gistfile1.txt

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.util.Map;

public class Main {

	public static void main(String args[]) throws IOException {

		net.minecraft.data.Main.main(new String[] {"--reports"});

		String content = new String(Files.readAllBytes(new File("generated/reports/blocks.json").toPath()));

		Gson gson = new GsonBuilder().setPrettyPrinting().disableHtmlEscaping().create();
		JsonObject object = gson.fromJson(content, JsonObject.class);

		JsonObject viaMappings = new JsonObject();
		JsonObject blocks = new JsonObject();
		viaMappings.add("blocks", blocks);

		for (Map.Entry<String, JsonElement> blocksEntry : object.entrySet()) {
			JsonObject block = blocksEntry.getValue().getAsJsonObject();
			JsonArray states = block.getAsJsonArray("states");
			for (JsonElement state : states) {
				StringBuilder value = new StringBuilder(blocksEntry.getKey());
				if (state.getAsJsonObject().has("properties")) {
					value.append("[");
					JsonObject properties = state.getAsJsonObject().getAsJsonObject("properties");
					boolean first = true;
					for (Map.Entry<String, JsonElement> propertyEntry : properties.entrySet()) {
						if (first) first = false;
						else value.append(',');
						value.append(propertyEntry.getKey()).append('=').append(propertyEntry.getValue().getAsJsonPrimitive().getAsString());
					}
					value.append("]");
				}
				blocks.add(state.getAsJsonObject().get("id").getAsString(), new JsonPrimitive(value.toString()));
			}
		}

		content = new String(Files.readAllBytes(new File("generated/reports/items.json").toPath()));
		object = gson.fromJson(content, JsonObject.class);

		JsonObject items = new JsonObject();
		viaMappings.add("items", items);

		for (Map.Entry<String, JsonElement> itemsEntry : object.entrySet()) {
			items.add(String.valueOf(itemsEntry.getValue().getAsJsonObject().getAsJsonPrimitive("protocol_id").getAsInt()), new JsonPrimitive(itemsEntry.getKey()));
		}

		try(  PrintWriter out = new PrintWriter( "mapping-1.13.json" )  ){
			out.print(gson.toJson(viaMappings));
		}
	}
}