"""
Browsing is never subject to a transfer slot — and is not unbounded either.

**Operator decision, 2026-09-08:** a member must be able to browse a group that
is at capacity exactly as they browse an idle one. Not the poster grid, not the
covers, not opening a photo or a PDF to look at it. §3.4 of
~/next/improve-downloads.md satisfies that structurally: a transfer is what the
transfers widget shows, and nothing else takes a slot.

But "not leased" cannot mean "unbounded". With MNP 3.0 making leases
compulsory, a client that simply omits `tr` would otherwise transfer outside
every cap, and the caps would be decoration — the leaseless branch left
reachable is finding C6's lesson (a transport that accepted a bare token) one
feature later.

So a leaseless read is bounded by a small count of *files in flight*, not by
bytes: a RAW photo out of a camera is 60–80 MB and is browsing, a 40 MB archive
is a download, and no size threshold separates them. What separates them is
which function asked.
"""

from meshbay_node.transfers import (
    LEASELESS_IDLE_SECS, MAX_LEASELESS_IN_FLIGHT, LeaselessReads,
)


def test_a_viewer_looking_at_one_file_is_never_refused():
    reads = LeaselessReads()
    for chunk in range(20):
        assert reads.admit("photo-1", now=float(chunk)) is True


def test_a_second_file_is_allowed_so_prefetching_stays_possible():
    """One is what a viewer needs; two is so the photo viewer can fetch the
    next one while showing this one."""
    reads = LeaselessReads()
    assert reads.admit("photo-1", now=0.0) is True
    assert reads.admit("photo-2", now=0.0) is True


def test_a_third_file_is_refused():
    reads = LeaselessReads()
    reads.admit("a", now=0.0)
    reads.admit("b", now=0.0)
    assert reads.admit("c", now=0.0) is False


def test_a_file_already_being_read_is_never_cut_off():
    """Even once the limit is reached. Refusing a chunk halfway through a photo
    because the count moved would be worse than never having admitted it — the
    viewer would show half an image and no error anyone can act on."""
    reads = LeaselessReads()
    reads.admit("a", now=0.0)
    reads.admit("b", now=0.0)
    assert reads.admit("c", now=0.0) is False
    assert reads.admit("a", now=1.0) is True


def test_finishing_one_frees_it_at_once():
    """The last chunk is the only "close" a leaseless read has. Waiting for the
    idle timeout instead would mean somebody who looked at two photos cannot
    look at a third for a minute."""
    reads = LeaselessReads()
    reads.admit("a", now=0.0)
    reads.admit("b", now=0.0)
    reads.finish("a")
    assert reads.admit("c", now=0.0) is True


def test_a_viewer_closed_mid_file_does_not_hold_its_place_for_ever():
    """It stops asking and says nothing — there is no message for "I closed the
    tab". Without the idle expiry the session would carry two dead entries and
    refuse every later preview, which is the bound turning into a bug."""
    reads = LeaselessReads()
    reads.admit("a", now=0.0)
    reads.admit("b", now=0.0)
    assert reads.admit("c", now=1.0) is False
    assert reads.admit("c", now=LEASELESS_IDLE_SECS + 2) is True


def test_the_bound_is_two():
    """Stated here so that changing it is a decision rather than a typo: it is
    the number §3.4.1 argues for, and the argument is about viewers, not about
    tuning."""
    assert MAX_LEASELESS_IN_FLIGHT == 2