"""两阶段路由缓存（对齐实现方案）：
- L1 精确缓存：完全相同的查询 -> 直接命中
- L2 语义缓存：字符 n-gram 余弦相似度（零依赖）-> 相似查询命中
- 命中 N 次（promote_frequency）后提升为精确缓存

说明：语义缓存中的"完全相同查询"（相似度=1.0）直接计为 exact 命中；
高频语义命中会提升为 O(1) 的精确缓存条目。

只缓存"未升级"的结果（升级路径每次都走大模型，不缓存，避免陈旧）。

性能设计（2026-09 优化）：
- 每条语义缓存条目在写入时预计算并缓存向量范数，查询时免重复计算（原来每对比较都重算）
- 语义查找单遍完成：扫描即跟踪最优条目与命中计数，命中后不再二次线性查找
- 相似度达到 1.0（完全相同查询）时提前终止扫描（余弦相似度上界，不可能更优）
"""
from __future__ import annotations

import re
from dataclasses import dataclass
from typing import Any, Dict, List, Optional, Tuple


@dataclass
class CacheEntry:
    result: Dict[str, Any]
    hits: int = 1


def _ngrams(text: str, n: int = 3) -> List[str]:
    """字符 n-gram（去空白、小写），用于轻量语义相似度。"""
    cleaned = re.sub(r"\s+", "", text.lower())
    if len(cleaned) < n:
        return [cleaned]
    return [cleaned[i:i + n] for i in range(len(cleaned) - n + 1)]


def _tf_vector(grams: List[str]) -> Dict[str, float]:
    vec: Dict[str, float] = {}
    for g in grams:
        vec[g] = vec.get(g, 0.0) + 1.0
    return vec


def _norm(vec: Dict[str, float]) -> float:
    return sum(v * v for v in vec.values()) ** 0.5


def _dot(vec_a: Dict[str, float], vec_b: Dict[str, float]) -> float:
    """点积：遍历较小的一方，另一侧用 get 兜底。"""
    if len(vec_a) > len(vec_b):
        vec_a, vec_b = vec_b, vec_a
    return sum(v * vec_b.get(k, 0.0) for k, v in vec_a.items())


class RouterCache:
    """L1 精确缓存 + L2 语义缓存。"""

    def __init__(self, semantic_enabled: bool = True, similarity_threshold: float = 0.88,
                 promote_frequency: int = 5, max_exact: int = 10000, max_semantic: int = 5000):
        self.semantic_enabled = semantic_enabled
        self.similarity_threshold = similarity_threshold
        self.promote_frequency = promote_frequency
        self.max_exact = max_exact
        self.max_semantic = max_semantic
        self._exact: Dict[str, CacheEntry] = {}
        self._semantic: List[Tuple[str, CacheEntry]] = []  # (query, entry)
        self._sem_vecs: Dict[str, Dict[str, float]] = {}
        self._sem_norms: Dict[str, float] = {}             # 预计算范数，避免查询期重算
        self.hits = {"exact": 0, "semantic": 0}
        self.misses = 0

    # ---- 查询 ----
    def get(self, query: str) -> Optional[Tuple[Optional[str], Dict[str, Any]]]:
        """返回 (level, result)；未命中返回 None。level: 'exact' | 'semantic'"""
        entry = self._exact.get(query)
        if entry is not None:
            self.hits["exact"] += 1
            return ("exact", entry.result)

        if self.semantic_enabled:
            q_vec = _tf_vector(_ngrams(query))
            q_norm = _norm(q_vec)
            best_sim = 0.0
            best_idx = -1
            if q_norm > 0.0:
                # 单遍扫描：同时跟踪最优相似度与条目位置
                for i, (q, _e) in enumerate(self._semantic):
                    n_q = self._sem_norms.get(q, 0.0)
                    if n_q <= 0.0:
                        continue
                    sim = _dot(q_vec, self._sem_vecs.get(q, {})) / (q_norm * n_q)
                    if sim > best_sim:
                        best_sim = sim
                        best_idx = i
                        if sim >= 1.0:
                            break  # 余弦相似度上界：完全相同查询，提前终止
            if best_idx >= 0 and best_sim >= self.similarity_threshold:
                best_q, best_entry = self._semantic[best_idx]
                # 完全相同查询（相似度=1.0）计为 exact 命中
                is_exact = best_sim >= 0.999
                level = "exact" if is_exact else "semantic"
                self.hits[level] += 1
                self._bump_semantic(best_idx, best_q, best_entry)
                return (level, best_entry.result)

        self.misses += 1
        return None

    def _bump_semantic(self, idx: int, query: str, entry: CacheEntry):
        """语义命中：累计命中次数，达到阈值提升为精确缓存（O(1)，无需二次查找）。"""
        entry.hits += 1
        if entry.hits >= self.promote_frequency:
            self._exact[query] = entry
            self._semantic.pop(idx)
            self._sem_vecs.pop(query, None)
            self._sem_norms.pop(query, None)

    # ---- 写入 ----
    def put(self, query: str, result: Dict[str, Any]):
        if query in self._exact:
            return
        entry = CacheEntry(result=result)
        if self.semantic_enabled:
            if len(self._semantic) >= self.max_semantic:
                old_q, _ = self._semantic.pop(0)
                self._sem_vecs.pop(old_q, None)
                self._sem_norms.pop(old_q, None)
            self._semantic.append((query, entry))
            vec = _tf_vector(_ngrams(query))
            self._sem_vecs[query] = vec
            self._sem_norms[query] = _norm(vec)
        else:
            self._exact[query] = entry
            if len(self._exact) > self.max_exact:
                self._exact.pop(next(iter(self._exact)))

    # ---- 统计 ----
    def stats(self) -> Dict[str, Any]:
        total = self.hits["exact"] + self.hits["semantic"] + self.misses
        return {
            "exact_hits": self.hits["exact"],
            "semantic_hits": self.hits["semantic"],
            "misses": self.misses,
            "hit_rate": round((self.hits["exact"] + self.hits["semantic"]) / total, 4) if total else 0.0,
            "exact_size": len(self._exact),
            "semantic_size": len(self._semantic),
        }

    def clear(self):
        self._exact.clear()
        self._semantic.clear()
        self._sem_vecs.clear()
        self._sem_norms.clear()
        self.hits = {"exact": 0, "semantic": 0}
        self.misses = 0