"""Unit: SSE frame serialization for POST /api/chat (PLAN §4 contract)."""
from __future__ import annotations

import json

from app.api.chat import sse_event


def _payload(frame: str) -> dict:
    assert frame.startswith("data: ")
    assert frame.endswith("\n\n")
    return json.loads(frame.removeprefix("data: ").strip())


def test_delta_frame_serializes_exactly() -> None:
    frame = sse_event({"type": "delta", "text": "hi"})
    assert frame == 'data: {"type": "delta", "text": "hi"}\n\n'
    assert _payload(frame) == {"type": "delta", "text": "hi"}


def test_done_frame_carries_full_contract_shape() -> None:
    payload = {
        "type": "done",
        "deflected": False,
        "sources": [{"source": "Homelab", "path": "kubernetes.md", "title": "K8s"}],
        "suggestions": [],
    }
    assert _payload(sse_event(payload)) == payload


def test_error_frame_serializes() -> None:
    frame = sse_event({"type": "error", "detail": "boom"})
    assert _payload(frame) == {"type": "error", "detail": "boom"}


def test_unicode_survives_roundtrip() -> None:
    frame = sse_event({"type": "delta", "text": "🧠 café — \"quoted\""})
    # ensure_ascii=False keeps the frame readable (no \uXXXX escapes).
    assert "🧠 café" in frame
    assert _payload(frame)["text"] == "🧠 café — \"quoted\""


def test_multi_line_text_stays_one_frame() -> None:
    """Newlines inside the JSON payload must be escaped so the frame
    delimiter ``\\n\\n`` remains unambiguous."""
    frame = sse_event({"type": "delta", "text": "line1\nline2\n\n"})
    assert frame.count("\n\n") == 1  # only the frame terminator
    assert _payload(frame)["text"] == "line1\nline2\n\n"