Created PDF viewer framework

modules/plugins/languages/tex/pdfViewer/viewers/default.nix

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+{ ... }:
+{
+  imports = [
+    ./okular.nix
+  ];
+}

modules/plugins/languages/tex/pdfViewer/viewers/okular.nix

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+{
+  pkgs,
+  lib,
+  ...
+} @ moduleInheritencePackage: let
+  # The name of the pdf viewer
+  name = "okular";
+
+  # The viewer template
+  template = import ./viewerTemplate.nix;
+
+  inherit (lib.options) mkOption mkEnableOption;
+  inherit (lib.types) package str listOf;
+in (
+  template {
+    inherit name moduleInheritencePackage;
+
+    options = {
+      enable = mkEnableOption "enable okular as the pdf file previewer.";
+
+      package = mkOption {
+        type = package;
+        default = pkgs.okular;
+        description = "okular package";
+      };
+
+      executable = mkOption {
+        type = str;
+        default = "okular";
+        description = "The executable name to call the viewer.";
+      };
+
+      args = mkOption {
+        type = listOf str;
+        default = [ "--unique" "file:%p#src:%l%f" ];
+        description = "Arguments to pass to the viewer.";
+      };
+    };
+
+    args = viewerCfg: ( viewerCfg.args );
+  }
+)

modules/plugins/languages/tex/pdfViewer/viewers/viewerTemplate.nix

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+# This function acts as a template for creating new pdf viewers.
+# It enforces providing all the parameters required for creating
+# a new pdf viewer for it to be able to work in the existing code.
+#
+# The first layer requirements are as follows:
+{
+  # This is the name of the pdf viewer, it will only be used internally and
+  # MUST match the <name>.nix file that the pdf viewer is implemented in.
+  name,
+  #
+  # Module attribute set. This is the attribute set that the module that is
+  # defining a pdf viewer is passed as its input.
+  moduleInheritencePackage,
+  #
+  # These are the standard options for the pdf viewer just like creating any
+  # other module. Some options are required and are described below but
+  # it will also accept any other options that are provided to it.
+  options,
+  #
+  # These are the command line arguments that will accompany the executable
+  # when the view command is called.
+  # This is a function that will take in the cfg of its own pdf viewer.
+  # i.e. it will be called as "args cfg.pdfViewer.viewers.${name}"
+  args,
+  ...
+}: let
+  # Inherit the necessary variables available to any module.
+  inherit (moduleInheritencePackage) lib config;
+  #
+  # Inherit other useful functions.
+  inherit (lib.modules) mkIf;
+  #
+  # Set the cfg variable
+  cfg = config.vim.languages.tex;
+  #
+  # Set the cfg of the viewer itself
+  viewerCfg = cfg.pdfViewer.viewers.${name};
+in {
+  # These are the options for the pdf viewer. It will accept any options
+  # provided to it but some options are mandatory:
+  options.vim.languages.tex.pdfViewer.viewers.${name} = ({
+      # The enable option. This one is self explanatory.
+      enable,
+      #
+      # This is the package option for the pdf viewer.
+      package,
+      #
+      # This is the executable that will be used to call the pdf viewer.
+      # It, along with package will result in:
+      # "<package_path>/bin/<executable>"
+      executable,
+      #
+      # Any other options provided are accepted.
+      ...
+    } @ opts:
+      opts)
+  options;
+
+  # Check that the language, overall pdf viewing, and this pdf viewer have been enabled before making any
+  # config.
+  config = mkIf (cfg.enable && viewerCfg.enable) {
+    vim.languages.tex.pdfViewer = {
+      inherit name;
+      inherit (viewerCfg) package executable;
+      args = args viewerCfg;
+    };
+  };
+}