"""Folders of podcasts and audiobooks (docs/library.md): like tags, any number per
subscription (PodcastFeed.folders), shown as filter chips in their order
(PodcastSettings.folder_order). Renaming onto an existing name merges; deleting
a folder leaves its subscriptions where they are."""
import json

from django.http import JsonResponse
from django.views.decorators.csrf import csrf_exempt
from django.views.decorators.http import require_http_methods

from .models import PodcastFeed, PodcastSettings

MAX_FOLDERS = 20
MAX_NAME = 100


def clean_name(value):
    return ' '.join(str(value or '').split())[:MAX_NAME]


def clean_list(value):
    """A list of folder names: trimmed, without empties and doubles (first spelling wins)."""
    if not isinstance(value, list):
        raise ValueError
    out, seen = [], set()
    for v in value:
        if not isinstance(v, str):
            raise ValueError
        name = clean_name(v)
        if name and name.casefold() not in seen:
            seen.add(name.casefold())
            out.append(name)
    return out[:MAX_FOLDERS]


def set_folders(feed, names):
    """The feed's folders, and `folder` (the first) for older clients."""
    feed.folders = names
    feed.folder = names[0] if names else ''


def _body(request):
    try:
        body = json.loads(request.body or b'{}')
    except (json.JSONDecodeError, ValueError):
        return None
    return body if isinstance(body, dict) else None


def _data(user):
    counts = {}
    for names in PodcastFeed.objects.filter(user=user).values_list('folders', flat=True):
        for n in names or []:
            counts[n] = counts.get(n, 0) + 1
    order = [n for n in PodcastSettings.for_user(user).folder_order if n in counts]
    rest = sorted((n for n in counts if n not in order), key=str.casefold)
    return {'order': order + rest, 'folders': [{'name': n, 'count': counts[n]} for n in order + rest]}


@csrf_exempt
@require_http_methods(['GET', 'POST'])
def folders(request):
    """GET {order, folders: [{name, count}]}; POST {order: [names]} sets the chip order."""
    if not request.user.is_authenticated:
        return JsonResponse({'error': 'authentication required'}, status=401)
    if request.method == 'POST':
        body = _body(request)
        try:
            order = clean_list((body or {}).get('order'))
        except ValueError:
            return JsonResponse({'error': 'order: a list of names'}, status=400)
        s = PodcastSettings.for_user(request.user)
        s.folder_order = order
        s.save(update_fields=['folder_order'])
    return JsonResponse(_data(request.user))


def _rewrite(user, fn):
    for feed in PodcastFeed.objects.filter(user=user).only('id', 'folders', 'folder'):
        names = fn(list(feed.folders or []))
        if names != (feed.folders or []):
            set_folders(feed, clean_list(names))
            feed.save(update_fields=['folders', 'folder'])


@csrf_exempt
@require_http_methods(['POST'])
def rename_folder(request):
    """{old, new}: every subscription in `old` is in `new` instead (merged if it exists)."""
    if not request.user.is_authenticated:
        return JsonResponse({'error': 'authentication required'}, status=401)
    body = _body(request) or {}
    old, new = clean_name(body.get('old')), clean_name(body.get('new'))
    if not old or not new:
        return JsonResponse({'error': 'old and new required'}, status=400)
    _rewrite(request.user, lambda names: [new if n == old else n for n in names])
    s = PodcastSettings.for_user(request.user)
    s.folder_order = clean_list([new if n == old else n for n in s.folder_order])
    s.save(update_fields=['folder_order'])
    return JsonResponse(_data(request.user))


@csrf_exempt
@require_http_methods(['POST'])
def delete_folder(request):
    """{name}: the folder goes, its subscriptions stay."""
    if not request.user.is_authenticated:
        return JsonResponse({'error': 'authentication required'}, status=401)
    name = clean_name((_body(request) or {}).get('name'))
    if not name:
        return JsonResponse({'error': 'name required'}, status=400)
    _rewrite(request.user, lambda names: [n for n in names if n != name])
    s = PodcastSettings.for_user(request.user)
    s.folder_order = [n for n in s.folder_order if n != name]
    s.save(update_fields=['folder_order'])
    return JsonResponse(_data(request.user))