Initial working version with minor bugs

trades/forms.py

@@ -0,0 +1,70 @@
+from django import forms
+from django.core.exceptions import ValidationError
+from .models import TradeOffer
+from friend_codes.models import FriendCode
+from cards.models import Card
+
+class TradeOfferUpdateForm(forms.ModelForm):
+    class Meta:
+        model = TradeOffer
+        # We now only edit the `state` field
+        fields = ["state"]
+
+    def __init__(self, *args, **kwargs):
+        """
+        Expects additional keyword arguments:
+           - friend_codes: a list of friend code objects for the current user.
+        This initializer filters the available state choices based on:
+          - The current state's allowed transition.
+          - Which party (initiated_by or accepted_by) is acting.
+        """
+        friend_codes = kwargs.pop("friend_codes")
+        super().__init__(*args, **kwargs)
+
+        instance = self.instance
+        allowed_state = None
+
+        # Define permitted transitions based on the current state and user role:
+        if instance.state == TradeOffer.State.INITIATED:
+            # Allow the accepted_by party to accept the trade.
+            if instance.accepted_by in friend_codes:
+                allowed_state = TradeOffer.State.ACCEPTED
+        elif instance.state == TradeOffer.State.ACCEPTED:
+            # Allow the initiated_by party to mark the trade as sent.
+            if instance.initiated_by in friend_codes:
+                allowed_state = TradeOffer.State.SENT
+        elif instance.state == TradeOffer.State.SENT:
+            # Allow the accepted_by party to mark the trade as received.
+            if instance.accepted_by in friend_codes:
+                allowed_state = TradeOffer.State.RECEIVED
+
+        if allowed_state:
+            # Limit the `state` field's choices to only the permitted transition.
+            label = dict(TradeOffer.State.choices)[allowed_state]
+            self.fields["state"].choices = [(allowed_state, label)]
+        else:
+            # If no valid transition is available for this user, remove the field.
+            self.fields.pop("state")
+
+    def clean_have_cards(self):
+        have_cards = self.cleaned_data.get("have_cards")
+        if have_cards:
+            for card in have_cards.all():
+                if card.rarity not in ALLOWED_RARITIES:
+                    # Raising a ValidationError here will cause this error message to be shown beneath the 'have_cards' field.
+                    raise ValidationError(
+                        f"The card '{card}' has an invalid rarity: {card.rarity}. Allowed rarities are: {', '.join(ALLOWED_RARITIES)}."
+                    )
+        return have_cards
+
+class TradeOfferAcceptForm(forms.Form):
+    friend_code = forms.ModelChoiceField(
+        queryset=FriendCode.objects.none(),
+        label="Select a Friend Code to Accept This Trade Offer"
+    )
+
+    def __init__(self, *args, **kwargs):
+        # Expecting a keyword argument `friend_codes` with the user's friend codes.
+        friend_codes = kwargs.pop("friend_codes")
+        super().__init__(*args, **kwargs)
+        self.fields["friend_code"].queryset = friend_codes