/** The Loom's participant roster and the one handler that writes it. */
import {
  type Cell,
  type Default,
  handler,
  type Writable,
  type WriteAuthorizedBy,
} from "commonfabric";

/**
 * A participant's Fabric profile, held as the live cell in its own space.
 * The profile's label names its principal, so the roster records no DID and
 * no name: readers take both from the profile.
 */
export type ParticipantProfile = Cell<{ name?: string; avatar?: string }>;

/**
 * `items` changes only through `addParticipant`; a write from any other
 * action, or from another pattern holding this cell, is refused by the
 * runtime.
 */
export type ParticipantList = WriteAuthorizedBy<
  ParticipantProfile[],
  typeof addParticipant
>;

/**
 * Object-wrapped so each entry stays a live profile cell. `items` is absent
 * until the first participant is added: a default inside the write contract
 * would be a write no handler made.
 */
export interface ParticipantRoster {
  items?: ParticipantList;
}

/** The shared roster cell; a Loom with no participants yet holds `{}`. */
export type ParticipantRosterCell = Writable<
  ParticipantRoster | Default<Record<PropertyKey, never>>
>;

/** The roster's profiles, in the order they were added. */
export const rosterProfiles = (
  roster: { get(): ParticipantRoster | Record<PropertyKey, never> | undefined },
): ParticipantProfile[] =>
  Array.from((roster.get() as ParticipantRoster | undefined)?.items ?? []);

/**
 * Adds a profile to the roster once. Any participant may add any profile: a
 * reader keeps only entries whose profile names a principal that currently
 * holds access to the Loom, so an entry for anyone else is never shown.
 */
export const addParticipant = handler<
  { profile: ParticipantProfile },
  { roster: ParticipantRosterCell }
>(({ profile }, { roster }) => {
  // `addUnique` is a mergeable set-add: participants adding at once all
  // land, and a profile already listed is not added again. The terminal cell
  // is pinned so the entry names this profile, not whatever an alias later
  // resolves to.
  roster.key("items").addUnique(profile.resolveAsCell());
});