"""
Sync views for KeepItGoing.

Handles data synchronization between clients and server.
"""

import logging
import uuid
from datetime import datetime
from django.utils import timezone
from django.utils.dateparse import parse_datetime
from rest_framework import status
from rest_framework.decorators import api_view, permission_classes
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response

from tasks.models import Task, Tag, TimeEntry
from tasks.serializers import (
    TaskSerializer,
    TagSerializer,
    TimeEntrySerializer,
    TaskSyncSerializer,
    TagSyncSerializer,
    TimeEntrySyncSerializer,
)
from .models import SyncLog, SyncConflict
from .serializers import SyncConflictSerializer

logger = logging.getLogger(__name__)


@api_view(['POST'])
@permission_classes([IsAuthenticated])
def sync(request):
    """
    Main sync endpoint.

    Accepts client changes and returns server changes since last sync.

    Request body:
    {
        "device_id": "unique-device-id",
        "last_sync_token": "previous-sync-token-or-null",
        "changes": {
            "tasks": [...],
            "tags": [...],
            "time_entries": [...]
        }
    }

    Response:
    {
        "sync_token": "new-sync-token",
        "server_changes": {
            "tasks": [...],
            "tags": [...],
            "time_entries": [...]
        },
        "conflicts": [...]
    }
    """
    user = request.user
    device_id = request.data.get('device_id')
    last_sync_token = request.data.get('last_sync_token')
    changes = request.data.get('changes', {})

    # Debug logging
    task_changes = changes.get('tasks', [])
    deleted_task_count = sum(1 for t in task_changes if t.get('is_deleted', False))
    logger.debug(f"Received sync request with {len(task_changes)} tasks, {deleted_task_count} marked as deleted")

    if not device_id:
        return Response(
            {'error': 'device_id is required'},
            status=status.HTTP_400_BAD_REQUEST
        )

    # Get last sync time
    last_sync_at = None
    if last_sync_token:
        try:
            sync_log = SyncLog.objects.get(sync_token=last_sync_token, user=user)
            last_sync_at = sync_log.last_sync_at
        except SyncLog.DoesNotExist:
            pass  # Full sync

    # Process incoming changes
    conflicts = []
    conflicts.extend(process_tag_changes(user, changes.get('tags', []), last_sync_at))
    conflicts.extend(process_task_changes(user, changes.get('tasks', []), last_sync_at))
    conflicts.extend(process_time_entry_changes(user, changes.get('time_entries', []), last_sync_at))

    # Get server changes since last sync
    server_changes = get_server_changes(user, last_sync_at)

    # Generate new sync token
    new_sync_token = str(uuid.uuid4())
    current_time = timezone.now()

    # Update or create sync log
    SyncLog.objects.update_or_create(
        user=user,
        device_id=device_id,
        defaults={
            'last_sync_at': current_time,
            'sync_token': new_sync_token,
        }
    )

    return Response({
        'sync_token': new_sync_token,
        'server_time': current_time.isoformat(),
        'server_changes': server_changes,
        'conflicts': SyncConflictSerializer(conflicts, many=True).data,
    })


def process_task_changes(user, task_changes, last_sync_at):
    """Process task changes from client."""
    conflicts = []

    for task_data in task_changes:
        sync_id = task_data.get('sync_id')
        is_deleted = task_data.get('is_deleted', False)

        # Debug logging
        if is_deleted:
            logger.debug(f"Received deletion for task sync_id: {sync_id}")

        try:
            existing = Task.all_objects.get(sync_id=sync_id, user=user)

            if is_deleted:
                # Soft delete the task
                logger.debug(f"Soft deleting task: {existing.title} (id: {existing.id})")
                existing.is_deleted = True
                existing.save()
                logger.debug(f"Task soft deleted successfully")
                continue

            # Check for conflict
            if last_sync_at and existing.updated_at > last_sync_at:
                # Server version was modified since last sync
                conflict = SyncConflict.objects.create(
                    user=user,
                    entity_type='task',
                    entity_id=existing.id,
                    local_data=task_data,
                    server_data=TaskSerializer(existing).data,
                )
                conflicts.append(conflict)
            else:
                # Safe to update
                update_task_from_data(existing, task_data)

        except Task.DoesNotExist:
            if not is_deleted:
                # Create new task
                create_task_from_data(user, task_data)

    return conflicts


def process_tag_changes(user, tag_changes, last_sync_at):
    """Process tag changes from client."""
    conflicts = []

    for tag_data in tag_changes:
        sync_id = tag_data.get('sync_id')
        is_deleted = tag_data.get('is_deleted', False)

        try:
            existing = Tag.all_objects.get(sync_id=sync_id, user=user)

            if is_deleted:
                existing.is_deleted = True
                existing.save()
                continue

            if last_sync_at and existing.updated_at > last_sync_at:
                conflict = SyncConflict.objects.create(
                    user=user,
                    entity_type='tag',
                    entity_id=existing.id,
                    local_data=tag_data,
                    server_data=TagSerializer(existing).data,
                )
                conflicts.append(conflict)
            else:
                existing.name = tag_data.get('name', existing.name)
                existing.description = tag_data.get('description', existing.description)
                existing.color = tag_data.get('color', existing.color)
                existing.icon = tag_data.get('icon', existing.icon)
                existing.sort_order = tag_data.get('sort_order', existing.sort_order)
                existing.is_archived = tag_data.get('is_archived', existing.is_archived)
                existing.save()

        except Tag.DoesNotExist:
            if not is_deleted:
                Tag.objects.create(
                    user=user,
                    sync_id=sync_id,
                    name=tag_data.get('name'),
                    description=tag_data.get('description', ''),
                    color=tag_data.get('color', '#3B82F6'),
                    icon=tag_data.get('icon', ''),
                    sort_order=tag_data.get('sort_order', 0),
                    is_archived=tag_data.get('is_archived', False),
                )

    return conflicts


def process_time_entry_changes(user, entry_changes, last_sync_at):
    """Process time entry changes from client."""
    conflicts = []

    logger.debug(f"Processing {len(entry_changes)} time entry changes")

    for entry_data in entry_changes:
        sync_id = entry_data.get('sync_id')
        is_deleted = entry_data.get('is_deleted', False)
        logger.debug(f"Time entry sync_id: {sync_id}, is_deleted: {is_deleted}")

        try:
            existing = TimeEntry.all_objects.get(sync_id=sync_id, user=user)

            if is_deleted:
                existing.is_deleted = True
                existing.save()
                continue

            if last_sync_at and existing.updated_at > last_sync_at:
                conflict = SyncConflict.objects.create(
                    user=user,
                    entity_type='time_entry',
                    entity_id=existing.id,
                    local_data=entry_data,
                    server_data=TimeEntrySerializer(existing).data,
                )
                conflicts.append(conflict)
            else:
                # Parse datetime strings if needed
                started_at = entry_data.get('started_at', existing.started_at)
                if isinstance(started_at, str):
                    started_at = parse_datetime(started_at)

                ended_at = entry_data.get('ended_at', existing.ended_at)
                if ended_at and isinstance(ended_at, str):
                    ended_at = parse_datetime(ended_at)

                existing.started_at = started_at
                existing.ended_at = ended_at
                existing.notes = entry_data.get('notes', existing.notes)
                existing.save()

        except TimeEntry.DoesNotExist:
            if not is_deleted:
                task_sync_id = entry_data.get('task_sync_id')
                logger.debug(f"Creating new time entry for task_sync_id: {task_sync_id}")
                logger.debug(f"  started_at: {entry_data.get('started_at')}, ended_at: {entry_data.get('ended_at')}")
                try:
                    task = Task.objects.get(sync_id=task_sync_id, user=user)

                    # Parse datetime strings to datetime objects
                    started_at = entry_data.get('started_at')
                    if isinstance(started_at, str):
                        started_at = parse_datetime(started_at)

                    ended_at = entry_data.get('ended_at')
                    if ended_at and isinstance(ended_at, str):
                        ended_at = parse_datetime(ended_at)

                    new_entry = TimeEntry.objects.create(
                        user=user,
                        task=task,
                        sync_id=sync_id,
                        started_at=started_at,
                        ended_at=ended_at,
                        notes=entry_data.get('notes', ''),
                    )
                    logger.debug(f"Created time entry: {new_entry.id}, duration_seconds: {new_entry.duration_seconds}")
                except Task.DoesNotExist:
                    logger.debug(f"Task not found for sync_id: {task_sync_id}")
                    pass  # Skip if task doesn't exist

    return conflicts


def update_task_from_data(task, data):
    """Update a task from sync data."""
    task.title = data.get('title', task.title)
    task.description = data.get('description', task.description)
    task.status = data.get('status', task.status)
    task.priority = data.get('priority', task.priority)
    task.due_date = data.get('due_date', task.due_date)
    task.due_time = data.get('due_time', task.due_time)
    task.reminder_at = data.get('reminder_at', task.reminder_at)
    task.recurrence = data.get('recurrence', task.recurrence)
    task.recurrence_rule = data.get('recurrence_rule', task.recurrence_rule)
    task.sort_order = data.get('sort_order', task.sort_order)

    task.save()

    # Handle tags
    tag_sync_ids = data.get('tag_sync_ids', [])
    if tag_sync_ids is not None:
        tags = Tag.objects.filter(sync_id__in=tag_sync_ids, user=task.user)
        task.tags.set(tags)


def create_task_from_data(user, data):
    """Create a new task from sync data."""
    parent = None
    parent_sync_id = data.get('parent_sync_id')
    if parent_sync_id:
        try:
            parent = Task.all_objects.get(sync_id=parent_sync_id, user=user)
        except Task.DoesNotExist:
            pass

    # Get sync_id and convert to UUID if provided as string
    sync_id = data.get('sync_id')
    if sync_id and isinstance(sync_id, str):
        sync_id = uuid.UUID(sync_id)

    task = Task.objects.create(
        user=user,
        sync_id=sync_id,
        parent=parent,
        title=data.get('title'),
        description=data.get('description', ''),
        status=data.get('status', 'pending'),
        priority=data.get('priority', 'medium'),
        due_date=data.get('due_date'),
        due_time=data.get('due_time'),
        reminder_at=data.get('reminder_at'),
        recurrence=data.get('recurrence', 'none'),
        recurrence_rule=data.get('recurrence_rule', ''),
        sort_order=data.get('sort_order', 0),
    )

    # Handle tags
    tag_sync_ids = data.get('tag_sync_ids', [])
    if tag_sync_ids:
        tags = Tag.objects.filter(sync_id__in=tag_sync_ids, user=user)
        task.tags.set(tags)

    return task


def get_server_changes(user, last_sync_at):
    """Get all changes on server since last sync."""
    logger.debug(f"get_server_changes: last_sync_at={last_sync_at}")
    filter_kwargs = {'user': user}

    # For incremental sync, filter by updated_at
    # IMPORTANT: Use all_objects to include deleted items so clients can delete them too
    if last_sync_at:
        filter_kwargs['updated_at__gt'] = last_sync_at
        tasks = Task.all_objects.filter(**filter_kwargs).prefetch_related('tags')
        tags = Tag.all_objects.filter(**filter_kwargs)
        time_entries = TimeEntry.all_objects.filter(**filter_kwargs)
    else:
        # Full sync - send everything (including deleted items for cleanup)
        tasks = Task.all_objects.filter(user=user).prefetch_related('tags')
        tags = Tag.all_objects.filter(user=user)
        time_entries = TimeEntry.all_objects.filter(user=user)

    logger.debug(f"Returning {len(tasks)} tasks, {len(tags)} tags, {len(time_entries)} time entries")
    if time_entries:
        logger.debug(f"Time entries being sent to client:")
        for entry in time_entries:
            logger.debug(f"  sync_id: {entry.sync_id}, task: {entry.task.title}, duration: {entry.duration_seconds}s, updated_at: {entry.updated_at}")

    return {
        'tasks': TaskSyncSerializer(tasks, many=True).data,
        'tags': TagSyncSerializer(tags, many=True).data,
        'time_entries': TimeEntrySyncSerializer(time_entries, many=True).data,
    }


@api_view(['GET'])
@permission_classes([IsAuthenticated])
def get_conflicts(request):
    """Get pending sync conflicts for user."""
    conflicts = SyncConflict.objects.filter(
        user=request.user,
        status='pending'
    )
    return Response(SyncConflictSerializer(conflicts, many=True).data)


@api_view(['POST'])
@permission_classes([IsAuthenticated])
def resolve_conflict(request, conflict_id):
    """
    Resolve a sync conflict.

    Request body:
    {
        "resolution": "local" | "server" | "merged",
        "merged_data": {...}  // Only if resolution is "merged"
    }
    """
    try:
        conflict = SyncConflict.objects.get(
            id=conflict_id,
            user=request.user,
            status='pending'
        )
    except SyncConflict.DoesNotExist:
        return Response(
            {'error': 'Conflict not found'},
            status=status.HTTP_404_NOT_FOUND
        )

    resolution = request.data.get('resolution')

    if resolution == 'local':
        # Apply local changes
        apply_conflict_data(conflict.entity_type, conflict.entity_id, conflict.local_data)
        conflict.status = 'resolved_local'
    elif resolution == 'server':
        # Keep server version (no action needed)
        conflict.status = 'resolved_server'
    elif resolution == 'merged':
        merged_data = request.data.get('merged_data')
        if not merged_data:
            return Response(
                {'error': 'merged_data is required for merged resolution'},
                status=status.HTTP_400_BAD_REQUEST
            )
        apply_conflict_data(conflict.entity_type, conflict.entity_id, merged_data)
        conflict.status = 'resolved_merged'
    else:
        return Response(
            {'error': 'Invalid resolution type'},
            status=status.HTTP_400_BAD_REQUEST
        )

    conflict.resolved_at = timezone.now()
    conflict.save()

    return Response({'status': 'resolved'})


def apply_conflict_data(entity_type, entity_id, data):
    """Apply conflict resolution data to entity."""
    if entity_type == 'task':
        try:
            task = Task.objects.get(id=entity_id)
            update_task_from_data(task, data)
        except Task.DoesNotExist:
            pass
    elif entity_type == 'tag':
        try:
            tag = Tag.objects.get(id=entity_id)
            tag.name = data.get('name', tag.name)
            tag.description = data.get('description', tag.description)
            tag.color = data.get('color', tag.color)
            tag.icon = data.get('icon', tag.icon)
            tag.sort_order = data.get('sort_order', tag.sort_order)
            tag.is_archived = data.get('is_archived', tag.is_archived)
            tag.save()
        except Tag.DoesNotExist:
            pass