#!/usr/bin/env python3
"""Refresh dependency packages that Decman must ignore to guarantee no removal."""

from __future__ import annotations

import subprocess
from pathlib import Path

import pyalpm

ROOT = Path(__file__).resolve().parents[1]
OUTPUT = ROOT / "packages" / "ignored"


def repository_names(handle: pyalpm.Handle) -> set[str]:
    return {
        package.name
        for database in handle.get_syncdbs()
        for package in database.pkgcache
    }


def deep_orphans(handle: pyalpm.Handle, predicate) -> set[str]:
    local = {package.name: package for package in handle.get_localdb().pkgcache}
    candidates = {
        package.name
        for package in local.values()
        if package.reason == pyalpm.PKG_REASON_DEPEND and predicate(package.name)
    }
    while True:
        retained = {
            name
            for name in candidates
            if not (set(local[name].compute_requiredby()) - candidates)
        }
        if retained == candidates:
            return retained
        candidates = retained


def write(name: str, values: set[str]) -> None:
    (OUTPUT / name).write_text("\n".join(sorted(values)) + "\n", encoding="utf-8")


def main() -> None:
    handle = pyalpm.Handle("/", "/var/lib/pacman")
    repositories = subprocess.run(
        ["pacman-conf", "--repo-list"], check=True, text=True, stdout=subprocess.PIPE
    ).stdout.split()
    for repository in repositories:
        handle.register_syncdb(repository, 0)
    native = repository_names(handle)
    write("repo-dependencies.txt", deep_orphans(handle, lambda name: name in native))
    write("aur-dependencies.txt", deep_orphans(handle, lambda name: name not in native))


if __name__ == "__main__":
    main()