# Spur
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Loosely based on https://github.com/chaps-io/public_activity, a very simple utility for quickly setting up an activity stream in your Elixir/Ecto app.
More detailed examples of configuration and usage are in the tests.
## Installation
Basic steps are
1. Add Spur to your application deps
2. Generate and run a migration that adds an "activities" table to your repo (see priv/test/migrations). To use a different table name, set the `activities_table_name` config.
3. Add the following config:
```
config :spur, ecto_repos: [MyApp.Repo],
repo: MyApp.Repo
```
That's enough to start tracking arbitrary activities.
```
%Spur.Activity{actor: "caesar", action: "came", object: "your-county", meta: %{also: ["saw", "conquered"]}}
```
Fields are based on https://www.w3.org/TR/activitystreams-core/#example-1
## Getting fancy
### "Callbacks"
If you want to make use of automatic tracking of inserts, updates and deletes, make sure your objects implement the required fields as functions.
```
defmodule Battle do
defimpl Spur.Trackable, for: __MODULE__ do
def actor(war), do: "Accounts.User:#{war.general_id}"
def object(war), do: "war:#{war.id}"
def target(_war), do: nil
end
end
```
Now instead of using `Repo` to perform your operation, use `Spur` instead.
```
%MyApp.Battle{general_id: 5}
|> MyApp.Battle.changeset
|> Spur.insert
```
A record for both your `Battle` and an `Activity` with action set to insert will be stored in the DB. Of course, the `Battle` fails validations, neither will be inserted and the changeset will be returned with errors, just as Repo would. (*Note*: As of 0.3.0, Spur supports the `expose_transactions` config, which when sets to true returns the raw Ecto transaction. Us this if you need to access the created `Activity` struct.)
### Audience
To automatically associate the `Activity` with an [audience](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-audience) requires a bit of extra configuration:
1. Add `audience_module` to your app's Spur config: `audience_module: MyApp.Accounts.User`
2. Add a `many_to_many` association between your audience module's Ecto schema.By default Spur expects this to be named `:activities`
3. If you want to name it something else, add another line to the config: `audience_assoc_name: :silly_users`
4. Finally, make sure that your trackable objects implement `audience`. It should return either an Ecto query or a plain list of the audience objects configured with the above association.
Now when you use one of the callback's above to track an object, the resulting `Activity` will automatically be associated with the audience records returned for that object.
# SpurTest.TrackableStruct
def audience(trackable_struct), do: Ecto.assoc(trackable_struct, :watchers)
[watcher] = trackable_struct.watchers
Ecto.Changeset.change(trackable_struct)
|> Spur.update
[%Spur.Activity{action: update}] = watcher.activities
---
> <<Someone who finds a trace [Spur] certainly also knows that something has existed before and is now left behind. But one does not just take note of this. One begins to search and to ask oneself where it leads.>>
>
> Hans Georg-Gadamer, "Hermeneutik auf dem Spur"
