Generate without full build

Adds `elm-pages generate` command which only builds `gen/Pages.elm`.

Fixes #112

generator/src/Main.elm

@@ -3,16 +3,12 @@ port module Main exposing (main)
 import Cli.Option as Option
 import Cli.OptionsParser as OptionsParser exposing (with)
 import Cli.Program as Program
+import Json.Encode as Encode
 import List.Extra
 import String.Interpolate exposing (interpolate)
 
 
-port writeFile :
-    { watch : Bool
-    , debug : Bool
-    , customPort : Maybe Int
-    }
-    -> Cmd msg
+port writeFile : Encode.Value -> Cmd msg
 
 
 port printAndExitSuccess : String -> Cmd msg
@@ -156,6 +152,7 @@ generateMarkdownPage markdown =
 type CliOptions
     = Develop DevelopOptions
     | Build
+    | Generate
 
 
 type alias DevelopOptions =
@@ -179,6 +176,8 @@ application =
             )
         |> Program.add
             (OptionsParser.buildSubCommand "build" Build)
+        |> Program.add
+            (OptionsParser.buildSubCommand "generate" Generate)
 
 
 type alias Flags =
@@ -197,24 +196,63 @@ type alias MarkdownContent =
     { path : String, metadata : String, body : String }
 
 
+type DevelopMode
+    = None
+    | Run
+    | Start
+
+
 init : Flags -> CliOptions -> Cmd Never
 init flags cliOptions =
     let
-        ( watch, debug, customPort ) =
+        ( develop, debug, customPort ) =
             case cliOptions of
                 Develop options ->
-                    ( True, options.debugger, options.customPort )
+                    ( Start, options.debugger, options.customPort )
 
                 Build ->
-                    ( False, False, Nothing )
+                    ( Run, False, Nothing )
+
+                Generate ->
+                    ( None, False, Nothing )
     in
-    { watch = watch
+    { develop = develop
     , debug = debug
     , customPort = customPort
     }
+        |> encodeWriteFile
         |> writeFile
 
 
+encodeWriteFile : { develop : DevelopMode, debug : Bool, customPort : Maybe Int } -> Encode.Value
+encodeWriteFile { develop, debug, customPort } =
+    Encode.object
+        [ ( "develop", encodeDevelop develop )
+        , ( "debug", Encode.bool debug )
+        , ( "customPort", encodeCustomPort customPort )
+        ]
+
+
+encodeDevelop : DevelopMode -> Encode.Value
+encodeDevelop develop =
+    case develop of
+        None ->
+            Encode.string "none"
+
+        Run ->
+            Encode.string "run"
+
+        Start ->
+            Encode.string "start"
+
+
+encodeCustomPort : Maybe Int -> Encode.Value
+encodeCustomPort maybePort =
+    maybePort
+        |> Maybe.map Encode.int
+        |> Maybe.withDefault Encode.null
+
+
 generateFileContents : List MarkdownContent -> List ( String, String )
 generateFileContents =
     List.map

generator/src/elm-pages.js

@@ -81,7 +81,7 @@ function run() {
       });
     const routes = toRoutes(markdownContent);
 
-    global.mode = cliOptions.watch ? "dev" : "prod"
+    global.mode = cliOptions.develop === 'start' ? "dev" : "prod"
     generateRecords().then((staticRoutes) =>
       doCliStuff(
         global.mode,
@@ -89,7 +89,7 @@ function run() {
         markdownContent
       )
     ).then((payload) => {
-      if (cliOptions.watch) {
+      if (cliOptions.develop === 'start') {
         develop.start({
           routes,
           debug: cliOptions.debug,
@@ -97,7 +97,7 @@ function run() {
           manifestConfig: payload.manifest,
 
         });
-      } else {
+      } else if (cliOptions.develop === 'run') {
         develop.run({
           routes,
           debug: cliOptions.debug,
@@ -107,7 +107,7 @@ function run() {
       }
 
     }).catch(function (errorPayload) {
-      if (cliOptions.watch) {
+      if (cliOptions.develop === 'start') {
         develop.start({
           routes,
           debug: cliOptions.debug,