import { resolve } from "node:path";
import { SLUG_PATTERN } from "./paths.js";

/** Explicit, host-neutral identity for one notes store. */
export type NotesContext = Readonly<{
	home: string;
	sessionId: string;
	projectKey: string;
	agent: string;
	model: string;
}>;

function requireString(field: string, value: unknown): string {
	if (typeof value !== "string" || value.length === 0) throw new TypeError(`notes context ${field} must be a non-empty string`);
	return value;
}

function assertDirectoryComponent(field: string, value: string): void {
	if (value === "." || value === ".." || /[\\/\0:]/.test(value)) {
		throw new TypeError(`notes context ${field} must be a safe single directory component`);
	}
}

/** Validate and snapshot caller identity; no global or environment defaults are consulted. */
export function snapshotNotesContext(value: NotesContext): NotesContext {
	if (typeof value !== "object" || value === null || Array.isArray(value)) throw new TypeError("notes context must be a plain object");
	const prototype = Object.getPrototypeOf(value);
	if (prototype !== Object.prototype && prototype !== null) throw new TypeError("notes context must be a plain object");
	const homeValue = requireString("home", value.home);
	const sessionId = requireString("sessionId", value.sessionId);
	const projectKey = requireString("projectKey", value.projectKey);
	const agent = requireString("agent", value.agent);
	const model = requireString("model", value.model);
	assertDirectoryComponent("sessionId", sessionId);
	assertDirectoryComponent("projectKey", projectKey);
	if (!SLUG_PATTERN.test(agent)) throw new TypeError("notes context agent must be a canonical lowercase slug");
	if (!SLUG_PATTERN.test(model)) throw new TypeError("notes context model must be a canonical lowercase slug");
	const home = resolve(homeValue);
	return Object.freeze({ home, sessionId, projectKey, agent, model });
}