Initial commit: Setting up OpenRouter MCP server for multimodal capabilities

src/tool-handlers/chat-completion.ts

@@ -0,0 +1,135 @@
+import OpenAI from 'openai';
+import { ChatCompletionMessageParam } from 'openai/resources/chat/completions.js';
+
+// Maximum context tokens
+const MAX_CONTEXT_TOKENS = 200000;
+
+export interface ChatCompletionToolRequest {
+  model?: string;
+  messages: ChatCompletionMessageParam[];
+  temperature?: number;
+}
+
+// Utility function to estimate token count (simplified)
+function estimateTokenCount(text: string): number {
+  // Rough approximation: 4 characters per token
+  return Math.ceil(text.length / 4);
+}
+
+// Truncate messages to fit within the context window
+function truncateMessagesToFit(
+  messages: ChatCompletionMessageParam[], 
+  maxTokens: number
+): ChatCompletionMessageParam[] {
+  const truncated: ChatCompletionMessageParam[] = [];
+  let currentTokenCount = 0;
+
+  // Always include system message first if present
+  if (messages[0]?.role === 'system') {
+    truncated.push(messages[0]);
+    currentTokenCount += estimateTokenCount(messages[0].content as string);
+  }
+
+  // Add messages from the end, respecting the token limit
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i];
+    
+    // Skip if it's the system message we've already added
+    if (i === 0 && message.role === 'system') continue;
+    
+    // For string content, estimate tokens directly
+    if (typeof message.content === 'string') {
+      const messageTokens = estimateTokenCount(message.content);
+      if (currentTokenCount + messageTokens > maxTokens) break;
+      truncated.unshift(message);
+      currentTokenCount += messageTokens;
+    } 
+    // For multimodal content (array), estimate tokens for text content
+    else if (Array.isArray(message.content)) {
+      let messageTokens = 0;
+      for (const part of message.content) {
+        if (part.type === 'text' && part.text) {
+          messageTokens += estimateTokenCount(part.text);
+        } else if (part.type === 'image_url') {
+          // Add a token cost estimate for images - this is a simplification
+          // Actual image token costs depend on resolution and model
+          messageTokens += 1000; 
+        }
+      }
+      
+      if (currentTokenCount + messageTokens > maxTokens) break;
+      truncated.unshift(message);
+      currentTokenCount += messageTokens;
+    }
+  }
+
+  return truncated;
+}
+
+export async function handleChatCompletion(
+  request: { params: { arguments: ChatCompletionToolRequest } },
+  openai: OpenAI,
+  defaultModel?: string
+) {
+  const args = request.params.arguments;
+  
+  // Validate model selection
+  const model = args.model || defaultModel;
+  if (!model) {
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'No model specified and no default model configured in MCP settings. Please specify a model or set OPENROUTER_DEFAULT_MODEL in the MCP configuration.',
+        },
+      ],
+      isError: true,
+    };
+  }
+
+  // Validate message array
+  if (args.messages.length === 0) {
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'Messages array cannot be empty. At least one message is required.',
+        },
+      ],
+      isError: true,
+    };
+  }
+
+  try {
+    // Truncate messages to fit within context window
+    const truncatedMessages = truncateMessagesToFit(args.messages, MAX_CONTEXT_TOKENS);
+
+    const completion = await openai.chat.completions.create({
+      model,
+      messages: truncatedMessages,
+      temperature: args.temperature ?? 1,
+    });
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: completion.choices[0].message.content || '',
+        },
+      ],
+    };
+  } catch (error) {
+    if (error instanceof Error) {
+      return {
+        content: [
+          {
+            type: 'text',
+            text: `OpenRouter API error: ${error.message}`,
+          },
+        ],
+        isError: true,
+      };
+    }
+    throw error;
+  }
+}