import fs from 'fs';

import * as os from 'os';

interface ResolveUserShellDeps {

userInfo?: () => { shell: string | null | undefined };

env?: NodeJS.ProcessEnv;

platform?: NodeJS.Platform;

canUseShell?: (shell: string) => boolean;

}

function normalizeShell(shell: string | null | undefined): string | null {

const value = shell?.trim();

return value ? value : null;

}

function isExecutablePosixShell(shell: string): boolean {

try {

fs.accessSync(shell, fs.constants.X_OK);

return true;

} catch {

return false;

}

}

export function resolveUserShell(deps: ResolveUserShellDeps = {}): string {

const env = deps.env ?? process.env;

const platform = deps.platform ?? process.platform;

const userInfo = deps.userInfo ?? os.userInfo;

const canUseShell =

deps.canUseShell ?? ((shell: string) => platform === 'win32' || isExecutablePosixShell(shell));

try {

const osShell = normalizeShell(userInfo().shell);

if (osShell && canUseShell(osShell)) return osShell;

} catch {

// Fall back to inherited environment if the OS lookup is unavailable.

}

const envShell = normalizeShell(env.SHELL);

if (envShell && canUseShell(envShell)) return envShell;

return platform === 'win32' ? 'cmd.exe' : '/bin/sh';

}