.. _tutorial-chapter:

An Activipy tutorial
====================

.. TODO: Do we want to open up with a more "dive in" demo of the
   above?

.. TODO: Break this up into multiple pages, so it doesn't look
   intimidating?

This tutorial is fairly robust and is broken into sections.  Each one
of them builds upon each other like a ladder, but you can step off at
any time.  In this tutorial you'll learn:

1. How to use Activipy to express and share basic social networking
   features.
2. How to *do* cool things with Activipy using the method dispatch
   system.
3. Go beyond the basics and use extended vocabulary.
4. Why Activipy objects are "immutable" (or are intended to be)
   and how to use that to your advantage.

.. There's also an advanced tutorial for building environments and etc

You can read as much or as little as you like, but we hope this
tutorial is engaging enough where you won't be able to stop reading
until the end!

Sweet beginnings
----------------

So say you and your friends are all conspiring to meet up for root
beer floats.  How could we structure that in Python?  First, let's
look at the ActivityStreams representation of this note, and then
we'll look at how we got there.

What vocabulary do we want to use?  Let's look at what comes out of
the box::

  >>> vocab.Create.notes
  'Indicates that the actor has created the object.'
  >>> vocab.Person.notes
  'Represents an individual person.'
  >>> vocab.Note.notes
  'Represents a short work typically less than a single paragraph in length.'

Those sound like the things we mean.  Great!  It's nice that Activipy
includes the notes from the
`Activity Vocabulary <http://www.w3.org/TR/activitystreams-vocabulary/>`_
so it's easy for us to keep track of what things mean.

So it turns out we can use these vocabulary definitions as friendly
constructors::

  # gives us the core vocabulary
  from activipy import vocab

  post_this = vocab.Create(
      "http://tsyesika.co.uk/act/foo-id-here/",
      actor=vocab.Person(
          "http://tsyesika.co.uk/",
          displayName="Jessica Tallon"),
      to=["acct:cwebber@identi.ca",
          "acct:justaguy@rhiaro.co.uk",
          "acct:ladyaeva@hedgehog.example"],
      object=vocab.Note(
          "htp://tsyesika.co.uk/chat/sup-yo/",
          content="Up for some root beer floats?"))

Oh, okay, that's pretty easy to read!  We can see that we've specified
who we are, who we want to send the message to, and the actual message
we're posting.

What does our message look like?  Let's see::

  >>> post_this.json()
  {"@id": "http://tsyesika.co.uk/act/foo-id-here/",
   "@type": "Create",
   "actor": {
       "@type": "Person",
       "@id": "http://tsyesika.co.uk/",
       "displayName": "Jessica Tallon"},
   "to": ["acct:cwebber@identi.ca",
          "acct:justaguy@rhiaro.co.uk",
          "acct:ladyaeva@hedgehog.example"],
   "object": {
       "@type": "Note",
       "@id": "htp://tsyesika.co.uk/chat/sup-yo/",
       "content": "Up for some root beer floats?"}}

Oh interesting!  That looks pretty similar to the Python constructor
version.  In fact, we could have built this from the json itself::

  >>> from activipy import core, vocab
  >>> post_this = core.ASObj({
  ...     "@type": "Create",
  ...     "@id": "http://tsyesika.co.uk/act/foo-id-here/",
  ...     "actor": {
  ...         "@type": "Person",
  ...         "@id": "http://tsyesika.co.uk/",
  ...         "displayName": "Jessica Tallon"},
  ...     "to": ["acct:cwebber@identi.ca",
  ...            "acct:justaguy@rhiaro.co.uk",
  ...            "acct:ladyaeva@hedgehog.example"],
  ...     "object": {
  ...         "@type": "Note",
  ...         "@id": "htp://tsyesika.co.uk/chat/sup-yo/",
  ...         "content": "Up for some root beer floats?"}},
  ...   vocab.BasicEnv)
  <ASObj Create>

Hm!  So it's nice to have "pythonic" constructors, but this json
representation isn't so complex... is it worth having a whole library
just for this?  Let's see what else Activipy gives us.

Activipy gives simple dictionary-style access::

  >>> post_this["to"]
  ['acct:cwebber@identi.ca', 'acct:justaguy@rhiaro.co.uk', 'acct:ladyaeva@hedgehog.example']

Helpful, but we could have gotten that from running .json() and
pulling out the right values!  But this is kinda nice::

  >>> root_beer_note = post_this["object"]
  >>> root_beer_note
  <ASObj Note "http://tsyesika.co.uk/chat/sup-yo/">
  
Cool, we've extracted the actual object we were going to post, and it
came back wrapped in an ASObj object.  Of course, we could always get
the json version of this if we wanted::

  >>> root_beer_note.json()
  {'@id': 'http://tsyesika.co.uk/chat/sup-yo/',
   '@type': 'Note',
   'content': 'Up for some root beer floats?'}

What kind of type is our newly extracted `root_beer_note`?  Let's see::

  >>> root_beer_note.types
  ['Note']

Wait, "types", as in possibly plural?  That's right, an ActivityStreams
object's "type" is actually a "composite type".  It turns out this is
useful when handling extensions to the vocabulary, but we'll come back
to that later.

Strings are less fun as types than ASTypes, so can we get that back?
We sure can::

  >>> root_beer_note.types_astype
  [<ASType Note>]

But hey, what's this thing::

  >>> root_beer_note.types_expanded
  ['http://www.w3.org/ns/activitystreams#Note']
  
Huh?  A URL?  This starts to hint at something more
complicated... something to do with extensions!  But we're getting
ahead of ourselves.  Extension stuff comes later!  Right now we're
itching to *do* something with these objects... so what can we do, and
how do we do it?


Methods for our madness
-----------------------

New environments, new friends
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Before we hop right into methods, a quick refresher.  Remember when we
said we could have built our post_this object like this?

.. code-block:: pycon

  >>> from activipy import core, vocab
  >>> post_this = core.ASObj({
  ...     # ... json stuff here
  ...   },
  ...   vocab.BasicEnv)
  <ASObj Create>

Wait, what's that BasicEnv thing hanging off the end?  That's pretty
curious.  What does it do?

Since we're passing into the object, it's a good (and correct) guess
to assume that the ASObj instance has access to it::

  >>> post_this.env
  <activipy.core.Environment at 0x7fecf206f5c0>

The environment helps us in a few ways.  For one thing, it contains a
set of vocabulary that our environment "knows" about.  In fact, we
could even do constructors that implicitly pass in the environment
directly from the environment itself, using the vocabulary it's been
informed of::

  >>> env = vocab.BasicEnv
  >>> root_beer_note = env.c.Note(
  ...   "htp://tsyesika.co.uk/chat/sup-yo/",
  ...   content="Up for some root beer floats?")
  >>> root_beer_note
  <ASObj.Note>

Well that's pretty neat!  It looks like the `Environment.c` accessor
is a friendly way to access vocabulary classes.  Cool!  So you can
already guess at one purpose for environments: if your application is
working with an extended vocabulary, it's possible for Activipy to
"know" about your vocabulary while determining types, etc.  The
BasicEnv is, as you would expect, the default and most minimal
environment, containing the core vocabulary and nothing else.  For
many applications, this is all you need.  If your application needs
additional terminology, we will cover this later in the manual, but
for now, we will only concern ourselves with the core vocabulary.

Even if we stick with the core vocabulary, we may wish to use a
different environment than BasicEnv.  Why?  Well we keep saying that
we want to *do* something with our applications.  Aside from mapping
vocabulary, `Environment` objects can contain a mapping of methods!

So, we want to try something... what would be a good demo?  How about
storing things!  Sounds good to me!  In our case we're going to simply
serialize ActivityStreams objects to json and dump them in and out of
a minimalist key-value
`dbm database <https://docs.python.org/3/library/dbm.html>`_.
(Note: this will be a lot more efficient if you install the Python
bindings for `gdbm <http://www.gnu.org.ua/software/gdbm/>`_.)

Our dbm demo module contains a JsonDBM wrapper which conveniently
serializes/deserializes to/from json when pulling things in/out of the
database.  Let's give it a spin so we know what we're working with::

  >>> from activipy.demos import dbm
  >>> db = dbm.JsonDBM.open("/tmp/test.db")
  >>> db["foo"] = {"cat": "meow", "dog": "woof"}
  >>> db["foo"]
  {'cat': 'meow', 'dog': 'woof'}
  >>> "foo" in db
  True
  >>> del db["foo"]
  >>> "foo" in db
  False

Okay, so that's a pretty easy to use key-value store!  We could
clearly dump our ASObj objects to json and manually save them into
here.  It would be nice if there was a "save" method that could do
that for us though.  How could such a save method be made available?


Save one for me, please
~~~~~~~~~~~~~~~~~~~~~~~

Ah, here's a use for Environments!  You see, an `Environment`
object not only contains information about vocabulary, it contains
information about methods as well.  As it turns out, we have a handy
environment ready for you to play with which knows how to work with a
`JsonDBM` wrapped database.  Let's try it!

.. code-block:: pycon

  >>> env = dbm.DbmEnv
  >>> note = env.c.Note("http://example.org/notes/cookie-time/",
  ...                   content="I really want a cookie!")
  >>> note.m.save(db)
  >>> db["http://example.org/notes/cookie-time"]
  {'@id': 'http://example.org/notes/cookie-time/',
   '@type': 'Note',
   'content': 'I really want a cookie!'}

Hey, it worked!  That sure was handy... we got a .save() method
attached right to our Note!  How about a .delete()?

.. code-block:: pycon

  >>> "http://example.org/notes/cookie-time" in db
  True
  >>> note.m.delete(db)
  >>> "http://example.org/notes/cookie-time" in db
  False

How convenient!

You may notice that we don't call `note.save()` or `note.delete()`;
instead, we call `note.m.save()` and `note.m.delete()`!  That's
because the `.m` attribute is a proxy object to all the methods the
`ASObj.env` knows about (in this case, DbmEnv)::

  >>> dbm.DbmEnv.methods
  {(<MethodId save>, <ASType Object>): <function activipy.demos.dbm.dbm_save>,
   (<MethodId delete>, <ASType Object>): <function activipy.demos.dbm.dbm_delete>}

In fact, we could have used DbmEnv.m instead::

  >>> dbm.DvmEnv.m.save(note, db)
  >>> # is the same as
  >>> note.m.save(db)

But that's way more verbose!  Why not just use `note.m.save(db)`
instead?  So convenient!

What happens if we save a more complicated, nested note to the db?
Remember our root beer float friend?

.. code-block:: pycon

  >>> post_this.json()
  {"@id": "http://tsyesika.co.uk/act/foo-id-here/",
   "@type": "Create",
   "actor": {
       "@type": "Person",
       "@id": "http://tsyesika.co.uk/",
       "displayName": "Jessica Tallon"},
   "to": ["acct:cwebber@identi.ca",
          "acct:justaguy@rhiaro.co.uk",
          "acct:ladyaeva@hedgehog.example"],
   "object": {
       "@type": "Note",
       "@id": "htp://tsyesika.co.uk/chat/sup-yo/",
       "content": "Up for some root beer floats?"}}
  
So we now remember that when post_this was set up, it used the general
purpose environment.  This means that there is no `post_this.m.save()`
method for us to call, because that method is not set up in the
BasicEnv environment.  We can't even use `BasicEnv.m.save()`,
because Activipy safeguards against this::

  >>> dbm.DbmEnv.m.save(post_this, db)
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/cwebber/devel/activipy/activipy/core.py", line 464, in method_dispatcher
    method = self.asobj_get_method(asobj, method_id)
  File "/home/cwebber/devel/activipy/activipy/core.py", line 550, in asobj_get_method
    "ASObj attempted to call method with an Environment "
  activipy.core.EnvironmentMismatch: ASObj attempted to call method with an Environment it was not bound to!

This makes sense, because different environments provide different
vocabularies and handle different methods, and subtle bugs could creep
in if we permitted this.  Normally this is no problem, one application
will in general only make use of a single `Environment` tuned to that
application.  Even here, it is easy to correct... let's just recast
`post_this` to our new environment::

  >>> post_this = core.ASObj(post_this.json(), dbm.DbmEnv)

Now we can save away:::

  >>> post_this.m.save(db)
  >>> db["http://tsyesika.co.uk/act/foo-id-here/"]
  {"@id": "http://tsyesika.co.uk/act/foo-id-here/",
   "@type": "Create",
   "actor": {
       "@type": "Person",
       "@id": "http://tsyesika.co.uk/",
       "displayName": "Jessica Tallon"},
   "to": ["acct:cwebber@identi.ca",
          "acct:justaguy@rhiaro.co.uk",
          "acct:ladyaeva@hedgehog.example"],
   "object": {
       "@type": "Note",
       "@id": "htp://tsyesika.co.uk/chat/sup-yo/",
       "content": "Up for some root beer floats?"}}
  
Hooray, our note is in the database!  That's really nice.


Save a few more
~~~~~~~~~~~~~~~

But wait, is this really how we want?  Notice that this activity
contains two nested ActivityStreams objects: `actor` and `object`!
Wouldn't it be nice if the `.save()` method was able to be smart about
this and "normalize" the data for us, saving the child ActivityStreams
objects as their own database references, and pulling them out as
needed?

Let's think about this for a moment.  We know that the root activity
that we're posting here is of the type `Create`.  We could look at the
`ActivityStreams Vocabulary document <http://www.w3.org/TR/activitystreams-vocabulary/>`_
to find out the inheritance chain, but we don't even have to... Activipy
can help us out here::

  >>> post_this.types_inheritance
  [<ASType Create>, <ASType Activity>, <ASType Object>]

Looking at this, we know that `Create` is a type of `Activity`, which
is itself a type of `Object`.  Looking at the vocabulary document,
it's clear to us that the `actor` and `object` fields
`inherit from Activity <http://www.w3.org/TR/activitystreams-vocabulary/#dfn-activity>`_.

It seems fine to save a general `Object` type as-is as we already are,
and indeed, you may have noticed that the save method was operating
precisely on this ASType::

  >>> dbm.DbmEnv.methods
  {(<MethodId save>, <ASType Object>): <function activipy.demos.dbm.dbm_save>,
   (<MethodId delete>, <ASType Object>): <function activipy.demos.dbm.dbm_delete>}

So, since a `Create` *is* an Object, of course the basic save happens
here.  But it's even more an `Activity` than a mere `Object`, and if
we think about it, hey!  Pretty much on any `Activity` ASType (whether
it's a `Create` or a `Delete` or a `Like`...) it would be really nice
to normalize the `actor` and `object` fields.  Is there a way to
specify that we'd like to treat Activity objects a bit differently?
Indeed, there is!  As you've already guessed, if our `Environment` had
a separate method that did something different for `save` on
`Activity`, that would be really helpful.  And it turns out,
we've already supplied you with such an environment::

  >>> dbm.DbmNormalizedEnv.methods
  {(<MethodId save>, <ASType Object>): <function activipy.demos.dbm.dbm_save>,
   (<MethodId save>, <ASType Activity>): <function activipy.demos.dbm.dbm_activity_normalized_save>,
   (<MethodId denormalize>, <ASType Object>): <function activipy.demos.dbm.dbm_denormalize_object>,
   (<MethodId denormalize>, <ASType Activity>): <function activipy.demos.dbm.dbm_denormalize_activity>,
   (<MethodId delete>, <ASType Object>): <function activipy.demos.dbm.dbm_delete>}

Neat, this does indeed provide us with a separate method for Activity.
Let's switch to using the `DbmNormalizedEnv` instead and cast
`post_this` to use it (again, you wouldn't normally need to do this in
an application that uses just one environment)::

  >>> env = dbm.DbmNormalizedEnv
  >>> post_this = core.ASObj(post_this.json(), dbm.DbmNormalizedEnv)

Now what happens if we save the object?

.. code-block:: pycon

  >>> post_this.m.save(db)
  >>> db["http://tsyesika.co.uk/act/foo-id-here/"]
  {'@id': 'http://tsyesika.co.uk/act/foo-id-here/',
   '@type': 'Create',
   'actor': 'http://tsyesika.co.uk/',
   'object': 'http://tsyesika.co.uk/chat/sup-yo/',
   'to': ['acct:cwebber@identi.ca',
          'acct:justaguy@rhiaro.co.uk',
          'acct:ladyaeva@hedgehog.example']}
  >>> db["http://tsyesika.co.uk/"]
  {'@id': 'http://tsyesika.co.uk/',
   '@type': 'Person',
   'displayName': 'Jessica Tallon'}  
  >>> db["http://tsyesika.co.uk/chat/sup-yo/"]
  {'@id': 'http://tsyesika.co.uk/chat/sup-yo/',
   '@type': 'Note',
   'content': 'Up for some root beer floats?'}

Awesome... that is *exactly* what we were hoping for!

There and back again
~~~~~~~~~~~~~~~~~~~~

Just to bring things full circle, here's a method that demonstrates
pulling an object out of the database::

  >>> def dbm_fetch(id, db, env):
  ...     return core.ASObj(db[id], env)
  ...
  >>> normalized_post = dbm_fetch("http://tsyesika.co.uk/act/foo-id-here/",
  ...                             db, dbm.DbmNormalizedEnv)
  >>> normalized_post
  <ASObj Create "http://tsyesika.co.uk/act/foo-id-here/">
  >>> normalized_post.json()
  {'@id': 'http://tsyesika.co.uk/act/foo-id-here/',
   '@type': 'Create',
   'actor': 'http://tsyesika.co.uk/',
   'object': 'http://tsyesika.co.uk/chat/sup-yo/',
   'to': ['acct:cwebber@identi.ca',
          'acct:justaguy@rhiaro.co.uk',
          'acct:ladyaeva@hedgehog.example']}

We could make use of the environment's denormalize method::

  >>> normalized_post.m.denormalize(db)
  <ASObj Create "http://tsyesika.co.uk/act/foo-id-here/">
  >>> normalized_post.m.denormalize(db).json()
  {'@id': 'http://tsyesika.co.uk/act/foo-id-here/',
   '@type': 'Create',
   'actor': {'@id': 'http://tsyesika.co.uk/',
             '@type': 'Person',
             'displayName': 'Jessica Tallon'},
   'object': {'@id': 'http://tsyesika.co.uk/chat/sup-yo/',
              '@type': 'Note',
              'content': 'Up for some root beer floats?'},
   'to': ['acct:cwebber@identi.ca',
          'acct:justaguy@rhiaro.co.uk',
          'acct:ladyaeva@hedgehog.example']}

Hey look, it's our original post back, with the `actor` and `object`
filled in!  This time, they were extracted from their own entries'
key-value pairs in the database.  Neat!

And finally, we could simplify this whole thing, and write a method to
pull data out of the database in a denormalized fashion, making use of
our environment's denormalize methods::

  >>> def dbm_fetch_denormalized(id, db, env):
  ...     return env.m.denormalize(
  ...         dbm_fetch(id, db, env), db)
  ...
  >>> denormalized_post = dbm_fetch_denormalized(
  ...     "http://tsyesika.co.uk/act/foo-id-here/",
  ...     db, dbm.DbmNormalizedEnv)
  >>> denormalized_post
  <ASObj Create "http://tsyesika.co.uk/act/foo-id-here/"
  >>> denormalized_post.json()
  {'@id': 'http://tsyesika.co.uk/act/foo-id-here/',
   '@type': 'Create',
   'actor': {'@id': 'http://tsyesika.co.uk/',
             '@type': 'Person',
             'displayName': 'Jessica Tallon'},
   'object': {'@id': 'http://tsyesika.co.uk/chat/sup-yo/',
              '@type': 'Note',
              'content': 'Up for some root beer floats?'},
   'to': ['acct:cwebber@identi.ca',
          'acct:justaguy@rhiaro.co.uk',
          'acct:ladyaeva@hedgehog.example']}
  
Whew, what a round trip!

A word to the enwisened
~~~~~~~~~~~~~~~~~~~~~~~

This whole process above of calling the appropriate methods for the
appropriate type (or in our case, ASType) is called "method dispatch".
You may have noticed that we do things fairly differently from most
Python libraries, which usually use Python's native classes as an
inheritance chain, something like this::

  class Object(ASClass):
      class_id = "http://www.w3.org/ns/activitystreams#Object"
      # bla bla
      def save(self, db):
           # save thing here
           pass

  class Activity(Object):
      class_id = "http://www.w3.org/ns/activitystreams#Activity"
      # more bla bla
      def save(self, db):
           # save a bit differently
           pass
           
  class Create(Activity):
      class_id = "http://www.w3.org/ns/activitystreams#Create"

  # also define Note, etc here

We aren't doing that... we're using this intermediate `Environment`
thing instead, and ASObj instances are all just instances of ASObj.
Why?  Why not just use Python's normal class hierarchy?  Why have an
`Environment` at all?

There are a few reasons:

1. ActivityStreams technically has "composite types"... an "@type" can
   actually have *multiple* values set here, and the functionality
   provided by the ASObj will be a union of those types.  Because of
   this, Python's classes really don't work at all to track
   inheritance.  Luckily, there are other benefits of going with an
   `Environment`....

2. Different applications need to do different things.  It's useful to
   have a general way of handling method dispatch that appropriately
   pays respect to the inheritance system of the ActivityStreams base
   vocabulary, and it's nice to make that as Pythonic as possible, but
   you might never save ActivityStreams objects to a DBM store (very
   few production applications would).  You very well may store
   objects to an SQL database, or some object store, or who knows
   what.  You may wish to use Activipy for a desktop client or a
   server application, and those might do very different things.  What
   methods you specify are up to you, but Environments are built in
   such a way that sharing methods between them, picking and choosing
   the ones useful to you, and defining entirely new methods is easy.

3. The core vocabulary is good enough for most social web
   applications, but not for all.  You may well need to define
   entirely new vocabulary, and Activipy allows you to do this.
   Allowing a user to define their own Environment means that this is
   not difficult to do, and how to transfer to those to the
   appropriate ASType representations (and then to know how to operate
   upon them) is very possible.

4. We didn't get into it here, but fancier method handling can also be
   done than just the traditional "dispatch hands off to a single
   procedure" approach.  You can also set up a method with a handler
   which maps or folds over the methods provided through the method
   mapping and inheritence chain.  (Cool, but advanced, stuff!  You
   can imagine how this might be helpful for writing a validator, or
   etc.)

There's more to say on these subjects, but hopefully this section
helped put some of this into perspective.  Hopefully the rest of this
will become clear shortly, including how to expand our vocabulary
without tripping over each others' definitions between applications.
   

Expanding our vocabulary
------------------------

Setting the stage
~~~~~~~~~~~~~~~~~

The default
`ActivityStreams vocabulary <http://www.w3.org/TR/activitystreams-vocabulary/>`_
is fairly comprehensive, and for most social networking applications,
probably has everything you need.

But what happens if it doesn't?  In this section we'll explore adding
vocabulary for an imaginary social network application that's a
"check-in" application (somewhere between Foursquare and Groupon in
design).  Users check in on their phones or other mobile devices when
they arrive somewhere, and their frequency of attendance is somewhat
gameified.  Frequent attendance increases a "royalty" status, and some
stores or other consumer outlets may reward users with one-time use
coupons for frequent attendance.

This is an intereresting application, but the default vocabulary
doesn't give us everything we need.  We'd like to define new types
like "CheckIn", but if someone comes up with a hospital application
that also defines CheckIn, we don't want our applications to get
confused while talking to each other.  How can we do this?

Luckily, Activipy has you covered... read on!


Some new terms
~~~~~~~~~~~~~~

Let's start out easy, and worry about the details later.

So let's say that we're a user of a CheckUp vocabulary using service.
We have a nice little demo for this, so let's import that, and we'll
start using the CheckUpEnv::

  >>> from activipy.demos import checkup    # contains vocab and environment
  >>> from activipy import vocab            # we'll use some of these too
  >>> env = checkup.CheckUpEnv              # for convenience of tutorial

We'll also already assume that we've got a user setup in this system.
Even though we're working with new vocabulary, the Core vocabulary is also
set up in the CheckUpEnv::

  >>> me = env.c.Person(
  ...   "http://social.example/u/sugartooth/",
  ...   displayName="Sarah Sugartooth")

We're also going to set up an imaginary connection to the CheckUp
server we're using, just for demonstration purposes::

.. TODO: Provide an actual FakeConnection() thing eventually

  >>> conn = FakeConnection()

So we know there's a CheckIn vocabulary available through CheckUpEnv...
let's say we just arrived at the "Sweet Expressions" ice cream parlor.
Time to check in!

.. code-block:: pycon

  >>> check_in = env.c.CheckIn(
  ...     actor=me,
  ...     location=env.c.Place(
  ...         "http://sweetexpressions.example/",
  ...          displayName="Sweet Expressions"))
  >>> check_in
  <ASObj CheckIn>

What does that check_in object look like in json form?

.. code-block:: pycon

  >>> check_in.json()
  {'@context': 'http://checkup.example/context.jld',
   '@type': 'CheckIn',
   'actor': {'@id': 'http://social.example/u/sugartooth/',
             '@type': 'Person',
             'displayName': 'Sarah Sugartooth'},
   'location': {'@id': 'http://sweetexpressions.example/',
                '@type': 'Place',
                'displayName': 'Sweet Expressions'}}

Huh, so this is kind of interesting.  The `@type` looks nice and
simple as "CheckIn", but there's also this `@context` thing.  We won't
worry too much about what that is yet, but a brief preview is given by
checking the types::

  >>> check_in.types_astype
  [<ASType CheckIn>]
  >>> check_in.types_expanded
  ['http://checkup.example/ns#CheckIn']

Hm, so this is pretty cool!  Something in that @context has helped
clarify exactly what "CheckIn" we're talking about.  We'll get into
this more later, but if in the future there was ever a DoctorVisit
vocabulary, we'd never mistake "http://checkup.example/ns#CheckIn" for
a "http://doctoroffice.example/terms#CheckIn".  Our doctor might be
fairly confused if we sent her a note telling her that we're out to
get ice cream, but now we can be sure that that mistake won't happen.
We'll get into this more later, but that's already good to know!

Okay, so we've made the `check_in` object, but we haven't *done*
anything with it yet.  We have this connection to our CheckUp service,
why not post it there!

.. code-block:: pycon

  >>> check_in.m.post(conn)

Well that was easy... what can we do now?  How about check out our
inbox?

.. code-block:: pycon

  >>> inbox_contents = me.m.inbox(conn)
  <ASObj Collection>
  >>> inbox_contents.json()
  {'@context': 'http://checkup.example/context.jld',
   '@type': 'Collection',
   'items': [
       {'@type': ['Coupon', 'Note'],
        'content': 'Thanks for 40 visits to Sweet Expressions!',
        'recipient': {'@id': 'http://social.example/u/sugartooth/',
                      '@type': 'Person',
                      'displayName': 'Sarah Sugartooth'},
        'redeem_uri': 'http://sweetexpressions.example/coupon/9ae37630/',
        'vendor': {'@id': 'http://sweetexpressions.example/',
                   '@type': 'Place',
                   'displayName': 'Sweet Expressions'}}
       {'@type': 'http://checkup.example/ns#RoyalStatus',
        'displayName': "Sarah Sugartooth's been upgraded to Queen status!",
        'recipient': {'@id': 'http://social.example/u/sugartooth/',
                      '@type': 'Person',
                      'displayName': 'Sarah Sugartooth'},
        'status': 'Queen',
        'vendor': {'@id': 'http://sweetexpressions.example/',
                   '@type': 'Place',
                   'displayName': 'Sweet Expressions'}}]}

Huh... that's interesting, so this is a collection... it has two items
in it.  We could pull out that first item individually and take a look
at it in detail::

  >>> coupon = inbox_contents["items"][0]
  >>> coupon
  <ASObj Coupon, Note>

Huh, that's interesting, it says it's a Coupon *and* a Note?  It sure
is::

  >>> coupon.json()
  {'@context': 'http://checkup.example/context.jld',
   '@type': ['Coupon', 'Note'],
   'content': 'Thanks for visiting Sweet Expressions!',
   'recipient': {'@id': 'http://social.example/u/sugartooth/',
                 '@type': 'Person',
                 'displayName': 'Sarah Sugartooth'},
   'redeem_uri': 'http://sweetexpressions.example/coupon/9ae37630/',
   'vendor': {'@id': 'http://sweetexpressions.example/',
              '@type': 'Place',
              'displayName': 'Sweet Expressions'}}
  >>> coupon.types_astype
  [<ASType Coupon>, <ASType Note>]
  >>> coupon.types_expanded
  ['http://checkup.example/ns#Coupon', 'http://www.w3.org/ns/activitystreams#Note']

So first of all, this makes sense.  All a Coupon is to our system is
something fairly functional, something by which a vendor can deliver a
`redeem_uri` (which is a one-time-use URI to redeem a coupon for
something special) to a recipient.  But our friends at Sweet
Expressions wanted to include a little thank-you along with the
coupon, so this object acts as a composite type of both of these.

As a user, for the most part, the details of handling composite types
are mostly taken care of for you by Activipy.  But as a side note,
it's interesting to look at what this means for the inheritence
chain::

  # inheritence chain for the Coupon ASType
  >>> checkup.Coupon.inheritance_chain
  [<ASType Coupon>, <ASType Object>]
  # inheritence chain for the Coupon ASType
  >>> vocab.Note.inheritance_chain
  [<ASType Note>, <ASType Content>, <ASType Object>]
  # The actual types for our coupon object
  >>> coupon.types_astype
  [<ASType Coupon>, <ASType Note>]
  # And the inheritence chain built by the composite type
  >>> coupon.types_inheritance
  [<ASType Coupon>, <ASType Note>, <ASType Content>, <ASType Object>]

You don't necessarily need to make use of composite types in your
system, but we can now see one possible reason you might want to: some
of your activities might be a union of actions, and composite types
are a great way to express them.  (As will be covered in the "advanced
tutorial", you can use the mapping/folding method features to maximize
composite types with your method handling, too.)

There's another reason that we might see composite types used...
let's look at our outbox from our connection::

  >>> me.m.outbox(conn).json()
  {'@context': 'http://checkup.example/context.jld',
   '@type': 'Collection',
   'items': [
       {'@type': ['CheckIn', 'Arrive'],
        'actor': {'@id': 'http://social.example/u/sugartooth/',
                  '@type': 'Person',
                  'displayName': 'Sarah Sugartooth'},
        'location': {'@id': 'http://sweetexpressions.example/',
                     '@type': 'Place',
                     'displayName': 'Sweet Expressions'}}]}

Huh... that's interesting.  So we've retreived from the connection our
recent activities, but whatever server is on the other end is showing
the CheckIn we just did as a composite type of both `CheckIn` and
`Arrive`!  This seems kind of stange, because `CheckIn` is just a
subclass of `Arrive` anyway::

  >>> checkup.CheckIn.inheritance_chain
  ... [<ASType CheckIn>,
  ...  <ASType Arrive>,
  ...  <ASType IntransitiveActivity>,
  ...  <ASType Activity>,
  ...  <ASType Object>]

So if a `CheckIn` is technically part of an `Arrive`, why might our server
do this?  Well, not all servers might have the `CheckIn` vocabulary (or
know that it's a parent to `Arrive`), so since `CheckIn` can technically
be displayed as an `Arrive`, so if a recipient of this activity knows
how to display an `Arrive` but not a `Checkin`, they could do that.

So anyway!  Now you've seen how to work with new types.  Now you're
maybe starting to wonder, what's the theoretical model of all this
under the hood?  (What, you weren't wondering that before?  Okay, now
you are!)  Let's take a look!

Expanding into json-ld
~~~~~~~~~~~~~~~~~~~~~~

Remember when we did this?

.. code-block:: pycon

  >>> root_beer_note.types_expanded
  ['http://www.w3.org/ns/activitystreams#Note']
  >>> coupon.types_expanded
  ['http://checkup.example/ns#Coupon', 'http://www.w3.org/ns/activitystreams#Note']

This starts to make more sense when we think about naming
conflicts... if you send me a message about "running a mile", and I
send you a message about "running a program", those are obviously two
very different definitions of "running", and it might create a lot of
problems if they become confused.  There should be an unambiguous way
to represent things, and that's exactly where `json-ld
<http://json-ld.org/>`_ comes in.  In json-ld, json objects can be
"expanded" to an unambiguous format, and then "compacted" to the right
definitions for our own local server, so we'll never get confused
between two different definitions of "running" again.  Here's a brief
hint towards that right now::

  >>> post_this.expanded()
  [{'@id': 'http://tsyesika.co.uk/act/foo-id-here/',
    '@type': ['http://www.w3.org/ns/activitystreams#Create'],
    'http://www.w3.org/ns/activitystreams#actor': [
        {'@id': 'http://tsyesika.co.uk/',
         '@type': ['http://www.w3.org/ns/activitystreams#Person'],
         'http://www.w3.org/ns/activitystreams#displayName': [
             {'@value': 'Jessica Tallon'}]}],
    'http://www.w3.org/ns/activitystreams#object': [
        {'@id': 'htp://tsyesika.co.uk/chat/sup-yo/',
         '@type': ['http://www.w3.org/ns/activitystreams#Note'],
         'http://www.w3.org/ns/activitystreams#content': [
             {'@value': 'Up for some root beer floats?'}]}],
    'http://www.w3.org/ns/activitystreams#to': [
        {'@id': 'acct:cwebber@identi.ca'},
        {'@id': 'acct:justaguy@rhiaro.co.uk'},
        {'@id': 'acct:ladyaeva@hedgehog.example'}]}]

That might look a bit complicated, but normally you wouldn't work in
an expanded document, you'd compact to your local context.  If this
seems confusing, you don't really need to worry about; Activipy uses
json-ld under the hood but you usually won't need to interact with it.
One nice feature though is that ActivityStreams 2.0 documents have an
"implied context" of
`the core ActivityStreams vocabulary <http://www.w3.org/TR/activitystreams-vocabulary/>`_.
This means that a "Note" will always mean the ActivityStreams version
of a Note, even if you don't do any fancy context things and are using
just plain old json.  Even when you get into extension land, Activipy
makes things so that you can think as in terms of pythonic constructors
rather than json-ld, so your code will look like simple Python, just
like at the very beginning of our tutorial.

So if you nearly never need to work with this super-extensible version
of things, what's the point of us showing you it?  Well the
interesting here is, since that's the unambiguous "expanded" version,
we can now understand how we can get information from another source
and clearly understand its meaning.

We can also now begin to understand what "compacted" means: the simple
JSON representations we've been showing for most of this post!

So we can take data from the outside world, expand it into an
unambiguous format, and then compact it down to the terminology we
actually know.  Once compacted, it's in a format that's so simple even
poor Billy Scripter with his json and ruby toolbox can use it.  And
since we've compacted it to a context *we* know, we know that an
`Activity` is an `Activity <http://www.w3.org/TR/activitystreams-vocabulary/#dfn-activity>`_
and we'll never confuse "run a program" with someone else's "run a
mile" again.  Horray!

But... the `CheckIn` / `Coupon` examples above included this
`@context` key.  What is that thing?  Let's take a look.


It's all contextual
~~~~~~~~~~~~~~~~~~~

As a refresher, some of our early examples looked like this::

  >>> root_beer_note
  {'@id': 'http://tsyesika.co.uk/chat/sup-yo/',
   '@type': 'Note',
   'content': 'Up for some root beer floats?'}
  >>> root_beer_note.types_expanded
  ['http://www.w3.org/ns/activitystreams#Note']

No `@context` there.  And yet just recently we saw this::

  >>> check_in.json()
  {'@context': 'http://checkup.example/context.jld',
   '@type': 'CheckIn',
   'actor': {'@id': 'http://social.example/u/sugartooth/',
             '@type': 'Person',
             'displayName': 'Sarah Sugartooth'},
   'location': {'@id': 'http://sweetexpressions.example/',
                '@type': 'Place',
                'displayName': 'Sweet Expressions'}}
  >>> check_in.types_expanded
  ['http://checkup.example/ns#CheckIn']

Okay, that does have an `@context`!  Well, we're working with
extensions, so it's obvious that this maps our vocabulary to the
unambiguous definitions we saw in the expanded version.

So that's kind of cool, we can imagine that
`'http://checkup.example/context.jld'` somehow maps `'CheckIn'` ->
`'http://checkup.example/ns#CheckIn'` in our second example.  But
wait, how did `'Note'` get mapped to
`'http://www.w3.org/ns/activitystreams#Note'` in our first example?
We didn't specify any context at all!  This is because ActivityStreams
has an "implied context" of its own vocabulary at
`'http://www.w3.org/TR/activitystreams-core/activitystreams2-context.jsonld'`,
so that vocabulary mapping context is there without us even having to
specify it.

You might have noticed a small amount of trickery:
`http://checkup.example/context.jld` doesn't exist!  You caught us, this
is just a demonstration, so we overrode the `default_loader` in the
environment to pretend that it knew what was at that URL already.
Tricky!

It turns out we could have rewritten the `CheckIn` example with the
contents of what we were "pretending" was at
`http://checkup.example/context.jld`, and it would have worked during
expansion just as well::

  {'@context': {'CheckIn': {'@id': 'http://checkup.example/ns#CheckIn',
                            '@type': '@id'},
                'Coupon': {'@id': 'http://checkup.example/ns#Coupon',
                           '@type': '@id'},
                'RoyalStatus': {'@id': 'http://checkup.example/ns#RoyalStatus',
                                '@type': '@id'}},
   '@type': 'CheckIn',
   'actor': {'@id': 'http://social.example/u/sugartooth/',
             '@type': 'Person',
             'displayName': 'Sarah Sugartooth'},
   'location': {'@id': 'http://sweetexpressions.example/',
                '@type': 'Place',
                'displayName': 'Sweet Expressions'}}

Wow, that's *quite* verbose.  But that's basically dumping what would
have been at `http://checkup.example/context.jld` inline.

It turns out there's another kind of interesting way to specify terms
in an `@context`, which is namespacing::

  {'@context': {'CheckUp': 'http://checkup.example/ns#'},
   '@type': 'CheckUp:CheckIn',
   'actor': {'@id': 'http://social.example/u/sugartooth/',
             '@type': 'Person',
             'displayName': 'Sarah Sugartooth'},
   'location': {'@id': 'http://sweetexpressions.example/',
                '@type': 'Place',
                'displayName': 'Sweet Expressions'}}

If you'd like to play with these, we have environments set up for them
at `activipy.demos.checkup` under the varibles `CheckUpVerboseEnv` and
`CheckUpNSEnv`.


Consume the world
~~~~~~~~~~~~~~~~~

So now you have a solid theoretical understanding of how information
can be unambiguously represented in Activipy.  But what if we want to
consume activities from the outside world?

*TODO: Finish this section!*



The more we change, the more we stay the same
---------------------------------------------

.. TODO: We need functional setters for this part to work :)

*TODO: Fill in this section on the immutable properties of Activipy*
