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

let
  inherit (lib)
    any
    attrValues
    concatStringsSep
    escapeShellArg
    hasInfix
    hasSuffix
    optionalAttrs
    optionals
    literalExpression
    mapAttrs'
    mkEnableOption
    mkOption
    mkPackageOptionMD
    mkIf
    nameValuePair
    types
  ;

  inherit (utils)
    escapeSystemdPath
  ;

  cfg = config.services.gitea-actions-runner;

  # Check whether any runner instance label requires a container runtime
  # Empty label strings result in the upstream defined defaultLabels, which require docker
  # https://gitea.com/gitea/act_runner/src/tag/v0.1.5/internal/app/cmd/register.go#L93-L98
  hasDockerScheme = instance:
    instance.labels == [] || any (label: hasInfix ":docker:" label) instance.labels;
  wantsContainerRuntime = any hasDockerScheme (attrValues cfg.instances);

  hasHostScheme = instance: any (label: hasSuffix ":host" label) instance.labels;

  # provide shorthands for whether container runtimes are enabled
  hasDocker = config.virtualisation.docker.enable;
  hasPodman = config.virtualisation.podman.enable;

  tokenXorTokenFile = instance:
    (instance.token == null && instance.tokenFile != null) ||
    (instance.token != null && instance.tokenFile == null);
in
{
  meta.maintainers = with lib.maintainers; [
    hexa
  ];

  options.services.gitea-actions-runner = with types; {
    package = mkPackageOptionMD pkgs "gitea-actions-runner" { };

    instances = mkOption {
      default = {};
      description = lib.mdDoc ''
        Gitea Actions Runner instances.
      '';
      type = attrsOf (submodule {
        options = {
          enable = mkEnableOption (lib.mdDoc "Gitea Actions Runner instance");

          name = mkOption {
            type = str;
            example = literalExpression "config.networking.hostName";
            description = lib.mdDoc ''
              The name identifying the runner instance towards the Gitea/Forgejo instance.
            '';
          };

          url = mkOption {
            type = str;
            example = "https://forge.example.com";
            description = lib.mdDoc ''
              Base URL of your Gitea/Forgejo instance.
            '';
          };

          token = mkOption {
            type = nullOr str;
            default = null;
            description = lib.mdDoc ''
              Plain token to register at the configured Gitea/Forgejo instance.
            '';
          };

          tokenFile = mkOption {
            type = nullOr (either str path);
            default = null;
            description = lib.mdDoc ''
              Path to an environment file, containing the `TOKEN` environment
              variable, that holds a token to register at the configured
              Gitea/Forgejo instance.
            '';
          };

          labels = mkOption {
            type = listOf str;
            example = literalExpression ''
              [
                # provide a debian base with nodejs for actions
                "debian-latest:docker://node:18-bullseye"
                # fake the ubuntu name, because node provides no ubuntu builds
                "ubuntu-latest:docker://node:18-bullseye"
                # provide native execution on the host
                #"native:host"
              ]
            '';
            description = lib.mdDoc ''
              Labels used to map jobs to their runtime environment. Changing these
              labels currently requires a new registration token.

              Many common actions require bash, git and nodejs, as well as a filesystem
              that follows the filesystem hierarchy standard.
            '';
          };

          hostPackages = mkOption {
            type = listOf package;
            default = with pkgs; [
              bash
              coreutils
              curl
              gawk
              gitMinimal
              gnused
              nodejs
              wget
            ];
            defaultText = literalExpression ''
              with pkgs; [
                bash
                coreutils
                curl
                gawk
                gitMinimal
                gnused
                nodejs
                wget
              ]
            '';
            description = lib.mdDoc ''
              List of packages, that are available to actions, when the runner is configured
              with a host execution label.
            '';
          };
        };
      });
    };
  };

  config = mkIf (cfg.instances != {}) {
    assertions = [ {
      assertion = any tokenXorTokenFile (attrValues cfg.instances);
      message = "Instances of gitea-actions-runner can have `token` or `tokenFile`, not both.";
    } {
      assertion = wantsContainerRuntime -> hasDocker || hasPodman;
      message = "Label configuration on gitea-actions-runner instance requires either docker or podman.";
    } ];

    systemd.services = let
      mkRunnerService = name: instance: let
        wantsContainerRuntime = hasDockerScheme instance;
        wantsHost = hasHostScheme instance;
        wantsDocker = wantsContainerRuntime && config.virtualisation.docker.enable;
        wantsPodman = wantsContainerRuntime && config.virtualisation.podman.enable;
      in
        nameValuePair "gitea-runner-${escapeSystemdPath name}" {
          inherit (instance) enable;
          description = "Gitea Actions Runner";
          after = [
            "network-online.target"
          ] ++ optionals (wantsDocker) [
            "docker.service"
          ] ++ optionals (wantsPodman) [
            "podman.service"
          ];
          wantedBy = [
            "multi-user.target"
          ];
          environment = optionalAttrs (instance.token != null) {
            TOKEN = "${instance.token}";
          } // optionalAttrs (wantsPodman) {
            DOCKER_HOST = "unix:///run/podman/podman.sock";
          };
          path = with pkgs; [
            coreutils
          ] ++ lib.optionals wantsHost instance.hostPackages;
          serviceConfig = {
            DynamicUser = true;
            User = "gitea-runner";
            StateDirectory = "gitea-runner";
            WorkingDirectory = "-/var/lib/gitea-runner/${name}";
            ExecStartPre = pkgs.writeShellScript "gitea-register-runner-${name}" ''
              export INSTANCE_DIR="$STATE_DIRECTORY/${name}"
              mkdir -vp "$INSTANCE_DIR"
              cd "$INSTANCE_DIR"

              # force reregistration on changed labels
              export LABELS_FILE="$INSTANCE_DIR/.labels"
              export LABELS_WANTED="$(echo ${escapeShellArg (concatStringsSep "\n" instance.labels)} | sort)"
              export LABELS_CURRENT="$(cat $LABELS_FILE 2>/dev/null || echo 0)"

              if [ ! -e "$INSTANCE_DIR/.runner" ] || [ "$LABELS_WANTED" != "$LABELS_CURRENT" ]; then
                # remove existing registration file, so that changing the labels forces a re-registration
                rm -v "$INSTANCE_DIR/.runner" || true

                # perform the registration
                ${cfg.package}/bin/act_runner register --no-interactive \
                  --instance ${escapeShellArg instance.url} \
                  --token "$TOKEN" \
                  --name ${escapeShellArg instance.name} \
                  --labels ${escapeShellArg (concatStringsSep "," instance.labels)}

                # and write back the configured labels
                echo "$LABELS_WANTED" > "$LABELS_FILE"
              fi

            '';
            ExecStart = "${cfg.package}/bin/act_runner daemon";
            SupplementaryGroups = optionals (wantsDocker) [
              "docker"
            ] ++ optionals (wantsPodman) [
              "podman"
            ];
          } // optionalAttrs (instance.tokenFile != null) {
            EnvironmentFile = instance.tokenFile;
          };
        };
    in mapAttrs' mkRunnerService cfg.instances;
  };
}