Add Nix packaging with NixOS module

- nix/package.nix: derivation for personal-backlog server + webapp
- nix/module.nix: NixOS module for services.personal-backlog
- Expose packages and nixosModules in flake.nix

Usage in NixOS configuration:
  services.personal-backlog = {
    enable = true;
    port = 8080;
    dataDir = "/var/lib/personal-backlog";
    openFirewall = false;
  };

flake.nix

@@ -18,17 +18,18 @@
         "x86_64-linux"
       ];
 
+      flake = {
+        nixosModules.default = import ./nix/module.nix;
+        nixosModules.personal-backlog = import ./nix/module.nix;
+      };
+
       perSystem =
         {
           system,
+          pkgs,
           ...
         }:
         let
-          pkgs = import nixpkgs {
-            inherit system;
-            config.allowUnfree = true;
-          };
-
           pre-commit-check = git-hooks.lib.${system}.run {
             src = ./.;
             hooks = {
@@ -39,6 +40,11 @@
         {
           formatter = pkgs.nixfmt-tree;
 
+          packages = {
+            default = pkgs.callPackage ./nix/package.nix { };
+            personal-backlog = pkgs.callPackage ./nix/package.nix { };
+          };
+
           checks = {
             inherit pre-commit-check;
           };

nix/module.nix

@@ -0,0 +1,91 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.services.personal-backlog;
+  package = pkgs.callPackage ./package.nix { };
+in
+{
+  options.services.personal-backlog = {
+    enable = lib.mkEnableOption "Personal Backlog task manager";
+
+    package = lib.mkOption {
+      type = lib.types.package;
+      default = package;
+      defaultText = lib.literalExpression "pkgs.personal-backlog";
+      description = "The personal-backlog package to use.";
+    };
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 8080;
+      description = "Port to listen on.";
+    };
+
+    dataDir = lib.mkOption {
+      type = lib.types.path;
+      default = "/var/lib/personal-backlog";
+      description = "Directory to store backlog data.";
+    };
+
+    user = lib.mkOption {
+      type = lib.types.str;
+      default = "backlog";
+      description = "User account under which the service runs.";
+    };
+
+    group = lib.mkOption {
+      type = lib.types.str;
+      default = "backlog";
+      description = "Group under which the service runs.";
+    };
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Whether to open the firewall for the service port.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    users.users.${cfg.user} = {
+      isSystemUser = true;
+      group = cfg.group;
+      home = cfg.dataDir;
+      createHome = true;
+    };
+
+    users.groups.${cfg.group} = { };
+
+    systemd.services.personal-backlog = {
+      description = "Personal Backlog Task Manager";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+
+      serviceConfig = {
+        Type = "simple";
+        User = cfg.user;
+        Group = cfg.group;
+        WorkingDirectory = cfg.dataDir;
+        ExecStart = "${cfg.package}/bin/personal-backlog --port ${toString cfg.port} --dir ${cfg.dataDir}";
+        Restart = "on-failure";
+        RestartSec = 5;
+
+        StateDirectory = "personal-backlog";
+        StateDirectoryMode = "0750";
+
+        NoNewPrivileges = true;
+        ProtectSystem = "strict";
+        ProtectHome = true;
+        PrivateTmp = true;
+        ReadWritePaths = [ cfg.dataDir ];
+      };
+    };
+
+    networking.firewall.allowedTCPPorts = lib.mkIf cfg.openFirewall [ cfg.port ];
+  };
+}

nix/package.nix

@@ -0,0 +1,42 @@
+{
+  lib,
+  stdenv,
+  python3,
+  makeWrapper,
+}:
+
+stdenv.mkDerivation {
+  pname = "personal-backlog";
+  version = "0.1.0";
+
+  src = ./..;
+
+  nativeBuildInputs = [ makeWrapper ];
+
+  buildInputs = [ python3 ];
+
+  dontBuild = true;
+
+  installPhase = ''
+    runHook preInstall
+
+    mkdir -p $out/bin $out/share/personal-backlog
+
+    cp server/server.py $out/share/personal-backlog/
+    cp -r webapp $out/share/personal-backlog/
+
+    makeWrapper ${python3}/bin/python3 $out/bin/personal-backlog \
+      --add-flags "$out/share/personal-backlog/server.py"
+
+    runHook postInstall
+  '';
+
+  meta = with lib; {
+    description = "A minimalist, single-user task manager where a Markdown file is your database";
+    homepage = "https://github.com/alfishe/personal-backlog";
+    license = licenses.mit;
+    maintainers = [ ];
+    platforms = platforms.unix;
+    mainProgram = "personal-backlog";
+  };
+}