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// SPDX-FileCopyrightText: 2025 Shota FUJI <pockawoooh@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-only

const wasmURL = new URL("../zig-out/bin/yamori_backend.wasm", import.meta.url);

export interface IncomingMessage {
	type: "request";

	id?: unknown;

	service: string;
	method: string;
	data: Uint8Array;
}

function isIncomingMessage(x: unknown): x is IncomingMessage {
	if (!x || typeof x !== "object") {
		return false;
	}

	if (!("type" in x && x.type === "request")) {
		return false;
	}

	return true;
}

export type OutgoingMessage =
	| {
			type: "response";

			id?: unknown;

			service: string;
			method: string;
			data: Uint8Array;
	  }
	| {
			type: "error";

			id?: unknown;
			error: string;
	  }
	| {
			type: "ready";
	  };

type CorePtr = number & { [type: symbol]: "Core" };
type ResponsePtr = number & { [type: symbol]: "Response" };
type BytesPtr = number & { [type: symbol]: "Bytes" };
type Uint8Slice = { ptr: BytesPtr; len: number };

interface WasmExports {
	memory: InstanceType<WebAssembly.Memory>;

	init_core(): CorePtr;
	deinit_core(ptr: CorePtr): void;

	allocate_bytes(len: number): BytesPtr;
	free_bytes(ptr: BytesPtr, len: number): void;

	create_response(): ResponsePtr;
	get_response_ptr(ptr: ResponsePtr): number;
	get_response_len(ptr: ResponsePtr): number;
	destroy_response(ptr: ResponsePtr): void;

	handle(
		core: CorePtr,
		service_ptr: BytesPtr,
		service_len: number,
		method_ptr: BytesPtr,
		method_len: number,
		bytes_ptr: BytesPtr,
		bytes_len: number,
		resp_ptr: ResponsePtr,
	): number;
}

class Backend {
	#utf8enc: TextEncoder = new TextEncoder();
	#exports: WasmExports;
	#core: CorePtr;

	constructor(instance: WebAssembly.Instance) {
		this.#exports = instance.exports as unknown as WasmExports;
		this.#core = this.#exports.init_core();
	}

	static async init(): Promise<Backend> {
		const { instance } = await WebAssembly.instantiateStreaming(fetch(wasmURL));

		return new Backend(instance);
	}

	#allocateBytes(len: number): Uint8Slice {
		const ptr = this.#exports.allocate_bytes(len);

		return { ptr, len };
	}

	#send(data: Uint8Array): Uint8Slice {
		const slice = this.#allocateBytes(data.length);
		if (slice.len === 0) {
			return slice;
		}

		const view = new Uint8Array(this.#exports.memory.buffer, slice.ptr, slice.len);
		view.set(data);
		return slice;
	}

	#sendUtf8(string: string): Uint8Slice {
		const bytes = this.#utf8enc.encode(string);

		return this.#send(bytes);
	}

	handle(service: string, method: string, data: Uint8Array): Uint8Array {
		const serviceSlice = this.#sendUtf8(service);
		const methodSlice = this.#sendUtf8(method);
		const dataSlice = this.#send(data);

		const resp = this.#exports.create_response();

		const result = this.#exports.handle(
			this.#core,
			serviceSlice.ptr,
			serviceSlice.len,
			methodSlice.ptr,
			methodSlice.len,
			dataSlice.ptr,
			dataSlice.len,
			resp,
		);

		try {
			if (result !== 0) {
				throw new Error("Handler returned non-zero result");
			}

			const ptr = this.#exports.get_response_ptr(resp);
			const len = this.#exports.get_response_len(resp);
			if (len === 0) {
				return new Uint8Array([]);
			}

			const cloned = this.#exports.memory.buffer.slice(ptr, len);

			return new Uint8Array(cloned);
		} finally {
			this.#exports.destroy_response(resp);
			this.#exports.free_bytes(dataSlice.ptr, dataSlice.len);
			this.#exports.free_bytes(methodSlice.ptr, methodSlice.len);
			this.#exports.free_bytes(serviceSlice.ptr, serviceSlice.len);
		}
	}
}

Backend.init().then((backend) => {
	addEventListener("message", async (event) => {
		if (!isIncomingMessage(event.data)) {
			console.warn("Received invalid message: ", event);
			return;
		}

		const { id, service, method, data } = event.data;

		try {
			const resp = backend.handle(service, method, data);

			self.postMessage(
				{
					type: "response",
					id,
					service,
					method,
					data: resp,
				} satisfies OutgoingMessage,
				{
					transfer: [resp.buffer],
				},
			);
		} catch (error) {
			console.error(error);

			self.postMessage({
				type: "error",
				id,
				error: String(error),
			} satisfies OutgoingMessage);
		}
	});

	self.postMessage({
		type: "ready",
	} satisfies OutgoingMessage);
});