import { SvelteMap } from 'svelte/reactivity';
import type { ChatMessage } from '$lib/types';

export interface Session {
	id: string;
	title: string;
	messages: ChatMessage[];
	createdAt: Date;
}

const STORAGE_KEY = 'llm-multiverse-sessions';
const ACTIVE_SESSION_KEY = 'llm-multiverse-active-session';

function loadSessions(): SvelteMap<string, Session> {
	if (typeof localStorage === 'undefined') return new SvelteMap();
	try {
		const raw = localStorage.getItem(STORAGE_KEY);
		if (!raw) return new SvelteMap();
		const arr: [string, Session][] = JSON.parse(raw);
		return new SvelteMap(
			arr.map(([id, s]) => [
				id,
				{ ...s, createdAt: new Date(s.createdAt), messages: s.messages.map(m => ({ ...m, timestamp: new Date(m.timestamp) })) }
			])
		);
	} catch {
		return new SvelteMap();
	}
}

function saveSessions(sessions: SvelteMap<string, Session>) {
	if (typeof localStorage === 'undefined') return;
	localStorage.setItem(STORAGE_KEY, JSON.stringify([...sessions.entries()]));
}

function loadActiveSessionId(): string | null {
	if (typeof localStorage === 'undefined') return null;
	return localStorage.getItem(ACTIVE_SESSION_KEY);
}

function saveActiveSessionId(id: string) {
	if (typeof localStorage === 'undefined') return;
	localStorage.setItem(ACTIVE_SESSION_KEY, id);
}

function createSessionStore() {
	const sessions = $state<SvelteMap<string, Session>>(loadSessions());
	let activeSessionId = $state<string | null>(loadActiveSessionId());

	function createSession(id?: string): Session {
		const session: Session = {
			id: id ?? crypto.randomUUID(),
			title: 'New Chat',
			messages: [],
			createdAt: new Date()
		};
		sessions.set(session.id, session);
		activeSessionId = session.id;
		saveSessions(sessions);
		saveActiveSessionId(session.id);
		return session;
	}

	function getOrCreateSession(id?: string): Session {
		if (id && sessions.has(id)) {
			activeSessionId = id;
			saveActiveSessionId(id);
			return sessions.get(id)!;
		}
		return createSession(id);
	}

	function updateMessages(sessionId: string, messages: ChatMessage[]) {
		const session = sessions.get(sessionId);
		if (!session) return;
		session.messages = messages;
		// Update title from first user message if still default
		if (session.title === 'New Chat') {
			const firstUser = messages.find(m => m.role === 'user');
			if (firstUser) {
				session.title = firstUser.content.slice(0, 50) + (firstUser.content.length > 50 ? '...' : '');
			}
		}
		sessions.set(sessionId, session);
		saveSessions(sessions);
	}

	function switchSession(id: string) {
		if (sessions.has(id)) {
			activeSessionId = id;
			saveActiveSessionId(id);
		}
	}

	function deleteSession(id: string) {
		sessions.delete(id);
		if (activeSessionId === id) {
			const remaining = getAllSessions();
			activeSessionId = remaining.length > 0 ? remaining[0].id : null;
			if (activeSessionId) saveActiveSessionId(activeSessionId);
		}
		saveSessions(sessions);
	}

	function getAllSessions(): Session[] {
		return [...sessions.values()].sort((a, b) => b.createdAt.getTime() - a.createdAt.getTime());
	}

	return {
		get activeSessionId() { return activeSessionId; },
		get activeSession() { return activeSessionId ? sessions.get(activeSessionId) ?? null : null; },
		createSession,
		getOrCreateSession,
		updateMessages,
		switchSession,
		deleteSession,
		getAllSessions
	};
}

export const sessionStore = createSessionStore();