webapp.nix

{options, config, lib, pkgs, ...}:
with lib;
let
  cfg = config.webapp;
in {
  ## Interface ##
  options.webapp = {
    presets = mkOption {
      default = {};
      example = literalExample ''
        {
          name = {
            options: { <additional options> }
            mkConfig: config: virtualHost
          };
        }
      '';
      description = "Presets";
      type = types.attrsOf (types.submodule ({config, ...}: {
        options = {
          options = mkOption {
            type = types.attrs;
            default = {};
            description = "Preset specific options";
          };
          mkConfig = mkOption {
            type = mkOptionType {
              name = "function";
              check = f: (builtins.typeOf f) == "lambda";
            };
            default = opts: {};
            description = "Preset config function";
          };
        };
      }));
    };
    applications = mkOption {
      default = {};
      example = ''{
        "example.com" = {
          preset = "static";
          # preset specific options
          root = "/var/www/example_com";
        }
      }'';
      description = "Applications";
      type = types.attrsOf (types.submodule ({config, ...}: {
        options = {
          preset = mkOption {
            example = "static";
            type = types.enum (attrNames cfg.presets);
            description = "The preset for application.";
            default = "base";
          };
        } // cfg.presets."${config.preset}".options; # <- infinite recursion occurs here
      }));
    };
  };

  ## Implementation ##
  config = {
    environment.systemPackages = [ pkgs.libidn ];

    services.nginx.virtualHosts = mapAttrs (serverName: opts@{preset, ...}:
      (cfg.presets."${preset}".mkConfig opts)) cfg.applications;

    webapp.presets.static = {
      options = {
        root = mkOption {
          type = types.str;
          description = "Root directory of application";
        };
      };
      mkConfig = {root, ...}: {
        locations."/".root = root;
      };
    };

    ## Test app config ##
    webapp.applications."example.com" = {
      preset = "static";
      root = "/var/www/example.com";
    };
  };
}