pandoc: add new module

Add a module for pandoc that provides the following:

1. Setting default configuration options.
2. Installing templates.
3. Installing citation styles.

modules/misc/news.nix

@@ -2380,6 +2380,13 @@ in
           A new module is available: 'programs.tint2'.
         '';
       }
+
+      {
+        time = "2022-01-22T17:39:20+00:00";
+        message = ''
+          A new module is available: 'programs.pandoc'.
+        '';
+      }
     ];
   };
 }

modules/modules.nix

@@ -117,6 +117,7 @@ let
     ./programs/octant.nix
     ./programs/offlineimap.nix
     ./programs/opam.nix
+    ./programs/pandoc.nix
     ./programs/password-store.nix
     ./programs/pazi.nix
     ./programs/pet.nix

modules/programs/pandoc.nix

@@ -0,0 +1,104 @@
+{ config, lib, pkgs, ... }:
+
+let
+
+  cfg = config.programs.pandoc;
+
+  inherit (lib) literalExpression mkEnableOption mkIf mkOption types;
+
+  jsonFormat = pkgs.formats.json { };
+
+  makeTemplateFile = name: file:
+    lib.nameValuePair "pandoc/templates/${name}" { source = file; };
+
+  getFileName = file:
+    # This is actually safe here, since it is just a file name
+    builtins.unsafeDiscardStringContext (baseNameOf file);
+
+  makeCslFile = file:
+    lib.nameValuePair "pandoc/csl/${getFileName file}" { source = file; };
+
+in {
+  meta.maintainers = [ lib.maintainers.kirelagin ];
+
+  options.programs.pandoc = {
+    enable = mkEnableOption "pandoc";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.pandoc;
+      defaultText = literalExpression "pkgs.pandoc";
+      description = "The pandoc package to use.";
+    };
+
+    # We wrap the executable to pass some arguments
+    finalPackage = mkOption {
+      type = types.package;
+      readOnly = true;
+      description = "Resulting package.";
+    };
+
+    defaults = mkOption {
+      type = jsonFormat.type;
+      default = { };
+      example = literalExpression ''
+        {
+          metadata = {
+            author = "John Doe";
+          };
+          pdf-engine = "xelatex";
+          citeproc = true;
+        }
+      '';
+      description = ''
+        Options to set by default.
+        These will be converted to JSON and written to a defaults
+        file (see Default files in pandoc documentation).
+      '';
+    };
+
+    defaultsFile = mkOption {
+      type = types.path;
+      readOnly = true;
+      description = "Resulting defaults file.";
+    };
+
+    templates = mkOption {
+      type = types.attrsOf types.path;
+      default = { };
+      example = literalExpression ''
+        {
+          "default.latex" = path/to/your/template;
+        }
+      '';
+      description = "Custom templates.";
+    };
+
+    citationStyles = mkOption {
+      type = types.listOf types.path;
+      default = [ ];
+      example = literalExpression "[ path/to/file.csl ]";
+      description = "List of .csl files to install.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    programs.pandoc = {
+      defaultsFile = jsonFormat.generate "hm.json" cfg.defaults;
+
+      finalPackage = pkgs.symlinkJoin {
+        name = "pandoc-with-defaults";
+        paths = [ cfg.package ];
+        nativeBuildInputs = [ pkgs.makeWrapper ];
+        postBuild = ''
+          wrapProgram "$out/bin/pandoc" \
+            --add-flags '--defaults "${cfg.defaultsFile}"'
+        '';
+      };
+    };
+
+    home.packages = [ cfg.finalPackage ];
+    xdg.dataFile = lib.mapAttrs' makeTemplateFile cfg.templates
+      // lib.listToAttrs (map makeCslFile cfg.citationStyles);
+  };
+}