feat: add language detector

src/index.ts

@@ -9,6 +9,7 @@ import { contextRegistry } from "./introspection/contextRegistry";
 import { ModelRouter } from "./router/modelRouter";
 import { ModelRouterOptions, ApiKeyConfig } from "./router/types";
 import { apiKeyManager } from "./router/apiKeyManager";
+import { detectLanguage } from "./router/languageDetector";
 
 let globalBudgetManager: BudgetManager | null = null;
 let globalModelRouter: ModelRouter | null = null;
@@ -228,6 +229,8 @@ export async function listModels(options: Omit<ListModelsOptions, 'budgetManager
 // Keep the original export for backward compatibility
 export { listAvailableModels };
 
+export { detectLanguage };
+
 // Export types for TypeScript users
 export type {
   BudgetGuardOptions,
@@ -252,6 +255,8 @@ export type {
   ApiKeyConfig
 } from "./router/types";
 
+export type { LanguageDetectionResult } from "./router/languageDetector";
+
 /**
  * Model configuration for bulk registration
  */

src/router/languageDetector.ts

@@ -0,0 +1,124 @@
+export interface LanguageDetectionResult {
+  language: string;
+  confidence: number;
+  matchedSignals: string[];
+}
+
+interface LanguageRule {
+  language: string;
+  patterns: RegExp[];
+  keywords: string[];
+}
+
+const MAX_SCAN_LENGTH = 12000;
+
+const LANGUAGE_RULES: LanguageRule[] = [
+  {
+    language: "typescript",
+    patterns: [/\binterface\s+\w+/i, /\btype\s+\w+\s*=/i, /:\s*(string|number|boolean)\b/i],
+    keywords: ["typescript", "tsx", "tsconfig", "readonly", "implements"]
+  },
+  {
+    language: "javascript",
+    patterns: [/\bconst\s+\w+\s*=/i, /\bfunction\s+\w+\s*\(/i, /=>\s*[{(]/],
+    keywords: ["javascript", "node", "react", "promise", "async"]
+  },
+  {
+    language: "python",
+    patterns: [/\bdef\s+\w+\s*\(/i, /\bimport\s+\w+/i, /\bclass\s+\w+:/i],
+    keywords: ["python", "pytest", "django", "flask", "pandas"]
+  },
+  {
+    language: "go",
+    patterns: [/\bpackage\s+\w+/i, /\bfunc\s+\w+\s*\(/i, /\bgo\s+test\b/i],
+    keywords: ["golang", "goroutine", "gofmt", "interface{}", "go.mod"]
+  },
+  {
+    language: "rust",
+    patterns: [/\bfn\s+\w+\s*\(/i, /\blet\s+mut\b/i, /\bimpl\s+\w+/i],
+    keywords: ["rust", "cargo", "borrow", "trait", "lifetime"]
+  },
+  {
+    language: "sql",
+    patterns: [/\bselect\s+.+\s+from\b/i, /\binsert\s+into\b/i, /\bwhere\s+\w+\s*=/i],
+    keywords: ["sql", "postgres", "mysql", "sqlite", "query"]
+  },
+  {
+    language: "shell",
+    patterns: [/#!\/(?:usr\/bin\/env\s+)?(?:ba|z)?sh/i, /\bnpm\s+(ci|run)\b/i, /\bdocker\s+compose\b/i],
+    keywords: ["bash", "shell", "terminal", "cli", "docker"]
+  },
+  {
+    language: "markdown",
+    patterns: [/^#{1,6}\s+\S/m, /\[[^\]]+\]\([^)]+\)/, /```[\s\S]*?```/],
+    keywords: ["markdown", "readme", "mdx", "frontmatter", "table"]
+  }
+];
+
+export function detectLanguage(input: unknown): LanguageDetectionResult {
+  const text = extractText(input).slice(0, MAX_SCAN_LENGTH);
+  const normalized = text.toLowerCase();
+
+  if (!normalized.trim()) {
+    return { language: "unknown", confidence: 0, matchedSignals: [] };
+  }
+
+  const ranked = LANGUAGE_RULES
+    .map(rule => {
+      const matchedPatterns = rule.patterns
+        .filter(pattern => pattern.test(text))
+        .map(pattern => pattern.source);
+      const matchedKeywords = rule.keywords
+        .filter(keyword => normalized.includes(keyword.toLowerCase()));
+      const score = matchedPatterns.length * 2 + matchedKeywords.length;
+
+      return {
+        language: rule.language,
+        score,
+        matchedSignals: [...matchedKeywords, ...matchedPatterns]
+      };
+    })
+    .sort((a, b) => b.score - a.score);
+
+  const best = ranked[0];
+  if (!best || best.score === 0) {
+    return { language: "unknown", confidence: 0.15, matchedSignals: [] };
+  }
+
+  return {
+    language: best.language,
+    confidence: Math.min(0.98, 0.3 + best.score * 0.12),
+    matchedSignals: best.matchedSignals
+  };
+}
+
+function extractText(value: unknown): string {
+  if (!value) {
+    return "";
+  }
+
+  if (typeof value === "string") {
+    return value;
+  }
+
+  if (Array.isArray(value)) {
+    return value.map(extractText).filter(Boolean).join(" ");
+  }
+
+  if (typeof value !== "object") {
+    return "";
+  }
+
+  const record = value as Record<string, unknown>;
+  return [
+    record.prompt,
+    record.input,
+    record.query,
+    record.text,
+    record.content,
+    record.messages
+  ]
+    .map(extractText)
+    .filter(Boolean)
+    .join(" ");
+}

tests/language-detector.test.js

@@ -0,0 +1,50 @@
+const assert = require("assert");
+const { detectLanguage } = require("../dist/index.js");
+
+const cases = [
+  {
+    name: "detects TypeScript from typed declarations",
+    input: "interface User { id: string; active: boolean }",
+    language: "typescript"
+  },
+  {
+    name: "detects Python from function syntax",
+    input: "def normalize_user(row):\n    import pandas as pd\n    return row",
+    language: "python"
+  },
+  {
+    name: "detects Go from package and func syntax",
+    input: "package main\n\nfunc handler() error { return nil }",
+    language: "go"
+  },
+  {
+    name: "detects SQL from query shape",
+    input: "SELECT id, email FROM users WHERE active = true",
+    language: "sql"
+  },
+  {
+    name: "extracts nested chat messages",
+    input: {
+      messages: [
+        { role: "user", content: "Please fix this pytest failure in my Flask app" }
+      ]
+    },
+    language: "python"
+  }
+];
+
+for (const testCase of cases) {
+  const result = detectLanguage(testCase.input);
+  assert.equal(result.language, testCase.language, testCase.name);
+  assert(result.confidence > 0.3, `${testCase.name} should be confident`);
+  assert(result.matchedSignals.length > 0, `${testCase.name} should include signals`);
+}
+
+const unknown = detectLanguage("Can you help me think through this vague idea?");
+assert.equal(unknown.language, "unknown");
+assert(unknown.confidence > 0);
+
+const bounded = detectLanguage(`${"x".repeat(20000)} def late_signal(): pass`);
+assert.equal(bounded.language, "unknown");
+
+console.log("language-detector tests passed");