"""Composite writes: a file at the target path is always a complete JPEG.

Every renderer resumes by skipping composites that already exist, so a JPEG cut
short by a kill mid-write would be kept forever.  The real 2024 run was killed
exactly that way when an unrelated process exhausted host memory.
"""

import os

import pytest
from PIL import Image

import bench
import merger_FITS


@pytest.fixture
def composite(monkeypatch):
    monkeypatch.setattr(merger_FITS, "composite_from_arrays",
                        lambda arrays, timestamp: Image.new("RGB", (64, 36), (200, 90, 10)))


def test_a_rendered_composite_is_a_complete_jpeg(tmp_path, composite):
    target = str(tmp_path / "Composite-1.jpg")
    path, error = bench._render_one(([], 1, target))
    assert (path, error) == (target, None)
    with open(target, "rb") as handle:
        data = handle.read()
    assert data[:2] == b"\xff\xd8" and data[-2:] == b"\xff\xd9"
    assert os.listdir(tmp_path) == ["Composite-1.jpg"]


def test_a_write_cut_short_leaves_no_composite(tmp_path, composite, monkeypatch):
    """The interrupted bytes never appear at the target, and nothing is left over."""
    def dies_mid_write(self, fp, format=None, **params):
        with open(fp, "wb") as handle:
            handle.write(b"\xff\xd8 half a jpeg")
        raise OSError("killed")

    monkeypatch.setattr(Image.Image, "save", dies_mid_write)
    target = str(tmp_path / "Composite-1.jpg")
    path, error = bench._render_one(([], 1, target))
    assert path == target and "killed" in error
    assert os.listdir(tmp_path) == []


def test_a_failed_render_never_touches_an_existing_composite(tmp_path, monkeypatch):
    def broken(arrays, timestamp):
        raise ValueError("bad arrays")

    monkeypatch.setattr(merger_FITS, "composite_from_arrays", broken)
    target = tmp_path / "Composite-1.jpg"
    target.write_bytes(b"done")
    _, error = bench._render_one(([], 1, str(target)))
    assert "bad arrays" in error
    assert target.read_bytes() == b"done"
    assert os.listdir(tmp_path) == ["Composite-1.jpg"]