fix: implemented TD-06 real SSE implementation

lib/bds/ai/sse.ex

@@ -0,0 +1,176 @@
+defmodule BDS.AI.SSE do
+  @moduledoc """
+  Incremental assembler for OpenAI-compatible `text/event-stream` chat
+  completions.
+
+  Fed raw transport chunks via `feed/2`, it buffers partial events, decodes
+  `data:` payloads, and accumulates content deltas, tool-call fragments, and
+  usage. Content is reported to the optional `on_event` callback as
+  **cumulative snapshots** (`%{content: binary}`) — replace semantics, which
+  matches how the chat editor renders streaming state and resets naturally
+  between tool rounds. Emissions are throttled to `:emit_interval_ms`
+  (the first delta always emits immediately for perceived latency).
+
+  `finish/1` returns the assembled message in OpenAI wire shape so the
+  runtime can reuse its non-streaming normalization:
+  `%{content: binary | nil, tool_calls: [%{"id" => _, "function" => %{"name" => _, "arguments" => json_string}}], usage: map | nil}`.
+  """
+
+  defstruct buffer: "",
+            raw: [],
+            content: [],
+            content?: false,
+            tool_calls: %{},
+            usage: nil,
+            done?: false,
+            on_event: nil,
+            emit_interval_ms: 100,
+            last_emit_at: nil
+
+  @type t :: %__MODULE__{}
+
+  @spec new((map() -> any()) | nil, keyword()) :: t()
+  def new(on_event \\ nil, opts \\ []) when is_list(opts) do
+    %__MODULE__{
+      on_event: on_event,
+      emit_interval_ms: Keyword.get(opts, :emit_interval_ms, 100)
+    }
+  end
+
+  @spec feed(t(), binary()) :: t()
+  def feed(%__MODULE__{done?: true} = sse, _chunk), do: sse
+
+  def feed(%__MODULE__{} = sse, chunk) when is_binary(chunk) do
+    sse = %{sse | raw: [chunk | sse.raw]}
+    parts = String.split(sse.buffer <> chunk, ~r/\r?\n\r?\n/)
+    {complete_events, [rest]} = Enum.split(parts, -1)
+
+    Enum.reduce(complete_events, %{sse | buffer: rest}, &process_event(&2, &1))
+  end
+
+  @doc """
+  The unparsed transport bytes, for callers that discover after the fact
+  that the response was not an event stream (e.g. a provider that ignored
+  the `stream` flag and answered with plain JSON).
+  """
+  @spec raw_body(t()) :: binary()
+  def raw_body(%__MODULE__{} = sse) do
+    sse.raw |> Enum.reverse() |> IO.iodata_to_binary()
+  end
+
+  @spec finish(t()) :: %{content: binary() | nil, tool_calls: [map()], usage: map() | nil}
+  def finish(%__MODULE__{} = sse) do
+    # A final event may arrive without its trailing blank line.
+    sse =
+      case String.trim(sse.buffer) do
+        "" -> sse
+        remnant -> process_event(%{sse | buffer: ""}, remnant)
+      end
+
+    %{
+      content: assembled_content(sse),
+      tool_calls: assembled_tool_calls(sse),
+      usage: sse.usage
+    }
+  end
+
+  defp process_event(%{done?: true} = sse, _event), do: sse
+
+  defp process_event(sse, event) do
+    data =
+      event
+      |> String.split(~r/\r?\n/)
+      |> Enum.flat_map(&data_line/1)
+      |> Enum.join("\n")
+
+    cond do
+      data == "" ->
+        sse
+
+      String.trim(data) == "[DONE]" ->
+        %{sse | done?: true}
+
+      true ->
+        case Jason.decode(data) do
+          {:ok, payload} when is_map(payload) -> apply_payload(sse, payload)
+          _other -> sse
+        end
+    end
+  end
+
+  defp data_line("data: " <> rest), do: [rest]
+  defp data_line("data:" <> rest), do: [rest]
+  defp data_line(_line), do: []
+
+  defp apply_payload(sse, payload) do
+    delta = get_in(payload, ["choices", Access.at(0), "delta"]) || %{}
+
+    sse
+    |> apply_content(delta["content"])
+    |> apply_tool_calls(delta["tool_calls"])
+    |> apply_usage(payload["usage"])
+  end
+
+  defp apply_content(sse, content) when is_binary(content) and content != "" do
+    %{sse | content: [content | sse.content], content?: true}
+    |> maybe_emit()
+  end
+
+  defp apply_content(sse, _content), do: sse
+
+  defp apply_tool_calls(sse, [_ | _] = fragments) do
+    Enum.reduce(fragments, sse, fn fragment, acc ->
+      index = fragment["index"] || 0
+      existing = Map.get(acc.tool_calls, index, %{id: nil, name: nil, arguments: []})
+      function_part = fragment["function"] || %{}
+
+      merged = %{
+        id: existing.id || fragment["id"],
+        name: existing.name || function_part["name"],
+        arguments: [existing.arguments, function_part["arguments"] || ""]
+      }
+
+      %{acc | tool_calls: Map.put(acc.tool_calls, index, merged)}
+    end)
+  end
+
+  defp apply_tool_calls(sse, _fragments), do: sse
+
+  defp apply_usage(sse, usage) when is_map(usage) and map_size(usage) > 0,
+    do: %{sse | usage: usage}
+
+  defp apply_usage(sse, _usage), do: sse
+
+  defp maybe_emit(%{on_event: nil} = sse), do: sse
+
+  defp maybe_emit(sse) do
+    now = System.monotonic_time(:millisecond)
+
+    if is_nil(sse.last_emit_at) or now - sse.last_emit_at >= sse.emit_interval_ms do
+      sse.on_event.(%{content: assembled_content(sse) || ""})
+      %{sse | last_emit_at: now}
+    else
+      sse
+    end
+  end
+
+  defp assembled_content(%{content?: false}), do: nil
+
+  defp assembled_content(sse) do
+    sse.content |> Enum.reverse() |> IO.iodata_to_binary()
+  end
+
+  defp assembled_tool_calls(sse) do
+    sse.tool_calls
+    |> Enum.sort_by(fn {index, _tool_call} -> index end)
+    |> Enum.map(fn {_index, tool_call} ->
+      %{
+        "id" => tool_call.id,
+        "function" => %{
+          "name" => tool_call.name,
+          "arguments" => IO.iodata_to_binary(tool_call.arguments)
+        }
+      }
+    end)
+  end
+end