Create app.py

app.py

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+
+"""
+Flask Login System with SQLite
+Features:
+- Signup (create new account)
+- Login (check user credentials)
+- Session (to remember login state)
+- Cookies (to store last visit info)
+- "Remember Me" option (stay logged in even after closing browser)
+"""
+
+from flask import Flask, render_template, request, redirect, url_for, session, make_response
+import sqlite3
+from datetime import timedelta
+
+# Flask App Setup
+app = Flask(__name__)
+
+# Secret key is used to sign session data (must be kept secret in real apps!)
+app.secret_key = "supersecretkey"
+
+# Permanent sessions last for 7 days (used when "Remember Me" is checked)
+app.permanent_session_lifetime = timedelta(days=7)
+
+
+# Helper function to connect to SQLite database
+def get_db_connection():
+    # Connect to SQLite database (creates file users.db if it doesn’t exist)
+    conn = sqlite3.connect("users.db")
+    conn.row_factory = sqlite3.Row  # Makes rows behave like dictionaries
+    return conn
+
+
+# Initialize database with a "users" table
+def init_db():
+    conn = get_db_connection()
+    conn.execute("""
+        CREATE TABLE IF NOT EXISTS users (
+            id INTEGER PRIMARY KEY AUTOINCREMENT, -- Auto-increment ID
+            username TEXT UNIQUE NOT NULL,        -- Unique username
+            password TEXT NOT NULL                -- Password (plain text for demo, should use hashing!)
+        )
+    """)
+    conn.commit()
+    conn.close()
+
+# Call database initialization at startup
+init_db()
+
+
+# Home Page (only logged-in users can see this)
+@app.route("/")
+def home():
+    # Check if the user is logged in using session
+    if "username" in session:
+        username = session["username"]  # Get logged-in username from session
+
+        # Get last visit message from cookie (if not found, show default message)
+        last_visit = request.cookies.get("last_visit", "First time visiting!")
+
+        return render_template("home.html", username=username, last_visit=last_visit)
+
+    # If not logged in, redirect to login page
+    return redirect(url_for("login"))
+
+
+# Signup Page
+@app.route("/signup", methods=["GET", "POST"])
+def signup():
+    if request.method == "POST":  # When user submits the form
+        username = request.form["username"]
+        password = request.form["password"]
+
+        conn = get_db_connection()
+        try:
+            # Insert new user into database
+            conn.execute("INSERT INTO users (username, password) VALUES (?, ?)", (username, password))
+            conn.commit()
+            conn.close()
+
+            # After signup, redirect to login page
+            return redirect(url_for("login"))
+
+        except sqlite3.IntegrityError:
+            # This happens if the username already exists
+            return "Username already exists! Try another."
+    
+    # If GET request, show signup form
+    return render_template("signup.html")
+
+
+# Login Page
+@app.route("/login", methods=["GET", "POST"])
+def login():
+    if request.method == "POST":  # When user submits login form
+        username = request.form["username"]
+        password = request.form["password"]
+
+        # Checkbox value: will be "on" if user ticks "Remember Me"
+        remember = request.form.get("remember")
+
+        # Check if username & password exist in database
+        conn = get_db_connection()
+        user = conn.execute("SELECT * FROM users WHERE username=? AND password=?", 
+                            (username, password)).fetchone()
+        conn.close()
+
+        if user:
+            # ✅ User found → start session
+            if remember == "on":
+                # Session will survive browser close (7 days)
+                session.permanent = True
+            else:
+                # Session ends when browser closes
+                session.permanent = False
+
+            # Store username inside session
+            session["username"] = username
+
+            # Create response with cookie
+            resp = make_response(redirect(url_for("home")))
+
+            # Save a cookie with "last visit" info
+            # If "Remember Me" checked → cookie valid for 7 days
+            # Else → cookie lasts only until browser closes
+            resp.set_cookie("last_visit", "Welcome back, " + username, 
+                            max_age=(7*24*60*60 if remember == "on" else None))
+
+            return resp
+        else:
+            # If username or password is wrong
+            return "Invalid username or password. Try again."
+
+    # If GET request, show login form
+    return render_template("login.html")
+
+
+# Logout Page
+@app.route("/logout")
+def logout():
+    # Remove username from session
+    session.pop("username", None)
+
+    # Also delete the "last_visit" cookie
+    resp = make_response(redirect(url_for("login")))
+    resp.set_cookie("last_visit", "", expires=0)
+    return resp
+
+
+# Run the App
+if __name__ == "__main__":
+    app.run(debug=True, host="0.0.0.0", port=5000)