1 files changed, 90 insertions, 0 deletions
diff --git a/src/profile/launch.ts b/src/profile/launch.ts
new file mode 100644
index 0000000..4f8f65a
--- /dev/null
+++ b/src/profile/launch.ts
@@ -0,0 +1,90 @@
+/**
+ * Opening a browser window for a chosen profile.
+ *
+ * CDP cannot do this: `Target.createTarget` rejects another profile's
+ * browserContextId ("Failed to find browser context with id"), and a bare
+ * createTarget lands in `defaultBrowserContextId`, which follows window focus.
+ * The only way in is the browser's own command line — Chromium's
+ * ProcessSingleton hands a second launch's argv to the running browser, which
+ * "does what it would have done", i.e. opens a window in `--profile-directory`.
+ *
+ * The window is then identified by a unique `file://` sentinel page. That
+ * matters: a bare `about:blank#token` argument is discarded by Chrome (it opens
+ * chrome://newtab instead), so the token has to ride on a real URL. Polling for
+ * the sentinel URL — rather than diffing the target list — also keeps
+ * identification correct when the user opens tabs at the same moment.
+ */
+
+import { spawn } from "node:child_process";
+import { randomUUID } from "node:crypto";
+import { rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { pathToFileURL } from "node:url";
+import { type Result, err, ok } from "../util/result";
+
+export type ProfileWindowRequest = {
+  /** Browser binary to invoke. */
+  readonly exePath: string;
+  /** Profile subdirectory, e.g. "Profile 1". */
+  readonly profileDir: string;
+  /**
+   * Only set when the RUNNING browser was launched with an explicit
+   * --user-data-dir. ProcessSingleton keys on this path, so passing one that
+   * differs by case or normalisation would start a second browser instead of
+   * delegating to the running one.
+   */
+  readonly explicitUserDataDir?: string;
+};
+
+export type ProfileWindowHandle = {
+  /** file:// URL that will appear as the new window's page target. */
+  readonly sentinelUrl: string;
+  /** Remove the sentinel file. Safe to call more than once. */
+  readonly cleanup: () => Promise<void>;
+};
+
+const SENTINEL_HTML = (token: string): string =>
+  `<!doctype html><meta charset="utf-8"><title>${token}</title>` +
+  `<body style="font:14px system-ui;padding:2rem;color:#555">pi browser harness — opening this profile…</body>`;
+
+/**
+ * Ask the running browser to open a window in `profileDir`, marked with a
+ * unique sentinel page the caller can then find over CDP.
+ */
+export const openProfileWindow = async (
+  req: ProfileWindowRequest,
+): Promise<Result<ProfileWindowHandle, string>> => {
+  const token = `pi-harness-${randomUUID()}`;
+  const file = join(tmpdir(), `${token}.html`);
+  try {
+    await writeFile(file, SENTINEL_HTML(token), "utf8");
+  } catch (e) {
+    return err(`could not write the profile handshake page: ${e instanceof Error ? e.message : String(e)}`);
+  }
+
+  const sentinelUrl = pathToFileURL(file).href;
+  const args: string[] = [];
+  if (req.explicitUserDataDir) args.push(`--user-data-dir=${req.explicitUserDataDir}`);
+  args.push(`--profile-directory=${req.profileDir}`, "--new-window", sentinelUrl);
+
+  try {
+    // No shell: arguments are passed as an array, so profile names and paths
+    // containing spaces survive intact on every platform.
+    const child = spawn(req.exePath, args, { detached: true, stdio: "ignore" });
+    child.unref();
+    // The launcher process exits as soon as the running browser takes over the
+    // command line; an error here means the binary itself could not be started.
+    child.on("error", () => {});
+  } catch (e) {
+    await rm(file, { force: true }).catch(() => {});
+    return err(`could not launch ${req.exePath}: ${e instanceof Error ? e.message : String(e)}`);
+  }
+
+  return ok({
+    sentinelUrl,
+    cleanup: async () => {
+      await rm(file, { force: true }).catch(() => {});
+    },
+  });
+};