import os
from django.db import models
from django.utils.translation import gettext_lazy as _

from filer.fields.image import FilerImageField
from filer.fields.file import FilerFileField

from apps.account.models import StudentUser


def lesson_file_upload_to(instance, filename):
    return os.path.join(f"lessons/{filename}")



class Lesson(models.Model):
    """
    Base Lesson model that contains the actual content (video file or link)
    """
    class ContentTypeChoices(models.TextChoices):
        YOUTUBE_LINK = 'youtube_link', _('Youtube Link')
        VIDEO_FILE = 'video_file', _('Video File')
    
    title = models.CharField(max_length=255, verbose_name=_('Lesson Title'))
    content_type = models.CharField(max_length=50, choices=ContentTypeChoices.choices, verbose_name=_('Content Type'))

    content_file = models.FileField(
        null=True,
        blank=True,
        upload_to=lesson_file_upload_to,
    )
    video_link = models.CharField(max_length=500, null=True, blank=True, verbose_name=_('Link'))
    duration = models.PositiveIntegerField(verbose_name=_('Duration (in minutes)'))

    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_("Created at"))
    updated_at = models.DateTimeField(auto_now=True, verbose_name=_("Updated At"))

    def __str__(self):
        return self.title

    class Meta:
        verbose_name = _("Lesson")
        verbose_name_plural = _("Lessons")

        indexes = [
            models.Index(fields=['content_type']),
            models.Index(fields=['created_at']),
        ]


class CourseLesson(models.Model):
    """
    Intermediate model that connects Course with Lesson
    """
    course = models.ForeignKey("course.Course", on_delete=models.CASCADE, related_name='lessons', verbose_name=_('Course'))
    lesson = models.ForeignKey(Lesson, on_delete=models.CASCADE, related_name='course_lessons', verbose_name=_('Lesson'))
    title = models.CharField(max_length=255, verbose_name=_('Course Lesson Title'), null=True, blank=True)
    priority = models.IntegerField(null=True, blank=True, verbose_name=_('Priority'))

    is_active = models.BooleanField(default=True, verbose_name=_('Is Active'))
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_("Created at"))
    updated_at = models.DateTimeField(auto_now=True, verbose_name=_("Updated At"))

    def __str__(self):
        title = self.title or self.lesson.title
        return f"{self.course.title} - {title}"

    def is_completed_by(self, student):
        return self.completions.filter(student=student).exists()
    
    @property
    def content_type(self):
        return self.lesson.content_type
    
    @property
    def content_file(self):
        return self.lesson.content_file
    
    @property
    def video_link(self):
        return self.lesson.video_link
    
    @property
    def duration(self):
        return self.lesson.duration
    
    def save(self, *args, **kwargs):
        # If title is not provided, use the lesson's title
        if not self.title:
            self.title = self.lesson.title
            
        if self.priority is None:
            # If priority is not set, set it to the next available priority
            max_priority = self.course.lessons.aggregate(max_priority=models.Max('priority'))['max_priority']
            self.priority = (max_priority or 0) + 1
        else: 
            self._adjust_priorities()
        super().save(*args, **kwargs)

    def _adjust_priorities(self):
        # Adjust priorities of other lessons in the course
        lessons = self.course.lessons.exclude(pk=self.pk)
        # Shift priorities for lessons with the same or higher priority
        lessons.filter(priority__gte=self.priority).update(priority=models.F('priority') + 1)

    class Meta:
        verbose_name = _("Course Lesson")
        verbose_name_plural = _("Course Lessons")

        indexes = [
            models.Index(fields=['course']),
            models.Index(fields=['lesson']),
            models.Index(fields=['priority']),
            models.Index(fields=['is_active']),
            models.Index(fields=['course', 'priority']),
            models.Index(fields=['course', 'is_active']),
        ]


class LessonCompletion(models.Model):
    student = models.ForeignKey(
        StudentUser,
        on_delete=models.CASCADE,
        related_name='lesson_completions',
        verbose_name=_('Student')
    )
    course_lesson = models.ForeignKey(
        CourseLesson,
        on_delete=models.CASCADE,
        related_name='completions',
        verbose_name=_('Course Lesson')
    )

    completed_at = models.DateTimeField(auto_now_add=True)
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_("Created at"))

    class Meta:
        unique_together = ('student', 'course_lesson')
        verbose_name = _("Lesson Completion")
        verbose_name_plural = _("Lesson Completions")

        indexes = [
            models.Index(fields=['student']),
            models.Index(fields=['course_lesson']),
            models.Index(fields=['completed_at']),
            models.Index(fields=['student', 'course_lesson']),
        ]
        
    def __str__(self):
        return f"{self.student.fullname} - {self.course_lesson.title} - Completed"