feat(framework): Converted WSGI server to a Snow Framework

After creating a static HTML render and migrating it to a simple WSGI dynamic server, now we improve our knowledge by converting the WSGI server to a simple Web Framework called Snow.

We followed these steps:

- Create a class called Snow, that is our framework
- Instantiate an app object from our class
- Create business rules in a specific module to decouple our logic from our implementation

Closes #13

README.md

@@ -20,3 +20,13 @@ These libraries are on requirements.txt file.
 We'll follow these steps:
 
 - improve the app with Jinja2 template engine
+
+## Third way is to convert the WSGI server to a Web Framework
+
+After creating a static HTML render and migrating it to a simple WSGI dynamic server, now we improve our knowledge by converting the WSGI server to a simple Web Framework called Snow.
+
+We followed these steps:
+
+- Create a class called Snow, that is our framework
+- Instantiate an app object from our class
+- Create business rules in a specific module to decouple our logic from our implementation

blog/app.py

@@ -0,0 +1,38 @@
+from business_rules import add_new_post, get_posts_from_database
+from snow import Snow
+
+app = Snow()
+
+
+@app.route('^/$', template='list.template.html')
+def post_list():
+    posts = get_posts_from_database()
+    return {'post_list': posts}
+
+
+@app.route('^/api$')
+def post_list_api():
+    posts = get_posts_from_database()
+    return {'post_list': posts}, '200 OK', 'application/json'
+
+
+@app.route(r'^/(?P<post_id>\d{1,}$)', template='post.template.html')
+def post_detail(post_id):
+    post = get_posts_from_database(post_id=post_id)[0]
+    return {'post': post}
+
+
+@app.route('^/new$', template='form.template.html')
+def new_post_form():
+    return {}
+
+
+@app.route('^/new$', method='POST')
+def new_post_add(form):
+    post = {item.name: item.value for item in form.list}
+    add_new_post(post)
+    return "New post Created with Success", '201 Created', 'text/plain'
+
+
+if __name__ == '__main__':
+    app.run()

blog/business_rules.py

@@ -0,0 +1,23 @@
+from database import conn
+
+cursor = conn.cursor()
+
+
+def get_posts_from_database(post_id=None):
+    fields = ('id', 'title', 'content', 'author')
+    if post_id:
+        results = cursor.execute('SELECT * FROM post WHERE id = ?;', post_id)
+    else:
+        results = cursor.execute('SELECT * FROM post;')
+    posts = [dict(zip(fields, post)) for post in results]
+    return posts
+
+
+def add_new_post(post):
+    cursor.execute(
+        '''\
+        INSERT INTO post (title, content, author) VALUES (:title, :content, :author)
+        ''',
+        post
+    )
+    conn.commit()

blog/snow.py

@@ -0,0 +1,61 @@
+import cgi
+import json
+import re
+from wsgiref.simple_server import make_server
+
+from jinja2 import Environment, FileSystemLoader
+
+
+class Snow:
+    def __init__(self, template_folder='templates'):
+        self.url_map = []
+        self.env = Environment(loader=FileSystemLoader(template_folder))
+
+    def route(self, rule, method='GET', template=None):
+        def decorator(view):
+            self.url_map.append((rule, method, view, template))
+            return view
+
+        return decorator
+
+    def render_template(self, template_name, **context):
+        template = self.env.get_template(template_name)
+        return template.render(**context).encode('utf-8')
+
+    def __call__(self, environ, start_response):
+        body = b'Content not found'
+        status = '404 Not Found'
+        content_type = 'text/html'
+        path = environ['PATH_INFO']
+        request_method = environ['REQUEST_METHOD']
+
+        for rule, method, view, template in self.url_map:
+            if match := re.match(rule, path):
+                if method != request_method:
+                    continue
+                view_args = match.groupdict()
+
+                if method == 'POST':
+                    view_args['form'] = cgi.FieldStorage(fp=environ['wsgi.input'], environ=environ, keep_blank_values=1)
+
+                view_result = view(**view_args)
+
+                if isinstance(view_result, tuple):
+                    view_result, status, content_type = view_result
+                else:
+                    status = '200 OK'
+
+                if template:
+                    body = self.render_template(template, **view_result)
+                elif isinstance(view_result, dict) and content_type == 'application/json':
+                    body = json.dumps(view_result).encode('utf-8')
+                else:
+                    body = str(view_result).encode('utf-8')
+
+        headers = [('Content-type', content_type)]
+        start_response(status, headers)
+        return [body]
+
+    def run(self, host='0.0.0.0', port=8000):
+        server = make_server(host, port, self)
+        server.serve_forever()