private canActAsPrimary()

in packages/firestore/src/local/indexeddb_persistence.ts [535:635]
73 lines of code
20 McCabe index (conditional complexity)

  private canActAsPrimary(
    txn: PersistenceTransaction
  ): PersistencePromise<boolean> {
    if (this.forceOwningTab) {
      return PersistencePromise.resolve<boolean>(true);
    }
    const store = primaryClientStore(txn);
    return store
      .get(DbPrimaryClient.key)
      .next(currentPrimary => {
        const currentLeaseIsValid =
          currentPrimary !== null &&
          this.isWithinAge(
            currentPrimary.leaseTimestampMs,
            MAX_PRIMARY_ELIGIBLE_AGE_MS
          ) &&
          !this.isClientZombied(currentPrimary.ownerId);

        // A client is eligible for the primary lease if:
        // - its network is enabled and the client's tab is in the foreground.
        // - its network is enabled and no other client's tab is in the
        //   foreground.
        // - every clients network is disabled and the client's tab is in the
        //   foreground.
        // - every clients network is disabled and no other client's tab is in
        //   the foreground.
        // - the `forceOwningTab` setting was passed in.
        if (currentLeaseIsValid) {
          if (this.isLocalClient(currentPrimary) && this.networkEnabled) {
            return true;
          }

          if (!this.isLocalClient(currentPrimary)) {
            if (!currentPrimary!.allowTabSynchronization) {
              // Fail the `canActAsPrimary` check if the current leaseholder has
              // not opted into multi-tab synchronization. If this happens at
              // client startup, we reject the Promise returned by
              // `enablePersistence()` and the user can continue to use Firestore
              // with in-memory persistence.
              // If this fails during a lease refresh, we will instead block the
              // AsyncQueue from executing further operations. Note that this is
              // acceptable since mixing & matching different `synchronizeTabs`
              // settings is not supported.
              //
              // TODO(b/114226234): Remove this check when `synchronizeTabs` can
              // no longer be turned off.
              throw new FirestoreError(
                Code.FAILED_PRECONDITION,
                PRIMARY_LEASE_EXCLUSIVE_ERROR_MSG
              );
            }

            return false;
          }
        }

        if (this.networkEnabled && this.inForeground) {
          return true;
        }

        return clientMetadataStore(txn)
          .loadAll()
          .next(existingClients => {
            // Process all existing clients and determine whether at least one of
            // them is better suited to obtain the primary lease.
            const preferredCandidate = this.filterActiveClients(
              existingClients,
              MAX_PRIMARY_ELIGIBLE_AGE_MS
            ).find(otherClient => {
              if (this.clientId !== otherClient.clientId) {
                const otherClientHasBetterNetworkState =
                  !this.networkEnabled && otherClient.networkEnabled;
                const otherClientHasBetterVisibility =
                  !this.inForeground && otherClient.inForeground;
                const otherClientHasSameNetworkState =
                  this.networkEnabled === otherClient.networkEnabled;
                if (
                  otherClientHasBetterNetworkState ||
                  (otherClientHasBetterVisibility &&
                    otherClientHasSameNetworkState)
                ) {
                  return true;
                }
              }
              return false;
            });
            return preferredCandidate === undefined;
          });
      })
      .next(canActAsPrimary => {
        if (this.isPrimary !== canActAsPrimary) {
          logDebug(
            LOG_TAG,
            `Client ${
              canActAsPrimary ? 'is' : 'is not'
            } eligible for a primary lease.`
          );
        }
        return canActAsPrimary;
      });
  }