modules/nixos/clicks/services/fava/default.nix

# SPDX-FileCopyrightText: 2024 Clicks Codes
#
# SPDX-License-Identifier: GPL-3.0-only

{
  lib,
  config,
  pkgs,
  ...
}:
let
  cfg = config.clicks.services.fava;
in
{
  options.clicks.services.fava = {
    enable = lib.mkEnableOption "The fava web beancount accounting server";
    tailscaleAuth = lib.mkEnableOption "Lock fava to only be accessible on your tailnet - recommended as fava does not contain any authentication";
    readOnly = lib.mkEnableOption "Make fava unable to edit the files, only read them";
    iWillSetUpAuthMyself = lib.mkOption {
      type = lib.types.bool;
      internal = true;
      description = "Disable warnings about disrecommended or possibly unsafe authentication configurations";
    };
    accounts = lib.mkOption {
      type = lib.home-manager.hm.types.dagOf (lib.types.submodule (submodule: let
          filename = let
            optionPath = submodule.options._module.args.loc;
            len = lib.lists.length optionPath;
            index = len - 4; # Ends ["data" "_module" "args"] in a DAG
          in lib.lists.elemAt optionPath index;
        in {
        options = {
          name = lib.mkOption {
            type = lib.types.str;
            description = "The friendly name of the ledger";
            example = "Clicks Codes";
          };
          favaExtraOptions = lib.mkOption {
            type = lib.types.attrsOf (lib.types.nullOr lib.types.str);
            description = "Extra options to set on this ledger for fava. See https://fava.pythonanywhere.com/example-beancount-file/help/options/ for a list of valid options. These mostly control fava UI, etc. Setting an option to null means that it will be given without a value";
            example = {
              invert-income-liabilities-equity = true;
            };
          };
          beancountExtraOptions = lib.mkOption {
            type = lib.types.attrsOf lib.types.str;
            description = "Extra options to set on this ledger for beancount. See https://beancount.github.io/docs/beancount_options_reference.html for a list of valid options. These mostly control the way beancount interprets numbers, account names, etc.";
            example = {
              long_string_maxlines = "128";
            };
          };
          extraConfig = lib.mkOption {
            type = lib.types.str;
            description = "Extra lines to be added to the end of the beancount config file verbatim. Probably you want these to contain configuration, but it's not required - for example it would be valid to open accounts here to force those accounts to be opened";
            example = ''
              ; lines to be added to the beancount config file directly...
            '';
            default = "";
          };
          mainFile = lib.mkOption {
            type = lib.types.str;
            readOnly = true;
            internal = true;
            description = "The file that you will write your transactions, etc. in";
            default = "/var/lib/private/fava/${filename}.beancount";
          };
          configFile = lib.mkOption {
            type = lib.types.str;
            readOnly = true;
            internal = true;
            description = "The file with all of the beancount/fava/etc. options compiled";
          };
        };
        config = {
          beancountExtraOptions.title = lib.mkDefault submodule.config.name;
          favaExtraOptions.default-file = lib.mkDefault submodule.config.mainFile;

          configFile = builtins.toString (let
            generateFavaOption = name: value:
              if value == null
              then ''1970-01-01 custom "fava-option" "${name}"''
              else ''1970-01-01 custom "fava-option" "${name}" "${value}"'';
            favaOptions = lib.pipe submodule.config.favaExtraOptions [
              (lib.attrsets.mapAttrsToList generateFavaOption)
              (lib.strings.concatStringsSep "\n")
            ];

            generateBeancountOption = name: value: ''option "${name}" "${value}"'';
            beancountOptions = lib.pipe submodule.config.beancountExtraOptions [
              (lib.attrsets.mapAttrsToList generateBeancountOption)
              (lib.strings.concatStringsSep "\n")
            ];
          in pkgs.writeText "${filename}-config" ''
            ${favaOptions}
            ${beancountOptions}
            ${submodule.config.extraConfig}

            include "${submodule.config.mainFile}"
          '');
        };
      }));
      example = {
        "clicks" = lib.home-manager.hm.dag.entryAnywhere {
          name = "Clicks Codes";
          favaExtraOptions = {
            invert-income-liabilities-equity = true;
          };
          beancountExtraOptions = {
            long_string_maxlines = "128";
          };
          extraConfig = ''
            ; lines to be added to the beancount config file directly...
          '';
        };
      };
      description = "A mapping of file names to ledger settings. Ledger settings will not be written to ledgers that are already created, although accompanying files will still be written";
    };
    addr = lib.mkOption {
      type = lib.types.str;
      description = "The host to listen on";
      default = "127.0.0.1";
    };
    port = lib.mkOption {
      type = lib.types.int;
      description = "The port to listen on";
      default = 1025;
    };
    domain = lib.mkOption {
      type = lib.types.str;
      description = "The domain that fava should be hosted on";
    };
  };

  config = lib.mkIf cfg.enable {
    warnings =
      (if !(cfg.tailscaleAuth || cfg.readOnly || cfg.iWillSetUpAuthMyself)
      then [ ("You have not made fava either restricted to a tailnet or read only. " +
              "Unless you set up auth yourself or do not route traffic from the internet to this server, this is a really bad idea. " +
              "To confirm you know what you're doing, set 'clicks.services.fava.iWillSetUpAuthMyself = true' to turn off this warning") ]
       else []) ++
      (if cfg.addr == "0.0.0.0" && cfg.tailscaleAuth && !cfg.iWillSetUpAuthMyself
      then [ ("You have started hosting fava on '0.0.0.0' but additionally enabled tailnet-only access. We won't be able to control access " +
              "that doesn't come through nginx, so any traffic that is allowed to the machine on port ${cfg.port} will still get to fava, tailnet or not. "
              "To confirm you know what you're doing, set 'clicks.services.fava.iWillSetUpAuthMyself = true' to turn off this warning") ]
       else []);

    clicks = {
      services.nginx.enable = true;
      services.nginx.hosts.${cfg.domain} = {
        service = lib.clicks.nginx.http.reverseProxy cfg.addr cfg.port;
        www = false;
        authWith = if cfg.tailscaleAuth then "tailscale" else null;
      };
      networking.tailscale.enable = lib.mkIf cfg.tailscaleAuth true;

      storage.impermanence.persist.directories = [
        { directory = "/var/lib/private/fava"; mode = "0700"; defaultPerms.mode = "0700"; } # Set defaultperms.mode because systemd also needs /var/lib/private 0700
      ];
    };

    systemd.services.fava = let
      sortedAccounts = (lib.home-manager.hm.dag.topoSort cfg.accounts).result;

      fileNames = lib.trivial.pipe sortedAccounts [
        (map (account: account.data.configFile))
        (lib.strings.concatStringsSep " ")
      ];

      accountToCreationScript = { data, ... }: let
      in ''
        ${pkgs.coreutils}/bin/mkdir -p "$(${pkgs.coreutils}/bin/dirname "${data.mainFile}")"
        if [ ! -f "${data.mainFile}" ]; then
          touch ${data.mainFile}
        fi
      '';

      fileCreateCommands = lib.trivial.pipe sortedAccounts [
        (map accountToCreationScript)
        (lib.strings.concatStringsSep "\n")
      ];
    in {
      requires = (if config.clicks.services.nginx.enable then [ "nginx.service" ] else []);
      after = (if config.clicks.services.nginx.enable then [ "nginx.service" ] else []);

      environment = {
        FAVA_HOST = cfg.addr;
        FAVA_PORT = builtins.toString cfg.port;
      };

      serviceConfig = {
        StateDirectory = "fava";
        DynamicUser = true;
      };

      script = "${pkgs.fava}/bin/fava ${if cfg.readOnly then "--read-only" else ""} ${fileNames}";
      preStart = fileCreateCommands;

      wantedBy = ["multi-user.target"];
    };
  };
}