factor out function wrapper to module function (#503)

lifts the `{ input output }` function wrapper out of the user interface to `function.nix`, simplifying usage.

Reviewed-on: #503

deployment/data-model-test.nix

@@ -98,20 +98,18 @@ in
                     {
                       options.enable = lib.mkEnableOption "Hello in the shell";
                     };
-                  implementation = cfg: {
-                    input = cfg;
-                    output = lib.optionalAttrs cfg.enable {
+                  implementation =
+                    cfg:
+                    lib.optionalAttrs cfg.enable {
                       resources.hello.login-shell.packages.hello = pkgs.hello;
                     };
-                  };
                 };
               environments.single-nixos-vm =
                 { config, ... }:
                 {
                   resources.operator-environment.login-shell.username = "operator";
                   implementation = requests: {
-                    input = requests;
-                    output.nixops4 =
+                    nixops4 = (
                       { providers, ... }:
                       {
                         providers = {
@@ -130,7 +128,8 @@ in
                               );
                             };
                         };
-                      };
+                      }
+                    );
                   };
                 };
             };

deployment/data-model.nix

@@ -109,11 +109,11 @@ in
             };
             resources = mkOption {
               description = "Compute resources required by an application";
-              type = functionTo application.config.config-mapping.output-type;
+              type = application.config.config-mapping.function-type;
               readOnly = true;
-              default = input: (application.config.implementation input).output;
+              default = application.config.config-mapping.apply;
             };
-            # TODO(@fricklerhandwerk): this needs a better name, it's just the type
+            # TODO(@fricklerhandwerk): this needs a better name
             config-mapping = mkOption {
               description = "Function type for the mapping from application configuration to required resources";
               type = functionType;
@@ -121,6 +121,7 @@ in
               default = {
                 input-type = submodule application.config.module;
                 output-type = application-resources;
+                implementation = application.config.implementation;
               };
             };
           };
@@ -157,6 +158,25 @@ in
               default = {
                 input-type = application-resources;
                 output-type = deployment;
+                implementation = environment.config.implementation;
+              };
+            };
+            config-mapping = mkOption {
+              description = "Mapping from a configuration to a deployment";
+              type = submodule functionType;
+              readOnly = true;
+              default = {
+                input-type = config.configuration;
+                output-type = nixops4Deployment;
+                implementation =
+                  cfg:
+                  # TODO: check cfg.enable.true
+                  let
+                    required-resources = lib.mapAttrs (
+                      name: application-settings: config.applications.${name}.resources application-settings
+                    ) cfg.applications;
+                  in
+                  environment.config.resource-mapping.apply required-resources;
               };
             };
             # TODO(@fricklerhandwerk): maybe this should be a separate thing such as `fediversity-setup`,
@@ -164,18 +184,9 @@ in
             # then the deployments can simply be the result of the function application baked into this module.
             deployment = mkOption {
               description = "Generate a deployment from a configuration, by applying an environment's resource policies to the applications' resource mappings";
-              type = functionTo (environment.config.resource-mapping.output-type);
+              type = environment.config.config-mapping.function-type;
               readOnly = true;
-              default =
-                cfg:
-                # TODO: check cfg.enable.true
-                let
-                  required-resources = lib.mapAttrs (
-                    name: application-settings: config.applications.${name}.resources application-settings
-                  ) cfg.applications;
-                in
-                (environment.config.implementation required-resources).output;
-
+              default = environment.config.config-mapping.apply;
             };
           };
         })

deployment/function.nix

@@ -19,6 +19,11 @@ in
       type = optionType;
     };
     function-type = mkOption {
+      type = optionType;
+      readOnly = true;
+      default = functionTo config.output-type;
+    };
+    wrapper-type = mkOption {
       type = optionType;
       readOnly = true;
       default = functionTo (submodule {
@@ -32,5 +37,22 @@ in
         };
       });
     };
+    implementation = mkOption {
+      type = config.function-type;
+      default = _: { };
+    };
+    wrapper = mkOption {
+      type = config.wrapper-type;
+      readOnly = true;
+      default = input: fn: {
+        inherit input;
+        output = config.implementation fn.config.input;
+      };
+    };
+    apply = mkOption {
+      type = config.function-type;
+      readOnly = true;
+      default = input: (config.wrapper input).output;
+    };
   };
 }