"""
Where downloads are written.

The module is mostly browser plumbing — a directory handle from a picker, kept
in IndexedDB — but two pieces decide behaviour and can be checked here: that
automatic is the default, and that writing into the same folder repeatedly does
not quietly replace what is already there. The second one is the whole risk of
the automatic mode: a Save As dialog warns you about a collision, and a folder
you never look at does not.
"""

import json
import shutil
import subprocess
from pathlib import Path

import pytest

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

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


def _run(body, tmp_path):
    module = tmp_path / "downloads.mjs"
    module.write_text(DOWNLOADS.read_text())
    script = tmp_path / "case.mjs"
    script.write_text(
        # A localStorage good enough for a preference, so the module can be
        # imported outside a browser at all.
        "const store = new Map();\n"
        "globalThis.localStorage = {\n"
        "  getItem: k => (store.has(k) ? store.get(k) : null),\n"
        "  setItem: (k, v) => store.set(k, String(v)),\n"
        "};\n"
        f"const M = await import('{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_saving_automatically_is_the_default(tmp_path):
    """
    Grouped downloads are the reason this setting exists: twelve files must not
    mean twelve dialogs unless someone asked for that.
    """
    assert _run("say(M.getMode());", tmp_path) == ["auto"]


def test_the_choice_is_remembered_and_nothing_else_is_accepted(tmp_path):
    result = _run("""
M.setMode('ask');   say(M.getMode());
M.setMode('auto');  say(M.getMode());
M.setMode('nonsense'); say(M.getMode());
""", tmp_path)
    assert result == ["ask", "auto", "auto"]


def test_a_second_copy_does_not_replace_the_first(tmp_path):
    result = _run("""
const taken = new Set(['clip.mp4', 'clip (2).mp4', 'notes']);
const exists = async n => taken.has(n);
say(await M.freeName('clip.mp4', exists));
say(await M.freeName('other.mp4', exists));
say(await M.freeName('notes', exists));
say(await M.freeName('archive.tar.gz', exists));
""", tmp_path)
    assert result == [
        "clip (3).mp4",      # (2) was taken as well
        "other.mp4",         # free: left alone
        "notes (2)",         # no extension to keep
        "archive.tar.gz",    # free, and the double extension is not mangled
    ]


def test_the_suffix_goes_before_the_extension(tmp_path):
    """
    "clip.mp4 (2)" would stop being a video as far as the operating system is
    concerned, which is how a download folder ends up full of files nothing opens.
    """
    result = _run("""
say(await M.freeName('clip.mp4', async () => false));
say(await M.freeName('clip.mp4', async n => n === 'clip.mp4'));
""", tmp_path)
    assert result == ["clip.mp4", "clip (2).mp4"]


def test_a_browser_without_the_api_reports_it(tmp_path):
    """`SUPPORTED` decides whether Settings offers a choice or an explanation."""
    assert _run("say(M.SUPPORTED);", tmp_path) == [False]


def test_the_open_action_reads_the_file_back(tmp_path):
    """
    "Open" is the browser being handed the bytes, not a desktop application
    being started — no web page can do the second, and none can show a file
    manager either. It is only offered for a file written into a granted folder,
    since that is the one a page can read back.
    """
    src = DOWNLOADS.read_text()
    target = src[src.index("export async function openTarget"):]
    assert "getFile()" in target and "window.open(" in target
    assert "revokeObjectURL" in target, "the blob URL must not be leaked"


# ── Streaming to disk without the File System Access API ────────────────────

SW = STATIC / "sw.js"


def test_the_worker_only_answers_its_own_urls():
    """
    It is registered at the root scope, so it sees every request the page makes.
    Anything that is not a download of ours has to fall through untouched — a
    service worker that answers more than it should is a cache bug waiting to
    happen.
    """
    src = SW.read_text()
    assert "startsWith(PREFIX)" in src
    assert "self.location.origin" in src, "cross-origin requests must fall through"
    # The API, not the word: the file explains in prose that it caches nothing.
    for api in ("caches.open", "caches.match", "cache.put"):
        assert api not in src, f"this worker must not cache anything ({api})"


def test_the_download_is_announced_as_an_attachment():
    src = SW.read_text()
    assert "Content-Disposition" in src and "attachment" in src
    assert "filename*=UTF-8''" in src, "a name with accents would be mangled"
    assert "Content-Length" in src


def test_a_length_is_only_promised_when_it_is_known(tmp_path):
    """
    An archive is assembled as it goes and is larger than the files in it.
    Announcing the sum of their sizes would truncate the download at that mark.
    """
    src = SW.read_text()
    assert "if (entry.size > 0)" in src

    app = (STATIC / "app.js").read_text()
    zip_call = app[app.index("const target = await _openDownloadTarget(suggested"):]
    zip_call = zip_call[:zip_call.index(");") + 2]
    assert zip_call.rstrip().endswith(", 0);"), (
        "the zip download announces a Content-Length it will not match")


def test_backpressure_is_real(tmp_path):
    """
    The point of the service worker path is not holding the file. A stream that
    is transferred gives `writer.write()` something to wait on; posting chunks
    to a port would queue them in memory and look identical from here.
    """
    src = DOWNLOADS.read_text()
    fn = src[src.index("export async function openStreamedDownload"):]
    assert "new TransformStream()" in fn
    assert "[readable]" in fn, "the readable half must be transferred, not copied"
    assert "writer.write(bytes)" in fn
    assert "return null" in fn, "a browser that cannot transfer streams must say so"