Add basic logging

- Configure Python logging at INFO level.
- Log key events: database initialization, incoming requests, validation errors, and successful guest submissions.
- Log the number of guest entries displayed when rendering the page.

This improves observability and helps with troubleshooting.

app.py

@@ -1,6 +1,11 @@
 from flask import Flask, render_template, request, redirect, url_for
 import sqlite3
 import re
+import logging
+
+# Set up basic logging
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger(__name__)
 
 app = Flask(__name__)
 DATABASE = 'guestbook.db'
@@ -20,6 +25,7 @@ def init_db():
     ''')
     conn.commit()
     conn.close()
+    logger.info("Database initialized.")
 
 def is_valid_email(email):
     # A simple regex for basic email validation
@@ -30,6 +36,7 @@ def is_valid_email(email):
 def index():
     error = None
     if request.method == 'POST':
+        logger.info("Received POST request with form data.")
         first_name = request.form.get('first_name', '').strip()
         last_name = request.form.get('last_name', '').strip()
         email = request.form.get('email', '').strip()
@@ -38,8 +45,10 @@ def index():
         # Basic validation checks
         if not (first_name and last_name and email and location):
             error = "All fields are required."
+            logger.warning("Validation error: Missing required fields.")
         elif not is_valid_email(email):
             error = "Invalid email address."
+            logger.warning("Validation error: Invalid email address '%s'.", email)
 
         if error:
             # Retrieve guest entries to display on the page.
@@ -50,7 +59,7 @@ def index():
             conn.close()
             return render_template('index.html', error=error, guests=guests)
 
-        # If all validations pass, insert the data into the database.
+        # If validations pass, insert the data into the database.
         conn = sqlite3.connect(DATABASE)
         c = conn.cursor()
         c.execute(
@@ -59,6 +68,7 @@ def index():
         )
         conn.commit()
         conn.close()
+        logger.info("New guest entry added: %s from %s.", first_name, location)
         return redirect(url_for('index'))
 
     # For GET requests, retrieve guest entries to display.
@@ -67,8 +77,10 @@ def index():
     c.execute('SELECT first_name, location FROM guests ORDER BY id DESC')
     guests = c.fetchall()
     conn.close()
+    logger.info("Rendering guestbook page with %d entries.", len(guests))
     return render_template('index.html', error=error, guests=guests)
 
 if __name__ == '__main__':
     init_db()
+    logger.info("Starting Flask app on host 0.0.0.0, port 5000.")
     app.run(host='0.0.0.0', port=5000)