()
+  end
+
+  defp width_to_range(type) when is_atom(type), do: Map.fetch!(@postgres_type_ranges, type)
+  defp width_to_range(size) when is_integer(size), do: Map.fetch!(@generic_byte_size_ranges, size)
+
+  @impl true
+  def type(_range), do: :integer
+
+  @impl true
+  def cast(value, range) do
+    if is_integer(value) and value not in range do
+      :error
+    else
+      Ecto.Type.cast(:integer, value)
+    end
+  end
+
+  @impl true
+  def load(value, loader, _range) do
+    Ecto.Type.load(:integer, value, loader)
+  end
+
+  @impl true
+  def dump(value, dumper, _range) do
+    Ecto.Type.dump(:integer, value, dumper)
+  end
+
+  @impl true
+  def equal?(a, b, _range) do
+    a == b
+  end
+end
diff --git a/test/bitcrowd_ecto/fixed_width_integer_test.exs b/test/bitcrowd_ecto/fixed_width_integer_test.exs
new file mode 100644
index 0000000..4b0b34a
--- /dev/null
+++ b/test/bitcrowd_ecto/fixed_width_integer_test.exs
@@ -0,0 +1,50 @@
+defmodule BitcrowdEcto.FixedWidthIntegerTest do
+  use ExUnit.Case, async: true
+  import BitcrowdEcto.Assertions
+  import Ecto.Changeset
+
+  defmodule TestSchema do
+    use Ecto.Schema
+
+    embedded_schema do
+      field(:int_4, BitcrowdEcto.FixedWidthInteger, width: 4)
+      field(:int_smallint, BitcrowdEcto.FixedWidthInteger, width: :smallint)
+      field(:int_bigserial, BitcrowdEcto.FixedWidthInteger, width: :bigserial)
+    end
+  end
+
+  test "casting an out-of-range value results in a changeset error" do
+    for ok <- [-2, 2, 0, -2_147_483_648, 2_147_483_647] do
+      cs = cast(%TestSchema{}, %{int_4: ok}, [:int_4])
+      assert cs.valid?
+    end
+
+    for not_ok <- [-2_147_483_649, 2_147_483_648] do
+      cs = cast(%TestSchema{}, %{int_4: not_ok}, [:int_4])
+      refute cs.valid?
+      assert_error_on(cs, :int_4, :cast)
+    end
+
+    for ok <- [-2, 2, 0, -32_768, 32_767] do
+      cs = cast(%TestSchema{}, %{int_smallint: ok}, [:int_smallint])
+      assert cs.valid?
+    end
+
+    for not_ok <- [-32_769, 32_768] do
+      cs = cast(%TestSchema{}, %{int_smallint: not_ok}, [:int_smallint])
+      refute cs.valid?
+      assert_error_on(cs, :int_smallint, :cast)
+    end
+
+    for ok <- [1, 9_223_372_036_854_775_807] do
+      cs = cast(%TestSchema{}, %{int_bigserial: ok}, [:int_bigserial])
+      assert cs.valid?
+    end
+
+    for not_ok <- [-1, 0, 9_223_372_036_854_775_808] do
+      cs = cast(%TestSchema{}, %{int_bigserial: not_ok}, [:int_bigserial])
+      refute cs.valid?
+      assert_error_on(cs, :int_bigserial, :cast)
+    end
+  end
+end