# PandaPal

## LTI Configuration
A standard Canvas LTI may have a configuration similar to the one below

```ruby
# config/initializers/lti.rb
PandaPal.lti_options = { title: 'Teacher Reports' }
PandaPal.lti_properties = {oauth_compliant: 'true'}
# Environments reflect those used by Canvas
PandaPal.lti_environments = { domain: ENV['PROD_DOMAIN'], beta_domain: ENV['BETA_DOMAIN'], test_domain: ENV['TEST_DOMAIN'] }
PandaPal.lti_custom_params = { custom_canvas_role: '$Canvas.membership.roles' }
# :user_navigation, :course_navigation for user context and course context endpoints respectively
PandaPal::stage_navigation(:account_navigation, {
  enabled: true,
  # url: :account_index, # Optional if using lti_nav
  text: 'Teacher Reports',
  visibility: 'admins',
})
```

Configuration data for an installation can be set by creating a `PandaPal::Organization` record.  Due to the nature of the data segregation, once created, the name of the organization should not be changed (and will raise a validation error).

### Launch URL property
LTI Spec: `The launch_url contains the URL to which the LTI Launch is to be sent.   The secure_launch_url is the URL to use if secure http is required.  One of either the launch_url or the secure_launch_url must be specified.`

Bridge is now validating that this launch URL exists and requires it per the LTI spec. As of PandaPal 3.1.0, you now have 6 options to use this.
Use one of these 6 options in `PandaPal.lti_options` hash.
1. Use option `secure_launch_url: 'http://domain.com/path'` when a full static secure domain is needed.
2. Use option `secure_launch_path: '/path'` when you need the secure options and want the host to be dynamic and just need to provide a path.
3. Use option `launch_url: 'http://domain.com/path'` when a full static domain is needed.
4. Use option `launch_path: '/path'` when you don't need the secure options and want the host to be dynamic and just need to provide a path.
5. Leave this property off, and you will get the dynamic host with the root path ('http://appdomain.com/') by default.
6. If you really do not want this property use the option `launch_url: false` for it to be left off.

### Task Scheduling
`PandaPal` includes an integration with `sidekiq-scheduler`. You can define tasks on an Organization class Stub like so:
```ruby
# <your_app>/app/models/panda_pal/organization.rb
require File.expand_path('../../app/models/panda_pal/organization.rb', PandaPal::Engine.called_from)

module PandaPal
  class Organization
    # Will invoke CanvasSyncStarterWorker.perform_async() according to the cron schedule
    scheduled_task '0 15 05 * * *', :identifier, worker: CanvasSyncStarterWorker

    # Will invoke the method 'organization_method' on the Organization
    scheduled_task '0 15 05 * * *', :organization_method_and_identifier

    # If you need to invoke the same method on multiple schedules
    scheduled_task '0 15 05 * * *', :identifier, worker: :organization_method

    # You can also use a block
    scheduled_task '0 15 05 * * *', :identifier do
      # Do Stuff
    end

    # You can use a Proc (called in the context of the Organization) to determine the schedule
    scheduled_task -> { settings[:cron] }, :identifier

    # You can specify a timezone. If a TZ is not coded and settings[:timezone] is present, it will be appended automatically
    scheduled_task '0 15 05 * * * America/Denver', :identifier, worker: :organization_method

    # Setting settings[:task_schedules][:identifier] will override the code cron schedule. Setting it to false will disable the Task
    # :identifer values _must_ be unique, but can be nil, in which case they will be determined by where (lineno etc) scheduled_task is called
  end
end
```

### Organization Attributes
  `id`: Primary Key
  `name`: Name of the organization. Used to on requests to select the tenant
  `key`: Key field from CanvasLMS
  `secret`: Secret field from CanvasLMS
  `canvas_account_id`: ID of the corresponding Canvas account.
  `settings`: Hash of settings for this Organization
  `salesforce_id`: ID of this organization in Salesforce

XML for an installation can be generated by visiting `/lti/config` in your application.

### Routing

The following routes should be added to the routes.rb file of the implementing LTI. (substituting `account_navigation` with the other staged navigation routes, if necessary)

```ruby
# config/routes.rb
mount PandaPal::Engine, at: '/lti'
lti_nav account_navigation: 'accounts#launch' # Use lti_nav to provide a custom Launch implementation, otherwise use the url: param of stage_navigation to let PandaPal handle launch.
root to: 'panda_pal/lti#launch'
```

## Implementating data segregation
This engine uses Apartment to keep data segregated between installations of the implementing LTI tool.
By default, it does this by inspecting the path of the request, and matching URLs containing `orgs` or `organizations`,
followed by the numeric ID of the organization (path such as `/organizations/123/accounts`).
As such, all URLs should be built on top of a routing scope, such as the example below.

```ruby
scope '/organizations/:organization_id' do
  resources :accounts, only: :index do
    collection do
      get 'teachers' => 'accounts#teachers'
    end
  end
end
```

This can be overriden by creating an initializer, and adding a custom elevator

```ruby
Rails.application.config.middleware.delete 'Apartment::Elevators::Generic'
Rails.application.config.middleware.use 'Apartment::Elevators::Generic', lambda { |request|
  if match = request.path.match(/\/(?:orgs|organizations)\/(\d+)/)
    PandaPal::Organization.find_by(id: match[1]).try(:name)
  end
}
```

It is also possible to switch tenants by implementing `around_action :switch_tenant` in the controller.
However, it should be noted that calling `switch_tenant` must be used in an `around_action` hook (or given a block), and is only intended to be used for LTI launches, and not subsequent requests.

### Rake tasks and jobs
**Delayed Job Support has been removed. This allows each project to assess it's need to handle background jobs.**

The Apartment Gem makes it so background jobs need to be run within the current tenant. If using sidekiq, there is a gem that
does this automatically called `apartment-sidkiq`. If Delayed Jobs, see how it's done in version 1 of PandaPal.

For rake tasks, the current tenant will be set to `public`, and thus special handling must be taken when running the task or queueing jobs as part of it.

One potential solution is to create a method with switches between tenants, and invoke the job for each individual organization as necessary.

```ruby
# config/initializers/global_methods.rb
def switch_tenant(tenant, &block)
  if block_given?
    Apartment::Tenant.switch(tenant, &block)
  else
    Apartment::Tenant.switch! tenant
  end
end
```

```ruby
# lib/tasks/lti_tasks.rake
namespace :lti_tasks do
  desc 'some rake task'
  task some_rake_task: :environment do
    PandaPal::Organization.all.each do |org|
      switch_tenant(org.name) do
        SomeJob.perform_later
      end
    end
  end
end
```

## Controller helper methods
Controllers will automatically have access to a number of methods that can be helpful to implement.  A list with descriptions is provided below.

* `validate_launch!` - should be used in any tool launch points, and will verify that the launch request received from Canvas is legitimate based on the saved key and secret.
* `current_session` - PandaPal provides support to use database persisted sessions, rather than the standard rails variety, as these play better when the tool is launched in an `iframe`.  The `session_key` attribute from the returned object needs to be served to the client at some point during the launch and during subsequent requests.  The benefit from this is that sessions will exist entirely in the frame used to launch the tool, and will not be visible should the user be accessing the tool in other contexts simultaneously.  See section below for more information about this method.
* `current_session_data` - Shortcut method to access the `data` hash given by the above method.
* `current_organization` - Used to return the organization related to the currently selected tenant.  See section below for more information about this method.
* `session_changed?` - returns true if the session given by `current_session` has been modified during the request.
* `save_session` - Saves the session given by `current_session` to the database.

## Sessions and `current_session`
Because of the ever-increasing security around `<iframe>`s and cookies, a custom session implementation has been rolled into `PandaPal`.
The implementation is mostly passive, but requires some changes and caveats as opposed to the native Rails implementation.

The current session object can be accessed from any controller using `current_session`. This object isn't the actual data container (as `session` _is_ in Rails).
Session data can be accessed and modified using `current_session.data[:key]` or `current_session_data[:key]`.

Because cookies are unreliable, it becomes the responsibility of the LTI developer to ensure that a custom "cookie" is passed to the frontend with each response
and returned to the backend with each request, otherwise the backend won't be able to access the current session. There are a few ways to do this.

Generally, the method for passing the session "cookie" to the frontend looks something like:
```html
<meta name="session_key" content="<%= current_session.session_key %>">
```

### Returning to the backend
The `session_key` can be passed to the backend in multiple ways:
1. (Recommended) Via the `Authorization` Header (usually defining it as a default in your AJAX/XHR/`fetch` library):
  ```http
  Authorization: token=SESSION_KEY_HERE
  ```
2. Via a `session_key` parameter in a `POST` request (Useful for native HTML `<form>`s).
3. (Used for Dev, but not highly discouraged in Prod) via a `GET`/URL Query parameter: `?session_key=SESSION_KEY_HERE`.

The `session_key` does not contain any secrets itself, so it is safe to pass to the frontend, but it is encouraged to keep it away from the
end-user as much as possible because it should not be shared.

### Redirecting and Multi-Page Applications
Special instructions must be followed when using `link_to` or `redirect_to` to ensure that the Session is passed correctly:

Add a `session_token:` (notice the use of _`_token`_ as opposed to _`_key`_!) parameter when using `link_to` or `redirect_to`:
```ruby
  link_to "Link Name", somewhere_else_path(session_token: link_nonce)
  redirect_to somewhere_else_path(session_token: link_nonce)
```
You can also use the `redirect_with_session_to` helper, which will automatically add `organization_id:` and `session_token:` params:
```ruby
  redirect_with_session_to :somewhere_else_path, other_param: 1
```
For each request (not each call), `link_nonce` generates a nonce and stores it in the Session. The generated value can be used
for at-most-one future request. This means that browser back-forward navigation **will not work** (if it actually ever worked for
iframe-based LTIs in the first place).

### Persisting the session
The session is automatically saved using an `after_action` callback. This callback is poised to run last, but if that causes issues
(eg some other callback running afterwards and needing to modify the session), `skip_after_action :auto_save_session` can be used
and a custom implementation can be supplemented.

### Session cleanup
Over time, the sessions table will become bloated with sessions that are no longer active.
As such, `rake panda_pal:clean_sessions` should be run periodically to clean up sessions that haven't been updated in over a week.

## Organizations and `current_organization`
Similar to `current_session`, `current_organization` can be returned with a number of methods, shown below

## Security

### Tool Launches
Any time a tool launch request is received, we should **always** validate that it originated from within Canvas and that it wasn't spoofed.
The easiest way to do this is to call `validate_launch!` in any controller action that is expecting to receive launch requests.

### Validate active session is present
It is easier to implement this if a purely javascript frontend is used (such as React).
Any controller actions that are not designated as launch points, or externally available API endpoints (such as in the case where an endpoint should be exposed outside the context of a tool launch, and has its own authentication mechanisms in place) should implement a line similar to the one below in `application_controller.rb`

```ruby
# app/controllers/application_controller.rb
prepend_before_action :forbid_access_if_lacking_session
```

This will render an unauthorized message any time a request is received and a valid session is not present.
It can be overridden on a action-by-action basis by using `skip_before_action`.

```ruby
skip_before_action :forbid_access_if_lacking_session, only: :launch
```

### Secure Headers
PandaPal bundles the `secure_headers` Gem and provides a default config. The PandaPal default works for really basic apps, but you may need to provide
a custom configuration. This can be done by creating a `secure_headers.rb` initializer in you App like so:
```ruby
SecureHeaders::Configuration.default do |config|
  PandaPal::SecureHeaders.apply_defaults(config) # Optional, but recommended
  # ...
end
```

## Validating settings in your LTI.

You can specify a structure that you would like to have enforced for your settings.

In your panda_pal initializer (i.e. `config/initializers/panda_pal.rb` or `config/initializers/lti.rb`)

You can specify options that can include a structure for your settings.  If specified, PandaPal will
enforce this structure on any new / updated organizations.

```ruby
PandaPal.lti_options = {
  title: 'LBS Gradebook',
  settings_structure: {
    allow_additional: true, # Allow additional properties that aren't included in the :properties Hash.
    allow_additional: { type: 'String' }, # You can also set :allow_additional to a settings specification that will be used to validate each additional setting
    validate: ->(value, spec, **kwargs) {
      # kwargs currently includes:
      #   :errors => [An array to push errors to]
      #   :path => [An array representation of the current path in the settings object]

      # To add errors, you may:
      # Push strings to the kwargs[:errors] Array:
      kwargs[:errors] << "Your error message at <path>" unless value < 10
      # Or return a string or string array:
      value.valid? ? nil : "Your error message at <path>" # <path> will be replaced with the actual path that the error occurred at
    },
    properties: {
      canvas_api_token: { type: 'String', required: true, },
      catalog: { # :validate, :allow_additional, :properties keys are all supported at this level as well
        type: 'Hash',
        required: false,
        validate: -> (*args) {},
        allow_additional: false,
        properties: {

        },
      }
    }
  },
}
```

#### Legacy Settings Structure:
Here is an example options specification:

```ruby
PandaPal.lti_options = {
  title: 'LBS Gradebook',
  settings_structure: YAML.load("
    canvas:
      is_required: true
      data_type: Hash
      api_token:
        is_required: true
        data_type: String
      base_url:
        is_required: true
        data_type: String
    reports:
      is_required: true
      data_type: Hash
      active_term_allowance:
      submissions_report_time_length:
        is_required: true
        data_type: ActiveSupport::Duration
      recheck_wait:
        data_type: ActiveSupport::Duration
      max_recheck_time:
        is_required: true
  ").deep_symbolize_keys
}
```
(This loads the structure in from YAML, but you can specify a hash directly if you prefer.)

Each data attribute can have two children attributes to describe desired structure:

is_required: If specified, and specified as true, the parent attribute is required in the settings hash.

data_type: If specified, and a settings hash contains this attribute, attribute data type will be compared
           to the specified data type.  If you are not sure how to derive your class data type, you can
           use `class` to determine data type.  For example:  30.minutes.class.to_s => "ActiveSupport::Duration"

## Bridge vs Canvas
As of 3.2.0, the LTI XML config can have subtle differences based on whether your platform is bridge, or canvas. 
This is determined by `PandaPal.lti_options[:platform]`.
Set this to `platform: 'canvas.instructure.com'` (default)
OR `platform: 'bridgeapp.com'`

## Development:
### Running Specs:
Initialize the Specs DB:
`cd spec/dummy; bundle exec rake db:drop; bundle exec rake db:create; bundle exec rake db:schema:load`
Then `bundle exec rspec`

## Safari Support
Safari is weird (it blocks cookies in `<iframe>`s unless the site has set a cookie _outside_ of an `<iframe>` first), and you'll run into
issues with Rails-native Sessions and CSRF because of that.

This means that safari will likely refuse to send info about your rails session
back to the LTI, and the application will start up a new session each time the
browser navigates.  This likely means a new session each time the LTI launches.

### PandaPal 5
It has been a constant struggle to force safari to store and allow
access to a rails session while the application is embedded in Canvas.

As of PandaPal 5, a session cookie is no longer required by panda_pal.

See the Section on [Sessions and `current_session`](#sessions-and-current_session)

You will want to watch out for a few scenarios:
1) Make sure you are using `redirect_with_session_to` if you need to redirect
   and have your PandaPal session_key persisted server side.
2) Use the `Authorization` header with `token={session_key}` to send your
   PandaPal session info into api calls.
3) If you use `link_to` and navigate in your LTI (apps that are not single page)
   make sure you include the `link_nonce` like so: 
    ```ruby
      link_to "Link Name", somewhere_else_path(session_token: link_nonce)
    ```

### Previous Safari Instructions
Safari is weird and you'll potentially run into issues getting `POST` requests to properly validate CSRF if you don't do the following:

- Make sure you have both a `launch` controller and your normal controllers. The `launch` controller should call `before_action :validate_launch!` and then redirect
  to your other controller.
- Make sure your other controller calls `before_action :forbid_access_if_lacking_session`

This will allow `PandaPal` to apply an iframe cookie fix that will allow CSRF validation to work.

## Migrating Major Versions

### Upgrading to version 3

Before upgrading save existing settings somewhere safe in case you need to
restore them for whatever reason.

panda_pal v3 introduces an encrypted settings hash.  This should provide more security in the case where a
customer may have gained access to Organization information in the database.  Settings cannot be decrypted
without knowing the secret decryption key.  For panda_pal, we are relying on the secret_key_base to be set
(`typically in config/secrets.yml`), if that is not available we are falling back to directly use
`ENV['SECRET_KEY_BASE']`.  For production environments, `config/secrets.yml` should not have a plain-text secret,
it should be referencing an ENV variable.  Make sure your secret is not plain-text committed to a repository!

The secret key is used to encrypt / decrypt the settings hash as necessary.

Before upgrading to version 3, you should confirm that the secret key is set to a consistent value (if the
value is lost your settings will be hosed).

You should also rollback any local encryption you have done on the settings hash.  The settings hash
should just be plainly visible when you upgrade to V3.  Otherwise the panda_pal migrations will
probably fail.

Once you have upgraded your gem, you will need to run migrations.  Before doing that, I would store off your
unencrypted settings (just in case).

`rake db:migrate`

If all goes well, you should be set!  Log into console, and verify that you can still access settings:

`PandaPal::Organization.first.settings`

should show unencrypted settings in your console.

If anything goes wrong, you should be able to rollback the change:

`rake db:rollback STEP=2`

If you need to give up on the change, just make sure to change your gem version for panda_pal to be < 3.

### Upgrading from PandaPal 4 to 5:

If your tool is setup according to a pretty standard pattern (see pace_plans,
canvas_group_enrollment, etc), you shouldn't have to do anything to upgrade.

You will want to make sure that IF your launch controller is redirecting, it is
using "redirect_with_session_to".

Here is an example launch / account controller setup, assuming an account launch.

```ruby
class LaunchController < ApplicationController
  # We don't verify CSRF on launch because the LTI launch is done via a POST
  # request, and Canvas wouldn't know anything about the CSRF
  skip_before_action :verify_authenticity_token
  skip_before_action :forbid_access_if_lacking_session # We don't have a session yet
  around_action :switch_tenant
  before_action :validate_launch!
  before_action :handle_launch

  def handle_launch
    current_session_data[:canvas_user_id] = params[:custom_canvas_user_id]
    current_session_data[:canvas_course_id] = params[:custom_canvas_course_id]
  end

  def account
    redirect_with_session_to :accounts_url
  end
end

class AccountController < ApplicationController
  prepend_before_action :forbid_access_if_lacking_session

  def index
  end
end
```