watson: add module

Watson is a CLI for tracking your time.

Two unit tests were added to validate the module behavior for an empty
configuration and the example configuration.

modules/programs/watson.nix

@@ -0,0 +1,94 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.watson;
+
+  iniFormat = pkgs.formats.ini { };
+
+  configDir = if pkgs.stdenv.hostPlatform.isDarwin then
+    "Library/Application Support"
+  else
+    config.xdg.configHome;
+
+in {
+  meta.maintainers = [ maintainers.polykernel ];
+
+  options.programs.watson = {
+    enable = mkEnableOption "watson, a wonderful CLI to track your time";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.watson;
+      defaultText = literalExpression "pkgs.watson";
+      description = "Package providing the <command>watson</command>.";
+    };
+
+    enableBashIntegration = mkEnableOption "watson's bash integration" // {
+      default = true;
+    };
+
+    enableZshIntegration = mkEnableOption "watson's zsh integration" // {
+      default = true;
+    };
+
+    enableFishIntegration = mkEnableOption "watson's fish integration" // {
+      default = true;
+    };
+
+    settings = mkOption {
+      type = iniFormat.type;
+      default = { };
+      description = ''
+        Configuration written to
+        <filename>$XDG_CONFIG_HOME/watson/config</filename> on Linux or
+        <filename>$HOME/Library/Application Support/watson/config</filename> on Darwin.
+        </para><para>
+        See <link xlink:href="https://github.com/TailorDev/Watson/blob/master/docs/user-guide/configuration.md"/>
+        for an example configuration.
+      '';
+      example = literalExpression ''
+        {
+          backend = {
+            url = "https://api.crick.fr";
+            token = "yourapitoken";
+          };
+
+          options = {
+            stop_on_start = true;
+            stop_on_restart = false;
+            date_format = "%Y.%m.%d";
+            time_format = "%H:%M:%S%z";
+            week_start = "monday";
+            log_current = false;
+            pager = true;
+            report_current = false;
+            reverse_log = true;
+          };
+        }
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+
+    home.file."${configDir}/watson/config" = mkIf (cfg.settings != { }) {
+      source = iniFormat.generate "watson-config" cfg.settings;
+    };
+
+    programs.bash.initExtra = mkIf cfg.enableBashIntegration ''
+      source ${cfg.package}/share/bash-completion/completions/watson
+    '';
+
+    programs.zsh.initExtra = mkIf cfg.enableZshIntegration ''
+      source ${cfg.package}/share/zsh/site-functions/_watson
+    '';
+
+    programs.fish.shellInit = mkIf cfg.enableFishIntegration ''
+      source ${cfg.package}/share/fish/vendor_completions.d/watson.fish
+    '';
+  };
+}