# The hive-matrix container's database-size step: measures a directory and
# pushes the byte count as the gauge `hyperhive.matrix.database_bytes` to the
# forwarder's OTLP/HTTP metrics receiver on loopback.
#
# `dir` is a `DynamicUser` unit's `/var/lib/<name>`, which systemd makes a
# symlink to `/var/lib/private/<name>`. `--dereference-args` measures the
# directory behind the link and works unchanged when `dir` is a real
# directory; without it `du` reports the link itself (a few bytes).
#
# A result under 4096 bytes is not a database, since a directory entry alone
# is that big: the step warns on stderr and pushes nothing, so the gauge
# stays absent rather than wrong.
#
# Pure function — NOT a NixOS module. Needs `du`, `cut`, `date` and `curl`.
{ lib }:
{ dir, otlpPort }:
''
  set -euo pipefail

  bytes="$(du --summarize --bytes --dereference-args ${lib.escapeShellArg dir} | cut -f1)"
  case "$bytes" in
    "" | *[!0-9]*)
      echo "du answered a non-number: bytes='$bytes'" >&2
      exit 1
      ;;
  esac
  if [ "$bytes" -lt 4096 ]; then
    echo "warning: ${dir} measures $bytes bytes, too small for a database; pushing nothing" >&2
    exit 0
  fi

  printf '{"resourceMetrics":[{"resource":{"attributes":[{"key":"service.name","value":{"stringValue":"hive-matrix"}}]},"scopeMetrics":[{"metrics":[{"name":"hyperhive.matrix.database_bytes","gauge":{"dataPoints":[{"asInt":"%s","timeUnixNano":"%s"}]}}]}]}]}' \
    "$bytes" "$(date +%s%N)" |
    curl --fail --silent --show-error --max-time 20 \
      -H 'Content-Type: application/json' --data-binary @- \
      http://127.0.0.1:${toString otlpPort}/v1/metrics
''