"""神识客户端：灵台唯一的模型出口边界。

两种实现可互换（Protocol）：
- ``HttpShenshiClient``：经 HTTP+SSE 调用 Go 神识服务（SHENSHI_BASE_URL 配置时启用）；
- ``EchoShenshi``：进程内回声桩，逐字回流输入，供本地开发与测试在无神识时跑通端到端。

领域模块禁止绕过本边界 import Provider SDK（docs/architecture/service-boundaries.md §4）。
"""

from __future__ import annotations

import json
from collections.abc import AsyncIterator
from typing import Protocol

import httpx

from app.shenshi_client.types import ShenshiChatRequest, ShenshiDelta, ShenshiError


class ShenshiClient(Protocol):
    """神识数据面契约：流式对话补全。"""

    def stream_chat(self, request: ShenshiChatRequest) -> AsyncIterator[ShenshiDelta]: ...


class EchoShenshi:
    """进程内回声桩：把最后一条用户消息按固定粒度切分回流。

    只用于 M0 骨架验证（登录 → 占位 Run → SSE 端到端），不模拟任何 Provider 行为。
    """

    chunk_size = 8

    async def stream_chat(self, request: ShenshiChatRequest) -> AsyncIterator[ShenshiDelta]:
        prompt = next((m.content for m in reversed(request.messages) if m.role == "user"), "")
        text = f"【回声桩】{prompt}"
        for i in range(0, len(text), self.chunk_size):
            yield ShenshiDelta(delta=text[i : i + self.chunk_size])
        yield ShenshiDelta(
            finish_reason="stop",
            usage_prompt_tokens=max(len(prompt) // 4, 1),
            usage_completion_tokens=max(len(text) // 4, 1),
        )


class HttpShenshiClient:
    """HTTP+SSE 神识客户端。

    认证：服务令牌经 ``Authorization: Bearer`` 透传（管理面 RBAC 不在此层）。
    流解析：``data:`` 帧为 ShenshiDelta JSON，``[DONE]`` 结束；非 2xx 映射 ShenshiError。
    """

    def __init__(self, base_url: str, service_token: str, timeout: float = 120.0) -> None:
        self._base_url = base_url.rstrip("/")
        self._headers = {"Authorization": f"Bearer {service_token}"} if service_token else {}
        self._timeout = timeout

    async def stream_chat(self, request: ShenshiChatRequest) -> AsyncIterator[ShenshiDelta]:
        payload = request.model_dump(mode="json")
        assert payload.get("stream") is True  # 数据面当前只有流式形态
        async with httpx.AsyncClient(trust_env=False, timeout=self._timeout) as client:
            async with client.stream(
                "POST",
                f"{self._base_url}/v1/chat/completions",
                json=payload,
                headers=self._headers,
            ) as response:
                if response.status_code >= 400:
                    body = (await response.aread()).decode("utf-8", errors="replace")
                    code = f"HJ-2{max(response.status_code - 400, 0):03d}"
                    try:
                        detail = json.loads(body)
                        code = detail.get("error", {}).get("code", code)
                        body = detail.get("error", {}).get("message", body)
                    except json.JSONDecodeError:
                        pass
                    raise ShenshiError(code, body)
                async for line in response.aiter_lines():
                    if not line.startswith("data:"):
                        continue
                    data = line[len("data:") :].strip()
                    if data == "[DONE]":
                        return
                    if data:
                        yield ShenshiDelta.model_validate_json(data)


def build_shenshi_client(base_url: str, service_token: str) -> ShenshiClient:
    """按配置装配客户端：未配置神识地址时降级为回声桩（M0 骨架形态）。"""
    if base_url:
        return HttpShenshiClient(base_url, service_token)
    return EchoShenshi()