import uuid
import random
from django.conf import settings
from django.db import models
from django.utils import timezone
from django.utils.text import slugify
from django.utils.translation import gettext_lazy as _
from apps.profiles.models import Institution


class CourseCategory(models.TextChoices):
    RAZAVI_TEACHINGS = 'razavi_teachings', _('Razavi Teachings & Lifestyle')
    CULTURAL_DIPLOMACY = 'cultural_diplomacy', _('Cultural Diplomacy & Interfaith')
    CENTER_MANAGEMENT = 'center_management', _('Center & Mosque Management')
    INTERNATIONAL_MEDIA = 'international_media', _('International Media & Content')
    SPECIALIZED_LANGUAGES = 'specialized_languages', _('Specialized Languages & Translation')
    GENERAL = 'general', _('General Religious Studies')


class CourseLevel(models.TextChoices):
    INTRODUCTORY = 'introductory', _('Introductory')
    INTERMEDIATE = 'intermediate', _('Intermediate')
    ADVANCED = 'advanced', _('Advanced')


class CourseLanguage(models.TextChoices):
    FA = 'fa', _('Persian')
    AR = 'ar', _('Arabic')
    EN = 'en', _('English')
    UR = 'ur', _('Urdu')
    FR = 'fr', _('French')


class Course(models.Model):
    title = models.CharField(max_length=255, verbose_name=_('Course Title'))
    slug = models.SlugField(
        max_length=280,
        unique=True,
        blank=True,
        null=True,
        allow_unicode=True,
        verbose_name=_('Slug / URL Identifier')
    )
    category = models.CharField(
        max_length=50,
        choices=CourseCategory.choices,
        default=CourseCategory.RAZAVI_TEACHINGS,
        verbose_name=_('Category')
    )
    language = models.CharField(
        max_length=10,
        choices=CourseLanguage.choices,
        default=CourseLanguage.EN,
        verbose_name=_('Language')
    )
    level = models.CharField(
        max_length=20,
        choices=CourseLevel.choices,
        default=CourseLevel.INTRODUCTORY,
        verbose_name=_('Difficulty Level')
    )
    cover_image = models.ImageField(
        upload_to='lms/covers/%Y/%m/',
        blank=True,
        null=True,
        verbose_name=_('Cover Image')
    )
    instructor_name = models.CharField(max_length=255, verbose_name=_('Instructor Name'))
    instructor_title = models.CharField(
        max_length=255,
        blank=True,
        null=True,
        verbose_name=_('Instructor Title / Specialty')
    )
    instructor_avatar = models.ImageField(
        upload_to='lms/instructors/%Y/%m/',
        blank=True,
        null=True,
        verbose_name=_('Instructor Avatar')
    )
    institution = models.ForeignKey(
        Institution,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='courses',
        verbose_name=_('Partner Institution / Center')
    )
    organization_name = models.CharField(
        max_length=255,
        blank=True,
        null=True,
        verbose_name=_('Organization / Academy Name')
    )
    description = models.TextField(verbose_name=_('Course Description & Syllabus Summary'))
    duration_hours = models.FloatField(default=1.0, verbose_name=_('Duration (Hours)'))
    rating = models.FloatField(default=5.0, verbose_name=_('Average Rating'))
    reviews_count = models.PositiveIntegerField(default=0, verbose_name=_('Reviews Count'))
    is_published = models.BooleanField(default=True, verbose_name=_('Is Published'))
    is_featured = models.BooleanField(default=False, verbose_name=_('Is Featured'))
    created_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='created_courses',
        verbose_name=_('Created By')
    )
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_('Created At'))
    updated_at = models.DateTimeField(auto_now=True, verbose_name=_('Updated At'))

    class Meta:
        ordering = ('-is_featured', '-created_at')
        verbose_name = _('Course')
        verbose_name_plural = _('Courses')

    def __str__(self):
        return f"{self.title} ({self.get_language_display()} - {self.get_level_display()})"

    def save(self, *args, **kwargs):
        if not self.slug:
            base_slug = slugify(self.title, allow_unicode=True) or f"course-{random.randint(1000, 9999)}"
            slug = base_slug
            counter = 1
            while Course.objects.filter(slug=slug).exclude(pk=self.pk).exists():
                slug = f"{base_slug}-{counter}"
                counter += 1
            self.slug = slug
        super().save(*args, **kwargs)

    @property
    def total_lessons_count(self):
        return Lesson.objects.filter(module__course=self).count()

    @property
    def total_students_count(self):
        return self.enrollments.count()


class CourseModule(models.Model):
    course = models.ForeignKey(
        Course,
        on_delete=models.CASCADE,
        related_name='modules',
        verbose_name=_('Course')
    )
    title = models.CharField(max_length=255, verbose_name=_('Module Title'))
    description = models.TextField(blank=True, null=True, verbose_name=_('Module Description'))
    order = models.IntegerField(default=0, verbose_name=_('Display Order'))
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_('Created At'))

    class Meta:
        ordering = ('order', 'id')
        verbose_name = _('Course Module')
        verbose_name_plural = _('Course Modules')

    def __str__(self):
        return f"{self.course.title} - Module {self.order + 1}: {self.title}"


class Lesson(models.Model):
    class LessonType(models.TextChoices):
        VIDEO = 'video', _('Video Lesson')
        READING = 'reading', _('Reading & Text')
        QUIZ = 'quiz', _('Interactive Quiz')
        ASSIGNMENT = 'assignment', _('Practical Assignment')

    module = models.ForeignKey(
        CourseModule,
        on_delete=models.CASCADE,
        related_name='lessons',
        verbose_name=_('Module')
    )
    title = models.CharField(max_length=255, verbose_name=_('Lesson Title'))
    slug = models.SlugField(
        max_length=280,
        blank=True,
        null=True,
        allow_unicode=True,
        verbose_name=_('Slug')
    )
    lesson_type = models.CharField(
        max_length=20,
        choices=LessonType.choices,
        default=LessonType.VIDEO,
        verbose_name=_('Lesson Type')
    )
    duration_minutes = models.PositiveIntegerField(default=15, verbose_name=_('Duration (Minutes)'))
    video_url = models.URLField(
        max_length=500,
        blank=True,
        null=True,
        verbose_name=_('Video URL (YouTube, Vimeo, HLS, MP4)')
    )
    content = models.TextField(
        blank=True,
        null=True,
        verbose_name=_('Lesson Content / Notes (Markdown)')
    )
    slides_attachment = models.FileField(
        upload_to='lms/slides/%Y/%m/',
        blank=True,
        null=True,
        verbose_name=_('Slides / PDF Handout')
    )
    order = models.IntegerField(default=0, verbose_name=_('Display Order'))
    is_preview = models.BooleanField(
        default=False,
        verbose_name=_('Is Free Preview (Public)')
    )
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_('Created At'))

    class Meta:
        ordering = ('order', 'id')
        verbose_name = _('Lesson')
        verbose_name_plural = _('Lessons')

    def __str__(self):
        return f"{self.module.course.title} -> {self.title} ({self.get_lesson_type_display()})"

    def save(self, *args, **kwargs):
        if not self.slug:
            base_slug = slugify(self.title, allow_unicode=True) or f"lesson-{random.randint(1000, 9999)}"
            self.slug = base_slug
        super().save(*args, **kwargs)


class QuizQuestion(models.Model):
    lesson = models.ForeignKey(
        Lesson,
        on_delete=models.CASCADE,
        related_name='quiz_questions',
        verbose_name=_('Lesson')
    )
    question_text = models.TextField(verbose_name=_('Question Text'))
    options = models.JSONField(
        default=list,
        verbose_name=_('Options Array'),
        help_text=_('List of multiple-choice strings: ["Option A", "Option B", "Option C", "Option D"]')
    )
    correct_option_index = models.PositiveSmallIntegerField(
        default=0,
        verbose_name=_('Correct Option Index (0-indexed)')
    )
    explanation = models.TextField(
        blank=True,
        null=True,
        verbose_name=_('Explanation / Reference for Correct Answer')
    )
    order = models.IntegerField(default=0, verbose_name=_('Display Order'))

    class Meta:
        ordering = ('order', 'id')
        verbose_name = _('Quiz Question')
        verbose_name_plural = _('Quiz Questions')

    def __str__(self):
        return f"Q{self.order + 1}: {self.question_text[:60]}"


class CourseEnrollment(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='course_enrollments',
        verbose_name=_('User')
    )
    course = models.ForeignKey(
        Course,
        on_delete=models.CASCADE,
        related_name='enrollments',
        verbose_name=_('Course')
    )
    enrolled_at = models.DateTimeField(auto_now_add=True, verbose_name=_('Enrolled At'))
    completed_at = models.DateTimeField(null=True, blank=True, verbose_name=_('Completed At'))
    progress_percentage = models.PositiveSmallIntegerField(
        default=0,
        verbose_name=_('Progress Percentage (0-100)')
    )

    class Meta:
        unique_together = ('user', 'course')
        ordering = ('-enrolled_at',)
        verbose_name = _('Course Enrollment')
        verbose_name_plural = _('Course Enrollments')

    def __str__(self):
        return f"{self.user} enrolled in {self.course.title} ({self.progress_percentage}%)"

    def recalculate_progress(self):
        """
        Recalculates progress percentage based on completed lessons for this course.
        If progress reaches 100%, marks completed_at and issues digital certificate.
        """
        all_lesson_ids = Lesson.objects.filter(module__course=self.course).values_list('id', flat=True)
        total_count = len(all_lesson_ids)
        if total_count == 0:
            self.progress_percentage = 100
        else:
            completed_count = LessonProgress.objects.filter(
                user=self.user,
                lesson_id__in=all_lesson_ids,
                is_completed=True
            ).count()
            self.progress_percentage = int((completed_count / total_count) * 100)

        if self.progress_percentage >= 100 and not self.completed_at:
            self.completed_at = timezone.now()
            # Auto-issue certificate if not already issued
            DigitalCertificate.issue_for_enrollment(self)
        self.save()
        return self.progress_percentage


class LessonProgress(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='lesson_progresses',
        verbose_name=_('User')
    )
    lesson = models.ForeignKey(
        Lesson,
        on_delete=models.CASCADE,
        related_name='user_progresses',
        verbose_name=_('Lesson')
    )
    is_completed = models.BooleanField(default=False, verbose_name=_('Is Completed'))
    completed_at = models.DateTimeField(null=True, blank=True, verbose_name=_('Completed At'))
    quiz_score = models.FloatField(
        null=True,
        blank=True,
        verbose_name=_('Quiz Score (Percentage)')
    )

    class Meta:
        unique_together = ('user', 'lesson')
        verbose_name = _('Lesson Progress')
        verbose_name_plural = _('Lesson Progresses')

    def __str__(self):
        status_str = "Completed" if self.is_completed else "In Progress"
        return f"{self.user} - {self.lesson.title}: {status_str}"


class DigitalCertificate(models.Model):
    certificate_code = models.CharField(
        max_length=100,
        unique=True,
        verbose_name=_('Verification Code'),
        help_text=_('e.g. CERT-RAZAVI-2026-AB12CD')
    )
    uuid = models.UUIDField(default=uuid.uuid4, unique=True, editable=False, verbose_name=_('Unique UUID'))
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='certificates',
        verbose_name=_('Student / User')
    )
    course = models.ForeignKey(
        Course,
        on_delete=models.CASCADE,
        related_name='certificates',
        verbose_name=_('Course')
    )
    issue_date = models.DateField(default=timezone.now, verbose_name=_('Issue Date'))
    final_score = models.FloatField(default=100.0, verbose_name=_('Final Score (%)'))
    certificate_file = models.FileField(
        upload_to='lms/certificates/%Y/%m/',
        blank=True,
        null=True,
        verbose_name=_('Certificate PDF Document')
    )
    is_revoked = models.BooleanField(default=False, verbose_name=_('Is Revoked'))
    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_('Created At'))

    class Meta:
        unique_together = ('user', 'course')
        ordering = ('-created_at',)
        verbose_name = _('Digital Certificate')
        verbose_name_plural = _('Digital Certificates')

    def __str__(self):
        return f"Certificate {self.certificate_code} ({self.user} - {self.course.title})"

    @classmethod
    def issue_for_enrollment(cls, enrollment):
        """
        Creates a new certificate for a finished course enrollment if none exists.
        """
        existing = cls.objects.filter(user=enrollment.user, course=enrollment.course).first()
        if existing:
            return existing

        year = timezone.now().year
        rand_code = ''.join(random.choices('ABCDEFGHJKLMNPQRSTUVWXYZ23456789', k=6))
        code = f"CERT-RAZAVI-{year}-{rand_code}"

        # Calculate average quiz score if any quizzes were taken
        lesson_ids = Lesson.objects.filter(module__course=enrollment.course).values_list('id', flat=True)
        quiz_progresses = LessonProgress.objects.filter(
            user=enrollment.user,
            lesson_id__in=lesson_ids,
            quiz_score__isnull=False
        )
        if quiz_progresses.exists():
            avg_score = sum(p.quiz_score for p in quiz_progresses) / quiz_progresses.count()
        else:
            avg_score = 100.0

        certificate = cls.objects.create(
            certificate_code=code,
            user=enrollment.user,
            course=enrollment.course,
            issue_date=timezone.now().date(),
            final_score=round(avg_score, 1),
        )
        return certificate