selector: add Edgehog.Selector.Filter protocol

Allow converting a group filter into an Ash expression

Signed-off-by: Riccardo Binetti <[email protected]>

backend/lib/edgehog/selector/ast/attribute_filter.ex

@@ -222,4 +222,11 @@ defmodule Edgehog.Selector.AST.AttributeFilter do
         where: compare(cast_json_variant(a.typed_value, unquote(type)), unquote(operator), ^value)
     end
   end
+
+  defimpl Edgehog.Selector.Filter do
+    # TODO: see https://github.com/edgehog-device-manager/edgehog/issues/486
+    def to_ash_expr(_attribute_filter) do
+      raise "TODO"
+    end
+  end
 end

backend/lib/edgehog/selector/ast/binary_op.ex

@@ -20,4 +20,18 @@
 
 defmodule Edgehog.Selector.AST.BinaryOp do
   defstruct [:operator, :lhs, :rhs]
+
+  require Ash.Query
+
+  defimpl Edgehog.Selector.Filter do
+    def to_ash_expr(binary_op) do
+      lhs = Edgehog.Selector.Filter.to_ash_expr(binary_op.lhs)
+      rhs = Edgehog.Selector.Filter.to_ash_expr(binary_op.rhs)
+
+      case binary_op.operator do
+        :and -> Ash.Query.expr(^lhs and ^rhs)
+        :or -> Ash.Query.expr(^lhs or ^rhs)
+      end
+    end
+  end
 end

backend/lib/edgehog/selector/ast/tag_filter.ex

@@ -29,6 +29,7 @@ defmodule Edgehog.Selector.AST.TagFilter do
   import Ecto.Query
   alias Edgehog.Labeling
   alias Edgehog.Selector.AST.TagFilter
+  require Ash.Query
 
   @doc """
   Converts a `%TagFilter{}` to a dynamic where clause filtering `Astarte.Device`s that match the
@@ -51,4 +52,15 @@ defmodule Edgehog.Selector.AST.TagFilter do
 
     {:ok, dynamic}
   end
+
+  defimpl Edgehog.Selector.Filter do
+    def to_ash_expr(tag_filter) do
+      tag_name = tag_filter.tag
+
+      case tag_filter.operator do
+        :in -> Ash.Query.expr(exists(tags, name == ^tag_name))
+        :not_in -> Ash.Query.expr(not exists(tags, name == ^tag_name))
+      end
+    end
+  end
 end

backend/lib/edgehog/selector/filter.ex

@@ -0,0 +1,24 @@
+#
+# This file is part of Edgehog.
+#
+# Copyright 2024 SECO Mind Srl
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+defprotocol Edgehog.Selector.Filter do
+  @doc "Converts the filter into an `%Ash.Expr{}` matching it"
+  def to_ash_expr(filter)
+end

backend/lib/edgehog/selector.ex → backend/lib/edgehog/selector/selector.ex

@@ -21,6 +21,7 @@
 defmodule Edgehog.Selector do
   alias Edgehog.Devices
   alias Edgehog.Selector.AST.{AttributeFilter, BinaryOp, TagFilter}
+  alias Edgehog.Selector.Filter
   alias Edgehog.Selector.Parser
   alias Edgehog.Selector.Parser.Error
 
@@ -50,6 +51,18 @@ defmodule Edgehog.Selector do
     end
   end
 
+  @doc """
+  Translates a selector to an `%Ash.Expr{}` matching all devices matched by the selector.
+
+  It accepts the AST root (the Selector must be parsed separately).
+
+  Returns `%Ash.Expr{}`.
+  """
+  def to_ash_expr(%node{} = ast_root)
+      when node in [AttributeFilter, BinaryOp, TagFilter] do
+    Filter.to_ash_expr(ast_root)
+  end
+
   @doc """
   Parses a selector, returning an AST (or an error). The root node can be one of the structs contained in
   the `Edgehog.Selector.AST` namespace.