import os, shutil
browser_stack = os.path.expanduser('~/.cache/browser-stack')

def get_stack():
    try:
        with open(browser_stack, 'r') as stack_file:
            return stack_file.readlines()
    except IOError: # No such file
        return []

def save_stack(stack):
    os.umask(0o066) # octal -rw-------
    with open(browser_stack+'.tmp', 'w') as stack_file:
        stack_file.writelines(stack)
    shutil.copy(browser_stack+'.tmp', browser_stack)
    os.remove(browser_stack+'.tmp')

def set_current_browser():
    stack = get_stack()
    if stack:
        os.environ['BROWSER'] = browser = stack[0].strip()
        return browser