defmodule Gemini.Client.HTTP do
  @moduledoc """
  Unified HTTP client for both Gemini and Vertex AI APIs using Req.

  Supports multiple authentication strategies and provides both
  regular and streaming request capabilities.

  ## Rate Limiting

  All requests are automatically routed through the rate limiter unless
  `disable_rate_limiter: true` is passed in options. The rate limiter:

  - Enforces concurrency limits per model
  - Honors 429 RetryInfo delays from the API
  - Retries transient failures with backoff
  - Tracks token usage for budget estimation

  See `Gemini.RateLimiter` for configuration options.
  """

  alias Gemini.Config
  alias Gemini.Auth
  alias Gemini.Error
  alias Gemini.Telemetry
  alias Gemini.RateLimiter

  @doc """
  Make a GET request using the configured authentication.
  """
  def get(path, opts \\ []) do
    auth_config = Config.auth_config()
    request(:get, path, nil, auth_config, opts)
  end

  @doc """
  Make a POST request using the configured authentication.
  """
  def post(path, body, opts \\ []) do
    auth_config = Config.auth_config()
    request(:post, path, body, auth_config, opts)
  end

  @doc """
  Make an authenticated HTTP request.

  ## Options

  In addition to standard request options, supports rate limiter options:

  - `:disable_rate_limiter` - Bypass rate limiting (default: false)
  - `:non_blocking` - Return immediately if rate limited (default: false)
  - `:max_concurrency_per_model` - Override concurrency limit
  """
  def request(method, path, body, auth_config, opts \\ []) do
    Config.validate!()

    case auth_config do
      nil ->
        {:error, Error.config_error("No authentication configured")}

      %{type: auth_type, credentials: credentials} ->
        url = build_authenticated_url(auth_type, path, credentials)
        headers = Auth.build_headers(auth_type, credentials)
        model = extract_model_from_path(path)

        # Execute through rate limiter
        request_fn = fn ->
          execute_request(method, url, headers, body, opts)
        end

        if Keyword.get(opts, :disable_rate_limiter, false) do
          request_fn.()
        else
          RateLimiter.execute_with_usage_tracking(request_fn, model, opts)
        end
    end
  end

  # Execute the actual HTTP request with telemetry
  defp execute_request(method, url, headers, body, opts) do
    start_time = System.monotonic_time()
    metadata = Telemetry.build_request_metadata(url, method, opts)
    measurements = %{system_time: System.system_time()}

    Telemetry.execute([:gemini, :request, :start], measurements, metadata)

    req_opts = [
      method: method,
      url: url,
      headers: headers,
      receive_timeout: Config.timeout(),
      json: body
    ]

    try do
      result = Req.request(req_opts) |> handle_response()

      case result do
        {:ok, _response} ->
          duration = Telemetry.calculate_duration(start_time)

          stop_measurements = %{
            duration: duration,
            status: 200
          }

          Telemetry.execute([:gemini, :request, :stop], stop_measurements, metadata)

        {:error, error} ->
          Telemetry.execute(
            [:gemini, :request, :exception],
            measurements,
            Map.put(metadata, :reason, error)
          )
      end

      result
    rescue
      exception ->
        Telemetry.execute(
          [:gemini, :request, :exception],
          measurements,
          Map.put(metadata, :reason, exception)
        )

        reraise exception, __STACKTRACE__
    end
  end

  @doc """
  Stream a POST request for Server-Sent Events using configured authentication.
  """
  def stream_post(path, body, opts \\ []) do
    auth_config = Config.auth_config()
    stream_post_with_auth(path, body, auth_config, opts)
  end

  @doc """
  Stream a POST request with specific authentication configuration.
  """
  def stream_post_with_auth(path, body, auth_config, opts \\ []) do
    Config.validate!()

    start_time = System.monotonic_time()

    case auth_config do
      nil ->
        {:error, Error.config_error("No authentication configured")}

      %{type: auth_type, credentials: credentials} ->
        url = build_authenticated_url(auth_type, path, credentials)
        headers = Auth.build_headers(auth_type, credentials)

        # Add SSE parameter to URL
        sse_url = if String.contains?(url, "?"), do: "#{url}&alt=sse", else: "#{url}?alt=sse"

        stream_id = Telemetry.generate_stream_id()
        metadata = Telemetry.build_stream_metadata(sse_url, :post, stream_id, opts)
        measurements = %{system_time: System.system_time()}

        Telemetry.execute([:gemini, :stream, :start], measurements, metadata)

        req_opts = [
          url: sse_url,
          headers: headers,
          receive_timeout: Config.timeout(),
          json: body,
          into: :self
        ]

        try do
          result =
            case Req.post(req_opts) do
              {:ok, %Req.Response{status: status, body: body}} when status in 200..299 ->
                events = parse_sse_stream(body)

                duration = Telemetry.calculate_duration(start_time)

                stop_measurements = %{
                  total_duration: duration,
                  total_chunks: length(events)
                }

                Telemetry.execute([:gemini, :stream, :stop], stop_measurements, metadata)

                {:ok, events}

              {:ok, %Req.Response{status: status}} ->
                error = {:http_error, status, "Stream request failed"}

                Telemetry.execute(
                  [:gemini, :stream, :exception],
                  measurements,
                  Map.put(metadata, :reason, error)
                )

                {:error, Error.http_error(status, "Stream request failed")}

              {:error, reason} ->
                Telemetry.execute(
                  [:gemini, :stream, :exception],
                  measurements,
                  Map.put(metadata, :reason, reason)
                )

                {:error, Error.network_error(reason)}
            end

          result
        rescue
          exception ->
            Telemetry.execute(
              [:gemini, :stream, :exception],
              measurements,
              Map.put(metadata, :reason, exception)
            )

            reraise exception, __STACKTRACE__
        end
    end
  end

  @doc """
  Raw streaming POST with full URL (used by streaming manager).
  """
  def stream_post_raw(url, body, headers, _opts \\ []) do
    req_opts = [
      url: url,
      headers: headers,
      receive_timeout: Config.timeout(),
      json: body,
      into: :self
    ]

    case Req.post(req_opts) do
      {:ok, %Req.Response{status: status, body: body}} when status in 200..299 ->
        events = parse_sse_stream(body)
        {:ok, events}

      {:ok, %Req.Response{status: status}} ->
        {:error, Error.http_error(status, "Stream request failed")}

      {:error, reason} ->
        {:error, Error.network_error(reason)}
    end
  end

  # Private functions

  defp build_authenticated_url(auth_type, path, credentials) do
    base_url = Auth.get_base_url(auth_type, credentials)

    # Check if this is a model-specific endpoint (contains ":" separator)
    # or a general endpoint like "models" for listing
    if String.contains?(path, ":") do
      # Model-specific endpoint, use the auth strategy to build the path
      full_path =
        Auth.build_path(
          auth_type,
          extract_model_from_path(path),
          extract_endpoint_from_path(path),
          credentials
        )

      "#{base_url}/#{full_path}"
    else
      # General endpoint (like "models"), use path directly
      "#{base_url}/#{path}"
    end
  end

  defp extract_model_from_path(path) do
    # Extract model from paths like "models/gemini-2.0-flash:generateContent"
    case String.split(path, ":") do
      [model_path, _endpoint] ->
        model_path |> String.replace_prefix("models/", "") |> String.trim_leading("/")

      _ ->
        # fallback
        Config.default_model()
    end
  end

  defp extract_endpoint_from_path(path) do
    # Extract endpoint from paths like "models/gemini-2.0-flash:generateContent"
    case String.split(path, ":") do
      [_model, endpoint] -> String.split(endpoint, "?") |> hd()
      # fallback
      _ -> "generateContent"
    end
  end

  defp handle_response({:ok, %Req.Response{status: status, body: body}})
       when status in 200..299 do
    case body do
      decoded when is_map(decoded) ->
        {:ok, decoded}

      json_string when is_binary(json_string) ->
        case Jason.decode(json_string) do
          {:ok, decoded} -> {:ok, decoded}
          {:error, _} -> {:error, Error.invalid_response("Invalid JSON response")}
        end

      _ ->
        {:error, Error.invalid_response("Invalid response format")}
    end
  end

  defp handle_response({:ok, %Req.Response{status: status, body: body}}) do
    error_info =
      case body do
        %{"error" => error} ->
          error

        json_string when is_binary(json_string) ->
          case Jason.decode(json_string) do
            {:ok, %{"error" => error}} -> error
            _ -> %{"message" => "HTTP #{status}"}
          end

        _ ->
          %{"message" => "HTTP #{status}"}
      end

    {:error, Error.api_error(status, error_info)}
  end

  defp handle_response({:error, reason}) do
    {:error, Error.network_error(reason)}
  end

  # Parse Server-Sent Events format
  defp parse_sse_stream(data) when is_binary(data) do
    data
    |> String.split("\n\n")
    |> Enum.filter(&(String.trim(&1) != ""))
    |> Enum.map(&parse_sse_event/1)
    |> Enum.filter(&(&1 != nil))
  rescue
    _ -> []
  end

  defp parse_sse_stream(_), do: []

  defp parse_sse_event(event_data) do
    lines = String.split(event_data, "\n")

    Enum.reduce(lines, %{}, fn line, acc ->
      case String.split(line, ": ", parts: 2) do
        ["data", json_data] ->
          case Jason.decode(json_data) do
            {:ok, decoded} -> Map.put(acc, :data, decoded)
            _ -> acc
          end

        [field, value] ->
          Map.put(acc, String.to_atom(field), value)

        _ ->
          acc
      end
    end)
    |> case do
      %{data: data} -> data
      _ -> nil
    end
  end
end