"""
The transfer store, which is what keeps a download alive after you leave a group.

Run under Node, because the behaviour worth pinning is timing and lifetime:
that a cancel actually stops the work rather than only greying out a row, that a
stalled transfer reads as slow instead of reporting its historical average, and
that a transport handed over by a departing page is closed by the last transfer
using it — not before, and not never.
"""

import json
import shutil
import subprocess
from pathlib import Path

import pytest

STATIC = Path(__file__).resolve().parents[1] / "src" / "meshbay_hub" / "static"
TRANSFERS = STATIC / "transfers.js"

pytestmark = pytest.mark.skipif(
    shutil.which("node") is None or not TRANSFERS.exists(),
    reason="node or the SPA sources are not available")


def _run(body, tmp_path):
    module = tmp_path / "transfers.mjs"
    module.write_text(TRANSFERS.read_text())
    script = tmp_path / "case.mjs"
    script.write_text(
        f"import {{ TransferStore, formatSpeed }} from '{module.as_posix()}';\n"
        "const out = [];\n"
        "const say = (...a) => out.push(...a);\n"
        f"{body}\n"
        "console.log(JSON.stringify(out));\n")
    proc = subprocess.run(["node", str(script)], capture_output=True, text=True)
    assert proc.returncode == 0, proc.stderr
    return json.loads(proc.stdout)


def test_a_cancel_actually_stops_the_work(tmp_path):
    """
    The flag has to be read by the thing doing the work. A store that only
    marks a row cancelled gives you a button that lies.
    """
    result = _run("""
const store = new TransferStore();
let chunksWritten = 0;
const id = store.start({
  kind: 'download', name: 'big.mp4', total: 100,
  run: async ({ signal, onProgress }) => {
    for (let i = 0; i < 100; i++) {
      if (signal.aborted) throw Object.assign(new Error('stop'), { name: 'AbortError' });
      chunksWritten++;
      onProgress(i + 1, 100);
      await new Promise(r => setTimeout(r, 1));
    }
  },
});
await new Promise(r => setTimeout(r, 20));
store.cancel(id);
await new Promise(r => setTimeout(r, 40));
say(chunksWritten < 100, store.list()[0].status, store.active);
""", tmp_path)
    assert result[0] is True, "the work ran to completion despite being cancelled"
    assert result[1] == "cancelled"
    assert result[2] == 0


def test_speed_is_measured_over_a_window_not_since_the_start(tmp_path):
    """A transfer that stalls should read as slow now, not as its own average."""
    result = _run("""
let clock = 0;
const store = new TransferStore(() => clock);
let report;
store.start({
  kind: 'download', name: 'x', total: 100_000_000,
  run: async ({ onProgress }) => { report = onProgress; await new Promise(() => {}); },
});
await new Promise(r => setTimeout(r, 1));   // start() defers run() by a tick
// A fast megabyte a second, for six seconds.
for (let i = 1; i <= 6; i++) { clock = i * 1000; report(i * 1_000_000, 100_000_000); }
say(Math.round(store.list()[0].speed));
// Then it stalls: the clock moves, the bytes do not.
for (let i = 7; i <= 12; i++) { clock = i * 1000; report(6_000_000, 100_000_000); }
say(Math.round(store.list()[0].speed));
""", tmp_path)
    assert 900_000 <= result[0] <= 1_100_000, f"expected ~1 MB/s, got {result[0]}"
    assert result[1] == 0, f"a stalled transfer still reports {result[1]} B/s"


def test_a_transport_is_closed_by_the_last_transfer_that_needed_it(tmp_path):
    """
    Leaving a group page must not kill a running download, and must not leak
    the connection either.
    """
    result = _run("""
const store = new TransferStore();
let closed = 0;
const transport = { close: () => { closed++; }, onIndexSync: () => {} };
let done1, done2;
store.start({ kind: 'download', name: 'a', transport,
  run: () => new Promise(r => { done1 = r; }) });
store.start({ kind: 'download', name: 'b', transport,
  run: () => new Promise(r => { done2 = r; }) });

store.releaseWhenIdle(transport);          // the page goes away
await new Promise(r => setTimeout(r, 5));
say(closed);                                // still working: must stay open

done1(); await new Promise(r => setTimeout(r, 5));
say(closed);                                // one left: still open

done2(); await new Promise(r => setTimeout(r, 5));
say(closed);                                // now it can go
""", tmp_path)
    assert result == [0, 0, 1], f"close() calls after each step: {result}"


def test_an_idle_transport_is_closed_straight_away(tmp_path):
    result = _run("""
const store = new TransferStore();
let closed = 0;
store.releaseWhenIdle({ close: () => { closed++; } });
say(closed);
""", tmp_path)
    assert result == [1], "leaving a group with nothing running should close it"


def test_signing_out_cancels_everything_and_lets_go(tmp_path):
    """
    Navigating is not signing out. The second one has to stop transfers running
    on tokens that are about to stop being ours.
    """
    result = _run("""
const store = new TransferStore();
let closed = 0;
const transport = { close: () => { closed++; } };
store.start({ kind: 'upload', name: 'a', transport,
  run: () => new Promise(() => {}) });
store.reset();
await new Promise(r => setTimeout(r, 5));
say(store.list().length, closed, store.active);
""", tmp_path)
    assert result == [0, 1, 0]


def test_a_failure_is_kept_and_named(tmp_path):
    """A transfer that dies silently is one the user retries at random."""
    result = _run("""
const store = new TransferStore();
store.start({ kind: 'download', name: 'gone.mp4',
  run: async () => { throw new Error('File not found'); } });
await new Promise(r => setTimeout(r, 5));
const row = store.list()[0];
say(row.status, row.error);
store.clearFinished();
say(store.list().length);
""", tmp_path)
    assert result[0] == "failed"
    assert result[1] == "File not found"
    assert result[2] == 0


def test_the_rate_is_readable(tmp_path):
    result = _run("""
say(formatSpeed(0), formatSpeed(2048), formatSpeed(5 * 1024 * 1024));
""", tmp_path)
    assert result == ["", "2 KB/s", "5.0 MB/s"]


# ── What the widget shows without being opened ──────────────────────────────

APP = STATIC / "app.js"


def _widget() -> str:
    source = APP.read_text(encoding="utf-8")
    start = source.index("function TransferWidget(")
    return source[start:source.index("\nfunction ", start + 1)]


def test_the_widget_marks_itself_while_transfers_run():
    """
    The badge counts them, but a count has to be read. Colour is what says
    "something is moving" from across the room, which is the point of a widget
    that lives in the nav bar rather than on the page.
    """
    widget = _widget()
    assert "running.length ? 'active' : ''" in widget, (
        "the button no longer marks itself while transfers are running")


def test_the_mark_comes_off_when_the_last_one_finishes():
    """`running` is derived from the live list on every render, not stored — so
    there is no state to forget to clear."""
    widget = _widget()
    assert "const running = items.filter(i => i.status === 'running');" in widget


def test_the_colour_is_defined_for_that_mark():
    """The class is set in one file and coloured in another; either alone does
    nothing, and neither fails loudly."""
    css = (STATIC / "style.css").read_text(encoding="utf-8")
    assert ".transfer-btn.active" in css


# ── The file list ───────────────────────────────────────────────────────────

def test_a_folder_name_carries_no_trailing_slash():
    """The folder icon in the cell beside it already says what it is."""
    source = STATIC.joinpath("files-app.js").read_text(encoding="utf-8")
    row = source[source.index('class="file-row dir-row"'):]
    row = row[:row.index("</tr>")]
    assert "${d}/" not in row, "the folder name is rendered with a trailing slash"
    assert "${d}" in row