"""
Task models for KeepItGoing.
"""

import uuid
from django.conf import settings
from django.db import models


class SoftDeleteManager(models.Manager):
    """Manager that excludes soft-deleted items by default."""

    def get_queryset(self):
        return super().get_queryset().filter(is_deleted=False)


class AllObjectsManager(models.Manager):
    """Manager that includes soft-deleted items."""
    pass


class Tag(models.Model):
    """
    Tags for organizing and categorizing tasks.
    Supports multiple tags per task.
    """
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='tags'
    )
    name = models.CharField(max_length=255)
    description = models.TextField(blank=True)
    color = models.CharField(max_length=7, default='#3B82F6')  # Hex color
    icon = models.CharField(max_length=50, blank=True)  # Icon name
    sort_order = models.IntegerField(default=0)
    is_archived = models.BooleanField(default=False)

    # Sync fields
    sync_id = models.UUIDField(default=uuid.uuid4, unique=True)
    is_deleted = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    # Managers
    objects = SoftDeleteManager()
    all_objects = AllObjectsManager()

    class Meta:
        db_table = 'tags'
        ordering = ['sort_order', 'name']

    def __str__(self):
        return self.name


class Task(models.Model):
    """
    Main task model with support for subtasks, recurrence, and time tracking.
    """
    STATUS_CHOICES = [
        ('pending', 'Pending'),
        ('in_progress', 'In Progress'),
        ('completed', 'Completed'),
        ('cancelled', 'Cancelled'),
    ]

    PRIORITY_CHOICES = [
        ('low', 'Low'),
        ('medium', 'Medium'),
        ('high', 'High'),
        ('urgent', 'Urgent'),
    ]

    RECURRENCE_CHOICES = [
        ('none', 'None'),
        ('daily', 'Daily'),
        ('weekly', 'Weekly'),
        ('biweekly', 'Bi-weekly'),
        ('monthly', 'Monthly'),
        ('yearly', 'Yearly'),
        ('custom', 'Custom'),
    ]

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='tasks'
    )

    # Hierarchy
    parent = models.ForeignKey(
        'self',
        on_delete=models.CASCADE,
        null=True,
        blank=True,
        related_name='subtasks'
    )

    # Core fields
    title = models.CharField(max_length=500)
    description = models.TextField(blank=True)
    status = models.CharField(max_length=20, choices=STATUS_CHOICES, default='pending')
    priority = models.CharField(max_length=20, choices=PRIORITY_CHOICES, default='medium')

    # Dates and times
    due_date = models.DateField(null=True, blank=True)
    due_time = models.TimeField(null=True, blank=True)
    reminder_at = models.DateTimeField(null=True, blank=True)
    completed_at = models.DateTimeField(null=True, blank=True)

    # Recurrence (RRULE format for custom)
    recurrence = models.CharField(max_length=20, choices=RECURRENCE_CHOICES, default='none')
    recurrence_rule = models.CharField(max_length=500, blank=True)  # RRULE string
    recurrence_end_date = models.DateField(null=True, blank=True)

    # Tags (multiple per task)
    tags = models.ManyToManyField(Tag, blank=True, related_name='tasks')

    # Ordering
    sort_order = models.IntegerField(default=0)

    # Sync fields
    sync_id = models.UUIDField(default=uuid.uuid4, unique=True)
    is_deleted = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    # Managers
    objects = SoftDeleteManager()
    all_objects = AllObjectsManager()

    class Meta:
        db_table = 'tasks'
        ordering = ['sort_order', '-priority', 'due_date', 'created_at']

    # Fields that affect when/whether reminder notifications should fire.
    REMINDER_TRACKED_FIELDS = ('due_date', 'due_time', 'reminder_at', 'status', 'is_deleted')

    def __str__(self):
        return self.title

    @classmethod
    def from_db(cls, db, field_names, values):
        instance = super().from_db(db, field_names, values)
        instance._loaded_values = dict(zip(field_names, values))
        return instance

    def save(self, *args, **kwargs):
        # Auto-set completed_at when status changes to completed
        if self.status == 'completed' and self.completed_at is None:
            from django.utils import timezone
            self.completed_at = timezone.now()
        elif self.status != 'completed':
            self.completed_at = None

        is_new = self._state.adding
        loaded_values = getattr(self, '_loaded_values', None)
        reminder_fields_changed = is_new or loaded_values is None or any(
            loaded_values.get(field) != getattr(self, field) for field in self.REMINDER_TRACKED_FIELDS
        )

        super().save(*args, **kwargs)
        self._loaded_values = {field: getattr(self, field) for field in self.REMINDER_TRACKED_FIELDS}

        if reminder_fields_changed:
            self.reschedule_reminders()

    def _due_and_overdue_moments(self):
        """
        Returns (due_moment, overdue_moment) as timezone-aware datetimes in
        the owner's timezone, or (None, None) if there's nothing to schedule
        against. Mirrors is_overdue's rule that a date-only due task doesn't
        flip overdue until the day after due_date.
        """
        if not self.due_date:
            return None, None

        from datetime import datetime, time as dt_time, timedelta
        from zoneinfo import ZoneInfo

        try:
            user_tz = ZoneInfo(self.user.timezone)
        except Exception:
            user_tz = ZoneInfo('UTC')

        if self.due_time:
            due_moment = datetime.combine(self.due_date, self.due_time, tzinfo=user_tz)
            return due_moment, due_moment

        overdue_moment = datetime.combine(self.due_date + timedelta(days=1), dt_time.min, tzinfo=user_tz)
        return None, overdue_moment

    def reschedule_reminders(self):
        """
        Recompute this task's ScheduledReminder rows from its current
        due_date/due_time/reminder_at/status. Safe to call any time due
        info changes - clears out not-yet-sent reminders and, if the task
        is still active and due, schedules fresh ones for "before due"
        (from reminder_at, or user.default_reminder_minutes before due),
        "due now", and "overdue".
        """
        from datetime import timedelta
        from notifications.models import ScheduledReminder

        ScheduledReminder.objects.filter(task=self, is_sent=False).delete()

        if self.is_deleted or self.status in ('completed', 'cancelled'):
            return

        due_moment, overdue_moment = self._due_and_overdue_moments()
        reminders = []

        if due_moment:
            if self.reminder_at:
                before_due_moment = self.reminder_at
            elif self.user.default_reminder_minutes:
                before_due_moment = due_moment - timedelta(minutes=self.user.default_reminder_minutes)
            else:
                before_due_moment = None

            if before_due_moment:
                reminders.append(ScheduledReminder(task=self, reminder_type='reminder', remind_at=before_due_moment))
            reminders.append(ScheduledReminder(task=self, reminder_type='due_soon', remind_at=due_moment))

        if overdue_moment:
            reminders.append(ScheduledReminder(task=self, reminder_type='overdue', remind_at=overdue_moment))

        if reminders:
            ScheduledReminder.objects.bulk_create(reminders)

    @property
    def is_overdue(self):
        """Check if task is overdue."""
        if self.due_date and self.status not in ('completed', 'cancelled'):
            from django.utils import timezone
            from zoneinfo import ZoneInfo

            # Get current date/time in user's timezone
            try:
                user_tz = ZoneInfo(self.user.timezone)
                user_now = timezone.now().astimezone(user_tz)
            except (Exception,):
                # Fall back to UTC if user timezone is invalid or missing
                user_now = timezone.now()

            if self.due_date < user_now.date():
                return True
            if self.due_date == user_now.date() and self.due_time:
                return self.due_time < user_now.time()
            return False
        return False

    @property
    def total_time_spent(self):
        """Calculate total time spent on this task in seconds."""
        total_seconds = sum(
            entry.duration_seconds or 0
            for entry in self.time_entries.all()
        )
        return total_seconds

    @property
    def total_time_formatted(self):
        """Return total time spent formatted as H:MM:SS."""
        seconds = self.total_time_spent
        hours = seconds // 3600
        minutes = (seconds % 3600) // 60
        secs = seconds % 60
        return f"{hours}:{minutes:02d}:{secs:02d}"

    def calculate_next_due_date(self, from_date=None):
        """
        Calculate the next due date based on recurrence pattern.
        Returns None if task doesn't recur or has reached end date.
        """
        if self.recurrence == 'none':
            return None

        from datetime import timedelta
        from dateutil.relativedelta import relativedelta

        base_date = from_date or self.due_date
        if not base_date:
            from django.utils import timezone
            base_date = timezone.now().date()

        # Calculate next date based on recurrence type
        if self.recurrence == 'daily':
            next_date = base_date + timedelta(days=1)
        elif self.recurrence == 'weekly':
            next_date = base_date + timedelta(weeks=1)
        elif self.recurrence == 'biweekly':
            next_date = base_date + timedelta(weeks=2)
        elif self.recurrence == 'monthly':
            next_date = base_date + relativedelta(months=1)
        elif self.recurrence == 'yearly':
            next_date = base_date + relativedelta(years=1)
        elif self.recurrence == 'custom' and self.recurrence_rule:
            from dateutil.rrule import rrulestr
            from datetime import datetime, time as dt_time

            dtstart = datetime.combine(base_date, dt_time.min)
            try:
                next_occurrence = rrulestr(self.recurrence_rule, dtstart=dtstart).after(dtstart, inc=False)
            except Exception:
                return None
            if not next_occurrence:
                return None
            next_date = next_occurrence.date()
        else:
            return None

        # Check if we've passed the end date
        if self.recurrence_end_date and next_date > self.recurrence_end_date:
            return None

        return next_date

    @property
    def parsed_custom_recurrence(self):
        """
        Decompose recurrence_rule (an RRULE string) into simple fields for
        prepopulating the custom recurrence builder UI. Never raises; returns
        safe defaults for a blank or malformed rule.
        """
        result = {
            'freq': None,
            'interval': 1,
            'byweekday': [],
            'monthly_mode': None,
            'bymonthday': None,
            'nth_ordinal': None,
            'nth_weekday': None,
        }
        if not self.recurrence_rule:
            return result

        import re

        params = {}
        for part in self.recurrence_rule.split(';'):
            if '=' in part:
                key, value = part.split('=', 1)
                params[key.strip().upper()] = value.strip()

        freq = params.get('FREQ', '').upper()
        if freq not in ('WEEKLY', 'MONTHLY'):
            return result
        result['freq'] = freq.lower()

        try:
            result['interval'] = int(params.get('INTERVAL', '1'))
        except ValueError:
            result['interval'] = 1

        byday = params.get('BYDAY', '')

        if freq == 'WEEKLY':
            if byday:
                result['byweekday'] = [d.strip() for d in byday.split(',') if d.strip()]
        elif freq == 'MONTHLY':
            bymonthday = params.get('BYMONTHDAY')
            if bymonthday:
                try:
                    result['bymonthday'] = int(bymonthday)
                    result['monthly_mode'] = 'day'
                except ValueError:
                    pass
            elif byday:
                match = re.match(r'^(-?\d+)([A-Z]{2})$', byday)
                if match:
                    result['nth_ordinal'] = int(match.group(1))
                    result['nth_weekday'] = match.group(2)
                    result['monthly_mode'] = 'nth'

        return result

    def create_next_recurrence(self):
        """
        Create the next instance of this recurring task.
        Returns the new task or None if no recurrence should be created.
        """
        if self.recurrence == 'none':
            return None

        next_due_date = self.calculate_next_due_date()
        if not next_due_date:
            return None

        # Create new task with same properties
        new_task = Task.objects.create(
            user=self.user,
            parent=self.parent,
            title=self.title,
            description=self.description,
            status='pending',
            priority=self.priority,
            due_date=next_due_date,
            due_time=self.due_time,
            recurrence=self.recurrence,
            recurrence_rule=self.recurrence_rule,
            recurrence_end_date=self.recurrence_end_date,
            sort_order=self.sort_order,
        )

        # Copy tags
        new_task.tags.set(self.tags.all())

        return new_task


class TimeEntry(models.Model):
    """
    Time tracking entries for tasks.
    """
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    task = models.ForeignKey(Task, on_delete=models.CASCADE, related_name='time_entries')
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='time_entries'
    )

    started_at = models.DateTimeField()
    ended_at = models.DateTimeField(null=True, blank=True)
    duration_seconds = models.IntegerField(null=True, blank=True)
    notes = models.TextField(blank=True)

    # Sync fields
    sync_id = models.UUIDField(default=uuid.uuid4, unique=True)
    is_deleted = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    # Managers
    objects = SoftDeleteManager()
    all_objects = AllObjectsManager()

    class Meta:
        db_table = 'time_entries'
        ordering = ['-started_at']

    def __str__(self):
        return f"{self.task.title} - {self.started_at}"

    def save(self, *args, **kwargs):
        # Calculate duration if ended
        if self.ended_at and self.started_at:
            delta = self.ended_at - self.started_at
            self.duration_seconds = int(delta.total_seconds())
        super().save(*args, **kwargs)

    @property
    def is_running(self):
        """Check if this time entry is currently running."""
        return self.ended_at is None


class TaskShare(models.Model):
    """
    Sharing tasks or tags with other users.
    """
    PERMISSION_CHOICES = [
        ('viewer', 'Viewer'),
        ('editor', 'Editor'),
    ]

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    owner = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='shares_given'
    )
    shared_with = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='shares_received'
    )

    # Can share either a task or a tag
    task = models.ForeignKey(
        Task,
        on_delete=models.CASCADE,
        null=True,
        blank=True,
        related_name='shares'
    )
    tag = models.ForeignKey(
        Tag,
        on_delete=models.CASCADE,
        null=True,
        blank=True,
        related_name='shares'
    )

    permission = models.CharField(max_length=20, choices=PERMISSION_CHOICES, default='viewer')

    # Sync fields
    sync_id = models.UUIDField(default=uuid.uuid4, unique=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        db_table = 'task_shares'
        constraints = [
            models.CheckConstraint(
                check=(
                    models.Q(task__isnull=False, tag__isnull=True) |
                    models.Q(task__isnull=True, tag__isnull=False)
                ),
                name='share_task_or_tag_not_both'
            )
        ]

    def __str__(self):
        shared_item = self.task or self.tag
        return f"{shared_item} shared with {self.shared_with.email}"