import sys

from os.path import isfile
from . import cli


def write_graph(gen_g, filename=None, force_write=False):
    if filename is not None:
        if force_write or not isfile(filename):
            g = gen_g()
            bs = g.serialize(encoding='utf-8', format='turtle')
            with open(filename, "wb") as f:
                f.write(bs)
            cli.info("Wrote %s" % filename)
        else:
            cli.info("Skipped writing %s, already exists" % filename)
    else:
        g = gen_g()
        bs = g.serialize(encoding='utf-8', format='turtle')
        sys.stdout.buffer.write(bs)