From 92d473e359e44294a2a564ab3d598327fd5386ed Mon Sep 17 00:00:00 2001
From: Georgy Shabunin <georgy.shabunin@gmail.com>
Date: Mon, 9 Sep 2024 18:59:17 +0100
Subject: [PATCH] Add constraints phase

---
 lib/constraints.ex                            |   5 +
 lib/constraints/max.ex                        |  23 +++
 lib/constraints/min.ex                        |  23 +++
 lib/directives/constraints.ex                 |  75 +++++++++
 lib/phases/apply_constraints.ex               | 152 ++++++++++++++++++
 mix.exs                                       |   3 +-
 mix.lock                                      |   1 +
 .../constraints/apply_constraints_test.exs    |  76 +++++++++
 8 files changed, 357 insertions(+), 1 deletion(-)
 create mode 100644 lib/constraints.ex
 create mode 100644 lib/constraints/max.ex
 create mode 100644 lib/constraints/min.ex
 create mode 100644 lib/directives/constraints.ex
 create mode 100644 lib/phases/apply_constraints.ex
 create mode 100644 test/absinthe_helpers/constraints/apply_constraints_test.exs

diff --git a/lib/constraints.ex b/lib/constraints.ex
new file mode 100644
index 0000000..d59ad5c
--- /dev/null
+++ b/lib/constraints.ex
@@ -0,0 +1,5 @@
+defmodule AbsintheHelpers.Constraint do
+  @moduledoc false
+
+  @callback call(Tuple.t(), Input.Value.t()) :: {:ok, Input.Value.t()} | {:error, atom()}
+end
diff --git a/lib/constraints/max.ex b/lib/constraints/max.ex
new file mode 100644
index 0000000..7dd52e8
--- /dev/null
+++ b/lib/constraints/max.ex
@@ -0,0 +1,23 @@
+defmodule AbsintheHelpers.Constraints.Max do
+  @moduledoc false
+
+  @behaviour AbsintheHelpers.Constraint
+
+  def call({:max, max}, node = %{data: decimal = %Decimal{}}) do
+    if is_integer(max) and Decimal.gt?(decimal, max),
+      do: {:error, :max},
+      else: {:ok, node}
+  end
+
+  def call({:max, max}, node = %{data: data}) when is_binary(data) do
+    if String.length(data) > max,
+      do: {:error, :max},
+      else: {:ok, node}
+  end
+
+  def call({:max, max}, node = %{data: data}) do
+    if data > max,
+      do: {:error, :max},
+      else: {:ok, node}
+  end
+end
diff --git a/lib/constraints/min.ex b/lib/constraints/min.ex
new file mode 100644
index 0000000..326b474
--- /dev/null
+++ b/lib/constraints/min.ex
@@ -0,0 +1,23 @@
+defmodule AbsintheHelpers.Constraints.Min do
+  @moduledoc false
+
+  @behaviour AbsintheHelpers.Constraint
+
+  def call({:min, min}, node = %{data: decimal = %Decimal{}}) do
+    if is_integer(min) and Decimal.lt?(decimal, min),
+      do: {:error, :min},
+      else: {:ok, node}
+  end
+
+  def call({:min, min}, node = %{data: data}) when is_binary(data) do
+    if String.length(data) < min,
+      do: {:error, :min},
+      else: {:ok, node}
+  end
+
+  def call({:min, min}, node = %{data: data}) do
+    if data < min,
+      do: {:error, :min},
+      else: {:ok, node}
+  end
+end
diff --git a/lib/directives/constraints.ex b/lib/directives/constraints.ex
new file mode 100644
index 0000000..a53e4a5
--- /dev/null
+++ b/lib/directives/constraints.ex
@@ -0,0 +1,75 @@
+defmodule AbsintheHelpers.Directives.Constraints do
+  @moduledoc """
+  Defines a GraphQL directive to add constraints to field definitions and argument definitions.
+
+  Example
+
+  ```elixir
+  input_object :my_input do
+    field(:my_field, :integer, directives: [constraints: [min: 1]])
+  end
+
+  #...
+  object :my_query do
+    field :my_field, non_null(:string) do
+      arg(:my_arg, non_null(:string), directives: [constraints: [format: "uuid"]])
+      resolve(&MyResolver.resolve/2)
+    end
+  end
+  ```
+  """
+
+  use Absinthe.Schema.Prototype
+
+  alias Absinthe.Blueprint.TypeReference.NonNull
+
+  @string_args [:min, :max]
+  @number_args [:min, :max]
+
+  directive :constraints do
+    on([:argument_definition, :field_definition])
+
+    arg(:min, :integer, description: "Ensure value is greater than or equal to")
+    arg(:max, :integer, description: "Ensure value is less than or equal to")
+
+    expand(&__MODULE__.expand_constraints/2)
+  end
+
+  def expand_constraints(args, %{type: type} = node),
+    do: do_expand(args, node, get_args(type))
+
+  defp get_args(:string), do: @string_args
+  defp get_args(:integer), do: @number_args
+  defp get_args(:float), do: @number_args
+  defp get_args(:decimal), do: @number_args
+  defp get_args(%NonNull{of_type: of_type}), do: get_args(of_type)
+  defp get_args(type), do: raise("Unsupported type: #{inspect(type)}")
+
+  defp do_expand(args, node, args_list) do
+    {valid_args, invalid_args} = Map.split(args, args_list)
+    handle_invalid_args(node, invalid_args)
+
+    update_node(valid_args, node)
+  end
+
+  defp handle_invalid_args(_, args) when args == %{}, do: nil
+
+  defp handle_invalid_args(%{type: type, name: name} = node, invalid_args) do
+    args = Map.keys(invalid_args)
+    location_line = get_in(node.__reference__, [:location, :line])
+
+    raise Absinthe.Schema.Error,
+      phase_errors: [
+        %Absinthe.Phase.Error{
+          phase: __MODULE__,
+          message:
+            "Invalid constraints for field/arg `#{name}` of type `#{inspect(type)}`: #{inspect(args)}",
+          locations: [%{line: location_line, column: 0}]
+        }
+      ]
+  end
+
+  defp update_node(args, node) do
+    %{node | __private__: Keyword.put(node.__private__, :constraints, args)}
+  end
+end
diff --git a/lib/phases/apply_constraints.ex b/lib/phases/apply_constraints.ex
new file mode 100644
index 0000000..6cb9a27
--- /dev/null
+++ b/lib/phases/apply_constraints.ex
@@ -0,0 +1,152 @@
+defmodule AbsintheHelpers.Phases.ApplyConstraints do
+  @moduledoc """
+  This module validates input nodes against constraints defined by the `constraints`
+  directive in your Absinthe schema. Constraints can be applied to fields and arguments,
+  enforcing rules such as `min`, `max`, etc.
+
+  ## Example Usage
+
+  To add this phase to your pipeline, add the following to your router:
+
+      forward "/graphql",
+          to: Absinthe.Plug,
+          init_opts: [
+            schema: MyProject.Schema,
+            pipeline: {__MODULE__, :absinthe_pipeline},
+          ]
+
+      def absinthe_pipeline(config, opts) do
+        config
+        |> Absinthe.Plug.default_pipeline(opts)
+        |> AbsintheHelpers.Phases.ApplyConstraints.add_to_pipeline(opts)
+      end
+
+  Then add the constraints directive's prototype schema to your schema
+
+      defmodule MyApp.Schema do
+        use Absinthe.Schema
+
+        @prototype_schema AbsintheHelpers.Directives.Constraints
+
+        ...
+      end
+
+  Then apply constraints to a field:
+
+      field :my_field, :integer do
+        directives [constraints: [min: 1, max: 10]]
+
+        resolve(&MyResolver.resolve/3)
+      end
+
+  Or an argument:
+
+      arg :my_arg, non_null(:string), directives: [constraints: [min: 10]]
+  """
+
+  use Absinthe.Phase
+
+  alias Absinthe.Blueprint
+  alias Absinthe.Blueprint.Input
+
+  def add_to_pipeline(pipeline, opts) do
+    Absinthe.Pipeline.insert_before(
+      pipeline,
+      Absinthe.Phase.Document.Validation.Result,
+      {__MODULE__, opts}
+    )
+  end
+
+  @impl Absinthe.Phase
+  def run(input, _opts \\ []) do
+    {:ok, Blueprint.postwalk(input, &handle_node/1)}
+  end
+
+  defp handle_node(
+         %{
+           input_value: %{normalized: normalized},
+           schema_node: %{__private__: private}
+         } = node
+       ) do
+    if constraints?(private), do: apply_constraints(node, normalized), else: node
+  end
+
+  defp handle_node(node), do: node
+
+  defp apply_constraints(node, %Input.List{items: items}) do
+    case validate_items(items, node.schema_node.__private__) do
+      {:ok, new_items} ->
+        %{node | input_value: %{node.input_value | normalized: %Input.List{items: new_items}}}
+
+      {:error, reasons} ->
+        add_custom_errors(node, reasons)
+    end
+  end
+
+  defp apply_constraints(node, %{value: _value}) do
+    case validate_item(node.input_value, node.schema_node.__private__) do
+      {:ok, _validated_value} -> node
+      {:error, reason} -> add_custom_errors(node, reason)
+    end
+  end
+
+  defp apply_constraints(node, _), do: node
+
+  defp validate_items(items, private_tags) do
+    Enum.reduce(items, {:ok, []}, fn item, {:ok, acc} ->
+      case validate_item(item, private_tags) do
+        {:ok, validated_item} -> {:ok, acc ++ [validated_item]}
+        {:error, reason} -> {:error, acc ++ reason}
+      end
+    end)
+  end
+
+  defp validate_item(item, private_tags) do
+    apply_constraints_in_sequence(item, get_constraints(private_tags))
+  end
+
+  defp apply_constraints_in_sequence(item, constraints) do
+    Enum.reduce(constraints, {:ok, item, []}, fn constraint, {:ok, prev_output, errors} ->
+      case call_constraint(constraint, prev_output) do
+        {:ok, result} -> {:ok, result, errors}
+        {:error, reason} -> {:ok, prev_output, errors ++ [reason]}
+      end
+    end)
+    |> handle_constraint_results()
+  end
+
+  defp handle_constraint_results({:ok, item, []}), do: {:ok, item}
+  defp handle_constraint_results({:ok, _item, errors}), do: {:error, errors}
+
+  defp call_constraint(constraint = {name, _args}, input) do
+    constraint_module = get_constraint_module(name)
+    constraint_module.call(constraint, input)
+  end
+
+  defp get_constraint_module(constraint_name) do
+    constraint_name
+    |> Atom.to_string()
+    |> Macro.camelize()
+    |> then(&String.to_existing_atom("Elixir.AbsintheHelpers.Constraints.#{&1}"))
+  end
+
+  defp get_constraints(private) do
+    private
+    |> Keyword.get(:constraints, [])
+  end
+
+  defp constraints?(private) do
+    private
+    |> get_constraints()
+    |> Enum.any?()
+  end
+
+  defp add_custom_errors(node, reasons) do
+    Enum.reduce(reasons, node, fn reason, acc ->
+      Absinthe.Phase.put_error(acc, %Absinthe.Phase.Error{
+        phase: __MODULE__,
+        message: reason
+      })
+    end)
+  end
+end
diff --git a/mix.exs b/mix.exs
index a95914e..45c67ca 100644
--- a/mix.exs
+++ b/mix.exs
@@ -32,7 +32,8 @@ defmodule AbsintheHelpers.MixProject do
       {:dialyxir, "~> 1.0", only: :dev, runtime: false},
       {:ex_doc, "~> 0.34", only: :dev, runtime: false},
       {:absinthe, "~> 1.0"},
-      {:mimic, "~> 1.10", only: :test}
+      {:mimic, "~> 1.10", only: :test},
+      {:decimal, "~> 1.9"}
     ]
   end
 
diff --git a/mix.lock b/mix.lock
index 9433c7c..f90720c 100644
--- a/mix.lock
+++ b/mix.lock
@@ -2,6 +2,7 @@
   "absinthe": {:hex, :absinthe, "1.7.8", "43443d12ad2b4fcce60e257ac71caf3081f3d5c4ddd5eac63a02628bcaf5b556", [:mix], [{:dataloader, "~> 1.0.0 or ~> 2.0", [hex: :dataloader, repo: "hexpm", optional: true]}, {:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}, {:nimble_parsec, "~> 1.2.2 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}, {:opentelemetry_process_propagator, "~> 0.2.1 or ~> 0.3", [hex: :opentelemetry_process_propagator, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "c4085df201892a498384f997649aedb37a4ce8a726c170d5b5617ed3bf45d40b"},
   "bunt": {:hex, :bunt, "1.0.0", "081c2c665f086849e6d57900292b3a161727ab40431219529f13c4ddcf3e7a44", [:mix], [], "hexpm", "dc5f86aa08a5f6fa6b8096f0735c4e76d54ae5c9fa2c143e5a1fc7c1cd9bb6b5"},
   "credo": {:hex, :credo, "1.7.7", "771445037228f763f9b2afd612b6aa2fd8e28432a95dbbc60d8e03ce71ba4446", [:mix], [{:bunt, "~> 0.2.1 or ~> 1.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2 or ~> 1.0", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "8bc87496c9aaacdc3f90f01b7b0582467b69b4bd2441fe8aae3109d843cc2f2e"},
+  "decimal": {:hex, :decimal, "1.9.0", "83e8daf59631d632b171faabafb4a9f4242c514b0a06ba3df493951c08f64d07", [:mix], [], "hexpm", "b1f2343568eed6928f3e751cf2dffde95bfaa19dd95d09e8a9ea92ccfd6f7d85"},
   "dialyxir": {:hex, :dialyxir, "1.4.3", "edd0124f358f0b9e95bfe53a9fcf806d615d8f838e2202a9f430d59566b6b53b", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "bf2cfb75cd5c5006bec30141b131663299c661a864ec7fbbc72dfa557487a986"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.41", "ab34711c9dc6212dda44fcd20ecb87ac3f3fce6f0ca2f28d4a00e4154f8cd599", [:mix], [], "hexpm", "a81a04c7e34b6617c2792e291b5a2e57ab316365c2644ddc553bb9ed863ebefa"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},
diff --git a/test/absinthe_helpers/constraints/apply_constraints_test.exs b/test/absinthe_helpers/constraints/apply_constraints_test.exs
new file mode 100644
index 0000000..9d7ee40
--- /dev/null
+++ b/test/absinthe_helpers/constraints/apply_constraints_test.exs
@@ -0,0 +1,76 @@
+defmodule AbsintheHelpers.Phases.ApplyConstraintsTest do
+  use ExUnit.Case, async: true
+
+  alias AbsintheHelpers.Phases.ApplyConstraints
+  alias AbsintheHelpers.TestResolver
+
+  describe "apply constraints phase with min/max on integers, decimals, and strings" do
+    defmodule TestSchema do
+      use Absinthe.Schema
+
+      import_types(Absinthe.Type.Custom)
+
+      @prototype_schema AbsintheHelpers.Directives.Constraints
+
+      query do
+        field :get_booking, non_null(:string) do
+          resolve(&TestResolver.run/3)
+        end
+      end
+
+      mutation do
+        field(:create_booking, :string) do
+          arg(:customer_id, non_null(:integer), directives: [constraints: [min: 1, max: 1000]])
+          arg(:service, non_null(:service_input))
+
+          resolve(&TestResolver.run/3)
+        end
+      end
+
+      input_object :service_input do
+        field(:cost, :decimal, directives: [constraints: [min: 10, max: 1000]])
+        field(:description, :string, directives: [constraints: [min: 5, max: 50]])
+      end
+
+      def run_query(query) do
+        Absinthe.run(
+          query,
+          __MODULE__,
+          pipeline_modifier: &ApplyConstraints.add_to_pipeline/2
+        )
+      end
+    end
+
+    test "validates mutation arguments including decimal and string constraints and returns success" do
+      query = """
+      mutation {
+        create_booking(
+          customer_id: 1,
+          service: {
+            cost: "150.75",
+            description: "Valid description"
+          }
+        )
+      }
+      """
+
+      assert TestSchema.run_query(query) == {:ok, %{data: %{"create_booking" => ""}}}
+    end
+
+    test "returns errors for invalid decimal and string arguments" do
+      query = """
+      mutation {
+        create_booking(
+          customer_id: 1001,
+          service: {
+            cost: "5.00",
+            description: "Too short"
+          }
+        )
+      }
+      """
+
+      assert TestSchema.run_query(query) == {:ok, %{errors: [%{message: :max}, %{message: :min}]}}
+    end
+  end
+end