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import { Counter, Gauge, Histogram } from "prom-client";
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type Aspect = "db" | "database" | "server" | "llm";
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function withPrefix(aspect: Aspect, name: string): string {
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  return `cocalc_${aspect}_${name}`;
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}
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const cache: any = {};
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export function newCounter(
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  aspect: Aspect,
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  name: string,
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  help: string,
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  labelNames: string[] = [],
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) {
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  name = withPrefix(aspect, name);
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  const key = `counter-${name}`;
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  if (cache[key] != null) {
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    return cache[key];
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  }
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  // a prometheus counter -- https://github.com/siimon/prom-client#counter
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  // use it like counter.labels(labelA, labelB).inc([positive number or default is 1])
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  if (!name.endsWith("_total")) {
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    throw Error(
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      `Counter metric names have to end in [_unit]_total but got '${name}' -- https://prometheus.io/docs/practices/naming/`,
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    );
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  }
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  const C = new Counter({
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    name,
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    help,
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    labelNames,
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  });
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  cache[key] = C;
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  return C;
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}
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export function newGauge(
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  aspect: Aspect,
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  name: string,
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  help,
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  labelNames: string[] = [],
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) {
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  name = withPrefix(aspect, name);
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  const key = `gauge-${name}`;
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  if (cache[key] != null) {
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    return cache[key];
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  }
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  const G = new Gauge({
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    name,
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    help,
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    labelNames,
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  });
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  cache[key] = G;
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  return G;
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}
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export function newHistogram(
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  aspect: Aspect,
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  name: string,
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  help,
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  config: { buckets?: number[]; labels?: string[] } = {},
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) {
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  name = withPrefix(aspect, name);
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  const key = `hist-${name}`;
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  if (cache[key] != null) {
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    return cache[key];
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  }
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  // invoked as histogram.observe(value)
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  if (!config.buckets) {
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    config.buckets = [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10];
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  }
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  if (!config.labels) {
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    config.labels = [];
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  }
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  const H = new Histogram({
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    name,
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    help,
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    labelNames: config.labels,
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    buckets: config.buckets,
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  });
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  cache[key] = H;
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  return H;
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}
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