"""Era rollups: only re-digest months whose session count changed (incremental)."""
from __future__ import annotations

import importlib

import pytest

from lyra.memory import Era


@pytest.fixture
def era(monkeypatch):
    import lyra.era as era
    importlib.reload(era)
    return era


def test_rebuild_eras_is_incremental(era, monkeypatch):
    by_month = {"2025-01": ["a", "b"], "2025-02": ["c"]}
    stored: dict[str, int] = {}
    built: list[str] = []

    monkeypatch.setattr(era.memory, "summaries_by_month", lambda: dict(by_month))
    monkeypatch.setattr(era.memory, "list_eras",
                        lambda: [Era(m, "x", c, "t") for m, c in stored.items()])
    monkeypatch.setattr(era.memory, "store_era",
                        lambda month, content, n: (stored.__setitem__(month, n), built.append(month)))
    monkeypatch.setattr(era, "_digest_month", lambda gists, backend: "digest")  # no LLM

    r1 = era.rebuild_eras(backend="local")               # first pass: both built
    assert r1["built"] == 2 and r1["skipped"] == 0

    built.clear()
    r2 = era.rebuild_eras(backend="local")               # nothing changed: all skipped
    assert r2["built"] == 0 and r2["skipped"] == 2 and built == []

    built.clear()
    by_month["2025-02"].append("d")                       # one month gains a session
    r3 = era.rebuild_eras(backend="local")
    assert r3["built"] == 1 and r3["skipped"] == 1 and built == ["2025-02"]

    built.clear()
    r4 = era.rebuild_eras(backend="local", force=True)   # force rebuilds all
    assert r4["built"] == 2