export const LAUNCHER_MODE_FLAGS = new Set(["--web", "--cli", "--tui"]);

export type LauncherMode = "web" | "cli" | "tui";

export type ParseLauncherArgvResult = {
  mode: LauncherMode;
  forwardedArgv: string[];
  hasPrefixModeFlag: boolean;
};

/**
 * Launcher mode flags are read only from a contiguous prefix of user args
 * (argv[2…]). Everything after the first non-mode token is forwarded
 * unchanged so values like `--cli` can appear in app/server config.
 */
export function parseLauncherArgv(argv: string[]): ParseLauncherArgvResult {
  const executable = argv.slice(0, 2);
  const userArgs = argv.slice(2);

  const prefixFlags: string[] = [];
  let index = 0;
  while (index < userArgs.length && LAUNCHER_MODE_FLAGS.has(userArgs[index]!)) {
    prefixFlags.push(userArgs[index]!);
    index++;
  }

  if (prefixFlags.length > 1) {
    throw new Error("Specify at most one of --web, --cli, or --tui.");
  }

  const mode: LauncherMode =
    prefixFlags[0] === "--tui"
      ? "tui"
      : prefixFlags[0] === "--cli"
        ? "cli"
        : "web";

  return {
    mode,
    forwardedArgv: [...executable, ...userArgs.slice(index)],
    hasPrefixModeFlag: prefixFlags.length > 0,
  };
}