error messages

[mpeck]

This adds/updates a number of error messages to make it easier for users to troubleshoot issues.

resolves #1092

• Executing a command in a bundle not assigned to a relay group
  • Bundle 'test' is not assigned to a relay group. Assign the bundle to a relay group and try again.
• Executing a command that only exists on a disabled relay
  • No Cog Relays supporting thetestbundle are currently available. There are one or more relays serving the bundle, but they are disabled. Enable an appropriate relay and try again.
• Updates to the standard "No Cog Relays supporting..." error
  • No Cog Relays supporting thetestbundle are currently online. If you just assigned the bundle to a relay group you will need to wait for the relay refresh interval to pick up the new bundle.

Provided by piper:

• Executing a command in a disabled bundle
  • Bundle 'mybundle' is disabled. Please enable it and try running the command again.
• Executing a command that does not exist in a bundle
  • Bundle '#{bundle}' doesn't contain a command named '#{text}'.

[kevsmith]

Flipping the logic will reduce the number of DB queries issued to execute a pipeline:

case Map.get(relays, bundle_name) do
  # No assignment so let's pick one
  nil ->
    case Relays.pick_one(bundle_name, bundle_version) do
      # No relays available
      {:error, :no_relays} ->
        {nil, relays}
        # relays exist, but are disabled
      {:error, :no_enabled_relays} ->
        # Query database to clarify error condition before reporting to user
        if Cog.Repository.Bundles.assigned_to_group?(bundle_name) do
          {:no_enabled_relays, relays}
        else
          {:no_relay_group, relays}
        end
      # Store the selected relay in the relay cache
      {:ok, relay} ->
        {relay, Map.put(relays, bundle_name, relay)}
    end
    # Relay was previously assigned
  relay ->
  # Is the bundle still available on the relay? If not, remove the current assignment from the cache
  # and select a new relay
    if Relays.relay_available?(relay, bundle_name, bundle_version) do
      {relay, relays}
    else
      relays = Map.delete(relays, bundle_name)
      assign_relay(relays, bundle_name, bundle_version)
    end
end

[kevsmith]

I think returning descriptive atoms instead of sets of relays would be more intention revealing.

{[], []} becomes :no_relays
{[...], []} becomes :no_enabled_relays
{[...], [...]} becomes [...]

where [...] indicates a non-empty list.

[kevsmith]

Does this work if relays/3 returns one of the error tuples?

[mpeck]

nope, that's a bug. Missed that bit from the previous function return.