dashboard/backend/curve_client.py

"""Luxsin 曲线 API：拉取、自定义 Base64 解码与 parametric_eq 校验。"""
import base64
import json
import logging
from typing import Any, Optional, Tuple
from urllib.parse import urlencode

import requests

logger = logging.getLogger(__name__)

LUXSIN_CURVE_API_BASE = "https://api.luxsin.com.cn/audio/getCurve"

CUSTOM_CHARS = "KLMPQRSTUVWXYZABCGHdefIJjkNOlmnopqrstuvwxyzabcghiDEF34501289+67/"
STANDARD_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

TARGET_OVER_EAR = "Harman over-ear 2018"
TARGET_IN_EAR = "Harman in-ear 2019"

FORM_TARGET_MAP = {
    "over-ear": TARGET_OVER_EAR,
    "in-ear": TARGET_IN_EAR,
}


def curve_target_for_form(form: Optional[str]) -> Optional[str]:
    if not form:
        return None
    return FORM_TARGET_MAP.get(form.strip().lower())


def custom_base64_to_string(encoded: str) -> str:
    """将 Luxsin 自定义 Base64 字母表映射为标准 Base64 后解码为 UTF-8 字符串。"""
    if not encoded or not isinstance(encoded, str):
        raise ValueError("曲线数据为空")

    standard_b64 = []
    for c in encoded:
        idx = CUSTOM_CHARS.find(c)
        if idx != -1:
            standard_b64.append(STANDARD_CHARS[idx])
        else:
            standard_b64.append(c)

    try:
        raw = base64.b64decode("".join(standard_b64), validate=False)
    except Exception as e:
        raise ValueError(f"Base64 解码失败：{e}") from e

    try:
        return raw.decode("utf-8")
    except UnicodeDecodeError as e:
        raise ValueError(f"UTF-8 解码失败：{e}") from e


def is_valid_parametric_eq_payload(data: Any) -> bool:
    if not isinstance(data, dict):
        return False
    peq = data.get("parametric_eq")
    if not isinstance(peq, dict):
        return False
    filters = peq.get("filters")
    return isinstance(filters, list) and len(filters) == 10


def extract_encoded_payload(response: requests.Response) -> str:
    """从 getCurve 响应中提取待解码字符串。"""
    text = (response.text or "").strip()
    if not text:
        raise ValueError("曲线接口响应为空")

    try:
        body = response.json()
    except ValueError:
        return text

    if isinstance(body, str):
        return body.strip()

    if not isinstance(body, dict):
        raise ValueError("曲线接口响应格式异常")

    for key in ("data", "curve", "result", "content", "body"):
        val = body.get(key)
        if isinstance(val, str) and val.strip():
            return val.strip()

    nested = body.get("data")
    if isinstance(nested, dict):
        for key in ("curve", "data", "content", "encoded"):
            val = nested.get(key)
            if isinstance(val, str) and val.strip():
                return val.strip()

    if isinstance(nested, str) and nested.strip():
        return nested.strip()

    raise ValueError("曲线接口响应中未找到可解码数据")


def fetch_and_validate_curve(
    brand: str,
    name: str,
    form: str,
    *,
    timeout: float = 20.0,
) -> Tuple[bool, str]:
    """
    拉取并校验曲线。返回 (是否通过, 失败原因)；通过时原因为空字符串。
    """
    brand = (brand or "").strip()
    name = (name or "").strip()
    if not brand or not name:
        return False, "品牌名称或型号名称为空"

    target = curve_target_for_form(form)
    if not target:
        return False, "佩戴方式须为入耳式(in-ear)或头戴式(over-ear)才能校验曲线"

    query = urlencode({"brand": brand, "name": name, "target": target})
    url = f"{LUXSIN_CURVE_API_BASE}?{query}"

    try:
        resp = requests.get(url, timeout=timeout)
    except requests.RequestException as e:
        logger.warning("getCurve request failed: %s %s", url, e)
        return False, f"无法连接曲线接口：{e}"

    if resp.status_code != 200:
        return False, f"曲线接口返回 HTTP {resp.status_code}"

    try:
        encoded = extract_encoded_payload(resp)
    except ValueError as e:
        return False, str(e)

    try:
        decoded_text = custom_base64_to_string(encoded)
        payload = json.loads(decoded_text)
    except json.JSONDecodeError:
        return False, "解码后的数据不是合法 JSON"
    except ValueError as e:
        return False, str(e)

    if not is_valid_parametric_eq_payload(payload):
        return False, "曲线数据异常"

    return True, ""