{ config, lib, ... }:

# hydra user needs to be manually crated
# sudo -u hydra -s
# hydra-create-user $USERNAME --password $PASSWORD --role admin

# https://qfpl.io/posts/nix/starting-simple-hydra/
# also for reference a well written hydra config:
# https://github.com/NixOS/nixos-org-configurations/blob/master/delft/hydra.nix

with lib;

let
  cacheDir = "/var/cache/hydra";
in mkIf (elem "hydra" config.machine.services) {
  # also take a look at ../conf/nix.nix
  nix.buildMachines = [
    {
      hostName = "localhost";
      system = "x86_64-linux";
      supportedFeatures = ["kvm" "nixos-test" "big-parallel" "benchmark"];
      maxJobs = 8;
    }
  ];

  services = let
    cfg = config.machine;
    domain = (findFirst (s: s.service == "hydra") cfg cfg.vHosts).domain;
  in {
    hydra = {
      enable = true;
      hydraURL = domain; # externally visible URL
      listenHost = "localhost";
      port = 3001;
      minimumDiskFree = 15;
      minimumDiskFreeEvaluator = 15;
      notificationSender = "hydra@mail.${cfg.domain}"; # e-mail of hydra service
      useSubstitutes = true;
      debugServer = false;
      # Hints from hydra-queue-runner:
      # binary_cache_dir is deprecated and ignored. use store_uri=file:// instead
      # hydra.conf: binary_cache_secret_key_file is deprecated and ignored. use store_uri=...?secret-key= instead
      extraConfig = ''
        max_output_size = 4294967296
        store_uri = file://${cacheDir}?secret-key=${cfg.secretPath}/hydra_cache&write-nar-listing=1&ls-compression=br&log-compression=br
        # add ?local-nar-cache= to set nar cache location
        server_store_uri = https://cache.${cfg.domain}
        binary_cache_public_uri https://cache.${cfg.domain}
        upload_logs_to_binary_cache = true
      '';
    };

    nix-serve = {
      enable = true;
      bindAddress = "0.0.0.0";
      port = 5000;
      secretKeyFile = "${cfg.secretPath}/hydra_cache";
      extraParams = ''
        # Dont know how to change the store root yet...
        # --user hydra-queue-runner
        # --group hydra
      '';
    };
  };
  systemd.services.nix-serve.serviceConfig.User = mkForce "hydra";
  systemd.services.nix-serve.environment.NIX_STORE_DIR = cacheDir;
}