"""Unit tests for the response transport codec (compression + msgpack)."""
import base64
import json

import pytest

from browser_cli import transport

def _sample(n=200):
    return {
        "id": "abc",
        "success": True,
        "data": {"items": [{"url": f"https://example.com/{i}", "title": f"Tab {i}"} for i in range(n)]},
    }

# ── backward compatibility ──────────────────────────────────────────────────────

def test_no_accept_encoding_returns_bare_json():
    obj = _sample()
    enc = transport.encode_response(obj, accept=None)
    assert enc == json.dumps(obj).encode("utf-8")  # byte-identical to old wire format
    assert enc[:1] in (b"{", b"[")

def test_empty_accept_returns_bare_json():
    obj = _sample()
    assert transport.encode_response(obj, accept={}) == json.dumps(obj).encode("utf-8")

def test_decode_plain_json_without_tag():
    obj = _sample()
    assert transport.decode_response(json.dumps(obj).encode("utf-8")) == obj

def test_decode_none_and_empty():
    assert transport.decode_response(None) is None
    with pytest.raises(ValueError):
        transport.decode_response(b"")

# ── compression roundtrips ───────────────────────────────────────────────────────

@pytest.mark.parametrize("comp", ["zlib", "gzip", "zstd"])
def test_compression_roundtrip(comp):
    if comp == "zstd" and not transport.zstd_available():
        pytest.skip("zstandard not installed")
    obj = _sample()
    enc = transport.encode_response(obj, accept={"ser": ["json"], "comp": [comp]})
    assert enc[:1] not in (b"{", b"[")  # tagged, not plain
    assert len(enc) < len(json.dumps(obj))  # actually smaller
    assert transport.decode_response(enc) == obj

def test_small_payload_not_compressed():
    obj = {"id": "x", "success": True, "data": "ok"}
    enc = transport.encode_response(obj, accept={"ser": ["json"], "comp": ["zlib"]}, threshold=512)
    assert enc == json.dumps(obj).encode("utf-8")  # below threshold → bare json

def test_unknown_compression_in_accept_falls_back_to_plain():
    obj = _sample()
    enc = transport.encode_response(obj, accept={"ser": ["json"], "comp": ["brotli"]})
    assert enc == json.dumps(obj).encode("utf-8")

# ── msgpack ──────────────────────────────────────────────────────────────────────

def test_msgpack_roundtrip():
    if not transport.msgpack_available():
        pytest.skip("msgpack not installed")
    obj = _sample()
    enc = transport.encode_response(obj, accept={"ser": ["msgpack"], "comp": []})
    assert enc[0] >> 4 == transport.SER_MSGPACK
    assert transport.decode_response(enc) == obj

def test_msgpack_with_compression_roundtrip():
    if not (transport.msgpack_available() and transport.zstd_available()):
        pytest.skip("msgpack/zstd not installed")
    obj = _sample()
    enc = transport.encode_response(obj, accept={"ser": ["msgpack"], "comp": ["zstd"]})
    tag = enc[0]
    assert tag >> 4 == transport.SER_MSGPACK
    assert tag & 0x0F == transport.COMP_ZSTD
    assert transport.decode_response(enc) == obj

# ── raw screenshot hoisting ───────────────────────────────────────────────────────

def _screenshot_obj():
    png = bytes(range(256)) * 40
    url = "data:image/png;base64," + base64.b64encode(png).decode("ascii")
    return {"id": "x", "success": True, "data": {"dataUrl": url}}, url

def test_screenshot_roundtrip_restores_data_url_exactly():
    if not transport.msgpack_available():
        pytest.skip("msgpack not installed")
    obj, url = _screenshot_obj()
    enc = transport.encode_response(obj, accept={"ser": ["msgpack"], "comp": []}, command="tabs.screenshot")
    dec = transport.decode_response(enc)
    assert dec == obj
    assert dec["data"]["dataUrl"] == url

def test_screenshot_not_hoisted_for_other_commands():
    if not transport.msgpack_available():
        pytest.skip("msgpack not installed")
    import msgpack
    obj, _ = _screenshot_obj()
    enc = transport.encode_response(obj, accept={"ser": ["msgpack"], "comp": []}, command="extract.text")
    body = msgpack.unpackb(enc[1:], raw=False)
    assert isinstance(body["data"]["dataUrl"], str)  # left as base64 string

def test_screenshot_json_path_leaves_base64():
    obj, url = _screenshot_obj()
    enc = transport.encode_response(obj, accept={"ser": ["json"], "comp": ["gzip"]}, command="tabs.screenshot")
    assert transport.decode_response(enc)["data"]["dataUrl"] == url

# ── negotiation preference ────────────────────────────────────────────────────────

def test_server_prefers_strongest_mutual_codec():
    if not transport.zstd_available():
        pytest.skip("zstandard not installed")
    obj = _sample()
    # client accepts gzip and zstd; server should pick zstd (its top preference)
    enc = transport.encode_response(obj, accept={"ser": ["json"], "comp": ["gzip", "zstd"]})
    assert enc[0] & 0x0F == transport.COMP_ZSTD