import { BadRequestException } from '@nestjs/common';
import { createHash } from 'node:crypto';

export function alertHistoryRange(from?: string, to?: string, now = new Date()) {
  const dateKey = (date: Date) => new Date(date.getTime() + 8 * 3600_000).toISOString().slice(0, 10);
  const endDate = to || dateKey(now);
  const startDate = from || dateKey(new Date(now.getTime() - 6 * 86400_000));
  const parse = (value: string) => {
    const result = new Date(`${value}T00:00:00+08:00`);
    if (!/^\d{4}-\d{2}-\d{2}$/.test(value) || !Number.isFinite(result.getTime()) || dateKey(result) !== value) {
      throw new BadRequestException('告警日期无效');
    }
    return result.getTime() / 1000;
  };
  const start = parse(startDate);
  const end = parse(endDate) + 86400;
  if (end <= start || end - start > 31 * 86400) throw new BadRequestException('告警日期范围须为1至31天');
  return { startDate, endDate, start, end: Math.min(end, now.getTime() / 1000) };
}

export type AlertHistoryItem = {
  id: string;
  name: string;
  severity: string;
  service: string;
  instance: string;
  startedAt: string;
  firstObservedAt: string;
  lastObservedAt: string;
};

// ALERTS_FOR_STATE stores activeAt as the sample value, separating repeated trigger cycles.
// Observation boundaries are not claimed as exact recovery times.
export function mergeAlertHistory(
  target: Map<string, AlertHistoryItem>,
  series: Array<{ metric: Record<string, string>; values?: [number, string][] }>,
  start: number,
  end: number,
) {
  for (const { metric, values } of series) {
    const labels = Object.entries(metric)
      .filter(([key]) => key !== '__name__')
      .sort(([a], [b]) => a.localeCompare(b));
    const fingerprint = createHash('sha256').update(JSON.stringify(labels)).digest('hex');
    for (const [time, rawActiveAt] of values ?? []) {
      const activeAt = Number(rawActiveAt);
      if (time < start || time >= end || !Number.isFinite(activeAt) || activeAt <= 0 || activeAt > time) continue;
      const id = `${fingerprint}:${activeAt}`;
      const observed = new Date(time * 1000).toISOString();
      const item = target.get(id);
      if (item) {
        if (observed < item.firstObservedAt) item.firstObservedAt = observed;
        if (observed > item.lastObservedAt) item.lastObservedAt = observed;
      } else {
        target.set(id, {
          id,
          name: metric.alertname || '未命名告警',
          severity: metric.severity || 'info',
          service: metric.service || '',
          instance: metric.instance || '',
          startedAt: new Date(activeAt * 1000).toISOString(),
          firstObservedAt: observed,
          lastObservedAt: observed,
        });
      }
    }
  }
}