Four programs,
as they ran.

// Copyright 2026 Leo Cheng
// SPDX-License-Identifier: Apache-2.0

///|
/// A counter only goes up, so the only way to read it is to scrape it twice. This
/// program prints one scrape.
fn main raise {
  let registry = @metric.Registry::new()
  let jobs = registry.counter("jobs_processed", "Jobs finished.")
  jobs.inc()
  jobs.inc(by=11.0)
  println(@expo.text(registry.collect()))
}

// Copyright 2026 Leo Cheng
// SPDX-License-Identifier: Apache-2.0

///|
/// A gauge is the number at the moment of the scrape: it can go down, and it can be
/// taken from a function instead of stored.
fn main raise {
  let registry = @metric.Registry::new()
  let running = registry.gauge("jobs_running", "Jobs running now.")
  running.set(3.0)
  running.dec()
  println(@expo.text(registry.collect()))
}

// Copyright 2026 Leo Cheng
// SPDX-License-Identifier: Apache-2.0

///|
/// Two observations, counted into the fourteen bounds the official clients share.
/// The buckets are cumulative on the wire: `le="0.5"` counts everything at or below
/// half a second.
fn main raise {
  let registry = @metric.Registry::new()
  let latency = registry.histogram(
    "request_duration_seconds",
    "Request latency.",
  )
  latency.observe(0.041)
  latency.observe(0.317)
  println(@expo.text(registry.collect()))
}

// Copyright 2026 Leo Cheng
// SPDX-License-Identifier: Apache-2.0

///|
/// One snapshot, two formats. The counts are the same object; only the spelling of
/// the timestamp and the ending differ.
fn main raise {
  let registry = @metric.Registry::new()
  let latency = registry.histogram(
    "request_duration_seconds",
    "Request latency.",
  )
  latency.observe(0.041)
  latency.observe(0.317)
  let families = registry.collect(at=1_700_000_015.0)
  println("=== 0.0.4 ===")
  println(@expo.text(families))
  println("=== 1.0 ===")
  println(@expo.openmetrics(families))
}

///|
/// The work one worker did. The numbers differ per process so the merge has
/// something to add up.
fn registry_for(pid : Int) -> @metric.Registry raise @metric.Refused {
  let registry = @metric.Registry::new(
    prefix="p8s",
    labels=[("service", "checkout")],
  )
  let orders = registry.counter("orders", "Orders placed.")
  // ... a labelled counter, a histogram, a summary, a gauge
  orders.inc(by=(pid * 10).to_double())
  registry
}

///|
async fn flush(dir : String, pid : Int) -> Unit raise @metric.Refused {
  let registry = registry_for(pid)
  let written = @directory.write(
    dir, pid, registry.collect(),
    modes=[("p8s_queue_depth", @multiproc.Mode::Sum)],
  )
  println("worker " + pid.to_string() + ": "
    + written.files.to_string() + " files")
}