import type { Observation } from "@tff/core";
import type { Pattern } from "../../shared/value-objects/pattern.js";

export const extractNgrams = (observations: Observation[], n: number): Pattern[] => {
	if (observations.length < n) return [];

	// Group observations by session
	const sessions = new Map<string, Observation[]>();
	for (const obs of observations) {
		const list = sessions.get(obs.session) ?? [];
		list.push(obs);
		sessions.set(obs.session, list);
	}

	// Extract n-grams per session, track counts
	const ngramMap = new Map<
		string,
		{
			sequence: string[];
			count: number;
			sessionSet: Set<string>;
			projectSet: Set<string>;
			lastSeen: string;
		}
	>();

	for (const [sessionId, sessionObs] of sessions) {
		for (let i = 0; i <= sessionObs.length - n; i++) {
			const sequence = sessionObs.slice(i, i + n).map((o) => o.tool);
			const key = sequence.join("→");

			const existing = ngramMap.get(key);
			const lastTs = sessionObs[i + n - 1].ts;

			if (existing) {
				existing.count++;
				existing.sessionSet.add(sessionId);
				existing.projectSet.add(sessionObs[i].project);
				if (lastTs > existing.lastSeen) existing.lastSeen = lastTs;
			} else {
				ngramMap.set(key, {
					sequence,
					count: 1,
					sessionSet: new Set([sessionId]),
					projectSet: new Set([sessionObs[i].project]),
					lastSeen: lastTs,
				});
			}
		}
	}

	return [...ngramMap.values()].map((v) => ({
		sequence: v.sequence,
		count: v.count,
		sessions: v.sessionSet.size,
		projects: v.projectSet.size,
		lastSeen: v.lastSeen,
	}));
};