import asyncio
from datetime import datetime
from pathlib import Path
from typing import Sequence

import pytest

from py.services.downloader import Downloader


class FakeStream:
    def __init__(self, chunks: Sequence[Sequence] | Sequence[bytes]):
        self._chunks = list(chunks)

    async def read(self, _chunk_size: int) -> bytes:
        if not self._chunks:
            await asyncio.sleep(0)
            return b""

        item = self._chunks.pop(0)
        delay = 0.0
        payload = item

        if isinstance(item, tuple):
            payload = item[0]
            delay = item[1]

        await asyncio.sleep(delay)
        return payload


class FakeResponse:
    def __init__(self, status, headers, chunks):
        self.status = status
        self.headers = headers
        self.content = FakeStream(chunks)

    async def __aenter__(self):
        return self

    async def __aexit__(self, exc_type, exc, tb):
        return False


class FakeSession:
    def __init__(self, responses):
        self._responses = list(responses)
        self._get_calls = 0

    def get(self, url, headers=None, allow_redirects=True, proxy=None):  # noqa: D401 - signature mirrors aiohttp
        del url, headers, allow_redirects, proxy
        response_factory = self._responses[self._get_calls]
        self._get_calls += 1
        return response_factory()

    async def close(self):
        return None


def _build_downloader(responses, *, max_retries=0):
    downloader = Downloader()
    downloader.max_retries = max_retries
    downloader.base_delay = 0
    fake_session = FakeSession(responses)
    downloader._session = fake_session
    downloader._session_created_at = datetime.now()
    downloader._proxy_url = None
    async def _noop_create_session():
        downloader._session = fake_session
        downloader._session_created_at = datetime.now()
        downloader._proxy_url = None

    downloader._create_session = _noop_create_session  # type: ignore[assignment]
    return downloader


@pytest.mark.asyncio
async def test_download_file_fails_when_size_mismatch(tmp_path):
    target_path = tmp_path / "model" / "file.bin"
    target_path.parent.mkdir()

    responses = [
        lambda: FakeResponse(
            status=200,
            headers={"content-length": "10"},
            chunks=[b"abc"],
        )
    ]

    downloader = _build_downloader(responses)

    success, message = await downloader.download_file("https://example.com/file", str(target_path))

    assert success is False
    assert "mismatch" in message.lower()
    assert not target_path.exists()
    assert not Path(str(target_path) + ".part").exists()


@pytest.mark.asyncio
async def test_download_file_fails_when_zero_bytes(tmp_path):
    target_path = tmp_path / "model" / "file.bin"
    target_path.parent.mkdir()

    responses = [
        lambda: FakeResponse(
            status=200,
            headers={"content-length": "0"},
            chunks=[],
        )
    ]

    downloader = _build_downloader(responses)

    success, message = await downloader.download_file("https://example.com/file", str(target_path))

    assert success is False
    assert "empty" in message.lower()
    assert not target_path.exists()
    assert not Path(str(target_path) + ".part").exists()


@pytest.mark.asyncio
async def test_download_file_succeeds_when_sizes_match(tmp_path):
    target_path = tmp_path / "model" / "file.bin"
    target_path.parent.mkdir()

    payload = b"abcdef"
    responses = [
        lambda: FakeResponse(
            status=200,
            headers={"content-length": str(len(payload))},
            chunks=[payload],
        )
    ]

    downloader = _build_downloader(responses)

    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))

    assert success is True
    assert Path(result_path).read_bytes() == payload
    assert not Path(str(target_path) + ".part").exists()


@pytest.mark.asyncio
async def test_download_file_recovers_from_stall(tmp_path):
    target_path = tmp_path / "model" / "file.bin"
    target_path.parent.mkdir()

    payload = b"abcdef"

    responses = [
        lambda: FakeResponse(
            status=200,
            headers={"content-length": str(len(payload))},
            chunks=[(b"abc", 0.0), (b"def", 0.1)],
        ),
        lambda: FakeResponse(
            status=206,
            headers={"content-length": "3", "Content-Range": "bytes 3-5/6"},
            chunks=[(b"def", 0.0)],
        ),
    ]

    downloader = _build_downloader(responses, max_retries=1)
    downloader.stall_timeout = 0.05

    success, result_path = await downloader.download_file("https://example.com/file", str(target_path))

    assert success is True
    assert Path(result_path).read_bytes() == payload
    assert downloader._session._get_calls == 2
    assert not Path(str(target_path) + ".part").exists()