9router/open-sse/translator/response/openai-to-claude.js

import { register } from "../index.js";
import { FORMATS } from "../formats.js";

// Prefix for Claude OAuth tool names (must match request translator)
const CLAUDE_OAUTH_TOOL_PREFIX = "proxy_";

// Helper: stop thinking block if started
function stopThinkingBlock(state, results) {
  if (!state.thinkingBlockStarted) return;
  results.push({
    type: "content_block_stop",
    index: state.thinkingBlockIndex
  });
  state.thinkingBlockStarted = false;
}

// Helper: stop text block if started
function stopTextBlock(state, results) {
  if (!state.textBlockStarted || state.textBlockClosed) return;
  state.textBlockClosed = true;
  results.push({
    type: "content_block_stop",
    index: state.textBlockIndex
  });
  state.textBlockStarted = false;
}

// Convert OpenAI stream chunk to Claude format
export function openaiToClaudeResponse(chunk, state) {
  if (!chunk || !chunk.choices?.[0]) return null;

  const results = [];
  const choice = chunk.choices[0];
  const delta = choice.delta;

  // Track usage from OpenAI chunk if available
  if (chunk.usage && typeof chunk.usage === "object") {
    const promptTokens = typeof chunk.usage.prompt_tokens === "number" ? chunk.usage.prompt_tokens : 0;
    const outputTokens = typeof chunk.usage.completion_tokens === "number" ? chunk.usage.completion_tokens : 0;
    
    // Extract cache tokens from prompt_tokens_details
    const cachedTokens = chunk.usage.prompt_tokens_details?.cached_tokens;
    const cacheCreationTokens = chunk.usage.prompt_tokens_details?.cache_creation_tokens;
    const cacheReadTokens = typeof cachedTokens === "number" ? cachedTokens : 0;
    const cacheCreateTokens = typeof cacheCreationTokens === "number" ? cacheCreationTokens : 0;
    
    // input_tokens = prompt_tokens - cached_tokens - cache_creation_tokens
    // Because OpenAI's prompt_tokens includes all prompt-side tokens
    const inputTokens = promptTokens - cacheReadTokens - cacheCreateTokens;
    
    state.usage = {
      input_tokens: inputTokens,
      output_tokens: outputTokens
    };
    
    // Add cache_read_input_tokens if present
    if (cacheReadTokens > 0) {
      state.usage.cache_read_input_tokens = cacheReadTokens;
    }
    
    // Add cache_creation_input_tokens if present
    if (cacheCreateTokens > 0) {
      state.usage.cache_creation_input_tokens = cacheCreateTokens;
    }
    
    // Note: completion_tokens_details.reasoning_tokens is already included in output_tokens
    // No need to add separately as Claude expects total output_tokens
  }

  // First chunk - ALWAYS send message_start first
  if (!state.messageStartSent) {
    state.messageStartSent = true;
    state.messageId = chunk.id?.replace("chatcmpl-", "") || `msg_${Date.now()}`;
    if (!state.messageId || state.messageId === "chat" || state.messageId.length < 8) {
      state.messageId = chunk.extend_fields?.requestId ||
        chunk.extend_fields?.traceId ||
        `msg_${Date.now()}`;
    }
    state.model = chunk.model || "unknown";
    state.nextBlockIndex = 0;
    results.push({
      type: "message_start",
      message: {
        id: state.messageId,
        type: "message",
        role: "assistant",
        model: state.model,
        content: [],
        stop_reason: null,
        stop_sequence: null,
        usage: { input_tokens: 0, output_tokens: 0 }
      }
    });
  }

  // Handle reasoning_content (thinking) - GLM, DeepSeek, etc.
  const reasoningContent = delta?.reasoning_content || delta?.reasoning;
  if (reasoningContent) {
    stopTextBlock(state, results);

    if (!state.thinkingBlockStarted) {
      state.thinkingBlockIndex = state.nextBlockIndex++;
      state.thinkingBlockStarted = true;
      results.push({
        type: "content_block_start",
        index: state.thinkingBlockIndex,
        content_block: { type: "thinking", thinking: "" }
      });
    }

    results.push({
      type: "content_block_delta",
      index: state.thinkingBlockIndex,
      delta: { type: "thinking_delta", thinking: reasoningContent }
    });
  }

  // Handle regular content
  if (delta?.content) {
    stopThinkingBlock(state, results);

    if (!state.textBlockStarted) {
      state.textBlockIndex = state.nextBlockIndex++;
      state.textBlockStarted = true;
      state.textBlockClosed = false;
      results.push({
        type: "content_block_start",
        index: state.textBlockIndex,
        content_block: { type: "text", text: "" }
      });
    }

    results.push({
      type: "content_block_delta",
      index: state.textBlockIndex,
      delta: { type: "text_delta", text: delta.content }
    });
  }

  // Tool calls
  if (delta?.tool_calls) {
    for (const tc of delta.tool_calls) {
      const idx = tc.index ?? 0;

      if (tc.id) {
        stopThinkingBlock(state, results);
        stopTextBlock(state, results);

        const toolBlockIndex = state.nextBlockIndex++;
        state.toolCalls.set(idx, { id: tc.id, name: tc.function?.name || "", blockIndex: toolBlockIndex });
        
        // Strip prefix from tool name for response
        let toolName = tc.function?.name || "";
        if (toolName.startsWith(CLAUDE_OAUTH_TOOL_PREFIX)) {
          toolName = toolName.slice(CLAUDE_OAUTH_TOOL_PREFIX.length);
        }
        
        results.push({
          type: "content_block_start",
          index: toolBlockIndex,
          content_block: {
            type: "tool_use",
            id: tc.id,
            name: toolName,
            input: {}
          }
        });
      }

      if (tc.function?.arguments) {
        const toolInfo = state.toolCalls.get(idx);
        if (toolInfo) {
          results.push({
            type: "content_block_delta",
            index: toolInfo.blockIndex,
            delta: { type: "input_json_delta", partial_json: tc.function.arguments }
          });
        }
      }
    }
  }

  // Finish
  if (choice.finish_reason) {
    stopThinkingBlock(state, results);
    stopTextBlock(state, results);

    for (const [, toolInfo] of state.toolCalls) {
      results.push({
        type: "content_block_stop",
        index: toolInfo.blockIndex
      });
    }

    // Use tracked usage or default to 0
    const finalUsage = state.usage || { input_tokens: 0, output_tokens: 0 };
    results.push({
      type: "message_delta",
      delta: { stop_reason: convertFinishReason(choice.finish_reason) },
      usage: finalUsage
    });
    results.push({ type: "message_stop" });
  }

  return results.length > 0 ? results : null;
}

// Convert OpenAI finish_reason to Claude stop_reason
function convertFinishReason(reason) {
  switch (reason) {
    case "stop": return "end_turn";
    case "length": return "max_tokens";
    case "tool_calls": return "tool_use";
    default: return "end_turn";
  }
}

// Register
register(FORMATS.OPENAI, FORMATS.CLAUDE, null, openaiToClaudeResponse);