from django.db import models
from django.conf import settings
from django.urls import reverse
from django.utils import timezone
from django.core.validators import MinValueValidator, MaxValueValidator


class Task(models.Model):
    PRIORITY_CHOICES = [
        ('low', 'Low'),
        ('medium', 'Medium'),
        ('high', 'High'),
    ]
    
    STATUS_CHOICES = [
        ('todo', 'To Do'),
        ('in_progress', 'In Progress'),
        ('in_review', 'In Review'),
        ('done', 'Done'),
    ]
    
    APPROVAL_STATUS_CHOICES = [
        ('pending', 'Pending Approval'),
        ('approved', 'Approved'),
        ('rejected', 'Rejected'),
    ]
    
    SCOPE_CHOICES = [
        ('department', 'Department Level'),
        ('national', 'National Level'),
    ]
    
    title = models.CharField(max_length=200)
    description = models.TextField(blank=True, null=True)
    due_date = models.DateTimeField(blank=True, null=True)
    priority = models.CharField(
        max_length=10, 
        choices=PRIORITY_CHOICES, 
        default='medium'
    )
    status = models.CharField(
        max_length=20, 
        choices=STATUS_CHOICES, 
        default='todo'
    )
    created_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE, 
        related_name='created_tasks'
    )
    assigned_to = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL, 
        null=True, 
        blank=True,
        related_name='assigned_tasks'
    )
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    completed_at = models.DateTimeField(null=True, blank=True)
    
    # Approval fields
    requires_approval = models.BooleanField(default=False)
    approval_status = models.CharField(
        max_length=20,
        choices=APPROVAL_STATUS_CHOICES,
        default='approved',
        help_text='Approval status for high-priority or national-level tasks'
    )
    scope = models.CharField(
        max_length=20,
        choices=SCOPE_CHOICES,
        default='department',
        help_text='Scope of the task (Department or National Level)'
    )
    approved_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='approved_tasks'
    )
    approved_at = models.DateTimeField(null=True, blank=True)
    rejection_reason = models.TextField(blank=True, null=True)
    
    class Meta:
        ordering = ['-priority', 'due_date']
    
    def __str__(self):
        return f"{self.title} ({self.get_status_display()})"
    
    def get_absolute_url(self):
        return reverse('task-detail', kwargs={'pk': self.pk})
    
    def save(self, *args, **kwargs):
        # Update completed_at when status is set to 'done'
        if self.status == 'done' and not self.completed_at:
            self.completed_at = timezone.now()
        elif self.status != 'done' and self.completed_at:
            self.completed_at = None
        super().save(*args, **kwargs)


class TaskComment(models.Model):
    task = models.ForeignKey(
        Task, 
        on_delete=models.CASCADE, 
        related_name='comments'
    )
    author = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        ordering = ['-created_at']
    
    def __str__(self):
        return f"Comment by {self.author.username} on {self.task.title}"


class TaskAttachment(models.Model):
    task = models.ForeignKey(
        Task, 
        on_delete=models.CASCADE, 
        related_name='attachments'
    )
    file = models.FileField(upload_to='task_attachments/')
    uploaded_by = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    uploaded_at = models.DateTimeField(auto_now_add=True)
    
    def __str__(self):
        return f"Attachment for {self.task.title}"