/**
 * The session label: the one name another session addresses this one by.
 *
 * Two vocabularies share this module, and neither copies the other. `session-bus`
 * settles its own label for a session that did not ask for one — the Pi session name,
 * else the working directory's basename, else the id. The board names a session for
 * the team instead: the page's seat, or `team-agent-` and the id's tail, which is the
 * same name on every surface and cannot drift when a user renames a session. The rules
 * are here rather than in either extension because a label is a shared vocabulary: it
 * is displayed, it is a send target, and it is stored in a card file that outlives one
 * session.
 *
 * Value-only: no state, no I/O.
 */

import type { ExtensionContext } from "@earendil-works/pi-coding-agent";
import { sanitizeLine } from "./format.ts";

/** Longest label, in characters, that a session may be addressed by. */
export const MAX_LABEL = 40;

/**
 * A safe label, used both for display and as a target.
 *
 * Flattened to one line and capped, so a name can never wrap a row or open a
 * second line in a page; an empty one falls back rather than leaving a blank chip.
 */
export function normalizeLabel(raw: string | undefined, fallback: string): string {
	const text = sanitizeLine(raw ?? "")
		.replace(/\s+/g, " ")
		.trim();
	return (text || fallback).slice(0, MAX_LABEL);
}

/** A short, display-only suffix for a session id. */
export function shortId(id: string): string {
	const clean = id.replace(/[^a-zA-Z0-9]/g, "");
	return (clean || id).slice(-6);
}

/**
 * The automatic label, before uniqueness is applied.
 *
 * The bus appends a suffix when two live sessions share one; that decision belongs
 * to the registry, so this is only the name a session would pick for itself.
 */
export function defaultLabel(sessionName: string | undefined, cwd: string, id = "session"): string {
	const directory = cwd.split(/[\\/]/).filter(Boolean).at(-1);
	const base = normalizeLabel(sessionName, normalizeLabel(directory, "session"));
	return normalizeLabel(base, `session-${shortId(id)}`);
}

/** The prefix of the team's name for a session that is not the page's seat. */
export const TEAM_AGENT_PREFIX = "team-agent-";

/**
 * The team's name for a session: the prefix and the id's tail.
 *
 * A team is addressed by id, not by a name a user chose: an id is unique, so two
 * sessions cannot settle on one name, and a rename cannot strand the card that
 * recorded it. The seat is the one name that is a role instead.
 */
export function agentLabel(id: string): string {
	return normalizeLabel(`${TEAM_AGENT_PREFIX}${shortId(id)}`, "team-agent");
}

/**
 * Pi's session name, which is the first choice for a label.
 *
 * A host that has no session name, or refuses the call, yields `undefined` rather
 * than an error: a label is a convenience, and a session that cannot name itself
 * still works under the fallback chain above.
 */
export function sessionNameOf(ctx: Pick<ExtensionContext, "sessionManager">): string | undefined {
	try {
		return ctx.sessionManager.getSessionName();
	} catch {
		return undefined;
	}
}