import json

from django.http import JsonResponse, StreamingHttpResponse
from django.views.decorators.csrf import csrf_exempt
from django.views.decorators.http import require_http_methods
from gevent.threadpool import ThreadPool

from . import piper_engine

# One sentence per request, hard-capped — this is the load-bearing part of the
# "server never holds more than a small, transient snippet of book text"
# agreement (see CLAUDE.md), not just a client-side convention.
MAX_TEXT_LENGTH = 500

# Offloads the CPU-bound Piper inference off the gevent hub's event loop, so a
# synthesis call doesn't stall other concurrent greenlets (radio SSE, other
# requests) in the same worker the way a plain in-greenlet call would.
_synth_pool = ThreadPool(1)


def _require_auth(request):
    if not request.user.is_authenticated:
        return JsonResponse({'error': 'authentication required'}, status=401)
    return None


@csrf_exempt
@require_http_methods(['POST'])
def synthesize(request):
    err = _require_auth(request)
    if err:
        return err

    try:
        body = json.loads(request.body)
    except (json.JSONDecodeError, ValueError):
        return JsonResponse({'error': 'invalid JSON'}, status=400)

    text = body.get('text', '')
    if not isinstance(text, str) or not text.strip():
        return JsonResponse({'error': 'text required'}, status=400)
    if len(text) > MAX_TEXT_LENGTH:
        return JsonResponse({'error': f'text exceeds {MAX_TEXT_LENGTH} characters'}, status=400)

    try:
        audio = _synth_pool.apply(piper_engine.synthesize_wav, (text,))
    except Exception:
        return JsonResponse({'error': 'synthesis failed'}, status=500)

    response = StreamingHttpResponse(iter([audio]), content_type='audio/wav')
    response['Cache-Control'] = 'no-store'
    response['X-Accel-Buffering'] = 'no'
    return response