"""U10-1: resuming a Tracker after a torn tail must not glue records."""
import pytest

from align.utils import tracking
from align.utils.tracking import Tracker, read_history


def _torn_then_resume(tmp_path, tail):
    t = Tracker(str(tmp_path), "sft")
    t.log(1, loss=0.5)
    t.log(2, loss=0.6)
    t.finish()
    with open(t.history_path, "a") as fh:
        fh.write(tail)  # kill mid-append: no trailing newline
    t2 = Tracker(str(tmp_path), "sft")
    t2.log(3, loss=0.8)
    t2.log(4, loss=0.9)
    t2.finish()


def test_resume_after_torn_tail_keeps_history_readable(tmp_path):
    _torn_then_resume(tmp_path, '{"step": 3, "stage": "sft", "lo')
    assert [r["step"] for r in read_history(str(tmp_path))] == [1, 2, 3, 4]


def test_resume_after_complete_record_missing_newline_keeps_it(tmp_path):
    _torn_then_resume(tmp_path, '{"step": 9, "stage": "sft", "loss": 0.1}')
    assert [r["step"] for r in read_history(str(tmp_path))] == [1, 2, 9, 3, 4]


def test_resume_when_whole_file_is_one_torn_line(tmp_path):
    (tmp_path / "history.jsonl").write_text('{"step": 1, "lo')
    t = Tracker(str(tmp_path), "sft")
    t.log(2, loss=0.1)
    t.finish()
    assert [r["step"] for r in read_history(str(tmp_path))] == [2]