Add feature user can change mail address

app.py

@@ -406,6 +406,30 @@ def change_password():
     return render_template("password_form.html", mode="change")
 
 
+@app.route("/account/email", methods=("GET", "POST"))
+@login_required
+def change_email():
+    user = get_db().execute("SELECT email, password_hash FROM users WHERE id = ?", (session["user_id"],)).fetchone()
+    if request.method == "POST":
+        email = request.form.get("email", "").strip().lower()
+        current_password = request.form.get("current_password", "")
+        if not check_password_hash(user["password_hash"], current_password):
+            flash("Your current password is incorrect.", "error")
+        elif not valid_email(email):
+            flash("Enter a valid email address.", "error")
+        elif email == user["email"]:
+            flash("That is already your email address.", "notice")
+        else:
+            try:
+                get_db().execute("UPDATE users SET email = ? WHERE id = ?", (email, session["user_id"]))
+                get_db().commit()
+                flash("Email address updated.", "success")
+                return redirect(url_for("index"))
+            except sqlite3.IntegrityError:
+                flash("That email address is already in use.", "error")
+    return render_template("email_form.html", email=user["email"])
+
+
 @app.post("/logout")
 def logout():
     session.clear()