import os

def parse_config():
    em_config_file = os.getenv('EM_CONFIG') or os.path.expanduser('~/.emscripten')
    if not os.path.exists(em_config_file):
        raise RuntimeError("Emscripten configuration file '%s' does not exist" % em_config_file)

    normalized = {}
    em_config = {}
    with open(em_config_file) as f:
        try:
            # Emscripten configuration file is a Python file with simple assignments.
            exec(f.read(), em_config)
        except StandardError as e:
            raise RuntimeError("Emscripten configuration file '%s' is invalid:\n%s" % (em_config_file, e))
    normalized['EMCC_ROOT'] = em_config.get('EMSCRIPTEN_ROOT')
    normalized['NODE_JS'] = em_config.get('NODE_JS')
    normalized['CLOSURE_BIN'] = os.path.join(normalized['EMCC_ROOT'], 'node_modules', '.bin', 'google-closure-compiler')
    return normalized


def run_closure_compiler(target, source, env, for_signature):
    cfg = parse_config()
    cmd = [cfg['NODE_JS'], cfg['CLOSURE_BIN']]
    cmd.extend(['--compilation_level', 'ADVANCED_OPTIMIZATIONS'])
    for f in env['JSEXTERNS']:
        cmd.extend(['--externs', f.get_abspath()])
    for f in source:
        cmd.extend(['--js', f.get_abspath()])
    cmd.extend(['--js_output_file', target[0].get_abspath()])
    return ' '.join(cmd)


def create_engine_file(env, target, source, externs):
    if env['use_closure_compiler']:
        return env.BuildJS(target, source, JSEXTERNS=externs)
    return env.Textfile(target, [env.File(s) for s in source])
