import json
import re
from datetime import datetime
from urllib.parse import parse_qsl, urlencode, urlparse
from django.utils import timezone
from tracker import constants as C

_SENSITIVE = re.compile("|".join(C.SENSITIVE_KEY_PATTERNS), re.I)
_URL_DROP_KEY = re.compile("|".join(C.URL_PARAM_DROP_PATTERNS), re.I)

def sanitize_url(url: str) -> str:
    """按参数名整键删除（fullmatch 防止误伤 monkey 这类含 key 子串的参数）。"""
    p = urlparse(url)
    kept = [(k, v) for k, v in parse_qsl(p.query, keep_blank_values=True)
            if not _URL_DROP_KEY.fullmatch(k)]
    return p._replace(query=urlencode(kept)).geturl()

def _walk_props(v, depth=0):
    """单次递归同时做深度检查与敏感键扫描（dict 所有层级的键都过 _SENSITIVE）。
    返回 (depth_ok, sensitive_hit)。深度超限即停止下探，防恶意深嵌套递归爆栈。"""
    if depth > C.MAX_PROP_DEPTH:
        return False, False
    if isinstance(v, dict):
        depth_ok, sens = True, False
        for k, x in v.items():
            if _SENSITIVE.search(str(k)):
                sens = True
            d, s = _walk_props(x, depth + 1)
            depth_ok = depth_ok and d
            sens = sens or s
        return depth_ok, sens
    if isinstance(v, list):
        depth_ok, sens = True, False
        for x in v:
            d, s = _walk_props(x, depth + 1)
            depth_ok = depth_ok and d
            sens = sens or s
        return depth_ok, sens
    return True, False

def validate_event(ev) -> str | None:
    """返回 None 表示通过；否则返回拒绝原因码。类型/白名单/体积/深度全在此守门。"""
    if not isinstance(ev, dict):
        return "event_invalid_shape"
    if ev.get("event_name") not in C.EVENT_NAMES:
        return "event_name_not_allowed"
    eid = ev.get("event_id")
    if not isinstance(eid, str) or not eid or len(eid) > 64:
        return "invalid_event_id"
    for k in ("path", "title"):
        if ev.get(k) is not None and not isinstance(ev[k], str):
            return "invalid_field_type"
    occ = ev.get("occurred_at")
    if not isinstance(occ, datetime):
        return "invalid_occurred_at"
    if timezone.is_naive(occ):
        return "invalid_occurred_at"
    skew = (timezone.now() - occ).total_seconds()
    if abs(skew) > C.CLOCK_SKEW_REJECT_SEC:
        return "occurred_at_out_of_window"
    props = ev.get("properties") or {}
    if not isinstance(props, dict) or len(props) > C.MAX_PROP_KEYS:
        return "properties_invalid"
    # 敏感键扫描（含嵌套层级）先于属性白名单：白名单内无任何键命中敏感模式，
    # 若放在白名单之后，sensitive_field 将不可达（见 test_sensitive_property_rejected）。
    depth_ok, sensitive_hit = _walk_props(props)
    if sensitive_hit:
        return "sensitive_field"
    if not set(props) <= C.EVENT_PROP_WHITELIST.get(ev["event_name"], set()):
        return "property_not_allowed"
    if not depth_ok:
        return "properties_depth"
    if len(json.dumps(props, ensure_ascii=False, default=str)) > C.MAX_PROP_JSON_BYTES:
        return "properties_too_large"
    for v in props.values():
        if isinstance(v, str) and len(v) > C.MAX_STR_LEN:
            return "properties_too_long"
    if len(ev.get("path") or "") > C.MAX_PATH_LEN:
        ev["path"] = ev["path"][:C.MAX_PATH_LEN]
    if len(ev.get("title") or "") > C.MAX_TITLE_LEN:
        ev["title"] = ev["title"][:C.MAX_TITLE_LEN]
    if ev.get("path"):
        ev["path"] = sanitize_url(ev["path"])
    return None