OmniRoute/open-sse/handlers/sseParser.ts

/**
 * Convert OpenAI-style SSE chunks into a single non-streaming JSON response.
 * Used as a fallback when upstream returns text/event-stream for stream=false.
 */
export function parseSSEToOpenAIResponse(rawSSE, fallbackModel) {
  const lines = String(rawSSE || "").split("\n");
  const chunks = [];

  for (const line of lines) {
    const trimmed = line.trim();
    if (!trimmed.startsWith("data:")) continue;
    const payload = trimmed.slice(5).trim();
    if (!payload || payload === "[DONE]") continue;
    try {
      chunks.push(JSON.parse(payload));
    } catch {
      // Ignore malformed SSE lines and continue best-effort parsing.
    }
  }

  if (chunks.length === 0) return null;

  const first = chunks[0];
  const contentParts = [];
  const reasoningParts = [];
  let finishReason = "stop";
  let usage = null;

  for (const chunk of chunks) {
    const choice = chunk?.choices?.[0];
    const delta = choice?.delta || {};

    if (typeof delta.content === "string" && delta.content.length > 0) {
      contentParts.push(delta.content);
    }
    if (typeof delta.reasoning_content === "string" && delta.reasoning_content.length > 0) {
      reasoningParts.push(delta.reasoning_content);
    }
    if (choice?.finish_reason) {
      finishReason = choice.finish_reason;
    }
    if (chunk?.usage && typeof chunk.usage === "object") {
      usage = chunk.usage;
    }
  }

  const message: Record<string, any> = { role: "assistant",
    content: contentParts.join(""),
  };
  if (reasoningParts.length > 0) {
    message.reasoning_content = reasoningParts.join("");
  }

  const result: Record<string, any> = {
    id: first.id || `chatcmpl-${Date.now()}`,
    object: "chat.completion",
    created: first.created || Math.floor(Date.now() / 1000),
    model: first.model || fallbackModel || "unknown",
    choices: [
      {
        index: 0,
        message,
        finish_reason: finishReason,
      },
    ],
  };

  if (usage) {
    result.usage = usage;
  }

  return result;
}

/**
 * Convert Responses API SSE events into a single non-streaming response object.
 * Expects events such as response.created / response.in_progress / response.completed.
 */
export function parseSSEToResponsesOutput(rawSSE, fallbackModel) {
  const lines = String(rawSSE || "").split("\n");
  const events = [];

  for (const line of lines) {
    const trimmed = line.trim();
    if (!trimmed.startsWith("data:")) continue;
    const payload = trimmed.slice(5).trim();
    if (!payload || payload === "[DONE]") continue;
    try {
      events.push(JSON.parse(payload));
    } catch {
      // Ignore malformed lines and continue best-effort parsing.
    }
  }

  if (events.length === 0) return null;

  let completed = null;
  let latestResponse = null;

  for (const evt of events) {
    if (evt?.type === "response.completed" && evt.response) {
      completed = evt.response;
    }
    if (evt?.response && typeof evt.response === "object") {
      latestResponse = evt.response;
    } else if (evt?.object === "response") {
      latestResponse = evt;
    }
  }

  const picked = completed || latestResponse;
  if (!picked || typeof picked !== "object") return null;

  return {
    id: picked.id || `resp_${Date.now()}`,
    object: "response",
    model: picked.model || fallbackModel || "unknown",
    output: Array.isArray(picked.output) ? picked.output : [],
    usage: picked.usage || null,
    status: picked.status || (completed ? "completed" : "in_progress"),
    created_at: picked.created_at || Math.floor(Date.now() / 1000),
    metadata: picked.metadata || {},
  };
}