"""
HTTP 请求关联 ID 的 ASGI 适配器。
"""

from __future__ import annotations

from starlette.types import ASGIApp, Message, Receive, Scope, Send

from app.runtime.correlation import (
    CORRELATION_ID_HEADER,
    correlation_scope,
    normalize_correlation_id,
)


class CorrelationIdMiddleware:
    """
    验证入口 ID、绑定请求上下文并把同一 ID 写回响应。
    """

    def __init__(self, app: ASGIApp) -> None:
        """
        保存下游 ASGI 应用。
        """
        self._app = app

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        """
        为 HTTP 请求绑定关联 ID，绑定范围覆盖完整流式响应生命周期。

        其他连接类型直接转交下游；请求结束或抛出异常后恢复原有上下文。
        """
        if scope.get("type") != "http":
            await self._app(scope, receive, send)
            return
        raw_headers = dict(scope.get("headers") or [])
        candidate = raw_headers.get(CORRELATION_ID_HEADER.lower().encode("ascii"))
        correlation_id = normalize_correlation_id(
            candidate.decode("ascii", errors="ignore") if candidate else None
        )
        scope.setdefault("state", {})["request_id"] = correlation_id

        async def send_with_correlation(message: Message) -> None:
            """
            在响应开始帧中覆盖为当前请求的安全关联 ID。
            """
            if message.get("type") == "http.response.start":
                headers = list(message.get("headers") or [])
                header_name = CORRELATION_ID_HEADER.lower().encode("ascii")
                headers = [item for item in headers if item[0].lower() != header_name]
                headers.append((header_name, correlation_id.encode("ascii")))
                message["headers"] = headers
            await send(message)

        with correlation_scope(correlation_id):
            await self._app(scope, receive, send_with_correlation)