"""Reusable file-tree permission, validation and serialization helpers."""
import uuid
from django.core.exceptions import ValidationError
from django.http import Http404
from .models import DriveItem


from rest_framework.permissions import AllowAny, IsAuthenticated
from rest_framework.response import Response
from .models import DriveItem


def error(message, code=400):
    return Response({'detail':message}, status=code)


def item_info(item):
    return {
        'id':str(item.id), 'name':item.name, 'is_folder':item.is_folder,
        'size':item.size,'mime_type':item.mime_type,'owner_id':item.owner_id,
        'owner':item.owner.username,'parent':str(item.parent_id) if item.parent_id else None,
        'is_shared':item.is_shared,'is_starred':item.is_starred,
        'trashed_at':item.trashed_at.isoformat() if item.trashed_at else None,
        'created_at':item.created_at.isoformat(),'updated_at':item.updated_at.isoformat(),
    }


def get_item(pk):
    try:
        return DriveItem.objects.select_related('owner','parent').get(pk=pk)
    except (DriveItem.DoesNotExist,ValueError,ValidationError):
        raise Http404


def chain(item):
    ancestors=[]
    visited=set()
    while item is not None:
        if item.pk in visited:
            raise Http404
        visited.add(item.pk)
        ancestors.append(item)
        item=item.parent
    return ancestors


def readable(item, user, allow_trashed=False):
    ancestors=chain(item)
    if not allow_trashed and any(n.trashed_at is not None for n in ancestors):
        return False
    if user.is_staff or user.is_superuser or item.owner_id == user.pk:
        return True
    return bool(ancestors[-1].is_shared and ancestors[-1].owner_id == item.owner_id)


def writable(item,user):
    return user.is_staff or user.is_superuser or item.owner_id == user.pk


def valid_name(name):
    if not isinstance(name,str) or not name.strip() or len(name)>255:
        raise ValueError('Nom invalide (1 à 255 caractères).')
    name=name.strip()
    if name in ('.','..') or any(c in name for c in ('/','\\','\x00','\r','\n')):
        raise ValueError('Ce nom contient des caractères interdits.')
    return name.strip()


def target_parent(parent_id, user, owner_id=None):
    if not parent_id:
        return None
    try:
        parent=DriveItem.objects.select_related('parent').get(pk=uuid.UUID(str(parent_id)))
    except (ValueError,DriveItem.DoesNotExist,AttributeError):
        raise ValueError('Dossier de destination introuvable.')
    if not parent.is_folder or not readable(parent,user) or not writable(parent,user):
        raise PermissionError('Dossier de destination inaccessible en écriture.')
    if owner_id is not None and parent.owner_id != owner_id:
        raise PermissionError('Le propriétaire doit être identique.')
    return parent


def descendant_files(node):
    # Collect all physical paths before cascade delete.
    files=[]
    pending=[node.pk]
    while pending:
        batch=pending[:500];pending=pending[500:]
        children=list(DriveItem.objects.filter(parent_id__in=batch).values_list('pk','is_folder','storage_key'))
        pending.extend(row[0] for row in children)
        for _,is_folder,key in children:
            if not is_folder and key: files.append(key)
    if not node.is_folder and node.storage_key:files.append(node.storage_key)
    return files