# Inventory Refresh Overview
Tower should have an inventory view that is more aligned towards systems management
rather than merely maintaining inventory for automation.

## Inventory Source Promotion
Starting with Tower 3.2, `InventorySource` will be associated directly with an `Inventory`.

### API Concerns / Deprecation
The `group` field for `InventorySource` has been renamed to `deprecated_group` and will be removed
from `InventorySource` completely in Tower 3.3. As a result the related field on `Group` ,
`inventory_source` has been renamed `deprecated_inventory_source` and will also be removed in Tower 3.3.


## Fact Searching
Facts generated by an Ansible playbook during a Job Template run are stored by Tower into the database
whenever `use_fact_cache=True` is set per-Job-Template. New facts are merged with existing
facts and are per-host. These stored facts can be used to filter hosts via the
`/api/v2/hosts` endpoint, using the GET query parameter `host_filter` i.e.
`/api/v2/hosts?host_filter=ansible_facts__ansible_processor_vcpus=8`

The grammer of `host_filter` allows for:
* grouping via `()`
* the boolean `and` operator
* `__` to reference related fields in relational fields
* `__` is used on `ansible_facts` to separate keys in a JSON key path
* `[]` is used to denote a json array in the path specification
* `""` can be used in the value when spaces are wanted in the value
* "classic" Django queries may be embedded in the `host_filter`

Examples:
```
/api/v2/hosts/?host_filter=name=localhost
/api/v2/hosts/?host_filter=ansible_facts__ansible_date_time__weekday_number="3"
/api/v2/hosts/?host_filter=ansible_facts__ansible_processor[]="GenuineIntel"
/api/v2/hosts/?host_filter=ansible_facts__ansible_lo__ipv6[]__scope="host"
/api/v2/hosts/?host_filter=ansible_facts__ansible_processor_vcpus=8
/api/v2/hosts/?host_filter=ansible_facts__ansible_env__PYTHONUNBUFFERED="true"
/api/v2/hosts/?host_filter=(name=localhost or name=database) and (groups__name=east or groups__name="west coast") and ansible_facts__ansible_processor_vcpus=8
```

## Smart Inventory
Starting in Tower 3.2, Tower will support the ability to define a _Smart Inventory_.
You will define the inventories using the same language we currently support
in our _Smart Search_.

### Inventory Changes
* The `Inventory` model has a new field called `kind`. The default of this field will be blank
for normal inventories and set to `smart` for smart inventories.

* `Inventory` model has a new field called `host_filter`. The default of this field will be blank
for normal inventories. When `host_filter` is set AND the inventory `kind` is set to `smart`
is the combination that makes a _Smart Inventory_.

* `Host` model has a new field called `smart_inventories`. This field uses the `SmartInventoryMemberships`
lookup table to provide a set of all of the _Smart Inventory_ a host is a part of. The memberships
are generated by the `update_host_smart_inventory_memberships` task. This task is called when the view for
`/api/v2/hosts/:id/smart_inventories` is materialized. NOTE: This task is only run if the 
`AWX_REBUILD_SMART_MEMBERSHIP` is set to True. It defaults to False.

### Smart Filter (host_filter)
The `SmartFilter` class handles our translation of the smart search string. We store the
filter value in the `host_filter` field for an inventory. This value should be expressed
the same way we express our existing smart searches.

    host_filter="search=foo"
    host_filter="group__search=bar"
    host_filter="search=baz and group__search=bang"
    host_filter="name=localhost or group__name=local"

Creating a new _Smart Inventory_ for all of our GCE and EC2 groups might look like this:

    HTTP POST /api/v2/inventories/

    {
        "name": "GCE and EC2 Smart Inventory",
        "kind": "smart",
        "host_filter": "group__search=ec2 and group__search=gce"
        ...
    }

### More On Searching
The `host_filter` you set will search over the entirety of the hosts you have
access to in Tower. If you want to restrict your search in anyway, you will
want to declare that in your host filter.

For example, if you want to restrict the search to only hosts in an inventory
named "US-East", you would create a `host_filter` that looked something like this:

    {
        "name": "NYC Hosts",
        "kind": "smart",
        "host_filter": "inventory__name='US-East' and search='nyc'",
        ...
    }

In the above example, you are limiting the search to the "US-East" inventory and
hosts with a name containing "nyc".


### Acceptance Critera
When verifying acceptance we should ensure the following statements are true:

* `Inventory` has a new field named `kind` that defaults to empty and
can only be set to `smart`.
* `Inventory` has a new field named `host_filter` to empty and can only be
set to a valid _SmartFilter_ string.
* `Inventory` with a `host_filter` set and a `kind` of `smart` will have
a `hosts` list reflecting the results of searching `/api/v2/hosts` with the same
search that is set in the `host_filter`.

### API Concerns
There are no breaking or backwards incompatible changes for this feature.


## Other Changes

### Inventory update all inventory_sources
A new endpoint `/api/v2/inventories/:id/update_inventory_sources` has been added. This endpoint
functions in the same way that `/api/v2/inventory_source/:id/update` functions for a single
`InventorySource` with the exception that it updates all of the inventory sources for the
`Inventory`.

`HTTP GET /api/v2/inventories/:id/update_inventory_sources` will list all of the inventory
sources and if they will be updated when a POST to the same endpoint is made. The result of
this request will look like this:

    {
        results: [
            {"inventory_source": 1, "can_update": True},
            {"inventory_source": 2, "can_update": False},
        ]
    }

When making a POST to the same endpoint, the response will contain a status as well as the job ID for the update.

    POST /api/v2/inventories/:id/update_inventory_sources

    {
        results: [
            {"inventory_update": 20, "inventory_source": 1, "status": "started"},
            {"inventory_update": 21, "inventory_source": 2, "status": "Could not start because `can_update` returned False"}
        ]
    }


### Background deletion of Inventory

### InventorySource Hosts and Groups read-only
