"""Prometheus 兼容的 /metrics 端点"""
import time
import json
from collections import defaultdict
from typing import Optional


class MetricsCollector:
    """轻量级指标收集器，输出 Prometheus 兼容格式"""

    def __init__(self):
        self._counters: dict[str, int] = defaultdict(int)
        self._gauges: dict[str, float] = {}
        self._histograms: dict[str, list[float]] = defaultdict(list)
        self._start_time = time.time()

    def inc(self, name: str, labels: dict = None, value: int = 1):
        """增加计数器"""
        key = self._label_key(name, labels)
        self._counters[key] += value

    def set_gauge(self, name: str, value: float, labels: dict = None):
        """设置 gauge 值"""
        key = self._label_key(name, labels)
        self._gauges[key] = value

    def observe(self, name: str, value: float, labels: dict = None):
        """记录直方图观测值"""
        key = self._label_key(name, labels)
        self._histograms[key].append(value)

    def render(self) -> str:
        """渲染为 Prometheus 文本格式"""
        lines = []
        now = time.time()

        # HELP / TYPE 注释
        seen = set()
        for key in self._counters:
            metric_name = key.split("{")[0] if "{" in key else key
            if metric_name not in seen:
                lines.append(f"# HELP {metric_name} Counter metric")
                lines.append(f"# TYPE {metric_name} counter")
                seen.add(metric_name)
        for key in self._gauges:
            metric_name = key.split("{")[0] if "{" in key else key
            if metric_name not in seen:
                lines.append(f"# HELP {metric_name} Gauge metric")
                lines.append(f"# TYPE {metric_name} gauge")
                seen.add(metric_name)
        for key in self._histograms:
            metric_name = key.split("{")[0] if "{" in key else key
            if metric_name not in seen:
                lines.append(f"# HELP {metric_name} Histogram metric")
                lines.append(f"# TYPE {metric_name} histogram")
                seen.add(metric_name)

        # 计数器
        for key, val in sorted(self._counters.items()):
            lines.append(f"{key} {val}")

        # Gauges
        for key, val in sorted(self._gauges.items()):
            lines.append(f"{key} {val}")

        # 直方图
        buckets = [0.01, 0.05, 0.1, 0.5, 1.0, 5.0]
        for key, vals in sorted(self._histograms.items()):
            metric_name = key.split("{")[0]
            total = len(vals)
            for b in buckets:
                le = sum(1 for v in vals if v <= b)
                lines.append(f'{metric_name}_bucket{{{key.split("{", 1)[1] if "{" in key else ""},le="{b}"}} {le}')
            lines.append(f'{metric_name}_bucket{{le="+Inf"}} {total}')
            lines.append(f"{metric_name}_count {total}")
            if total > 0:
                lines.append(f"{metric_name}_sum {sum(vals)}")

        lines.append(f"nebula_uptime_seconds {now - self._start_time}")
        return "\n".join(lines) + "\n"

    @staticmethod
    def _label_key(name: str, labels: dict = None) -> str:
        if not labels:
            return name
        parts = ",".join(f'{k}="{v}"' for k, v in sorted(labels.items()))
        return f'{name}{{{parts}}}'


# 全局单例
_collector: Optional[MetricsCollector] = None


def get_metrics() -> MetricsCollector:
    global _collector
    if _collector is None:
        _collector = MetricsCollector()
    return _collector