"""Test for s7."""
import psycopg2


class Relations(object):
    """Wrapper class to iterate db rows as sets."""

    def __init__(self):
        """Setting up a cursor."""
        self.connection = psycopg2.connect('dbname=test user=postgres')
        self.cursor = self.connection.cursor('components')  # serverside cursor
        self.cursor.execute(
            'SELECT object_id, relative_ids FROM relations;'
        )

    def __iter__(self):
        """Iterator interface."""
        return self

    def __next__(self):
        """Python 3 compatibiliy."""
        return self.next()

    def next(self):
        """Next row as combined set."""
        # next() call will raise StopIteration on cursor exhaustion,
        # no need to wrap that since for-loop will handle it by itself
        # but we want to free resources as soon as possible.
        try:
            object_id, relations = next(self.cursor)
        except StopIteration:
            self.cursor.close()
            self.connection.close()
            raise

        return set([object_id] + relations)

    def __del__(self):
        """Free resources on gc."""
        self.cursor.close()
        self.connection.close()


class Ids(object):
    """Wrapper class to iterate db rows as single integers."""

    def __init__(self):
        """Setting up a cursor."""
        self.connection = psycopg2.connect('dbname=test user=postgres')
        self.cursor = self.connection.cursor('ids')  # serverside cursor
        self.cursor.execute('SELECT id FROM objects;')

    def __iter__(self):
        """Iterator interface."""
        return self

    def __next__(self):
        """Python 3 compatibiliy."""
        return self.next()

    def next(self):
        """Next row as combined set."""
        # next() call will raise StopIteration on cursor exhaustion,
        # no need to wrap that since for-loop will handle it by itself
        # but we have to free connection as soon as possible.
        ident = next(self.cursor)
        return ident[0]

    def __del__(self):
        """Free resources on gc."""
        self.cursor.close()
        self.connection.close()


def make_components(relations):
    """Return list of components (sets) from relations list of sets."""
    components = []
    for relation in relations:
        merged = True
        while merged:
            merged = False
            for index, component in enumerate(components):
                if relation & component:
                    relation |= components.pop(index)
                    merged = True
                    break
        components.append(relation)
    return components


def include_ids(ids, components):
    """Add id as sole-value component if one not found in relations."""
    for ident in ids:
        not_found = True
        for component in components:
            if ident in component:
                not_found = False
                break
        if not_found:
            components.append({ident})
    return components

relations = Relations()
components = make_components(relations)
ids = Ids()
components = include_ids(ids, components)

# components have not to intersect
assert all((
    (not a & b)
    for ia, a in enumerate(components)
    for ib, b in enumerate(components)
    if ia != ib
)), [  # Assertion error output
    (a, b, a & b)
    for ia, a in enumerate(components)
    for ib, b in enumerate(components)
    if ia != ib and a & b
]
# all ids have to take part in components, even empty ones
assert ids == set.union(*components), (ids, set.union(*components))