Initial commit

Signed-off-by: Ilan Bigio <ilan@openai.com>

codex-cli/src/utils/approximate-tokens-used.ts

@@ -0,0 +1,51 @@
+import type { ResponseItem } from "openai/resources/responses/responses.mjs";
+
+/**
+ * Roughly estimate the number of language‑model tokens represented by a list
+ * of OpenAI `ResponseItem`s.
+ *
+ * A full tokenizer would be more accurate, but would add a heavyweight
+ * dependency for only marginal benefit. Empirically, assuming ~4 characters
+ * per token offers a good enough signal for displaying context‑window usage
+ * to the user.
+ *
+ * The algorithm counts characters from the different content types we may
+ * encounter and then converts that char count to tokens by dividing by four
+ * and rounding up.
+ */
+export function approximateTokensUsed(items: Array<ResponseItem>): number {
+  let charCount = 0;
+
+  for (const item of items) {
+    switch (item.type) {
+      case "message": {
+        for (const c of item.content) {
+          if (c.type === "input_text" || c.type === "output_text") {
+            charCount += c.text.length;
+          } else if (c.type === "refusal") {
+            charCount += c.refusal.length;
+          } else if (c.type === "input_file") {
+            charCount += c.filename?.length ?? 0;
+          }
+          // images and other content types are ignored (0 chars)
+        }
+        break;
+      }
+
+      case "function_call": {
+        charCount += (item.name?.length || 0) + (item.arguments?.length || 0);
+        break;
+      }
+
+      case "function_call_output": {
+        charCount += item.output.length;
+        break;
+      }
+
+      default:
+        break;
+    }
+  }
+
+  return Math.ceil(charCount / 4);
+}