/**
 * Convert OpenAI Responses API format to standard chat completions format
 * Responses API uses: { input: [...], instructions: "..." }
 * Chat API uses: { messages: [...] }
 */
export function convertResponsesApiFormat(body) {
  if (!body.input) return body;

  const result = { ...body };
  result.messages = [];

  // Convert instructions to system message
  if (body.instructions) {
    result.messages.push({ role: "system", content: body.instructions });
  }

  // Group items by conversation turn
  let currentAssistantMsg = null;
  let pendingToolCalls = [];
  let pendingToolResults = [];

  for (const item of body.input) {
    if (item.type === "message") {
      // Flush any pending assistant message with tool calls
      if (currentAssistantMsg) {
        result.messages.push(currentAssistantMsg);
        currentAssistantMsg = null;
      }
      // Flush pending tool results
      if (pendingToolResults.length > 0) {
        for (const tr of pendingToolResults) {
          result.messages.push(tr);
        }
        pendingToolResults = [];
      }

      // Convert content: input_text → text, output_text → text
      const content = Array.isArray(item.content)
        ? item.content.map(c => {
            if (c.type === "input_text") return { type: "text", text: c.text };
            if (c.type === "output_text") return { type: "text", text: c.text };
            return c;
          })
        : item.content;
      result.messages.push({ role: item.role, content });
    } 
    else if (item.type === "function_call") {
      // Start or append to assistant message with tool_calls
      if (!currentAssistantMsg) {
        currentAssistantMsg = {
          role: "assistant",
          content: null,
          tool_calls: []
        };
      }
      currentAssistantMsg.tool_calls.push({
        id: item.call_id,
        type: "function",
        function: {
          name: item.name,
          arguments: item.arguments
        }
      });
    }
    else if (item.type === "function_call_output") {
      // Flush assistant message first if exists
      if (currentAssistantMsg) {
        result.messages.push(currentAssistantMsg);
        currentAssistantMsg = null;
      }
      // Add tool result
      pendingToolResults.push({
        role: "tool",
        tool_call_id: item.call_id,
        content: typeof item.output === "string" ? item.output : JSON.stringify(item.output)
      });
    }
    else if (item.type === "reasoning") {
      // Skip reasoning items - they are for display only
      continue;
    }
  }

  // Flush remaining
  if (currentAssistantMsg) {
    result.messages.push(currentAssistantMsg);
  }
  if (pendingToolResults.length > 0) {
    for (const tr of pendingToolResults) {
      result.messages.push(tr);
    }
  }

  // Cleanup Responses API specific fields
  delete result.input;
  delete result.instructions;
  delete result.include;
  delete result.prompt_cache_key;
  delete result.store;
  delete result.reasoning;

  return result;
}