/**
 * Converts OpenAI ChatCompletionMessageParam format to Vercel AI SDK CoreMessage format
 */

import type { ChatCompletionMessageParam } from "openai/resources/index.js";

export interface VercelCoreMessage {
  role: "system" | "user" | "assistant" | "tool";
  content: string | Array<any>;
}

/**
 * Converts OpenAI messages to Vercel AI SDK CoreMessage format.
 *
 * Key differences:
 * - OpenAI tool results: { role: "tool", tool_call_id: "...", content: "string" }
 * - Vercel tool results: { role: "tool", content: [{ type: "tool-result", toolCallId: "...", toolName: "...", result: any }] }
 *
 * IMPORTANT: For multi-turn conversations with tools:
 * - We EXCLUDE assistant messages that have tool_calls because Vercel AI SDK manages tool call state internally
 * - We only include tool results, and Vercel will associate them with its internal tool call tracking
 */
export function convertOpenAIMessagesToVercel(
  messages: ChatCompletionMessageParam[],
): VercelCoreMessage[] {
  const vercelMessages: VercelCoreMessage[] = [];

  // Build a map of tool_call_id => toolName from assistant messages
  const toolCallMap = new Map<string, string>();

  // First pass: collect tool call names
  for (const msg of messages) {
    if (msg.role === "assistant" && msg.tool_calls) {
      for (const tc of msg.tool_calls) {
        if (tc.type === "function") {
          toolCallMap.set(tc.id, tc.function.name);
        }
      }
    }
  }

  // Second pass: convert messages
  for (const msg of messages) {
    switch (msg.role) {
      case "system":
        vercelMessages.push({
          role: "system",
          content:
            typeof msg.content === "string"
              ? msg.content
              : JSON.stringify(msg.content),
        });
        break;

      case "user":
        vercelMessages.push({
          role: "user",
          content: msg.content,
        });
        break;

      case "assistant":
        // CRITICAL: Skip assistant messages with tool_calls in subsequent turns
        // Vercel AI SDK manages tool call state internally and doesn't expect us to re-send them
        // Only include assistant messages WITHOUT tool calls (normal responses)
        if (!msg.tool_calls || msg.tool_calls.length === 0) {
          vercelMessages.push({
            role: "assistant",
            content: msg.content || "",
          });
        }
        // Note: We skip assistant messages WITH tool_calls because:
        // 1. They were generated by Vercel AI SDK in a previous turn
        // 2. Vercel tracks tool call state internally
        // 3. Re-sending them causes Anthropic API errors about missing tool_use blocks
        break;

      case "tool":
        // Convert OpenAI tool result to Vercel format
        const toolName = toolCallMap.get(msg.tool_call_id) || "unknown_tool";
        vercelMessages.push({
          role: "tool",
          content: [
            {
              type: "tool-result",
              toolCallId: msg.tool_call_id,
              toolName,
              result: msg.content,
            },
          ],
        });
        break;
    }
  }

  return vercelMessages;
}