package com.jozufozu.flywheel.backend;

import java.util.Collection;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.jozufozu.flywheel.backend.instancing.InstancedRenderDispatcher;
import com.jozufozu.flywheel.backend.source.Resolver;
import com.jozufozu.flywheel.backend.source.ShaderLoadingException;
import com.jozufozu.flywheel.backend.source.ShaderSources;
import com.jozufozu.flywheel.core.crumbling.CrumblingRenderer;
import com.jozufozu.flywheel.core.shader.spec.ProgramSpec;
import com.jozufozu.flywheel.event.GatherContextEvent;
import com.jozufozu.flywheel.util.ResourceUtil;
import com.jozufozu.flywheel.util.StreamUtil;
import com.mojang.datafixers.util.Pair;
import com.mojang.serialization.DataResult;
import com.mojang.serialization.JsonOps;

import net.minecraft.client.Minecraft;
import net.minecraft.client.multiplayer.ClientLevel;
import net.minecraft.resources.ResourceLocation;
import net.minecraft.server.packs.resources.ReloadableResourceManager;
import net.minecraft.server.packs.resources.Resource;
import net.minecraft.server.packs.resources.ResourceManager;
import net.minecraft.server.packs.resources.ResourceManagerReloadListener;
import net.minecraftforge.fml.ModLoader;

/**
 * The main entity for loading shaders.
 *
 * <p>
 * This class is responsible for invoking the loading, parsing, and compilation stages.
 * </p>
 */
public class Loader implements ResourceManagerReloadListener {
	public static final String PROGRAM_DIR = "flywheel/programs/";
	private static final Gson GSON = new GsonBuilder().create();

	private final Backend backend;
	private boolean shouldCrash;

	private boolean firstLoad = true;

	public Loader(Backend backend) {
		this.backend = backend;

		// Can be null when running datagenerators due to the unfortunate time we call this
		Minecraft minecraft = Minecraft.getInstance();
		if (minecraft != null) {
			ResourceManager manager = minecraft.getResourceManager();
			if (manager instanceof ReloadableResourceManager) {
				((ReloadableResourceManager) manager).registerReloadListener(this);
			}
		}
	}

	public void notifyError() {
		shouldCrash = true;
	}

	@Override
	public void onResourceManagerReload(ResourceManager manager) {
		backend.refresh();

		if (backend.gl20()) {
			shouldCrash = false;
			backend._clearContexts();

			Resolver.INSTANCE.invalidate();
			ModLoader.get()
					.postEvent(new GatherContextEvent(backend, firstLoad));

			ShaderSources sources = new ShaderSources(manager);

			loadProgramSpecs(manager);

			Resolver.INSTANCE.resolve(sources);

			for (IShaderContext<?> context : backend.allContexts()) {
				context.load();
			}

			if (shouldCrash) {
				throw new ShaderLoadingException("Could not load all shaders, see log for details");
			}

			Backend.log.info("Loaded all shader programs.");

			ClientLevel world = Minecraft.getInstance().level;
			if (Backend.isFlywheelWorld(world)) {
				// TODO: looks like it might be good to have another event here
				InstancedRenderDispatcher.loadAllInWorld(world);
				CrumblingRenderer.reset();
			}
		}

		firstLoad = false;
	}

	private void loadProgramSpecs(ResourceManager manager) {
		Collection<ResourceLocation> programSpecs = manager.listResources(PROGRAM_DIR, s -> s.endsWith(".json"));

		for (ResourceLocation location : programSpecs) {
			try {
				Resource file = manager.getResource(location);

				String s = StreamUtil.readToString(file.getInputStream());

				ResourceLocation specName = ResourceUtil.trim(location, PROGRAM_DIR, ".json");

				DataResult<Pair<ProgramSpec, JsonElement>> result = ProgramSpec.CODEC.decode(JsonOps.INSTANCE, GSON.fromJson(s, JsonElement.class));

				ProgramSpec spec = result.get()
						.orThrow()
						.getFirst();

				spec.setName(specName);

				backend.register(spec);
			} catch (Exception e) {
				Backend.log.error(e);
			}
		}
	}
}