// Reads back the player's stored order for the current turn through
// `user.games.order.get`. Used by `OrderDraftStore` only when the
// local cache row is absent (fresh install, cleared storage, or a
// brand-new device): the local draft is the source of truth, so a
// present-but-empty cache row means "no commands" and is honoured
// over the server snapshot.

import { Builder, ByteBuffer } from "flatbuffers";

import type { GalaxyClient } from "../api/galaxy-client";
import { uuidToHiLo } from "../api/game-state";
import { UUID } from "../proto/galaxy/fbs/common";
import {
	CommandPayload,
	CommandPlanetRename,
	UserGamesOrderGet,
	UserGamesOrderGetResponse,
} from "../proto/galaxy/fbs/order";
import type { OrderCommand } from "./order-types";

const MESSAGE_TYPE = "user.games.order.get";

export class OrderLoadError extends Error {
	readonly resultCode: string;
	readonly code: string;

	constructor(resultCode: string, code: string, message: string) {
		super(message);
		this.name = "OrderLoadError";
		this.resultCode = resultCode;
		this.code = code;
	}
}

export interface FetchedOrder {
	commands: OrderCommand[];
	updatedAt: number;
}

/**
 * fetchOrder issues `user.games.order.get` for the given game and
 * turn, decodes the response, and returns the typed draft. A
 * `found = false` answer (no order stored on the server) surfaces as
 * an empty `commands` array — the caller treats this as a clean
 * draft. Unknown command kinds in the response are skipped with a
 * console warning so a backend-side schema bump never silently
 * corrupts the local draft.
 */
export async function fetchOrder(
	client: GalaxyClient,
	gameId: string,
	turn: number,
): Promise<FetchedOrder> {
	if (turn < 0) {
		throw new OrderLoadError(
			"invalid_request",
			"invalid_request",
			`turn must be non-negative, got ${turn}`,
		);
	}
	const payload = buildRequest(gameId, turn);
	const result = await client.executeCommand(MESSAGE_TYPE, payload);
	if (result.resultCode !== "ok") {
		const { code, message } = decodeError(result.payloadBytes, result.resultCode);
		throw new OrderLoadError(result.resultCode, code, message);
	}
	return decodeResponse(result.payloadBytes);
}

function buildRequest(gameId: string, turn: number): Uint8Array {
	const builder = new Builder(64);
	const [hi, lo] = uuidToHiLo(gameId);
	const gameIdOffset = UUID.createUUID(builder, hi, lo);
	UserGamesOrderGet.startUserGamesOrderGet(builder);
	UserGamesOrderGet.addGameId(builder, gameIdOffset);
	UserGamesOrderGet.addTurn(builder, BigInt(turn));
	const offset = UserGamesOrderGet.endUserGamesOrderGet(builder);
	builder.finish(offset);
	return builder.asUint8Array();
}

function decodeResponse(payload: Uint8Array): FetchedOrder {
	if (payload.length === 0) {
		throw new OrderLoadError(
			"internal_error",
			"internal_error",
			"empty user.games.order.get payload",
		);
	}
	const buffer = new ByteBuffer(payload);
	const response = UserGamesOrderGetResponse.getRootAsUserGamesOrderGetResponse(buffer);
	if (!response.found()) {
		return { commands: [], updatedAt: 0 };
	}
	const order = response.order();
	if (order === null) {
		throw new OrderLoadError(
			"internal_error",
			"internal_error",
			"order missing while found=true",
		);
	}
	const commands: OrderCommand[] = [];
	const length = order.commandsLength();
	for (let i = 0; i < length; i++) {
		const item = order.commands(i);
		if (item === null) continue;
		const cmd = decodeCommand(item);
		if (cmd === null) continue;
		commands.push(cmd);
	}
	return {
		commands,
		updatedAt: Number(order.updatedAt()),
	};
}

type CommandItemView = NonNullable<
	ReturnType<NonNullable<ReturnType<UserGamesOrderGetResponse["order"]>>["commands"]>
>;

function decodeCommand(item: CommandItemView): OrderCommand | null {
	if (item === null) return null;
	const id = item.cmdId();
	if (id === null) return null;
	const payloadType = item.payloadType();
	switch (payloadType) {
		case CommandPayload.CommandPlanetRename: {
			const inner = new CommandPlanetRename();
			item.payload(inner);
			return {
				kind: "planetRename",
				id,
				planetNumber: Number(inner.number()),
				name: inner.name() ?? "",
			};
		}
		default:
			console.warn(
				`fetchOrder: skipping unknown command kind (payloadType=${payloadType})`,
			);
			return null;
	}
}

function decodeError(
	payload: Uint8Array,
	resultCode: string,
): { code: string; message: string } {
	if (payload.length === 0) {
		return { code: resultCode, message: resultCode };
	}
	try {
		const text = new TextDecoder().decode(payload);
		const parsed = JSON.parse(text) as { code?: string; message?: string };
		return {
			code: typeof parsed.code === "string" ? parsed.code : resultCode,
			message: typeof parsed.message === "string" ? parsed.message : text,
		};
	} catch {
		return { code: resultCode, message: resultCode };
	}
}