/**
 * Self-hosted avatar imager — Phase 1.
 *
 * Pipeline (cascade):
 *   1. In-memory LRU cache  → instant
 *   2. Disk cache           → fast
 *   3. In-flight dedup      → coalesce thundering herd
 *   4. Upstream Habbo proxy → save to disk + memory
 *   5. Transparent fallback → never break the UI
 */

import { createHash } from "node:crypto";
import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { dirname, join } from "node:path";
import { siteSettings } from "@/lib/services/site-settings";
import { InFlight, LruCache, NegativeCache } from "./memory-cache";

const CACHE_DIR = join(process.cwd(), "public", "cache", "avatars");
const DEFAULT_UPSTREAM = "https://www.habbo.com/habbo-imaging/avatarimage";

const MEM_CACHE_CAPACITY = 500;
const NEGATIVE_CACHE_TTL_MS = 60_000;
const UPSTREAM_TIMEOUT_MS = 10_000;

// 1×1 transparent PNG (67 bytes) — served when both local and upstream fail.
const TRANSPARENT_PNG = Buffer.from(
	"iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkAAIAAAoAAv/lxKUAAAAASUVORK5CYII=",
	"base64",
);

export interface AvatarRenderOptions {
	figure: string;
	size?: "s" | "m" | "l";
	direction?: number;
	headDirection?: number;
	headOnly?: boolean;
	gesture?: string;
	action?: string;
}

export interface AvatarRenderResult {
	buffer: Buffer;
	etag: string;
	source: "memory" | "disk" | "upstream" | "fallback";
}

const memCache = new LruCache<Buffer>(MEM_CACHE_CAPACITY);
const inFlight = new InFlight<AvatarRenderResult>();
const negativeCache = new NegativeCache(NEGATIVE_CACHE_TTL_MS);

function getCacheKey(opts: AvatarRenderOptions): string {
	const raw = [
		opts.figure,
		opts.size ?? "m",
		opts.direction ?? 2,
		opts.headDirection ?? 3,
		opts.headOnly ? "h" : "f",
		opts.gesture ?? "",
		opts.action ?? "",
	].join("_");
	return createHash("md5").update(raw).digest("hex");
}

function getCachePath(key: string): string {
	return join(CACHE_DIR, key.slice(0, 2), `${key}.png`);
}

function makeEtag(key: string): string {
	return `W/"${key}"`;
}

function saveToCache(cachePath: string, data: Buffer): void {
	try {
		const dir = dirname(cachePath);
		if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
		writeFileSync(cachePath, data);
	} catch {
		/* non-fatal */
	}
}

function isPng(buf: Buffer): boolean {
	return (
		buf.length > 8 &&
		buf[0] === 0x89 &&
		buf[1] === 0x50 &&
		buf[2] === 0x4e &&
		buf[3] === 0x47
	);
}

async function resolveUpstreamBase(): Promise<string> {
	const fromEnv = process.env.IMAGING_UPSTREAM_URL?.trim();
	if (fromEnv) return fromEnv.replace(/\/+$/, "");
	const fromSettings =
		(await siteSettings.get("habbo_imaging_url", DEFAULT_UPSTREAM)) ??
		DEFAULT_UPSTREAM;
	return fromSettings.replace(/\/+$/, "") || DEFAULT_UPSTREAM;
}

async function fetchUpstream(opts: AvatarRenderOptions): Promise<Buffer | null> {
	try {
		const params = new URLSearchParams({
			figure: opts.figure,
			direction: String(opts.direction ?? 2),
			head_direction: String(opts.headDirection ?? 3),
			size: opts.size ?? "m",
		});
		if (opts.headOnly) params.set("headonly", "1");
		if (opts.gesture) params.set("gesture", opts.gesture);
		if (opts.action) params.set("action", opts.action);

		const base = await resolveUpstreamBase();
		const url = `${base}?${params.toString()}`;
		const res = await fetch(url, {
			signal: AbortSignal.timeout(UPSTREAM_TIMEOUT_MS),
			headers: { "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)" },
		});
		if (!res.ok) return null;

		const buffer = Buffer.from(await res.arrayBuffer());
		return isPng(buffer) ? buffer : null;
	} catch {
		return null;
	}
}

/**
 * Get an avatar image. Always returns a result — never throws, never returns
 * null. Worst case is a 1×1 transparent PNG so the UI never shows broken
 * images.
 */
export async function renderAvatar(
	opts: AvatarRenderOptions,
): Promise<AvatarRenderResult> {
	const key = getCacheKey(opts);
	const etag = makeEtag(key);

	const fromMem = memCache.get(key);
	if (fromMem) return { buffer: fromMem, etag, source: "memory" };

	const cachePath = getCachePath(key);
	if (existsSync(cachePath)) {
		try {
			const buf = readFileSync(cachePath);
			memCache.set(key, buf);
			return { buffer: buf, etag, source: "disk" };
		} catch {
			/* fall through to fetch */
		}
	}

	if (negativeCache.isMarked(key)) {
		return { buffer: TRANSPARENT_PNG, etag, source: "fallback" };
	}

	return inFlight.dedup(key, async () => {
		if (existsSync(cachePath)) {
			try {
				const buf = readFileSync(cachePath);
				memCache.set(key, buf);
				return { buffer: buf, etag, source: "disk" };
			} catch {
				/* fall through */
			}
		}

		const useUpstream =
			(await siteSettings.get("imaging_use_habbo_fallback", "1")) === "1";
		if (useUpstream) {
			const upstream = await fetchUpstream(opts);
			if (upstream) {
				saveToCache(cachePath, upstream);
				memCache.set(key, upstream);
				return { buffer: upstream, etag, source: "upstream" };
			}
		}

		negativeCache.mark(key);
		return { buffer: TRANSPARENT_PNG, etag, source: "fallback" };
	});
}

export function getImagerStats() {
	return {
		memCacheSize: memCache.size,
		memCacheCapacity: MEM_CACHE_CAPACITY,
		cacheDir: CACHE_DIR,
	};
}