"""
Referrals models for cross-clinic patient referrals.

This module handles referrals between departments/clinics,
referral tracking, and reception notifications.
"""

from django.db import models
from django.utils.translation import gettext_lazy as _
from simple_history.models import HistoricalRecords

from core.models import (
    UUIDPrimaryKeyMixin,
    TimeStampedMixin,
    TenantOwnedMixin,
)


class Referral(UUIDPrimaryKeyMixin, TimeStampedMixin, TenantOwnedMixin):
    """
    Patient referrals between clinics/departments.
    Tracks referral workflow from initiation to appointment booking.
    """
    
    class Status(models.TextChoices):
        PENDING = 'PENDING', _('Pending')
        ACKNOWLEDGED = 'ACKNOWLEDGED', _('Acknowledged')
        APPOINTMENT_BOOKED = 'APPOINTMENT_BOOKED', _('Appointment Booked')
        COMPLETED = 'COMPLETED', _('Completed')
        DECLINED = 'DECLINED', _('Declined')
        CANCELLED = 'CANCELLED', _('Cancelled')
    
    class Priority(models.TextChoices):
        ROUTINE = 'ROUTINE', _('Routine')
        URGENT = 'URGENT', _('Urgent')
        EMERGENCY = 'EMERGENCY', _('Emergency')
    
    class ReferralType(models.TextChoices):
        INITIAL_ASSESSMENT = 'INITIAL_ASSESSMENT', _('Initial Assessment')
        CONSULTATION = 'CONSULTATION', _('Consultation')
        FOLLOW_UP = 'FOLLOW_UP', _('Follow-up')
        SECOND_OPINION = 'SECOND_OPINION', _('Second Opinion')
    
    # Patient & Clinics
    patient = models.ForeignKey(
        'core.Patient',
        on_delete=models.CASCADE,
        related_name='referrals',
        verbose_name=_("Patient")
    )
    from_clinic = models.ForeignKey(
        'core.Clinic',
        on_delete=models.CASCADE,
        related_name='outgoing_referrals',
        verbose_name=_("From Clinic")
    )
    to_clinic = models.ForeignKey(
        'core.Clinic',
        on_delete=models.CASCADE,
        related_name='incoming_referrals',
        verbose_name=_("To Clinic")
    )
    
    # Referral Details
    referral_type = models.CharField(
        max_length=30,
        choices=ReferralType.choices,
        default=ReferralType.CONSULTATION,
        verbose_name=_("Referral Type")
    )
    priority = models.CharField(
        max_length=15,
        choices=Priority.choices,
        default=Priority.ROUTINE,
        verbose_name=_("Priority")
    )
    reason = models.TextField(
        verbose_name=_("Reason for Referral"),
        help_text=_("Clinical reason for referring to another department")
    )
    clinical_notes = models.TextField(
        blank=True,
        verbose_name=_("Clinical Notes"),
        help_text=_("Additional clinical information for receiving clinic")
    )
    
    # Workflow
    referred_by = models.ForeignKey(
        'core.User',
        on_delete=models.SET_NULL,
        null=True,
        related_name='made_referrals',
        verbose_name=_("Referred By")
    )
    referred_to = models.ForeignKey(
        'core.User',
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='received_referrals',
        verbose_name=_("Referred To"),
        help_text=_("Specific therapist if known")
    )
    
    # Status Tracking
    status = models.CharField(
        max_length=30,
        choices=Status.choices,
        default=Status.PENDING,
        verbose_name=_("Status")
    )
    acknowledged_at = models.DateTimeField(
        null=True,
        blank=True,
        verbose_name=_("Acknowledged At")
    )
    acknowledged_by = models.ForeignKey(
        'core.User',
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='acknowledged_referrals',
        verbose_name=_("Acknowledged By")
    )
    
    # Appointment Linkage
    appointment = models.ForeignKey(
        'appointments.Appointment',
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='referrals',
        verbose_name=_("Appointment"),
        help_text=_("Appointment booked for this referral")
    )
    appointment_booked_at = models.DateTimeField(
        null=True,
        blank=True,
        verbose_name=_("Appointment Booked At")
    )
    appointment_booked_by = models.ForeignKey(
        'core.User',
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='booked_referral_appointments',
        verbose_name=_("Appointment Booked By")
    )
    
    # Completion
    completed_at = models.DateTimeField(
        null=True,
        blank=True,
        verbose_name=_("Completed At")
    )
    outcome_notes = models.TextField(
        blank=True,
        verbose_name=_("Outcome Notes"),
        help_text=_("Notes about the referral outcome")
    )
    
    # Decline/Cancel
    declined_at = models.DateTimeField(
        null=True,
        blank=True,
        verbose_name=_("Declined At")
    )
    declined_by = models.ForeignKey(
        'core.User',
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='declined_referrals',
        verbose_name=_("Declined By")
    )
    decline_reason = models.TextField(
        blank=True,
        verbose_name=_("Decline Reason")
    )
    
    history = HistoricalRecords()
    
    class Meta:
        verbose_name = _("Referral")
        verbose_name_plural = _("Referrals")
        ordering = ['-created_at']
        indexes = [
            models.Index(fields=['patient', 'status']),
            models.Index(fields=['from_clinic', 'status']),
            models.Index(fields=['to_clinic', 'status']),
            models.Index(fields=['referred_by', 'status']),
            models.Index(fields=['status', 'created_at']),
            models.Index(fields=['tenant', 'status']),
        ]
    
    def __str__(self):
        return f"Referral: {self.patient} from {self.from_clinic.name_en} to {self.to_clinic.name_en}"
    
    def acknowledge(self, user):
        """Acknowledge receipt of referral."""
        from django.utils import timezone
        self.status = self.Status.ACKNOWLEDGED
        self.acknowledged_at = timezone.now()
        self.acknowledged_by = user
        self.save()
    
    def book_appointment(self, appointment, user):
        """Link appointment to referral."""
        from django.utils import timezone
        self.appointment = appointment
        self.status = self.Status.APPOINTMENT_BOOKED
        self.appointment_booked_at = timezone.now()
        self.appointment_booked_by = user
        self.save()
    
    def complete(self, outcome_notes=""):
        """Mark referral as completed."""
        from django.utils import timezone
        self.status = self.Status.COMPLETED
        self.completed_at = timezone.now()
        self.outcome_notes = outcome_notes
        self.save()
    
    def decline(self, user, reason):
        """Decline the referral."""
        from django.utils import timezone
        self.status = self.Status.DECLINED
        self.declined_at = timezone.now()
        self.declined_by = user
        self.decline_reason = reason
        self.save()
    
    @classmethod
    def get_pending_for_clinic(cls, clinic, tenant):
        """Get pending referrals for a clinic."""
        return cls.objects.filter(
            to_clinic=clinic,
            tenant=tenant,
            status=cls.Status.PENDING
        ).select_related('patient', 'from_clinic', 'referred_by')
    
    @classmethod
    def get_pending_for_reception(cls, tenant):
        """Get referrals pending appointment booking."""
        return cls.objects.filter(
            tenant=tenant,
            status__in=[cls.Status.PENDING, cls.Status.ACKNOWLEDGED],
            appointment__isnull=True
        ).select_related('patient', 'from_clinic', 'to_clinic', 'referred_by')