pablan/frontend/src/lib/chat/state.svelte.ts

// Chat state as a Svelte 5 runes class (no legacy stores).
//
// Query (RAG Q&A) only — capture is no longer a conversation; it writes a
// Document directly (see $lib/documents/WritingEditor.svelte).

import { api } from '$lib/api/client';
import { errorMessage } from '$lib/api/errors';
import { streamMessage, type SourceChunk, type StreamEvent } from '$lib/api/stream';
import { conversationStore } from '$lib/chat/conversations.svelte';
import { m } from '$lib/paraglide/messages';

export type { ConversationSummary } from '$lib/chat/conversations.svelte';

export type ChatMessage = {
	role: 'user' | 'assistant';
	content: string;
	sources: SourceChunk[];
	streaming: boolean;
	/** The streamed tokens, kept separate so the live view can fade each one
	 *  in (see StreamingText); `content` stays the source for the final render. */
	tokens: string[];
	/** Retrieval found nothing solid — offer to capture the knowledge. */
	noAnswer: boolean;
	/** The question that hit the gap (kept for a future retrieval-aware entry). */
	gapQuestion: string;
	/** No model answered this turn: the `llm_*` code that caused it, and
	 *  `sources` is a plain full-text hit list instead of citations. */
	fallback: string | null;
};

/** Transient query-mode progress; cleared when the turn ends. */
export type RetrievalProgress = { phase: string; count: number | null };

/** How long a turn may stay silent before we say so. Long enough that a
 *  normal local model never trips it, short enough to beat impatience. */
const SLOW_TURN_MS = 12_000;

export class ChatState {
	activeId = $state<string | null>(null);
	retrieval = $state<RetrievalProgress | null>(null);
	messages = $state<ChatMessage[]>([]);
	streaming = $state(false);
	error = $state<string | null>(null);
	/** Nothing has come back for a while: a busy endpoint queues the request
	 *  instead of refusing it, so silence is the only symptom the user gets. */
	slow = $state(false);
	#abort: AbortController | null = null;
	#slowTimer: ReturnType<typeof setTimeout> | null = null;

	/** Shared with the sidebar — same list, one fetch. */
	get conversations() {
		return conversationStore.items;
	}

	async loadConversations(): Promise<void> {
		await conversationStore.load();
	}

	async open(id: string): Promise<void> {
		this.error = null;
		this.activeId = id;
		this.retrieval = null;
		const { data } = await api.GET('/api/conversations/{conversation_id}', {
			params: { path: { conversation_id: id } }
		});
		this.messages = (data?.messages ?? [])
			.filter((message) => message.role === 'user' || message.role === 'assistant')
			.map((message) => ({
				role: message.role as 'user' | 'assistant',
				content: message.content,
				sources: message.sources ?? [],
				streaming: false,
				tokens: [],
				noAnswer: false,
				gapQuestion: '',
				fallback: message.fallback ?? null
			}));
	}

	startNew(): void {
		this.activeId = null;
		this.retrieval = null;
		this.messages = [];
		this.error = null;
	}

	async remove(id: string): Promise<void> {
		if (this.activeId === id) {
			this.startNew();
		}
		await conversationStore.remove(id);
	}

	#startSlowTimer(): void {
		this.#clearSlowTimer();
		this.slow = false;
		this.#slowTimer = setTimeout(() => (this.slow = true), SLOW_TURN_MS);
	}

	#clearSlowTimer(): void {
		if (this.#slowTimer !== null) clearTimeout(this.#slowTimer);
		this.#slowTimer = null;
		this.slow = false;
	}

	async send(content: string): Promise<void> {
		if (this.streaming) return;
		// Claim the turn before awaiting anything: creating the conversation
		// takes a round trip, and a second call in that window would create
		// a second conversation (double-click, or two navigation callbacks).
		this.streaming = true;
		this.error = null;

		let conversationId = this.activeId;
		if (!conversationId) {
			const { data } = await api.POST('/api/conversations', {
				body: { mode: 'query' }
			});
			if (!data) {
				this.error = m.chat_error_start_conversation();
				this.streaming = false;
				return;
			}
			conversationId = data.id;
			this.activeId = data.id;
		}

		this.messages.push({
			role: 'user',
			content,
			sources: [],
			streaming: false,
			tokens: [],
			noAnswer: false,
			gapQuestion: '',
			fallback: null
		});
		await this.#stream((signal) => streamMessage(conversationId, content, signal), content);
	}

	/** One streaming turn: append an assistant bubble and drain the events. */
	async #stream(
		open: (signal: AbortSignal) => AsyncGenerator<StreamEvent>,
		question = ''
	): Promise<void> {
		this.messages.push({
			role: 'assistant',
			content: '',
			sources: [],
			streaming: true,
			tokens: [],
			noAnswer: false,
			gapQuestion: '',
			fallback: null
		});
		const assistant = this.messages[this.messages.length - 1];
		this.streaming = true;
		this.#abort = new AbortController();
		this.#startSlowTimer();

		try {
			for await (const event of open(this.#abort.signal)) {
				if (event.type === 'token') {
					this.#clearSlowTimer();
					assistant.content += event.text;
					assistant.tokens.push(event.text);
				} else if (event.type === 'sources') {
					assistant.sources = event.chunks;
				} else if (event.type === 'state') {
					this.retrieval = { phase: event.phase, count: event.count };
					if (event.phase === 'no_answer') {
						assistant.noAnswer = true;
						assistant.gapQuestion = question;
					}
				} else if (event.type === 'error') {
					this.error = errorMessage(event.code);
				} else if (event.type === 'fallback') {
					// Not an error: the turn ends as a plain search the user reads.
					assistant.fallback = event.code;
				}
			}
		} catch (err) {
			const aborted = err instanceof DOMException && err.name === 'AbortError';
			if (!aborted) {
				this.error = m.chat_error_connection_lost();
			}
		} finally {
			this.#clearSlowTimer();
			// A turn that failed or was stopped before the first token leaves an
			// empty speech bubble behind, which reads as a broken reply. A
			// fallback turn is empty ON PURPOSE — its reply is the source list.
			if (
				!assistant.content &&
				!assistant.fallback &&
				this.messages[this.messages.length - 1] === assistant
			) {
				this.messages.pop();
			}
			assistant.streaming = false;
			this.streaming = false;
			this.retrieval = null;
			this.#abort = null;
			void this.loadConversations();
		}
	}

	stop(): void {
		this.#abort?.abort();
	}
}

/** One instance for the whole app, like `conversationStore`.
 *
 * The first message on /chat creates a conversation and the URL moves to
 * /chat/[id], which unmounts one page component and mounts another. A
 * per-component state would take the in-flight stream and the messages
 * already on screen down with it, so the state outlives the route.
 */
export const chatState = new ChatState();