import { openDB, type IDBPDatabase } from 'idb';
import { writable, get } from 'svelte/store';
import { getToken, getUserId } from './auth';
import { refreshQuota } from './quota-store';

export interface QueueItem {
	id: string;
	userId: string;
	fileName: string;
	fileSize: number;
	mimeType: string;
	caption: string;
	hashtags: string;
	status: 'pending' | 'uploading' | 'done' | 'error';
	progress: number;
	error?: string;
}

// Store does NOT hold file blobs — those stay in IndexedDB only
export const queueItems = writable<QueueItem[]>([]);
export const isProcessing = writable(false);

/** Set to the timestamp (ms) at which the rate-limit lifts, or null when clear. */
export const rateLimitRetryAt = writable<number | null>(null);

const DB_NAME = 'eventsnap-uploads';
const STORE_NAME = 'queue';

let db: IDBPDatabase | null = null;

async function getDb(): Promise<IDBPDatabase> {
	if (db) return db;
	// v1 → v2: add `userId` index so each guest's queue is isolated on shared devices.
	// Pre-existing entries (no userId) are dropped on upgrade; nothing useful was ever
	// persisted across logouts before this version.
	db = await openDB(DB_NAME, 2, {
		upgrade(database, oldVersion) {
			if (oldVersion < 1) {
				database.createObjectStore(STORE_NAME, { keyPath: 'id' });
			}
			if (oldVersion < 2) {
				// Wipe any pre-v2 entries — they have no userId field and would belong
				// to a now-indeterminate user. Safer to drop than to misattribute.
				const tx = database.transaction(STORE_NAME, 'readwrite');
				tx.objectStore(STORE_NAME).clear();
			}
		}
	});
	return db;
}

/**
 * Wipe every queue entry — both IndexedDB rows and the in-memory store. Called on
 * explicit logout so a second guest using the same device doesn't inherit (or be
 * blamed for) the previous guest's pending uploads.
 */
export async function clearQueue(): Promise<void> {
	const database = await getDb();
	await database.clear(STORE_NAME);
	queueItems.set([]);
	rateLimitRetryAt.set(null);
}

class RateLimitError extends Error {
	retryAfterSecs: number;
	constructor(secs: number) {
		super('rate_limited');
		this.retryAfterSecs = secs;
	}
}

export async function loadQueue(): Promise<void> {
	const database = await getDb();
	const myUserId = getUserId();
	const all = await database.getAll(STORE_NAME);
	// Only surface entries that belong to the current user. Entries from a previous
	// guest on this device are filtered out (and would also be wiped on their next
	// explicit logout via `clearQueue`).
	const items: QueueItem[] = all
		.filter((entry) => entry.userId && entry.userId === myUserId)
		.map((entry) => ({
			id: entry.id,
			userId: entry.userId,
			fileName: entry.fileName,
			fileSize: entry.fileSize,
			mimeType: entry.mimeType,
			caption: entry.caption ?? '',
			hashtags: entry.hashtags ?? '',
			status: entry.status === 'uploading' ? 'pending' : entry.status,
			progress: entry.status === 'done' ? 100 : 0,
			error: entry.error
		}));
	queueItems.set(items);
}

export async function addToQueue(
	file: File,
	caption: string,
	hashtags: string
): Promise<void> {
	const database = await getDb();
	const userId = getUserId();
	if (!userId) return; // not authenticated — nothing to do
	const id = crypto.randomUUID();
	const entry = {
		id,
		userId,
		fileName: file.name,
		fileSize: file.size,
		mimeType: file.type,
		caption,
		hashtags,
		status: 'pending',
		blob: file
	};
	await database.put(STORE_NAME, entry);

	queueItems.update((items) => [
		...items,
		{
			id,
			userId,
			fileName: file.name,
			fileSize: file.size,
			mimeType: file.type,
			caption,
			hashtags,
			status: 'pending',
			progress: 0
		}
	]);

	processQueue();
}

export async function retryItem(id: string): Promise<void> {
	const database = await getDb();
	const entry = await database.get(STORE_NAME, id);
	if (!entry) return;

	entry.status = 'pending';
	entry.error = undefined;
	await database.put(STORE_NAME, entry);

	queueItems.update((items) =>
		items.map((item) =>
			item.id === id ? { ...item, status: 'pending' as const, progress: 0, error: undefined } : item
		)
	);

	processQueue();
}

export async function removeItem(id: string): Promise<void> {
	const database = await getDb();
	await database.delete(STORE_NAME, id);
	queueItems.update((items) => items.filter((item) => item.id !== id));
}

export async function clearCompleted(): Promise<void> {
	const database = await getDb();
	const items = get(queueItems);
	for (const item of items) {
		if (item.status === 'done') {
			await database.delete(STORE_NAME, item.id);
		}
	}
	queueItems.update((items) => items.filter((item) => item.status !== 'done'));
}

let processing = false;

async function processQueue(): Promise<void> {
	if (processing) return;
	processing = true;
	isProcessing.set(true);

	try {
		while (true) {
			const items = get(queueItems);
			const next = items.find((item) => item.status === 'pending');
			if (!next) break;

			try {
				await uploadItem(next.id);
			} catch (e) {
				if (e instanceof RateLimitError) {
					// Keep all pending items as-is; schedule queue resume when limit lifts
					const retryAt = Date.now() + e.retryAfterSecs * 1000;
					rateLimitRetryAt.set(retryAt);
					setTimeout(() => {
						rateLimitRetryAt.set(null);
						processQueue();
					}, e.retryAfterSecs * 1000);
					break;
				}
				// Other errors are already handled inside uploadItem (marked as 'error')
			}
		}
	} finally {
		processing = false;
		isProcessing.set(false);
	}
}

async function uploadItem(id: string): Promise<void> {
	const database = await getDb();
	const entry = await database.get(STORE_NAME, id);
	if (!entry || !entry.blob) {
		updateItemStatus(id, 'error', 'Datei nicht gefunden.');
		return;
	}

	const token = getToken();
	const currentUserId = getUserId();
	if (!token || !currentUserId) {
		updateItemStatus(id, 'error', 'Nicht angemeldet.');
		return;
	}
	// Defense-in-depth: if the device's signed-in user changed since this entry was
	// queued, refuse to upload it under the new identity. `loadQueue` already filters
	// by user; this guards the in-memory store path too.
	if (entry.userId && entry.userId !== currentUserId) {
		updateItemStatus(id, 'error', 'Anderer Nutzer angemeldet.');
		return;
	}

	updateItemStatus(id, 'uploading');

	try {
		const formData = new FormData();
		formData.append('file', entry.blob, entry.fileName);
		if (entry.caption) formData.append('caption', entry.caption);
		if (entry.hashtags) formData.append('hashtags', entry.hashtags);

		await new Promise<void>((resolve, reject) => {
			const xhr = new XMLHttpRequest();
			xhr.open('POST', '/api/v1/upload');
			xhr.setRequestHeader('Authorization', `Bearer ${token}`);

			xhr.upload.addEventListener('progress', (e) => {
				if (e.lengthComputable) {
					const pct = Math.round((e.loaded / e.total) * 100);
					queueItems.update((items) =>
						items.map((item) => (item.id === id ? { ...item, progress: pct } : item))
					);
				}
			});

			xhr.addEventListener('load', () => {
				if (xhr.status >= 200 && xhr.status < 300) {
					resolve();
				} else if (xhr.status === 429) {
					try {
						const body = JSON.parse(xhr.responseText);
						const secs = typeof body.retry_after_secs === 'number' ? body.retry_after_secs : 60;
						reject(new RateLimitError(secs));
					} catch {
						reject(new RateLimitError(60));
					}
				} else {
					try {
						const body = JSON.parse(xhr.responseText);
						reject(new Error(body.message || `HTTP ${xhr.status}`));
					} catch {
						reject(new Error(`HTTP ${xhr.status}`));
					}
				}
			});

			xhr.addEventListener('error', () => reject(new Error('Netzwerkfehler')));
			xhr.addEventListener('abort', () => reject(new Error('Abgebrochen')));
			xhr.send(formData);
		});

		// Success — remove blob from IndexedDB, mark done
		entry.status = 'done';
		delete entry.blob;
		await database.put(STORE_NAME, entry);
		updateItemStatus(id, 'done');
		// Refresh the per-user quota snapshot so the My Account widget reflects this
		// upload's bytes without a manual reload.
		void refreshQuota();
	} catch (e) {
		if (e instanceof RateLimitError) {
			// Reset to pending so it will be retried when the queue resumes
			entry.status = 'pending';
			await database.put(STORE_NAME, entry);
			updateItemStatus(id, 'pending');
			throw e; // Propagate to processQueue for scheduling
		}
		const msg = e instanceof Error ? e.message : 'Upload fehlgeschlagen.';
		entry.status = 'error';
		entry.error = msg;
		await database.put(STORE_NAME, entry);
		updateItemStatus(id, 'error', msg);
	}
}

function updateItemStatus(
	id: string,
	status: QueueItem['status'],
	error?: string
): void {
	queueItems.update((items) =>
		items.map((item) =>
			item.id === id
				? {
						...item,
						status,
						progress: status === 'done' ? 100 : status === 'pending' ? 0 : item.progress,
						error
					}
				: item
		)
	);
}