Deploy Python app (Flask) to Heroku.txt

First things first. Sign Up on Heroku.

Then go to Google and INSTALL HEROKU CLI. It's an app that enables
you to use heroku commands in your terminal

After installation, check if it's installed to path by typing
	$env:PATH
In the terminal (Powershell)

Or heroku -v
To check the version.

If it doesn't show. Close VS code and open again.


INSTALL GUNICORN. It's the Python WSGI HTTP Server package that
acts like a UNIX server
	pip install gunicorn

On heroku, you can't use sqlite or file based dbs because of dynos (jargon)
but they provide free PostgreSQL service as an add-on (which we'll discuss later)
To use PostgreSQL on Python, you need to install a package:
	pip install psycopg2

Heroku needs to know the REQUIRED packages for your app to work
so we'll use create a requirements.txt file.
In the terminal type:
	pip freeze > requirements.txt
This creates the file automatically and names all the packages in use
with their version.


Next you'll create a file named 'Procfile'
You can create it manually or if you're using bash, enter:
	$ echo web: gunicorn <nameOfYOURapp>:app

If you're creating a Procfile manually:
	make sure it doesn't have an extension
	not 'Procfile.txt' or 'Procfile.doc' or .anything.
	Just Procfile.

	Inside the Procfile add the ff line:
		web: gunicorn <nameOfYourMainScript>:app	#JUST THE NAME OF APP WITHOUT THE EXTENSION

LOGIN TO HEROKU in your terminal.
Type:
	heroku login
and it will redirect to a browser
OR
	heroku login -i
to enter login details in terminal
Fill in your details


CREATE THE APP:
Inside the terminal:
	heroku create <nameOfYourProject>	#it has to be a unique name
If successful, you'll get a link to your project
	e.g https://yourapp.herokuapp.com

BUT...
We're not there yet.
You need extra services for your app to run remotely like for storing data - database,
logging, automatic email/SMS, analytics, searching, caching, content management, alerts,
Image & video processing and so on. Phew!

These services are called ADD-ONS
Luckily, Heroku has a free PostgreSQL add-on, so we'll use just that.

To add this addon, in your terminal, enter:
	heroku addons:create heroku-postgresql:hobby-dev --app <nameOfApp>

Doing this generates a database url and to get the url, we can get it by going to
the dashboard on our browser and copying it from the CONFIG VARS under Settings.
OR simply:
	heroku config --app <nameOfApp>
to get all config vars.

Now we can change the SQLALCHEMY_DATABSE_URI in our script from the sqlite file path
to the PostgreSQL link.

NOTE ⚠️:
	In the model class, PostgreSQL doesn't use length for it text fields.
	So if you have
		text_col = db.Column(db.Text(40))
	change to:
		text_col = db.Column(db.Text())
	the String type doesn't have this limitation so you're free to add length to it.

It's time for Git!
Heroku will run you app from a custom repo created on the server.
That means we'll
Add all files:
	git add -A
Commit:
	git commit -m "commit message"
Push:
to your personal repo:
	git push -u origin <nameOfBranch>
to heroku:
	git push heroku <same branch as above>

This will prompt Heroku to build your app and install all dependencies

AGAIN!
The landing page may not work but parts of your app that uses the DB
will likely not work because the DB is empty.

to initialize the db model.
We can do it two ways.
Running Python on our server:
	heroku run python
	>>> from main_script/app import db
	>>> db.create_all()		#if it runs w/o error, it was successful	
	db.create_all()
	>>> exit() 				#exit the python terminal
The above totally depends on your code structure and will only work
if in your main script, you did something like:
	app = Flask(__name__)
	db = SQLALCHEMY(app)

To avoid the stress of running Python terminals and what not,
inside your main script,
	inside your model.py, do this:
		db = SQLALCHEMY()
	then in main/app/server.py:
		from model import db	
	
		app = Flask(__name__)
		#make sure to init app after app config
		db.init_app(app)  

		with app.app_context():
			db.create_all()
this will save you much more stress.

AND C'EST FINI.
The app should be up and running now


IMPORTANT THINGS TO NOTE!!
Herkoku will not accept your .env especially if it's git ignored.
To use environment variables in production, you have to add them manually to the CONFIG VARS.
	To add them, go to the application dashboard and then Settings > Config Vars
	no need to change your code, the getenv function will read the config vars
	
Also the PostgreSQL Database Url can cause errors because the URL starts with
	"https:postgres://..."
The error is because PostgreSQL databse uri now start with "postgresql://.."
The 'L' being the difference.

The database is always maintained by Heroku and the uri keeps changing, it is therefore
not advisable to place the URI statically in the script.
To bypass this, in the SQLALCHEMY DATABASE URI configuration, do this:
	app.config['SQLALCHEMY_DATABASE_URI'] = os.getenv("DATABSE_URL").replace("postgres://", "postgresql:///")
	
Et voilà!