# The swarm's metrics store: one VictoriaMetrics for the whole swarm, in a
# `swarm-victoriametrics` nixos-container.
#
# A LOCAL time-series database rather than only an external sink, and that is
# the point rather than a convenience: the swarm dashboard has to stay
# readable when the outside world is unreachable. Same failure-domain property
# the hive-status KV has — a view of the system must not depend on the system
# it is viewing being healthy.
#
# It is the collector that feeds this (the gateway OTEL collector), not the
# agents directly: one ingest point per swarm, authenticated there.
{
  pkgs,
  lib,
  config,
  ...
}:
let
  cfg = config.services.hyperhive.swarm.victoriametrics;
  networkCfg = config.services.hyperhive.network;
  hyperhiveCfg = config.services.hyperhive;
  gatewayCfg = hyperhiveCfg.gateway;
  swarmDomain = hyperhiveCfg.swarm.domain;

  # Total on a null swarm domain for the same reason every sibling module is:
  # the required-domain assertion in hive-network.nix should be what an
  # operator sees, not a coercion error from here.
  domainBase = if swarmDomain == null then "invalid" else swarmDomain;
in
{
  options.services.hyperhive.swarm.victoriametrics = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = ''
        Run the swarm's metrics store on this host. Off by default and not
        derived from {option}`services.hyperhive.enable`: a swarm has one
        metrics store, so enabling it is a decision about swarm topology
        rather than about whether hyperhive is installed.
      '';
    };

    package = lib.mkOption {
      type = lib.types.package;
      default = pkgs.victoriametrics;
      defaultText = lib.literalExpression "pkgs.victoriametrics";
      description = "VictoriaMetrics package to run.";
    };

    machine = lib.mkOption {
      type = lib.types.str;
      readOnly = true;
      default = "swarm-victoriametrics";
      description = ''
        Container name. Read-only: the name appears in host paths and in
        `machinectl`, so it is a fact other modules may read rather than a
        knob.
      '';
    };

    domain = lib.mkOption {
      type = lib.types.str;
      default = "metrics.${domainBase}";
      defaultText = lib.literalExpression ''"metrics.''${services.hyperhive.swarm.domain}"'';
      description = ''
        Name the gateway serves this on. A sibling of the swarm's other
        service names, so the swarm-services sub-CA can issue for it — see
        `hive-tls.nix` for why a service name being a sibling rather than a
        child decides which CA may sign it.
      '';
    };

    port = lib.mkOption {
      type = lib.types.port;
      default = 8428;
      description = ''
        Port VictoriaMetrics listens on, bound to loopback only (see
        below). Upstream's own default, kept so an operator reading
        VictoriaMetrics documentation finds what they expect.
      '';
    };

    retentionPeriod = lib.mkOption {
      type = lib.types.str;
      default = "5y";
      example = "90d";
      description = ''
        How long samples are kept.

        Deliberately a high default rather than a required option: the two
        failure directions are not symmetric. Too long fills a disk, which
        is visible and recoverable by lowering this; too short **destroys
        history**, silently and permanently. So the safe default is generous
        and an operator lowers it once they have measured how fast this swarm
        actually accumulates data.
      '';
    };
  };

  config = lib.mkIf (hyperhiveCfg.enable && cfg.enable) {
    # The gateway name and the quick-link, both inside `cfg.enable` — that
    # guard is the load-bearing part. Every hive in a swarm may know this
    # store exists, but only the host that RUNS it may claim the name; a
    # client hive declaring the vhost would answer for a service it does not
    # have.
    services.hyperhive.gateway.localNames = [ cfg.domain ];

    services.hyperhive.swarm.controller.links = [
      {
        label = "Metrics";
        icon = "📈";
        url = "https://${cfg.domain}/";
      }
    ];

    # This store publishes its own health as prometheus metrics on the same
    # listener it serves queries on, so the swarm's collector can scrape it
    # with no exporter and no extra port.
    #
    # Declared here rather than in the collector's module because that is the
    # rule the option carries: an entry exists only where the service that
    # named it runs, which is what keeps scraper and target on one host by
    # construction instead of by luck.
    #
    # The loopback literal introduces no new assumption — it is the address
    # this module already pins the listener to, and the same one the
    # collector's `otlphttp/victoriametrics` exporter already writes to. If
    # that reach is ever wrong, it is wrong for the write path first.
    services.hyperhive.swarm.otel.scrapeTargets.victoriametrics = "127.0.0.1:${toString cfg.port}";

    services.nginx.virtualHosts."${cfg.domain}" = (gatewayCfg.lib.tlsFor cfg.domain) // {
      listen = gatewayCfg.lib.listen;
      extraConfig = gatewayCfg.lib.securityHeaders;
      locations."/" = {
        proxyPass = "http://127.0.0.1:${toString cfg.port}/";
      };
    };

    containers.${cfg.machine} = {
      autoStart = true;
      ephemeral = false;
      # Shared host netns, like every sibling swarm container: the gateway
      # reaches this at 127.0.0.1:<port>.
      privateNetwork = false;

      config =
        { ... }:
        {
          imports = [
            (import ./swarm-container-resolver.nix {
              inherit (networkCfg) bridgeIp;
              dnsConsumers = [ "victoriametrics.service" ];
            })
          ];

          system.stateVersion = "26.05";

          # This container shares the host netns, so its own firewall.service
          # would rewrite the HOST ruleset at every boot. The host firewall
          # owns all filtering.
          networking.firewall.enable = false;
          # resolvconf stays off because the resolver unit imported above
          # owns /etc/resolv.conf. Leaving it on would let host-tracking
          # regenerate the file empty, since the host's copy doesn't cross
          # the boundary after start.
          networking.resolvconf.enable = lib.mkForce false;

          services.victoriametrics = {
            enable = true;
            package = cfg.package;
            retentionPeriod = cfg.retentionPeriod;

            # ⚠️ PINNED TO LOOPBACK, and this is a correction rather than a
            # preference: upstream's default is `:8428`, i.e. every
            # interface. The gateway is the only intended client and it is on
            # this host, so binding wider would publish an unauthenticated
            # write endpoint (see the OTLP note below) to whatever the host
            # is reachable on.
            listenAddress = "127.0.0.1:${toString cfg.port}";
          };
        };
    };
  };

  # 🔑 OTLP ingest needs no flag. Measured against the pinned 1.146.0 rather
  # than inferred from the module's option list, which has no OTLP switch and
  # so reads as though the feature were absent: the running server answers
  # `POST /opentelemetry/api/v1/push` with 200 (a nonexistent path answers
  # 400, so that 200 means the route exists). The `-opentelemetry.*` flags
  # only tune naming and limits, and are reachable via `extraOptions` if a
  # deployment ever needs them.
  #
  # ⚠️ That endpoint is unauthenticated, which is why `listenAddress` above is
  # loopback and why the collector — not agents — is the writer.
}