# StateInspector
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This can fully inform on object method calls and parameters as well as instance variables before and after (when called via a setter method). In short this utilizes the decorator patttern and the observer pattern to hook and report when a method is called. In simple terms it will wrap any methods you choose with a hook that sends off all the details of the method call when it is executed to a reporter/observer of your choosing.
This project uses a variation of the observer pattern. There is a hash of Reporters where you can
mark the key as a class instance or the class itself and point it to an Observer object. Three
observers are included for you to use under StateInspector::Observers which are NullObserver (default),
InternalObserver, and SessionLoggerObserver. When you toggle on an "informant" on a class instance or
class then each time a setter method is called it will pass that information on to the relevant observer
which handles the behavior you want to occur with that information.
## Installation
Add this line to your application's Gemfile:
```ruby
gem 'state_inspector'
```
And then execute:
$ bundle
Or install it yourself as:
$ gem install state_inspector
## Complex Usage
The preferred usage is to pick what classes you want to track state change in and have them logged to
a session logger. To do this you would need to do the following.
```ruby
require 'state_inspector'
require 'state_inspector/observers/session_logger_observer'
include StateInspector::Observers
class MyClass
attr_writer :thing
end
StateInspector::Reporter[MyClass] = SessionLoggerObserver
MyClass.toggle_informant
m = MyClass.new
m.thing = :a
StateInspector::Reporter[MyClass].values
# => [["#", "@thing", nil, :a]]
```
SessionLoggerObserver will by default log reports to `log/state_inspector/`.
Now everytime the setter method is used for `thing` a new line will be entered into a log file
of the object, method, old value, and new value. So you will see what is changed from where in
the order that the changed occurred. This session logger will grab as many objects state changes
as you want and give you a nice ordered history of what has occurred.
If you don't want to inform on all instances of a class then instead of running `toggle_informant`
on the class itself then simply execute that method on the instances you want to observe.
If you want to see the expected results of the current observer/reporters then see [test/reporter_test.rb](https://github.com/danielpclark/state_inspector/blob/master/test/reporter_test.rb).
## Simple Usage
If you want to only toggle an informant for a small area you may use a helper method to toggle the
observer on and off for you.
When you include `StateInspector::Helper` it handles requiring the existing observers and bringing them
into scope. You are free to pass in an observer as a second paramater to the `toggle_snoop` helper method
which will only be assigned for the scope of the block of code.
```ruby
require 'state_inspector/helper'
include StateInspector::Helper
# instead of doing MyClass.toggle_informant as above, do this.
class MyClass
attr_writer :thing
end
m = MyClass.new
observer = InternalObserver.new
# observer parameter optional. Assign beforehand if not provided here.
toggle_snoop(m, observer) do
m.thing = 4
end
# look at the results
observer.values
# => [[#, "@thing", nil, 4]]
```
When writing tests for code and using StateInspector it's very important to ensure the informant is
untoggled. Otherwise you will have sporatic behavior in your tests. You may use the helpers provided
here for your tests to ensure you won't have glitchy tests as a result of using informants.
To include it in Minitest you would do:
```ruby
# test/test_helper.rb or test/minitest_helper.rb
require 'state_inspector/helper'
class Minitest::Test
include StateInspector::Helper
end
```
The default behavior for toggling on an informant for the first time is to inject code to observe all
setter methods. This is true for both the Object method `toggle_informant` and the helper method
`toggle_snoop`. If you would like to avoid injecting all setter methods for reporting you may either
use `state_inspector.skip_setter_snoops` (before any toggling) or the helper `toggle_snoop_clean` which
will cleanly remove its anti-setter hook once done (meaning the next `toggle_informant` will inject the
informant code into all setters).
## Observers
To include all Observers into scope you can do:
```ruby
require 'state_inspector/observers'
include StateInspector::Observers
```
You may look at the available observers in [state_inspector/observers](https://github.com/danielpclark/state_inspector/tree/master/lib/state_inspector/observers).
Observers will have a few methods they each have in common.
```ruby
module Observer
def update *vals
values() << vals
end
def display
values.join " "
end
def values
@values ||= []
end
def purge
@values = []
end
end
```
When you're writing your own observer you'll include this Observer onto a module's instance and
overwrite whatever methods you want there.
```ruby
module ExampleObserver
class << self
include Observer
def display
"Custom display code here"
end
end
end
```
And to register this observer to a target class you simply write:
```ruby
StateInspector::Reporter[MyTargetClass] = ExampleObserver
```
## Manually Create or Remove Informers
To manually create informant methods use `state_inspector.snoop_setters :a=, :b=` and
`state_inspector.snoop_methods :a, :b`.
```ruby
require 'state_inspector'
require 'state_inspector/observers/internal_observer'
include StateInspector::Observers
class MyClass
attr_writer :a, :b, :c
def x *args; end
end
# InternalObserver (it can be used with many classes and hold all of the data)
# InternalObserver.new (will hold data for only the specific reporter object pointing to it)
StateInspector::Reporter[MyClass] = InternalObserver
# This will allow us to manually define which setter methods to inform on
MyClass.state_inspector.skip_setter_snoops
m = MyClass.new
m.toggle_informant
m.state_inspector.snoop_setters :b=, :c=
m.state_inspector.snoop_methods :x
m.a= 1
m.b= 2
m.c= 3
m.x 4, 5, 6
StateInspector::Reporter[MyClass].values
# => [
# [#, "@b", nil, 2],
# [#, "@c", nil, 3],
# [#, :x, 4, 5, 6]
# ]
```
The nils in the values above represent the previous value the instance variable returned.
#### Remove Informers
To remove informers simply use `state_inspector.restore_methods`. This takes out the hook from
each method that waits for the `informer?` method to be true.
```ruby
# continuing from the above example
m.state_inspector.restore_methods :b=, :c=, :x
```
## Reporter Legend
The format of a report sent will always start with the object that sent it; aka `self`. Next you will
have either a string representing and instance variable of a symbol representing a method call. If it's
an instance variable then the next value will be the old value for that instance variable, and the next
value is the value given to the method to be set as the value for that instance variable. If the second
item is a symbol then every item after that is the parameters sent to that method.
LEGEND FOR SETTER| _ | _ | _
-----------------|---|---|---
`self` | `@instance_variable` | `:old_value` | `:new_value_given`
LEGEND FOR METHOD| _ | _
-----------------|---|---
`self` | `:method_name` | `:arguments`
## Session Logger
The session logger is an observer that saves all output to a log file. A default log file is saved to `log/state_inspector/.log`. You can manually set a log file with the `file=` method on the SessionLoggerObserver which may be helpful for situations where the code runs in a temporary directory and vanishes upon completion (like the rubygems test suite).
Here's an example that catches all setter method calls from constants within the `Gem` class. _Placed at start of file to observe._
```ruby
require 'state_inspector'
require 'state_inspector/observers/session_logger_observer'
include StateInspector::Observers
SessionLoggerObserver.file = "/home/myhomedir/dev/rubygems/log/output.log"
StateInspector::Reporter.default SessionLoggerObserver
Gem.constants.each {|c| a = eval("Gem::#{c}"); if a.is_a? Class; a.toggle_informant end}
```
This example is a very expensive one as we set the default observer/reporter to `SessionLoggerObserver` which means it catches **all reports not previously assigned**. The last line simply finds all class objects within the Gem namespace and toggles-on the informants (which by default hooks in listeners to each setter method). The `file=` method used here overwrites the default and guarantees where the data will be written.
I've tried the above code in the rubygems test suite on one file `test/rubygems/test_gem_dependency_installer.rb`. When running this file it records 7756 lines worth of information. This is clearly too much information to parse manually which is why I highly recommend using the scoped helper methods to toggle on and off the behavior around the code you are specifically interested in. You can still toggle informers on many classes like what was done above, but the more objects you do the more I recommend you narrow down the scope of what you're capturing (like to one specific test in a test suite).
## Development
After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
## Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/danielpclark/state_inspector.
## License
The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).