Initial working version with minor bugs

trades/models.py

@@ -0,0 +1,72 @@
+from django.db import models
+import hashlib  # <-- import hashlib for computing md5
+from cards.models import Card
+from friend_codes.models import FriendCode
+
+class TradeOffer(models.Model):
+  id = models.AutoField(primary_key=True)
+  hash = models.CharField(max_length=8, editable=False)
+  initiated_by = models.ForeignKey("friend_codes.FriendCode", on_delete=models.PROTECT, related_name='initiated_by')
+  accepted_by = models.ForeignKey("friend_codes.FriendCode", on_delete=models.PROTECT, null=True, blank=True, related_name='accepted_by')
+  want_cards = models.ManyToManyField("cards.Card", related_name='trade_offers_want')
+  have_cards = models.ManyToManyField("cards.Card", related_name='trade_offers_have')
+  created_at = models.DateTimeField(auto_now_add=True)
+  updated_at = models.DateTimeField(auto_now=True)
+
+  class State(models.TextChoices):
+    INITIATED = 'INITIATED', 'Initiated'
+    ACCEPTED = 'ACCEPTED', 'Accepted'
+    SENT = 'SENT', 'Sent'
+    RECEIVED = 'RECEIVED', 'Received'    
+
+  state = models.CharField(
+    max_length=10,
+    choices=State.choices,
+    default=State.INITIATED,
+  )
+
+  def __str__(self):
+    return f"Want: {', '.join([x.name for x in self.want_cards.all()])} -> Have: {', '.join([x.name for x in self.have_cards.all()])}"
+
+  def update_state(self, new_state):
+    """
+    Explicitly update the trade state to new_state if allowed.
+
+    Allowed transitions:
+      - INITIATED -> ACCEPTED
+      - ACCEPTED -> SENT
+      - SENT -> RECEIVED
+
+    Raises:
+        ValueError: If the new_state is not allowed.
+    """
+    allowed_transitions = {
+        self.State.INITIATED: self.State.ACCEPTED,
+        self.State.ACCEPTED: self.State.SENT,
+        self.State.SENT: self.State.RECEIVED
+    }
+
+    # Check that new_state is one of the defined State choices
+    if new_state not in [choice[0] for choice in self.State.choices]:
+        raise ValueError(f"'{new_state}' is not a valid state.")
+
+    # If the current state is already final, no further transition is allowed.
+    if self.state not in allowed_transitions:
+        raise ValueError(f"No transitions allowed from the final state '{self.state}'.")
+
+    # Verify that the desired new_state is the valid transition for the current state.
+    if allowed_transitions[self.state] != new_state:
+        raise ValueError(f"Transition from {self.state} to {new_state} is not allowed.")
+
+    self.state = new_state
+    # Save all changes so that any in-memory modifications (like accepted_by) are persisted.
+    self.save()  # Changed from self.save(update_fields=["state"])
+
+  def save(self, *args, **kwargs):
+    # Determine if the object is being created (i.e. it doesn't yet have a pk)
+    is_new = self.pk is None
+    super().save(*args, **kwargs)
+    # Once the object has a pk, compute and save the hash if it hasn't been set yet.
+    if is_new and not self.hash:
+        self.hash = hashlib.md5(str(self.id).encode('utf-8')).hexdigest()[:8]
+        super().save(update_fields=["hash"])