/**
 * [Gitea #118] Remember the voice room you were in so a crash, update or
 * reload can put you back. Device-local (localStorage), never synced;
 * cleared on a deliberate hangup and on logout.
 */

export const CALL_SESSION_KEY = 'lotus-call-session';
/** A record older than this (by last heartbeat) is stale — the call is over. */
export const CALL_REJOIN_MAX_AGE_MS = 10 * 60_000;
export const CALL_SESSION_HEARTBEAT_MS = 30_000;

export type CallSessionRecord = {
  roomId: string;
  deviceId: string;
  joinedAt: number;
  /** Refreshed while joined so a crash leaves a recent timestamp behind. */
  lastSeen: number;
  microphone: boolean;
  video: boolean;
};

export type CallRejoinMode = 'ask' | 'auto' | 'off';

export const readCallSession = (): CallSessionRecord | undefined => {
  try {
    const raw = localStorage.getItem(CALL_SESSION_KEY);
    if (!raw) return undefined;
    const r = JSON.parse(raw) as Partial<CallSessionRecord>;
    if (typeof r.roomId !== 'string' || typeof r.deviceId !== 'string') return undefined;
    return {
      roomId: r.roomId,
      deviceId: r.deviceId,
      joinedAt: Number(r.joinedAt) || 0,
      lastSeen: Number(r.lastSeen) || 0,
      microphone: r.microphone !== false,
      video: r.video === true,
    };
  } catch {
    return undefined;
  }
};

export const writeCallSession = (record: CallSessionRecord): void => {
  try {
    localStorage.setItem(CALL_SESSION_KEY, JSON.stringify(record));
  } catch {
    /* quota / private mode */
  }
};

export const clearCallSession = (): void => {
  try {
    localStorage.removeItem(CALL_SESSION_KEY);
  } catch {
    /* ignore */
  }
};

export type RejoinContext = {
  record: CallSessionRecord | undefined;
  mode: CallRejoinMode;
  now: number;
  myDeviceId: string;
  /** Whether the room still exists and we are joined to it. */
  roomJoined: boolean;
  /** Device ids of our own live call memberships in that room (other tabs/devices). */
  ownMemberDevices: string[];
  /** Number of call memberships in the room, ours included. */
  memberCount: number;
};

export type RejoinDecision = { action: 'none' } | { action: 'ask' | 'auto'; roomId: string };

/** Pure: whether startup should offer (or perform) a rejoin. */
export function decideRejoin(ctx: RejoinContext): RejoinDecision {
  const { record, mode, now, myDeviceId } = ctx;
  if (!record || mode === 'off') return { action: 'none' };
  if (record.deviceId !== myDeviceId) return { action: 'none' };
  if (now - record.lastSeen > CALL_REJOIN_MAX_AGE_MS) return { action: 'none' };
  if (!ctx.roomJoined) return { action: 'none' };
  // Already back in from another device/tab — don't double-join.
  if (ctx.ownMemberDevices.some((d) => d !== myDeviceId)) return { action: 'none' };
  // Nobody there any more (our own stale membership doesn't count).
  const others = ctx.memberCount - ctx.ownMemberDevices.length;
  if (others <= 0) return { action: 'none' };
  return { action: mode, roomId: record.roomId };
}