shooting-event/phoenix/lib/shooting_event_phx/ai/gemini.ex

defmodule ShootingEventPhx.AI.Gemini do
  @moduledoc false

  def generate_score_advice(stage, player_id, image_data, current_score) do
    with api_key when is_binary(api_key) and api_key != "" <- gemini_api_key(),
         {:ok, mime_type, raw_base64} <- parse_data_uri(image_data),
         {:ok, body} <- build_request_body(stage, current_score, mime_type, raw_base64),
         {:ok, response} <- request_gemini(body, api_key),
         {:ok, model_response} <- parse_gemini_response(response) do
      {:ok,
       %{
         "stage" => stage,
         "playerId" => player_id,
         "advisedScore" => clamp(model_response["advisedScore"] || 0, 0, 9999),
         "reason" => normalize_reason(model_response["reason"]),
         "generatedAt" =>
           DateTime.utc_now() |> DateTime.truncate(:second) |> DateTime.to_iso8601()
       }}
    else
      nil -> {:error, :service_unavailable, "gemini api key is not configured"}
      {:error, message} when is_binary(message) -> {:error, :bad_gateway, message}
      {:error, status, message} -> {:error, status, message}
      _ -> {:error, :bad_gateway, "failed to generate score advice"}
    end
  end

  defp gemini_api_key do
    System.get_env("GEMINI_API_KEY", "AIzaSyATpv4fmHpjPPLk-BEy4fCBL_r1EWtiWDc")
    |> String.trim()
    |> case do
      "" -> nil
      v -> v
    end
  end

  defp gemini_model do
    System.get_env("GEMINI_MODEL", "gemini-3.1-flash-lite-preview")
    |> String.trim()
    |> case do
      "" -> "gemini-3.1-flash-lite-preview"
      v -> v
    end
  end

  defp parse_data_uri(data_uri) do
    value = data_uri |> to_string() |> String.trim()

    if String.starts_with?(value, "data:") do
      case String.split(value, ",", parts: 2) do
        [header, payload] ->
          payload = String.trim(payload)

          if payload == "" do
            {:error, "invalid proof image data: empty payload"}
          else
            mime_type =
              case String.split(header, ";", parts: 2) do
                ["data:" <> mime, _] when mime != "" -> mime
                _ -> "image/jpeg"
              end

            {:ok, mime_type, payload}
          end

        _ ->
          {:error, "invalid proof image data: invalid data uri format"}
      end
    else
      {:error, "invalid proof image data: expected data uri"}
    end
  end

  defp build_request_body(stage, current_score, mime_type, raw_base64) do
    request = %{
      "contents" => [
        %{
          "role" => "user",
          "parts" => [
            %{"text" => score_advice_prompt(stage, current_score)},
            %{"inline_data" => %{"mime_type" => mime_type, "data" => raw_base64}}
          ]
        }
      ],
      "generationConfig" => %{
        "temperature" => 0,
        "responseMimeType" => "application/json",
        "maxOutputTokens" => 100
      }
    }

    {:ok, Jason.encode!(request)}
  end

  defp request_gemini(body, api_key) do
    endpoint =
      "https://generativelanguage.googleapis.com/v1beta/models/#{URI.encode(gemini_model())}:generateContent?key=#{URI.encode_www_form(api_key)}"

    case Req.post(endpoint,
           headers: [{"content-type", "application/json"}],
           body: body,
           receive_timeout: 25_000
         ) do
      {:ok, %Req.Response{status: status, body: response_body}} when status < 300 ->
        {:ok, response_body}

      {:ok, %Req.Response{status: status, body: response_body}} ->
        {:error, "gemini api status #{status}: #{inspect(response_body)}"}

      {:error, reason} ->
        {:error, "call gemini api: #{inspect(reason)}"}
    end
  end

  defp parse_gemini_response(response_body) when is_map(response_body) do
    cond do
      is_map(response_body["error"]) and is_binary(response_body["error"]["message"]) ->
        {:error, "gemini api error: #{response_body["error"]["message"]}"}

      true ->
        text =
          get_in(response_body, [
            "candidates",
            Access.at(0),
            "content",
            "parts",
            Access.at(0),
            "text"
          ])
          |> to_string()
          |> String.trim()

        json_text = extract_json_object(text)

        if json_text == "" do
          {:error, "gemini response was not valid json"}
        else
          case Jason.decode(json_text) do
            {:ok, parsed} -> {:ok, parsed}
            {:error, reason} -> {:error, "parse gemini advice json: #{inspect(reason)}"}
          end
        end
    end
  end

  defp parse_gemini_response(_), do: {:error, "decode gemini response: unexpected payload"}

  defp extract_json_object(raw) do
    text =
      raw
      |> String.trim()
      |> String.trim_leading("```json")
      |> String.trim_leading("```")
      |> String.trim_trailing("```")
      |> String.trim()

    start_idx = binary_index(text, "{")
    end_idx = binary_rindex(text, "}")

    if is_integer(start_idx) and is_integer(end_idx) and end_idx > start_idx do
      text
      |> String.slice(start_idx..end_idx)
      |> String.trim()
    else
      ""
    end
  end

  defp score_advice_prompt(stage, current_score) do
    "Target scoring assistant.\nStage: #{stage}. Current score: #{current_score}.\n" <>
      "Return STRICT JSON only:\n{\"advisedScore\":<int 0..9999>,\"reason\":\"<max 18 words>\"}\n" <>
      "Do not add markdown or extra fields."
  end

  defp normalize_reason(reason) do
    value = reason |> to_string() |> String.trim()
    if value == "", do: "AI estimated the score from visible impacts.", else: value
  end

  defp clamp(value, min, _max) when value < min, do: min
  defp clamp(value, _min, max) when value > max, do: max
  defp clamp(value, _min, _max), do: value

  defp binary_index(text, pattern) do
    case :binary.match(text, pattern) do
      :nomatch -> nil
      {idx, _len} -> idx
    end
  end

  defp binary_rindex(text, pattern) do
    text
    |> :binary.matches(pattern)
    |> List.last()
    |> case do
      nil -> nil
      {idx, _len} -> idx
    end
  end
end