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

#  sudo -u postgres vacuumdb --all --analyze-in-stages
#  /var/lib/postgresql/16/delete_old_cluster.sh
let
  vars = import ./vars.nix;
  dataDir = "${vars.primary_db}/postgresql/nix/${config.services.postgresql.package.psqlSchema}";
  backupLocation = "${vars.primary_db}/postgresql/nix_backups";
in
{
  services = {
    postgresql = {
      inherit dataDir;
      enable = true;
      enableJIT = true;
      package = pkgs.postgresql_16;
      identMap = ''
        # ArbitraryMapName systemUser DBUser
           superuser_map      root      postgres
           superuser_map      alice  postgres
           # Let other names login as themselves
           superuser_map      /^(.*)$   \1
      '';

      # initialScript = config.sops.secrets."postgres/init".path;
      ensureDatabases = [
        "atticd"
        "alice"
      ];
      ensureUsers = [
        {
          name = "atticd";
          ensureDBOwnership = true;
        }
        {
          name = "alice";
          ensureDBOwnership = true;
          ensureClauses = {
            superuser = true;
            login = true;
            createrole = true;
            createdb = true;
            replication = true;
          };
        }
      ];
      # Thank you NotAShelf
      # https://github.com/NotAShelf/nyx/blob/d407b4d6e5ab7f60350af61a3d73a62a5e9ac660/modules/core/roles/server/system/services/databases/postgresql.nix#L74
      # commented out statements are likely overriden by pgtune settings
      # https://pgtune.leopard.in.ua/?dbVersion=17&osType=linux&dbType=web&cpuNum=64&totalMemory=8&totalMemoryUnit=GB&connectionNum=1024&hdType=hdd
      settings = {
        # Connectivity;
        # max_connections = 100;
        superuser_reserved_connections = 3;

        # Memory Settings;
        #shared_buffers = "1024 MB";
        #work_mem = "32 MB";
        #maintenance_work_mem = "320 MB";
        #huge_pages = "off";
        #effective_cache_size = "2 GB";
        #effective_io_concurrency = 100; # concurrent IO only really activated if OS supports posix_fadvise function;
        #random_page_cost = 1.25; # speed of random disk access relative to sequential access (1.0);

        # Monitoring;
        shared_preload_libraries = "pg_stat_statements,auto_explain"; # per statement resource usage stats & log explain statements for slow queries
        track_io_timing = "on"; # measure exact block IO times;
        track_functions = "pl"; # track execution times of pl-language procedures if any;
        # Replication;
        wal_level = "replica"; # consider using at least "replica";
        max_wal_senders = 0;
        synchronous_commit = "on";

        # Checkpointing: ;
        checkpoint_timeout = "15 min";
        #checkpoint_completion_target = 0.9;
        #max_wal_size = "1024 MB";
        #min_wal_size = "512 MB";

        # WAL writing;
        wal_compression = "on";
        wal_buffers = -1; # auto-tuned by Postgres till maximum of segment size (16MB by default);
        wal_writer_delay = "200ms";
        wal_writer_flush_after = "1MB";

        # Background writer;
        bgwriter_delay = "200ms";
        bgwriter_lru_maxpages = 100;
        bgwriter_lru_multiplier = 2.0;
        bgwriter_flush_after = 0;

        # Parallel queries: ;
        #max_worker_processes = 6;
        #max_parallel_workers_per_gather = 3;
        #max_parallel_maintenance_workers = 3;
        #max_parallel_workers = 6;
        parallel_leader_participation = "on";

        # Advanced features ;
        enable_partitionwise_join = "on";
        enable_partitionwise_aggregate = "on";
        jit = "on";

        jit_above_cost = 100000;
        jit_inline_above_cost = 150000;
        jit_optimize_above_cost = 500000;

        # log slow queries
        log_min_duration_statement = 100;
        "auto_explain.log_min_duration" = 100;

        # logging configuration
        log_connections = true;
        log_statement = "all";
        logging_collector = true;
        log_disconnections = true;

        # from pgtune
        # DB Version: 17
        # OS Type: linux
        # DB Type: web
        # Total Memory (RAM): 8 GB
        # CPUs num: 64
        # Connections num: 1024
        # Data Storage: hdd

        max_connections = 1024;
        shared_buffers = "2GB";
        effective_cache_size = "6GB";
        maintenance_work_mem = "512MB";
        checkpoint_completion_target = 0.9;
        #wal_buffers = "16MB"; allow auto-tuning as per above
        default_statistics_target = 100;
        random_page_cost = 4;
        effective_io_concurrency = 2;
        work_mem = "512kB";
        huge_pages = "off";
        min_wal_size = "1GB";
        max_wal_size = "4GB";
        max_worker_processes = 64;
        max_parallel_workers_per_gather = 4;
        max_parallel_workers = 64;
        max_parallel_maintenance_workers = 4;

      };

      refreshCollation = true;
      vacuumAnalyzeTimer.enable = true;
      upgrade = {
        enable = true;
        stopServices = [
          "hydra-evaluator"
          "hydra-init"
          "hydra-notify"
          "hydra-queue-runner"
          "hydra-send-stats"
          "hydra-server"
          "atticd"
          "gitea"
        ];
      };
    };
    postgresqlBackup = {
      enable = true;
      compression = "zstd";
      compressionLevel = 19;
      pgdumpOptions = "--create --clean";
      location = backupLocation;
    };
  };
}