fix: tests for ai json parser

lib/bds/ai/json_content.ex

@@ -0,0 +1,42 @@
+defmodule BDS.AI.JsonContent do
+  @moduledoc """
+  Decodes JSON object payloads from model responses, tolerating the markdown
+  code fences and surrounding prose that smaller (local) models often emit
+  instead of bare JSON.
+  """
+
+  @fence_pattern ~r/```(?:json)?\s*\n?(.*?)```/is
+
+  @spec decode(term()) :: map() | nil
+  def decode(content) when is_binary(content) do
+    decode_strict(content) || decode_fenced(content) || decode_embedded_object(content)
+  end
+
+  def decode(_content), do: nil
+
+  defp decode_strict(content) do
+    case Jason.decode(content) do
+      {:ok, decoded} when is_map(decoded) -> decoded
+      _other -> nil
+    end
+  end
+
+  defp decode_fenced(content) do
+    case Regex.run(@fence_pattern, content, capture: :all_but_first) do
+      [inner] -> decode_strict(String.trim(inner)) || decode_embedded_object(inner)
+      _no_fence -> nil
+    end
+  end
+
+  defp decode_embedded_object(content) do
+    with {start, _length} <- :binary.match(content, "{"),
+         [{last, _} | _] <- content |> :binary.matches("}") |> Enum.take(-1),
+         true <- last > start do
+      content
+      |> binary_part(start, last - start + 1)
+      |> decode_strict()
+    else
+      _no_object -> nil
+    end
+  end
+end

test/bds/ai/json_content_test.exs

@@ -0,0 +1,69 @@
+defmodule BDS.AI.JsonContentTest do
+  use ExUnit.Case, async: true
+
+  alias BDS.AI.JsonContent
+
+  test "decodes a bare JSON object" do
+    assert %{"title" => "Sunset"} = JsonContent.decode(~s({"title": "Sunset"}))
+  end
+
+  test "decodes a JSON object wrapped in a json markdown fence" do
+    content = """
+    ```json
+    {
+      "title": "Ahornblätter im Herbstlicht",
+      "alt": "Nahaufnahme von Ahornblättern",
+      "caption": "Einige Ahornblätter verfärben sich."
+    }
+    ```
+    """
+
+    assert %{
+             "title" => "Ahornblätter im Herbstlicht",
+             "alt" => "Nahaufnahme von Ahornblättern",
+             "caption" => "Einige Ahornblätter verfärben sich."
+           } = JsonContent.decode(content)
+  end
+
+  test "decodes a JSON object wrapped in an untagged markdown fence" do
+    assert %{"language_code" => "de"} =
+             JsonContent.decode("```\n{\"language_code\": \"de\"}\n```")
+  end
+
+  test "decodes a fenced JSON object with an uppercase language tag" do
+    assert %{"slug" => "herbst"} = JsonContent.decode("```JSON\n{\"slug\": \"herbst\"}\n```")
+  end
+
+  test "decodes a fenced JSON object surrounded by prose" do
+    content = """
+    Here is the requested metadata:
+
+    ```json
+    {"title": "Herbst"}
+    ```
+
+    Let me know if you need anything else.
+    """
+
+    assert %{"title" => "Herbst"} = JsonContent.decode(content)
+  end
+
+  test "decodes a bare JSON object surrounded by prose" do
+    content = ~s(Sure! {"title": "Herbst", "alt": "Blätter"} Hope this helps.)
+
+    assert %{"title" => "Herbst", "alt" => "Blätter"} = JsonContent.decode(content)
+  end
+
+  test "returns nil for content without a JSON object" do
+    assert JsonContent.decode("This is not valid JSON") == nil
+  end
+
+  test "returns nil for a JSON array" do
+    assert JsonContent.decode(~s([1, 2, 3])) == nil
+  end
+
+  test "returns nil for nil and non-binary input" do
+    assert JsonContent.decode(nil) == nil
+    assert JsonContent.decode(42) == nil
+  end
+end