refactor: refactor for modern layout

- split frontend and backend.
- update backend with modern Python dev strategies.

backend/utils.py

@@ -0,0 +1,52 @@
+import hashlib
+import random
+import uuid
+import time
+import math
+
+ValidUsername = set(map(lambda x:chr(x), range(48, 58, 1))) | set(map(lambda x:chr(x), range(65, 91, 1))) | set(map(lambda x:chr(x), range(97, 123, 1)))
+ValidPassword = set(map(lambda x:chr(x), range(33, 127, 1)))
+
+def IsValidUsername(strl):
+    return (len(set(strl) - ValidUsername) == 0)
+
+def IsValidPassword(strl):
+    return (len(set(strl) - ValidPassword) == 0)
+
+def ComputePasswordHash(password):
+    s = hashlib.sha256()
+    s.update(password.encode('utf-8'))
+    return s.hexdigest()
+
+def GenerateUUID():
+    return str(uuid.uuid1())
+
+def GenerateToken(username):
+    s = hashlib.sha256()
+    s.update(username.encode('utf-8'))
+    s.update(GenerateUUID().encode('utf-8'))
+    return s.hexdigest()
+
+def GenerateSalt():
+    return random.randint(0, 6172748)
+
+def ComputePasswordHashWithSalt(passwordHashed, salt):
+    s = hashlib.sha256()
+    s.update((passwordHashed + str(salt)).encode('utf-8'))
+    return s.hexdigest()
+
+def GetCurrentTimestamp():
+    return int(time.time())
+
+def GetTokenExpireOn():
+    return GetCurrentTimestamp() + 60 * 60 * 24 * 2 # add 2 day from now
+
+def Str2Bool(strl):
+    return strl.lower() == 'true'
+
+def GCD(a, b):
+    return math.gcd(a, b)
+
+def LCM(a, b):
+    return int(a * b / GCD(a, b))
+