import contextlib
import os
import yaml
import sys

from glob import glob

@contextlib.contextmanager
def pushd(newDir):
    previousDir = os.getcwd()
    os.chdir(newDir)
    try:
        yield

    finally:
        os.chdir(previousDir)

class DependencyException(Exception):
    pass

def deptree(sources, deps=None):
    if deps is None:
        deps = []

    deferred = []
    for name in sources.keys():
        source = sources[name]
        if "depends" not in source:
            deps.append(name)

        else:
            deferred.append(name)

    while deferred:
        name = deferred.pop()
        depends = sources[name]["depends"]
        # todo - detect dependency loop
        if name in depends:
            raise DependencyException('Source {} depends upon itself'.format(name))

        elif set(depends).issubset(set(deps)):
            deps.append(name)

        elif not set(depends).issubset(set(deps)):
            missing = ', '.join(set(depends).difference(set(deps)))
            raise DependencyException(
                    'Source {0} has missing dependencies: {1}'.format(name, missing))

        else:
            deferred.append(name)


    return deps

def main(args):
    with pushd('etc/backup.d'):
        with open("backup.yml") as f:
            config = yaml.load(f)

        sources = {}
        for source in config['sources']:
            source = os.path.realpath(source)
            for path in glob('{}/*.yml'.format(source)):
                path = os.path.realpath(path)
                with pushd(os.path.dirname(path)), open(path) as f:
                    data = yaml.load(f)
                    if "depends" in data:
                        for i in range(0, len(data["depends"])):
                            data["depends"][i] = os.path.realpath('{}.yml'.format(data["depends"][i]))

                    sources[path] = data

    config['sources'] = sources
    import json
    for name in deptree(config["sources"]):
        source = config["sources"][name]
        print(json.dumps(source, indent=2))

if __name__ == '__main__':
    try:
        main(sys.argv[1:])

    except DependencyException as ex:
        print(ex)
        sys.exit(1)

    except Exception:
        from traceback import format_exc
        msg = "Error encountered:\n" + format_exc().strip()
        print(msg)
        sys.exit(1)