from __future__ import annotations
from collections import Counter
from dataclasses import dataclass
from typing import List
from .models import WorkingWithRelation


@dataclass
class DepartmentLink:
    source_department: str
    destination_department: str
    weight: int


def aggregate_department_links(relations: List[WorkingWithRelation]) -> List[DepartmentLink]:
    counter: Counter[tuple[str, str]] = Counter()
    for rel in relations:
        src = (rel.source.department or "").strip()
        dst = (rel.destination.department or "").strip()
        if not src or not dst:
            continue
        counter[(src, dst)] += 1

    links: List[DepartmentLink] = [
        DepartmentLink(source_department=s, destination_department=d, weight=w)
        for (s, d), w in counter.items()
    ]
    return sorted(links, key=lambda l: l.weight, reverse=True)