JSON Fabrication

- Add rudimentary JSON parsing to load a config on fabric
- Save the config file after a config command changes

fabric/src/main/java/com/jozufozu/flywheel/impl/FabricFlwConfig.java

@@ -1,15 +1,48 @@
 package com.jozufozu.flywheel.impl;
 
+import java.io.File;
+import java.io.FileReader;
+import java.io.FileWriter;
+import java.nio.file.Path;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import com.google.gson.JsonPrimitive;
+import com.jozufozu.flywheel.Flywheel;
 import com.jozufozu.flywheel.api.backend.Backend;
 import com.jozufozu.flywheel.api.backend.BackendManager;
 
-// TODO: Fabric config
+import net.fabricmc.loader.api.FabricLoader;
+import net.minecraft.ResourceLocationException;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.util.Mth;
+
 public class FabricFlwConfig implements FlwConfig {
-	public static final FabricFlwConfig INSTANCE = new FabricFlwConfig();
+	public static final Path PATH = FabricLoader.getInstance()
+			.getConfigDir()
+			.resolve("flywheel.json");
+
+	public static final FabricFlwConfig INSTANCE = new FabricFlwConfig(PATH.toFile());
+
+	protected static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
+
+	public static final int WORKER_THREADS_DEFAULT = -1;
+	public static final int WORKER_THREADS_MAX = Runtime.getRuntime()
+			.availableProcessors();
+	public static final boolean LIMIT_UPDATES_DEFAULT = true;
 
 	public Backend backend = BackendManager.getDefaultBackend();
-	public boolean limitUpdates = true;
+	public boolean limitUpdates = LIMIT_UPDATES_DEFAULT;
-	public int workerThreads = -1;
+	public int workerThreads = WORKER_THREADS_DEFAULT;
+
+	private final File file;
+
+	public FabricFlwConfig(File file) {
+		this.file = file;
+	}
 
 	@Override
 	public Backend backend() {
@@ -25,4 +58,106 @@ public class FabricFlwConfig implements FlwConfig {
 	public int workerThreads() {
 		return workerThreads;
 	}
+
+	public void load() {
+		if (file.exists()) {
+			try (FileReader reader = new FileReader(file)) {
+				fromJson(JsonParser.parseReader(reader));
+			} catch (Exception e) {
+				Flywheel.LOGGER.error("Could not load config from file '{}'", file.getAbsolutePath(), e);
+			}
+		}
+		// In case we found an error in the config file, immediately save to fix it.
+		save();
+	}
+
+	public void save() {
+		try (FileWriter writer = new FileWriter(file)) {
+			GSON.toJson(toJson(), writer);
+		} catch (Exception e) {
+			Flywheel.LOGGER.error("Could not save config to file '{}'", file.getAbsolutePath(), e);
+		}
+	}
+
+	public void fromJson(JsonElement json) {
+		if (!(json instanceof JsonObject object)) {
+			backend = BackendManager.getDefaultBackend();
+			limitUpdates = LIMIT_UPDATES_DEFAULT;
+			workerThreads = WORKER_THREADS_DEFAULT;
+			return;
+		}
+
+		readBackend(object);
+		readLimitUpdates(object);
+		readWorkerThreads(object);
+	}
+
+	private void readBackend(JsonObject object) {
+		var backendJson = object.get("backend");
+
+		String err = null;
+
+		if (backendJson instanceof JsonPrimitive primitive && primitive.isString()) {
+			var backendString = primitive.getAsString();
+			try {
+				this.backend = Backend.REGISTRY.getOrThrow(new ResourceLocation(backendString));
+				return;
+			} catch (IllegalArgumentException e) {
+				err = "backend ID '" + backendString + "' is not registered";
+			} catch (ResourceLocationException e) {
+				err = "backend '" + backendString + "' is not a valid resource location";
+			} catch (Exception e) {
+				// Something else went wrong? This should be dead code.
+				err = "backend '" + backendString + "' is invalid";
+			}
+		} else if (backendJson != null) {
+			err = "backend must be a string";
+		}
+
+		// Don't log an error if the field is missing.
+		if (err != null) {
+			Flywheel.LOGGER.warn(err);
+		}
+		backend = BackendManager.getDefaultBackend();
+	}
+
+	private void readLimitUpdates(JsonObject object) {
+		var limitUpdatesJson = object.get("limitUpdates");
+		if (limitUpdatesJson instanceof JsonPrimitive primitive && primitive.isBoolean()) {
+			limitUpdates = primitive.getAsBoolean();
+			return;
+		} else if (limitUpdatesJson != null) {
+			Flywheel.LOGGER.warn("limitUpdates must be a boolean");
+		}
+		limitUpdates = LIMIT_UPDATES_DEFAULT;
+	}
+
+	private void readWorkerThreads(JsonObject object) {
+		var workerThreadsJson = object.get("workerThreads");
+
+		if (workerThreadsJson instanceof JsonPrimitive primitive && primitive.isNumber()) {
+			int configuredValue = primitive.getAsInt();
+
+			int clamped = Mth.clamp(configuredValue, WORKER_THREADS_DEFAULT, WORKER_THREADS_MAX);
+
+			if (clamped != configuredValue) {
+				Flywheel.LOGGER.warn("workerThreads value of {} is out of range, clamping to {}", configuredValue, clamped);
+			}
+
+			workerThreads = clamped;
+			return;
+		} else if (workerThreadsJson != null) {
+			Flywheel.LOGGER.warn("workerThreads must be an integer");
+		}
+
+		workerThreads = WORKER_THREADS_DEFAULT;
+	}
+
+	public JsonObject toJson() {
+		JsonObject object = new JsonObject();
+		object.addProperty("limitUpdates", limitUpdates);
+		object.addProperty("workerThreads", workerThreads);
+		object.addProperty("backend", Backend.REGISTRY.getIdOrThrow(backend).toString());
+		return object;
+	}
 }

fabric/src/main/java/com/jozufozu/flywheel/impl/FlwCommands.java

@@ -25,8 +25,6 @@ public final class FlwCommands {
 	}
 
 	public static void registerClientCommands(CommandDispatcher<FabricClientCommandSource> dispatcher, CommandBuildContext buildContext) {
-		FabricFlwConfig config = FabricFlwConfig.INSTANCE;
-
 		LiteralArgumentBuilder<FabricClientCommandSource> command = ClientCommandManager.literal("flywheel");
 
 		command.then(ClientCommandManager.literal("backend")
@@ -40,7 +38,8 @@ public final class FlwCommands {
 				.then(ClientCommandManager.argument("id", BackendArgument.INSTANCE)
 					.executes(context -> {
 						Backend requestedBackend = context.getArgument("id", Backend.class);
-						config.backend = requestedBackend;
+						FabricFlwConfig.INSTANCE.backend = requestedBackend;
+						FabricFlwConfig.INSTANCE.save();
 
 						// Reload renderers so we can report the actual backend.
 						Minecraft.getInstance().levelRenderer.allChanged();
@@ -60,7 +59,7 @@ public final class FlwCommands {
 
 		command.then(ClientCommandManager.literal("limitUpdates")
 				.executes(context -> {
-					if (config.limitUpdates) {
+					if (FabricFlwConfig.INSTANCE.limitUpdates) {
 						context.getSource().sendFeedback(Component.translatable("command.flywheel.limit_updates.get.on"));
 					} else {
 						context.getSource().sendFeedback(Component.translatable("command.flywheel.limit_updates.get.off"));
@@ -69,14 +68,16 @@ public final class FlwCommands {
 				})
 				.then(ClientCommandManager.literal("on")
 						.executes(context -> {
-							config.limitUpdates = true;
+							FabricFlwConfig.INSTANCE.limitUpdates = true;
+							FabricFlwConfig.INSTANCE.save();
 							context.getSource().sendFeedback(Component.translatable("command.flywheel.limit_updates.set.on"));
 							Minecraft.getInstance().levelRenderer.allChanged();
 							return Command.SINGLE_SUCCESS;
 						}))
 				.then(ClientCommandManager.literal("off")
 						.executes(context -> {
-							config.limitUpdates = false;
+							FabricFlwConfig.INSTANCE.limitUpdates = false;
+							FabricFlwConfig.INSTANCE.save();
 							context.getSource().sendFeedback(Component.translatable("command.flywheel.limit_updates.set.off"));
 							Minecraft.getInstance().levelRenderer.allChanged();
 							return Command.SINGLE_SUCCESS;

fabric/src/main/java/com/jozufozu/flywheel/impl/FlywheelFabric.java

@@ -44,6 +44,9 @@ public final class FlywheelFabric implements ClientModInitializer {
 
 		// FIXME: Registries cannot be frozen this early.
 		FlywheelInit.freezeRegistries();
+		// Have to load the config after we freeze registries,
+		// so we can find third party backends.
+		FabricFlwConfig.INSTANCE.load();
 	}
 
 	private static void setupImpl() {