// Session-name resolution for the pi NATS channel adapter.
//
// Mirrors the OMP adapter's `extensions/session.ts`: composes the SDK's
// `readSessionLabel` (canonical SESH_SESSION + `.sesh/` state-walk) with the
// legacy `NATS_SESSION_NAME` operator override, per-context
// `config.sessionName`, and a `basename(cwd)` last-resort fallback.
// Centralised here so the resolution ladder is unit-testable without
// spinning up the whole extension.

import { basename } from "node:path";
import { readSessionLabel } from "@agent-ops/sesh-channels";

export interface SessionResolverInputs {
	env: NodeJS.ProcessEnv;
	configSessionName?: string;
	cwd: string;
	sanitize: (raw: string) => string;
	readSessionLabelImpl?: typeof readSessionLabel;
}

/**
 * Resolve the raw (pre-collision-check) session name. Returns the empty
 * string if no source yields a value — callers supply their own adapter
 * default.
 *
 * Resolution order (first non-empty wins):
 *   1. `readSessionLabel()` — SDK helper: `$SESH_SESSION` then `.sesh/`
 *      state-walk.
 *   2. `$NATS_SESSION_NAME` — operator override (kept for back-compat).
 *   3. `config.sessionName` — legacy NATS-context-bound setting.
 *   4. `sanitize(basename(cwd))` — final fallback.
 */
export function resolveRawSession(inputs: SessionResolverInputs): string {
	const reader = inputs.readSessionLabelImpl ?? readSessionLabel;
	const fromSdk = reader({ env: inputs.env });
	if (fromSdk && fromSdk.length > 0) return fromSdk;

	const fromOperator = inputs.env.NATS_SESSION_NAME;
	if (fromOperator && fromOperator.length > 0) return fromOperator;

	if (inputs.configSessionName && inputs.configSessionName.length > 0) {
		return inputs.configSessionName;
	}

	return inputs.sanitize(basename(inputs.cwd));
}