"""Generation-based write boundaries. Viewing and role grants are separate."""
from collections import deque

LIMIT = 5


def generations(people, links, self_id):
    ids = {p['id'] for p in people}
    if self_id not in ids:
        return {}, False
    graph = {key: [] for key in ids}
    for edge in links:
        a, b = edge.get('fromId'), edge.get('toId')
        if not edge.get('active') or a not in ids or b not in ids:
            continue
        delta = 1 if edge.get('kind') == 'parent' else 0
        if edge.get('kind') not in ('parent', 'spouse'):
            continue
        graph[a].append((b, delta))
        graph[b].append((a, -delta))
    levels, pending, conflict = {self_id: 0}, deque([self_id]), False
    while pending:
        current = pending.popleft()
        for other, delta in graph[current]:
            level = levels[current] + delta
            if other in levels:
                conflict |= levels[other] != level
            else:
                levels[other] = level
                pending.append(other)
    return levels, conflict


def within(levels, person_id):
    return person_id in levels and abs(levels[person_id]) <= LIMIT


def targets(kind, item):
    if kind == 'person':
        return [item['id']]
    if kind == 'link':
        return [item['fromId'], item['toId']]
    return item.get('personIds', [])