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"])