{ config, lib, pkgs, ... }:

let
  cfg = config.monitoring;
  helpers = import <top/helpers.nix> { inherit config lib pkgs; };
in
{
  options.monitoring = {
    lokiPort = lib.mkOption {
      type = lib.types.int;
    };
    alloyUiPort = lib.mkOption {
      type = lib.types.int;
    };
    prometheusNodeExporterPort = lib.mkOption {
      type = lib.types.int;
    };
    prometheusScrapeConfigs = lib.mkOption {
      type = lib.types.listOf lib.types.attrs;
      default = [];
    };
  };
  config = {
    services.prometheus = {
      enable = true;

      retentionTime = "1y";

      scrapeConfigs = [
        {
          job_name = "node";
          static_configs = [{
            targets = [ "localhost:${toString cfg.prometheusNodeExporterPort}" ];
          }];
        }
      ] ++ cfg.prometheusScrapeConfigs;

      exporters.node = {
        enable = true;
        enabledCollectors = [ "systemd" ];
        port = cfg.prometheusNodeExporterPort;
      };
    };

    services.loki = {
      enable = true;
      configuration = {
        server.http_listen_port = cfg.lokiPort;
        auth_enabled = false;

        ingester = {
          lifecycler = {
            address = "127.0.0.1";
            ring = {
              kvstore.store = "inmemory";
              replication_factor = 1;
            };
          };
        };

        schema_config = {
          configs = [{
            store = "tsdb";
            object_store = "filesystem";
            schema = "v13";
            index = {
              prefix = "index_";
              period = "24h";
            };
          }];
        };

        storage_config = {
          tsdb_shipper = {
            active_index_directory = "/var/lib/loki/tsdb-active";
            cache_location = "/var/lib/loki/tsdb-cache";
          };
        };

        compactor = {
          working_directory = "/var/lib/loki";
        };

        limits_config = {
          allow_structured_metadata = true;
        };
      };
    };

    systemd.services.alloy = {
      serviceConfig = {
        SupplementaryGroups = [
          "systemd-journal"
        ] ++ lib.optional config.services.nginx.enable config.services.nginx.group;
      };
    };

    services.alloy = {
      enable = true;
      extraFlags = ["--server.http.listen-addr=0.0.0.0:${toString cfg.alloyUiPort}"];
      configPath =
        let
          ref = helpers.alloyConfigRef;
        in
        helpers.writeAlloyConfig {
          "loki.source.journal".journal = {
            max_age = "12h0m0s";
            relabel_rules = ref "discovery.relabel.journal.rules";
            forward_to = [(ref "loki.process.journal.receiver")];
            labels = {
              host = "tente";
              job = "systemd-journal";
            };
          };
          "loki.process".journal = {
            forward_to = [(ref "loki.write.default.receiver")];
            blocks = [
              {
                name = "stage.match";
                # Select messages from systemd services that have LogExtraFields=LOG_FORMAT=logfmt.
                selector = ''{__journal_LOG_FORMAT="logfmt"}'';
                blocks = [
                  { name = "stage.logfmt"; mapping = { time = ""; level = ""; }; }
                  { name = "stage.timestamp"; source = "time"; format = "RFC3339"; }
                  {
                    # The slog package of the Go standard library prints levels as uppercase.
                    name = "stage.template";
                    source = "level";
                    template = "{{ ToLower .Value }}";
                  }
                  { name = "stage.structured_metadata"; values = { level = ""; }; }
                ];
              }
            ];
          };
          "discovery.relabel".journal = {
            targets = [];
            blocks = [
              {
                name = "rule";
                source_labels = ["__journal__systemd_unit"];
                target_label = "unit";
              }
            ];
          };

          "loki.source.file".nginx_access = {
            targets = ref "local.file_match.nginx_access.targets";
            forward_to = [(ref "loki.process.nginx_access.receiver")];
          };
          "local.file_match".nginx_access = {
            path_targets = [{
              __path__ = "/var/log/nginx/*.access.log";
            }];
          };
          "loki.process".nginx_access = {
            forward_to = [(ref "loki.write.default.receiver")];
            blocks = [
              { name = "stage.static_labels"; values = { job = "nginx"; }; }

              {
                # Extracting the log file name as vhost because it's more convenient
                # to query for than the full filename. We could also use server_name
                # but there could be wildcard server_names and Loki labels should have
                # a low cardinality for performance reasons.
                name = "stage.regex";
                source = "filename";
                expression = "(?P<vhost>[^/]+)\\.access\\.log$";
              }

              { name = "stage.labels"; values = { vhost = ""; }; }
              { name = "stage.json"; expressions = { msec = ""; path = ""; }; }
              { name = "stage.timestamp"; source = "msec"; format = "Unix"; }
              {
                # Setting level=info to prevent Loki's log level detection from wrongly
                # detecting messages with paths containing "error" as errors.
                # Creating the filetype entry via stage.template because there's no
                # static_structured_metadata stage yet. (https://github.com/grafana/loki/issues/16703)
                name = "stage.template";
                source = "level";
                template = "info";
              }
              { name = "stage.structured_metadata"; values = { level = ""; }; }

              # Temporarily adding path as a label so that we can use it in the match selectors.
              { name = "stage.labels"; values = { path = ""; }; }
              {
                name = "stage.match";
                selector = "{path=~\"/\\\\.well-known/.*\"}";
                # Creating the filetype entry via stage.template because there's no
                # static_structured_metadata stage yet. (https://github.com/grafana/loki/issues/16703)
                blocks = [
                  { name = "stage.template"; source = "filetype"; template = "well-known"; }
                ];
              }
              {
                name = "stage.match";
                selector = "{path=\"/robots.txt\"}";
                blocks = [
                  { name = "stage.template"; source = "filetype"; template = "robots.txt"; }
                ];
              }
              {
                name = "stage.match";
                selector = "{path=~\".*\\\\.atom$\"}";
                blocks = [
                  { name = "stage.template"; source = "filetype"; template = "feed"; }
                ];
              }
              {
                name = "stage.structured_metadata";
                values = { filetype = ""; };
              }

              # Dropping path again because it has a too high cardinality for a label.
              { name = "stage.label_drop"; values = ["path"]; }
            ];
          };
          "loki.write".default = {
            blocks = [
              {
                name = "endpoint";
                url = "http://127.0.0.1:${toString cfg.lokiPort}/loki/api/v1/push";
              }
            ];
            external_labels = {};
          };
        };
    };
  };
}