from django.db import models
from django.core.exceptions import ValidationError
from django.db.models import Q
import hashlib
from cards.models import Card
from accounts.models import FriendCode

class TradeOffer(models.Model):
    id = models.AutoField(primary_key=True)
    manually_closed = models.BooleanField(default=False)
    hash = models.CharField(max_length=8, editable=False)
    initiated_by = models.ForeignKey(
        "accounts.FriendCode",
        on_delete=models.PROTECT,
        related_name='initiated_trade_offers'
    )
    # Use custom through models to support multiples.
    want_cards = models.ManyToManyField(
        "cards.Card",
        related_name='trade_offers_want',
        through="TradeOfferWantCard"
    )
    have_cards = models.ManyToManyField(
        "cards.Card",
        related_name='trade_offers_have',
        through="TradeOfferHaveCard"
    )
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    def __str__(self):
        want_names = ", ".join([x.name for x in self.want_cards.all()])
        have_names = ", ".join([x.name for x in self.have_cards.all()])
        return f"Want: {want_names} -> Have: {have_names}"

    def save(self, *args, **kwargs):
        is_new = self.pk is None
        super().save(*args, **kwargs)
        if is_new and not self.hash:
            self.hash = hashlib.md5(str(self.id).encode('utf-8')).hexdigest()[:8]
            super().save(update_fields=["hash"])

    @property
    def is_closed(self):
        if self.manually_closed:
            return True

        from .models import TradeAcceptance  # local import to avoid circular dependencies
        active_states = [
            TradeAcceptance.AcceptanceState.ACCEPTED,
            TradeAcceptance.AcceptanceState.SENT,
            TradeAcceptance.AcceptanceState.RECEIVED,
            TradeAcceptance.AcceptanceState.COMPLETED
        ]

        closed_have = True
        for through_obj in self.trade_offer_have_cards.all():
            accepted_count = self.acceptances.filter(
                requested_card=through_obj.card,
                state__in=active_states
            ).count()
            if accepted_count < through_obj.quantity:
                closed_have = False
                break

        closed_want = True
        for through_obj in self.trade_offer_want_cards.all():
            accepted_count = self.acceptances.filter(
                offered_card=through_obj.card,
                state__in=active_states
            ).count()
            if accepted_count < through_obj.quantity:
                closed_want = False
                break

        return closed_have or closed_want

class TradeOfferHaveCard(models.Model):
    """
    Through model for TradeOffer.have_cards.
    Represents the card the initiator is offering along with the quantity available.
    """
    trade_offer = models.ForeignKey(
        TradeOffer,
        on_delete=models.CASCADE,
        related_name='trade_offer_have_cards'
    )
    card = models.ForeignKey("cards.Card", on_delete=models.PROTECT)
    quantity = models.PositiveIntegerField(default=1)

    def __str__(self):
        return f"{self.card.name} x{self.quantity} (Have side for offer {self.trade_offer.hash})"

    class Meta:
        unique_together = ("trade_offer", "card")

class TradeOfferWantCard(models.Model):
    """
    Through model for TradeOffer.want_cards.
    Represents the card the initiator is requesting along with the quantity requested.
    """
    trade_offer = models.ForeignKey(
        TradeOffer,
        on_delete=models.CASCADE,
        related_name='trade_offer_want_cards'
    )
    card = models.ForeignKey("cards.Card", on_delete=models.PROTECT)
    quantity = models.PositiveIntegerField(default=1)

    def __str__(self):
        return f"{self.card.name} x{self.quantity} (Want side for offer {self.trade_offer.hash})"

    class Meta:
        unique_together = ("trade_offer", "card")

class TradeAcceptance(models.Model):
    class AcceptanceState(models.TextChoices):
        ACCEPTED = 'ACCEPTED', 'Accepted'
        SENT = 'SENT', 'Sent'
        RECEIVED = 'RECEIVED', 'Received'
        COMPLETED = 'COMPLETED', 'Completed'
        REJECTED_BY_INITIATOR = 'REJECTED_BY_INITIATOR', 'Rejected by Initiator'
        REJECTED_BY_ACCEPTOR = 'REJECTED_BY_ACCEPTOR', 'Rejected by Acceptor'

    trade_offer = models.ForeignKey(
        TradeOffer,
        on_delete=models.CASCADE,
        related_name='acceptances'
    )
    accepted_by = models.ForeignKey(
        "accounts.FriendCode",
        on_delete=models.PROTECT,
        related_name='trade_acceptances'
    )
    # The acceptor selects one card the initiator is offering (from have_cards)
    requested_card = models.ForeignKey(
        "cards.Card",
        on_delete=models.PROTECT,
        related_name='accepted_requested'
    )
    # And one card from the initiator's wanted cards (from want_cards)
    offered_card = models.ForeignKey(
        "cards.Card",
        on_delete=models.PROTECT,
        related_name='accepted_offered'
    )
    state = models.CharField(
        max_length=25,
        choices=AcceptanceState.choices,
        default=AcceptanceState.ACCEPTED
    )
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    def clean(self):
        """
        Validate that:
          - The requested_card is associated with the trade offer's have_cards (via the through model).
          - The offered_card is associated with the trade offer's want_cards (via the through model).
          - The trade offer is not already closed.
          - The total number of active acceptances for each chosen card does not exceed the available quantity.
        """
        # Validate that requested_card is in trade_offer.have_cards
        try:
            have_through_obj = self.trade_offer.trade_offer_have_cards.get(card=self.requested_card)
        except TradeOfferHaveCard.DoesNotExist:
            raise ValidationError("The requested card must be one of the trade offer's available cards (have_cards).")

        # Validate that offered_card is in trade_offer.want_cards
        try:
            want_through_obj = self.trade_offer.trade_offer_want_cards.get(card=self.offered_card)
        except TradeOfferWantCard.DoesNotExist:
            raise ValidationError("The offered card must be one of the trade offer's requested cards (want_cards).")

        # For new acceptances, do not allow creation if the trade offer is closed.
        if not self.pk and self.trade_offer.is_closed:
            raise ValidationError("This trade offer is closed. No more acceptances are allowed.")

        active_states = [
            self.AcceptanceState.ACCEPTED,
            self.AcceptanceState.SENT,
            self.AcceptanceState.RECEIVED,
            self.AcceptanceState.COMPLETED,
        ]

        active_acceptances = self.trade_offer.acceptances.filter(state__in=active_states)
        if self.pk:
            active_acceptances = active_acceptances.exclude(pk=self.pk)

        # Count active acceptances for the requested card.
        requested_count = active_acceptances.filter(requested_card=self.requested_card).count()
        if requested_count >= have_through_obj.quantity:
            raise ValidationError("This requested card has been fully accepted.")

        # Count active acceptances for the offered card.
        offered_count = active_acceptances.filter(offered_card=self.offered_card).count()
        if offered_count >= want_through_obj.quantity:
            raise ValidationError("This offered card has already been fully used.")

    def update_state(self, new_state):
        """
        Update the trade acceptance state.
        Allowed transitions:
          - ACCEPTED -> SENT
          - SENT -> RECEIVED
          - RECEIVED -> COMPLETED
          Additionally, from any active state a transition to:
              REJECTED_BY_INITIATOR or REJECTED_BY_ACCEPTOR is allowed.
        Once in COMPLETED or any rejection state, no further transitions are allowed.
        """
        if new_state not in [choice[0] for choice in self.AcceptanceState.choices]:
            raise ValueError(f"'{new_state}' is not a valid state.")

        # Terminal states: no further transitions allowed.
        if self.state in [
            self.AcceptanceState.COMPLETED,
            self.AcceptanceState.REJECTED_BY_INITIATOR,
            self.AcceptanceState.REJECTED_BY_ACCEPTOR
        ]:
            raise ValueError(f"No transitions allowed from the terminal state '{self.state}'.")

        allowed_transitions = {
            self.AcceptanceState.ACCEPTED: {
                self.AcceptanceState.SENT,
                self.AcceptanceState.REJECTED_BY_INITIATOR,
                self.AcceptanceState.REJECTED_BY_ACCEPTOR,
            },
            self.AcceptanceState.SENT: {
                self.AcceptanceState.RECEIVED,
                self.AcceptanceState.REJECTED_BY_INITIATOR,
                self.AcceptanceState.REJECTED_BY_ACCEPTOR,
            },
            self.AcceptanceState.RECEIVED: {
                self.AcceptanceState.COMPLETED,
                self.AcceptanceState.REJECTED_BY_INITIATOR,
                self.AcceptanceState.REJECTED_BY_ACCEPTOR,
            },
        }

        if new_state not in allowed_transitions.get(self.state, {}):
            raise ValueError(f"Transition from {self.state} to {new_state} is not allowed.")

        self.state = new_state
        self.save(update_fields=["state"])

    def __str__(self):
        return (f"TradeAcceptance(offer_hash={self.trade_offer.hash}, "
                f"accepted_by={self.accepted_by}, "
                f"requested_card={self.requested_card}, "
                f"offered_card={self.offered_card}, state={self.state})")

    class Meta:
        # Unique constraints have been removed because validations now allow
        # multiple active acceptances per card based on the available quantity.
        pass