import { ChatbotBackend } from "@/types/backend";
import { Message } from "./messages";

/**
 * Gets a streaming chat response from OpenRouter API.
 * OpenRouter provides an OpenAI-compatible API with access to multiple models.
 */
export async function getOpenRouterChatResponseStream(
  config: ChatbotBackend["openrouter"],
  messages: Message[],
): Promise<ReadableStream> {
  const apiKey = config?.openrouter_apikey;
  if (!apiKey) {
    throw new Error("OpenRouter API key is required");
  }

  const baseUrl = config.openrouter_url ?? "https://openrouter.ai/api/v1";
  const model = config.openrouter_model ?? "openai/gpt-3.5-turbo";
  const appUrl = "https://amica.arbius.ai";

  const response = await fetch(`${baseUrl}/chat/completions`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${apiKey}`,
      "Content-Type": "application/json",
      "HTTP-Referer": appUrl,
      "X-Title": "Amica Chat",
    },
    body: JSON.stringify({
      model,
      messages: messages.map(({ role, content }) => ({ role, content })),
      stream: true,
    }),
  });

  const reader = response.body?.getReader();
  if (!response.ok || !reader) {
    const error = await response.json();
    // Handle OpenRouter-specific error format
    if (error.error?.message) {
      throw new Error(`OpenRouter error: ${error.error.message}`);
    }
    throw new Error(`OpenRouter request failed with status ${response.status}`);
  }

  const stream = new ReadableStream({
    async start(controller: ReadableStreamDefaultController) {
      const decoder = new TextDecoder("utf-8");
      try {
        // sometimes the response is chunked, so we need to combine the chunks
        let combined = "";
        while (true) {
          const { done, value } = await reader.read();
          if (done) break;
          const data = decoder.decode(value);
          const chunks = data
            .split("data:")
            .filter((val) => !!val && val.trim() !== "[DONE]");

          for (const chunk of chunks) {
            // skip comments
            if (chunk.length > 0 && chunk[0] === ":") {
              continue;
            }
            combined += chunk;

            try {
              const json = JSON.parse(combined);
              const messagePiece = json.choices[0].delta.content;
              combined = "";
              if (!!messagePiece) {
                controller.enqueue(messagePiece);
              }
            } catch (error) {
              console.error(error);
            }
          }
        }
      } catch (error) {
        console.error(error);
        controller.error(error);
      } finally {
        reader?.releaseLock();
        controller.close();
      }
    },
    async cancel() {
      await reader?.cancel();
      reader?.releaseLock();
    },
  });
  return stream;
}