import type { ChatCompletionRequest, ChatCompletionResult, ChatMessage, LlmClient } from "./types";

type OpenAiMessage = {
  role: string;
  content: ChatMessage["content"];
  tool_calls?: Array<{
    id: string;
    type: "function";
    function: { name: string; arguments: string };
  }>;
  tool_call_id?: string;
  name?: string;
};

export function createOpenAiCompatibleClient(options: {
  baseUrl: string;
  apiKey: string | null;
  model: string;
}): LlmClient {
  const completionsUrl = `${options.baseUrl.replace(/\/$/, "")}/chat/completions`;

  return {
    async chatCompletion(request: ChatCompletionRequest): Promise<ChatCompletionResult> {
      const headers: Record<string, string> = {
        "Content-Type": "application/json",
      };
      if (options.apiKey) {
        headers.Authorization = `Bearer ${options.apiKey}`;
      }

      const body = {
        model: options.model,
        messages: request.messages as OpenAiMessage[],
        tools: request.tools,
        tool_choice: request.tools?.length ? "auto" : undefined,
      };

      const response = await fetch(completionsUrl, {
        method: "POST",
        headers,
        body: JSON.stringify(body),
      });

      if (!response.ok) {
        const detail = await response.text();
        throw new Error(`LLM request failed (${response.status}): ${detail.slice(0, 400)}`);
      }

      const payload = (await response.json()) as {
        choices?: Array<{
          finish_reason?: string | null;
          message?: OpenAiMessage;
        }>;
      };

      const choice = payload.choices?.[0];
      const message = choice?.message;
      if (!message) {
        throw new Error("LLM response missing message");
      }

      return {
        message: {
          role: message.role as ChatCompletionResult["message"]["role"],
          content: message.content,
          tool_calls: message.tool_calls,
          tool_call_id: message.tool_call_id,
          name: message.name,
        },
        finishReason: choice.finish_reason ?? null,
      };
    },
  };
}