EventSnap/frontend/src/lib/upload-queue.ts

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

export interface QueueItem {
	id: string;
	userId: string;
	fileName: string;
	fileSize: number;
	/** Source file's last-modified ms; part of the dedup key so two distinct photos that
	 *  happen to share a name and byte length don't collapse into one. */
	lastModified?: number;
	mimeType: string;
	caption: string;
	hashtags: string;
	// 'error' is retryable (network / 5xx); 'blocked' is TERMINAL (a 4xx the server will
	// keep rejecting — locked event, banned user, released gallery, quota full). Blocked
	// items have had their blob purged from IndexedDB and offer no retry.
	status: 'pending' | 'uploading' | 'done' | 'error' | 'blocked';
	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';

/** Hard cap on queued items per device — bounds IndexedDB growth from stuck blobs. */
const MAX_QUEUE_ITEMS = 100;

let db: IDBPDatabase | null = null;

// Resume the queue as soon as connectivity returns. Registered once, guarded for SSR.
// This is the other half of the "flushes when you're back online" promise — without it
// a reconnect only resumes if the user manually re-stages a file.
let onlineBound = false;
function bindOnline(): void {
	if (onlineBound || typeof window === 'undefined') return;
	window.addEventListener('online', () => {
		void (async () => {
			await requeueRetriable();
			await processQueue();
		})();
	});
	onlineBound = true;
}
bindOnline();

// Resume the queue when the host reopens the event. A queued upload that hit a locked/
// released event kept its blob and parked as a retryable `error` (LockedError); flipping it
// back to pending and re-draining recovers it so a photo staged during a lock isn't lost.
// We resume on TWO signals:
//   - `event-opened`: the live reopen, when the SSE happens to be connected.
//   - `feed-delta`: fired on every SSE (re)connect (see sse.ts `deltaFetchAndFan`). Because
//     `event-opened` has no server-side replay and the SSE is disconnected on non-feed pages
//     / backgrounded tabs, a reopen is often MISSED live — this catches up on the next
//     reconnect. Retrying while still locked just re-parks the item (bounded, one per event).
// One-way import (sse.ts never imports this module).
let sseBound = false;
function bindSse(): void {
	if (sseBound || typeof window === 'undefined') return;
	const resume = () => {
		void (async () => {
			await requeueRetriable();
			await processQueue();
		})();
	};
	onSseEvent('event-opened', resume);
	onSseEvent('feed-delta', resume);
	sseBound = true;
}
bindSse();

/**
 * Flip transient `error` items (5xx / a network drop that got marked before we could
 * reclassify it) back to `pending` so a resume actually retries them. Terminal `blocked`
 * items (403/413) are left alone — retrying those never succeeds.
 */
async function requeueRetriable(): Promise<void> {
	const database = await getDb();
	const myUserId = getUserId();
	const all = await database.getAll(STORE_NAME);
	for (const entry of all) {
		if (entry.userId === myUserId && entry.status === 'error' && entry.blob) {
			entry.status = 'pending';
			entry.error = undefined;
			await database.put(STORE_NAME, entry);
		}
	}
	queueItems.update((items) =>
		items.map((item) =>
			item.status === 'error'
				? { ...item, status: 'pending' as const, progress: 0, error: undefined }
				: item
		)
	);
}

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.
	// Version 3 self-heals installs corrupted by a shipped v1→v2 bug: that upgrade
	// opened a *new* transaction inside the callback, which throws InvalidStateError
	// ("A version change transaction is running") and aborts the whole upgrade —
	// leaving some browsers at version 2 with NO 'queue' object store (so every queue
	// write failed and no upload ever fired). Bumping to 3 re-runs this upgrade for
	// those installs; the contains() guard recreates the missing store instead of
	// assuming createObjectStore only ever runs on a brand-new DB.
	db = await openDB(DB_NAME, 3, {
		upgrade(database, oldVersion, _newVersion, transaction) {
			if (!database.objectStoreNames.contains(STORE_NAME)) {
				database.createObjectStore(STORE_NAME, { keyPath: 'id' });
			} else if (oldVersion < 2) {
				// Existing v1 store: its entries predate the `userId` field, so drop them
				// rather than misattribute them to whoever is signed in now. Reuse the
				// active version-change transaction (never open a new one here — see above).
				// Skipped when we just created the store, which is already empty.
				transaction.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;
	}
}

/**
 * A permanent, non-retryable failure — the server returned a 4xx (other than 429) that
 * will never succeed on retry: uploads locked, user banned, gallery already released, or
 * per-user quota full. The item is moved to the terminal `blocked` state and its blob is
 * dropped from IndexedDB (no point keeping bytes we'll never send).
 */
class TerminalError extends Error {
	constructor(message: string) {
		super(message);
	}
}

/**
 * A connectivity failure — the request never reached the server (offline, DNS, dropped
 * connection). The item stays `pending` (not `error`) so the `online` listener and the
 * next `processQueue` pick it up automatically. This is what makes "the queue flushes
 * when you're back online" actually true for a file staged with no signal.
 */
class NetworkError extends Error {}

/**
 * The session is gone/expired (HTTP 401). This is emphatically NOT terminal: the blob is
 * KEPT (deleting it — the old behavior for any 4xx — destroyed a guest's staged photos the
 * instant their sliding session lapsed or a host reset their PIN, exactly when auto-resume
 * fires). We mark the item retryable and route to re-auth; once the user signs back in with
 * the same identity (via /recover), `loadQueue` re-associates these entries by userId and
 * they resume. Distinct from `TerminalError` so the 4xx branch can't purge the blob.
 */
class AuthError extends Error {}

/**
 * A REVERSIBLE 403 — the event is closed or the gallery was released, but a host can reopen
 * it. Backend tags these with code `uploads_locked` (distinct from a permanent `forbidden`
 * like a banned user). The blob is KEPT and the item parks as retryable; the `event-opened`
 * SSE (or a manual retry) resumes it. Without this, a photo staged during a lock was purged
 * as terminal and lost the moment the host reopened.
 */
class LockedError extends Error {}

/** Retry policy for an upload response status. */
export type UploadOutcome = 'success' | 'rate_limit' | 'auth' | 'transient' | 'terminal';

/**
 * Classify an upload HTTP status into a retry policy. Pure + exported so the
 * data-loss-critical rules are unit-testable without an XHR/IndexedDB harness:
 *  - 401 → `auth`      (session gone: KEEP the blob, re-auth — NEVER purge it)
 *  - 408 → `transient` (request timeout: retryable)
 *  - 429 → `rate_limit`(back off, auto-resume)
 *  - other 4xx → `terminal` (locked/banned/released/quota — the only case that purges)
 *  - 2xx → `success`; 5xx/other → `transient`
 * The one rule that must never regress: a 401 is `auth`, not `terminal`.
 */
export function classifyUploadStatus(status: number): UploadOutcome {
	if (status >= 200 && status < 300) return 'success';
	if (status === 429) return 'rate_limit';
	if (status === 401) return 'auth';
	if (status === 408) return 'transient';
	if (status >= 400 && status < 500) return 'terminal';
	return 'transient';
}

/**
 * Within the `terminal` bucket, decide whether a 4xx is a REVERSIBLE lock (keep the blob,
 * park retryable for a host reopen) rather than a permanent rejection (purge the blob).
 * Pure + exported so this data-loss-critical rule is unit-testable without an XHR harness.
 *
 * Reversible when:
 *  - the backend tagged it `uploads_locked` (event closed / gallery released — a host can reopen), OR
 *  - it's ANY 403 we can't positively identify as a permanent ban (`forbidden`). An unparseable
 *    403 body (proxy/WAF/captive portal) must NOT purge the blob — losing a photo is the worst
 *    outcome, and 403 is the reversible-lock status here.
 * A `forbidden` 403 (banned) and every non-403 4xx (e.g. 413 quota) are permanent → purge.
 */
export function isReversibleLock(status: number, errorCode: unknown): boolean {
	return errorCode === 'uploads_locked' || (status === 403 && errorCode !== 'forbidden');
}

/**
 * Rehydrate a persisted IndexedDB entry into an in-memory `QueueItem`. Pure + exported so the
 * field-mapping is unit-testable. The rule that must not regress: `lastModified` MUST be carried
 * across — addToQueue's dedup keys on it, so an item restored from IndexedDB (page reload / PWA
 * relaunch) with an undefined lastModified would fail to match a re-selection of the same file
 * and silently queue it twice. `uploading` is downgraded to `pending` (an interrupted in-flight
 * upload must resume, not stay stuck spinning).
 */
export function entryToQueueItem(entry: {
	id: string;
	userId: string;
	fileName: string;
	fileSize: number;
	lastModified?: number;
	mimeType: string;
	caption?: string;
	hashtags?: string;
	status: QueueItem['status'] | 'uploading';
	error?: string;
}): QueueItem {
	return {
		id: entry.id,
		userId: entry.userId,
		fileName: entry.fileName,
		fileSize: entry.fileSize,
		lastModified: entry.lastModified,
		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
	};
}

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(entryToQueueItem);
	queueItems.set(items);
	// Staged-but-unsent items from a prior session (queued offline, tab closed before
	// reconnect) must resume now — otherwise the "queue flushes when you're back online"
	// promise only holds if the user manually re-stages a file. Reclaim transient errors
	// (a network drop from a prior session) so they retry instead of stalling.
	void (async () => {
		await requeueRetriable();
		await processQueue();
	})();
}

/** Outcome of an `addToQueue` call, so the caller can tell the user when a file was NOT
 *  actually queued (deduped, or the queue is full of un-evictable in-flight items). */
export type EnqueueResult = 'queued' | 'duplicate' | 'full';

export async function addToQueue(
	file: File,
	caption: string,
	hashtags: string
): Promise<EnqueueResult> {
	const database = await getDb();
	const userId = getUserId();
	// Not authenticated — nothing to queue. Return the silent 'duplicate' outcome rather than
	// 'full' so the caller doesn't show a misleading "queue full" toast. Practically
	// unreachable: the upload view sits behind a token guard.
	if (!userId) return 'duplicate';

	// Dedup: don't queue the same file twice while an identical one is still unsent
	// (double-tap, re-added after a flaky reconnect). Matches on name+size+lastModified+user
	// — including lastModified so two genuinely different photos sharing a name and byte
	// length aren't silently collapsed into one.
	const mine = get(queueItems).filter((i) => i.userId === userId);
	const dup = mine.some(
		(i) =>
			i.fileName === file.name &&
			i.fileSize === file.size &&
			(i.lastModified ?? 0) === file.lastModified &&
			(i.status === 'pending' || i.status === 'uploading')
	);
	if (dup) return 'duplicate';

	// Cap the queue so stuck/blocked blobs can't grow IndexedDB without bound. When full,
	// evict the oldest item whose blob is already gone or unrecoverable — ONLY `done` (blob
	// deleted on success) or `blocked` (blob purged, terminal). NEVER evict `error`: those are
	// retryable and still hold a live blob (a network blip, or a locked/released upload that
	// resumes on reopen) — evicting one would silently lose a photo the fix deliberately kept.
	// If nothing is evictable, refuse and tell the caller so it can surface a "queue full"
	// message rather than dropping a photo the user believed was queued.
	if (mine.length >= MAX_QUEUE_ITEMS) {
		const evictable = get(queueItems).find(
			(i) => i.userId === userId && (i.status === 'done' || i.status === 'blocked')
		);
		if (evictable) {
			await database.delete(STORE_NAME, evictable.id);
			queueItems.update((items) => items.filter((it) => it.id !== evictable.id));
		} else {
			return 'full';
		}
	}

	const id = crypto.randomUUID();
	const entry = {
		id,
		userId,
		fileName: file.name,
		fileSize: file.size,
		lastModified: file.lastModified,
		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,
			lastModified: file.lastModified,
			mimeType: file.type,
			caption,
			hashtags,
			status: 'pending',
			progress: 0
		}
	]);

	processQueue();
	return 'queued';
}

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) {
			// Offline: leave items 'pending' rather than burning through them into 'error'.
			// The `online` listener re-enters here the moment connectivity returns.
			if (typeof navigator !== 'undefined' && navigator.onLine === false) break;

			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;
				}
				if (e instanceof AuthError) {
					// Dead session — stop the batch (every further item would 401 too). Items
					// stay retryable with blobs intact; the re-auth flow (clearAuth) takes over.
					break;
				}
				if (e instanceof LockedError) {
					// Event locked — stop the batch (every item would hit the same lock). Items
					// stay retryable with blobs intact; the `event-opened` SSE resumes them.
					break;
				}
				if (e instanceof NetworkError) {
					// Connectivity dropped mid-flight. If offline the item is back to 'pending'
					// and the `online` listener resumes it; if the failure hit while nominally
					// online it's now a retryable 'error'. Either way, stop hammering here.
					break;
				}
				// Other errors are already handled inside uploadItem (marked 'error'/'blocked')
			}
		}
	} 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', () => {
				const body = (() => {
					try {
						return JSON.parse(xhr.responseText);
					} catch {
						return null;
					}
				})();
				switch (classifyUploadStatus(xhr.status)) {
					case 'success':
						resolve();
						break;
					case 'rate_limit': {
						// Back off and auto-resume when the window lifts (quota-full is a distinct
						// 413, classified 'terminal' below).
						const secs = typeof body?.retry_after_secs === 'number' ? body.retry_after_secs : 60;
						reject(new RateLimitError(secs));
						break;
					}
					case 'auth':
						// Session expired/revoked. NOT terminal — keep the blob and re-auth. Lumping
						// this into the terminal bucket (which purges the blob) irrecoverably
						// destroyed queued photos whenever a sliding session lapsed or a host reset
						// the PIN — precisely when the `online` auto-resume kicks in.
						reject(new AuthError('Sitzung abgelaufen. Bitte melde dich erneut an.'));
						break;
					case 'transient':
						// 408 (request timeout) behaves like a network blip so it stays retryable;
						// 5xx is a generic retryable error. Neither purges the blob.
						if (xhr.status === 408) reject(new NetworkError('Zeitüberschreitung'));
						else reject(new Error(body?.message || `HTTP ${xhr.status}`));
						break;
					case 'terminal': {
						// A REVERSIBLE lock (event closed / gallery released) is tagged
						// `uploads_locked` by the backend — keep the blob and park it retryable so
						// a host reopen resumes it, instead of purging it like a permanent 4xx.
						// Also treat ANY 403 we can't positively identify as permanent (`forbidden`
						// = banned) as reversible: an unparseable 403 body (proxy/WAF/captive
						// portal) must NOT purge the blob — losing a photo is the worst outcome, and
						// 403 is the reversible-lock status here.
						if (isReversibleLock(xhr.status, body?.error)) {
							reject(new LockedError(body?.message || 'Event ist geschlossen.'));
							break;
						}
						// Any other 4xx the server will keep rejecting (banned / quota).
						let msg = body?.message || 'Upload nicht möglich.';
						if (!body?.message && xhr.status === 413) msg = 'Speicher-Limit erreicht.';
						reject(new TerminalError(msg));
						break;
					}
				}
			});

			xhr.addEventListener('error', () => reject(new NetworkError('Netzwerkfehler')));
			xhr.addEventListener('abort', () => reject(new NetworkError('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
		}
		if (e instanceof LockedError) {
			// Event closed / gallery released, but a host can reopen — KEEP the blob and park
			// the item as retryable so it survives until reopen. The `event-opened` SSE
			// (bindSse) auto-resumes it; a manual "Erneut" also works. Never purge here.
			entry.status = 'error';
			entry.error = e.message;
			await database.put(STORE_NAME, entry);
			updateItemStatus(id, 'error', e.message);
			throw e;
		}
		if (e instanceof AuthError) {
			// Dead session — KEEP the blob (never purge on auth failure) and mark retryable so
			// the file survives re-auth. Route through the app's single de-auth path (matches
			// api.ts's 401 handling). The blob persists in IndexedDB keyed by userId; once the
			// user signs back in with the SAME identity (via /recover), the next time the upload
			// view loads `loadQueue` re-associates this entry and it can be retried/resumed.
			entry.status = 'error';
			entry.error = e.message;
			await database.put(STORE_NAME, entry);
			updateItemStatus(id, 'error', e.message);
			clearAuth();
			throw e;
		}
		if (e instanceof NetworkError) {
			const offline = typeof navigator !== 'undefined' && navigator.onLine === false;
			if (offline) {
				// Genuinely offline — keep the item pending; the `online` listener resumes it
				// automatically with no user action.
				entry.status = 'pending';
				await database.put(STORE_NAME, entry);
				updateItemStatus(id, 'pending');
			} else {
				// Network-level failure while the OS still reports online (server down,
				// connection refused, TLS error, captive portal). The `online` event will
				// NEVER fire in this case, so leaving it 'pending' would strand the item with
				// no retry path and no spinner. Mark it retryable 'error' so the user gets a
				// working "Erneut" button and a later real reconnect requeues it.
				entry.status = 'error';
				entry.error = 'Netzwerkfehler. Erneut versuchen.';
				await database.put(STORE_NAME, entry);
				updateItemStatus(id, 'error', 'Netzwerkfehler. Erneut versuchen.');
			}
			throw e;
		}
		if (e instanceof TerminalError) {
			// Permanent rejection — drop the blob (we'll never resend it) and mark blocked
			// so the UI shows a clear reason and offers no retry.
			delete entry.blob;
			entry.status = 'blocked';
			entry.error = e.message;
			await database.put(STORE_NAME, entry);
			updateItemStatus(id, 'blocked', e.message);
			// Tell the user NOW. The queue list only lives on /upload, and the flow sends
			// them straight to /feed after staging a photo — so without this a rejected
			// upload was silently swallowed: the blob is gone, the FAB badge drops exactly
			// as if it had succeeded, and the photo simply never appears.
			toast(`${entry.fileName}: ${e.message}`, 'error');
			return;
		}
		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
		)
	);
}