deltacast-sdi-recorder/backend/app/recorders/scte35.py

import struct
import binascii
import asyncio
import aiohttp
import logging
from datetime import datetime
from typing import Optional
from ..models import SCTE35Marker

logger = logging.getLogger(__name__)


def _encode_33bit_pts(value: int) -> bytes:
    """Encode 33-bit PTS value into 5 bytes per MPEG-2 spec."""
    byte1 = ((value >> 30) & 0x07) << 1 | 0x01  # top 3 bits + marker
    byte2 = (value >> 22) & 0xFF
    byte3 = ((value >> 15) & 0x7F) << 1 | 0x01  # 7 bits + marker
    byte4 = (value >> 7) & 0xFF
    byte5 = (value & 0x7F) << 1 | 0x01  # bottom 7 bits + marker
    return struct.pack('>BBBBB', byte1, byte2, byte3, byte4, byte5)


class SCTE35Manager:
    """Manage SCTE35 splice insert cues for broadcast recording."""
    
    def __init__(self):
        """Initialize the SCTE35 manager with empty history."""
        self._marker_history: list[SCTE35Marker] = []
    
    def encode_splice_insert(
        self,
        event_id: int,
        duration_seconds: float,
        pts_time: int = 0,
        out_of_network: bool = True,
        splice_immediate: bool = False
    ) -> bytes:
        """
        Encode a SCTE35 splice_insert command as binary bytes.
        Returns the binary SCTE35 cue.
        """
        if not (0 <= event_id <= 0xFFFFFFFF):
            raise ValueError(f"event_id must be a 32-bit unsigned integer (0-4294967295), got {event_id}")
        if duration_seconds < 0:
            raise ValueError(f"duration_seconds must be non-negative, got {duration_seconds}")

        flags = 0x00
        if out_of_network:
            flags |= 0x80
        flags |= 0x40  # program_splice_flag
        
        if duration_seconds > 0:
            flags |= 0x20  # duration_flag
        
        if splice_immediate:
            flags |= 0x10

        splice_cmd = struct.pack('>I', event_id)
        splice_cmd += struct.pack('>B', 0x00)  # cancel_indicator
        splice_cmd += struct.pack('>B', flags)
        
        if not splice_immediate:
            pts_90k = pts_time * 90000
            pts_bytes = _encode_33bit_pts(pts_90k)
            splice_cmd += pts_bytes
        
        if duration_seconds > 0:
            dur_90k = int(duration_seconds * 90000)
            duration_byte = 0xFE  # auto_return=1
            splice_cmd += struct.pack('>B', duration_byte)
            dur_bytes = _encode_33bit_pts(dur_90k)
            splice_cmd += dur_bytes
        
        splice_cmd += struct.pack('>H', 0x0001)  # unique_program_id
        splice_cmd += struct.pack('>B', 0x00)   # avail_num
        splice_cmd += struct.pack('>B', 0x00)   # avails_expected
        
        splice_cmd_length = len(splice_cmd)
        
        section = struct.pack('>B', 0xFC)
        section += struct.pack('>B', 0x30)
        
        payload = struct.pack('>B', 0x00)  # protocol_version
        payload += struct.pack('>B', 0x00)  # encrypted_packet
        payload += struct.pack('>5s', b'\x00\x00\x00\x00\x00')  # PTS adjustment
        payload += struct.pack('>B', 0x00)  # CW index
        payload += struct.pack('>H', 0xFFF0)  # tier
        payload += struct.pack('>H', splice_cmd_length)
        payload += splice_cmd
        payload += struct.pack('>H', 0x0000)  # descriptor_loop_length
        
        section_length = len(payload)
        section += struct.pack('>H', section_length)
        section += payload
        
        crc = binascii.crc32(section) & 0xFFFFFFFF
        section += struct.pack('>I', crc)
        
        return section
    
    async def inject_marker(
        self,
        event_id: int,
        duration_seconds: float,
        webhook_url: Optional[str] = None,
        out_of_network: bool = True,
        splice_immediate: bool = False,
        port_index: Optional[int] = None,
        srt_destination_url: Optional[str] = None,
    ) -> SCTE35Marker:
        """
        Create SCTE35 marker, trigger webhook if configured, add to history.
        
        Args:
            event_id: Unique identifier for the splice event
            duration_seconds: Duration of the ad break in seconds
            webhook_url: Optional webhook URL to POST marker data to
            out_of_network: Whether this is an out-of-network splice
            splice_immediate: Whether splice should happen immediately
            port_index: Which port this marker is for (None = global/all)
            srt_destination_url: Target specific SRT destination (None = all)
        
        Returns:
            The created SCTE35Marker object
        """
        cue_bytes = self.encode_splice_insert(
            event_id=event_id,
            duration_seconds=duration_seconds,
            out_of_network=out_of_network,
            splice_immediate=splice_immediate
        )
        
        marker = SCTE35Marker(
            event_id=str(event_id),
            duration_seconds=int(duration_seconds),
            out_of_network=out_of_network,
            splice_immediate=splice_immediate,
            timestamp=datetime.utcnow(),
            webhook_url=webhook_url,
            port_index=port_index,
            srt_destination_url=srt_destination_url,
        )
        
        self._marker_history.append(marker)
        
        if webhook_url:
            try:
                await self._trigger_webhook(marker, cue_bytes)
            except Exception as e:
                logger.error(f"Webhook trigger failed for event_id {event_id}: {e}")
        
        return marker
    
    async def _trigger_webhook(self, marker: SCTE35Marker, cue_bytes: bytes) -> None:
        """POST JSON payload to webhook_url with marker metadata."""
        if not marker.webhook_url:
            return
        
        payload = {
            "event_id": marker.event_id,
            "duration_seconds": marker.duration_seconds,
            "out_of_network": marker.out_of_network,
            "splice_immediate": marker.splice_immediate,
            "timestamp": marker.timestamp.isoformat(),
            "cue_hex": cue_bytes.hex(),
            "port_index": marker.port_index,
            "srt_destination_url": marker.srt_destination_url,
        }
        
        async with aiohttp.ClientSession() as session:
            async with session.post(marker.webhook_url, json=payload) as response:
                if response.status != 200:
                    logger.warning(f"Webhook returned status {response.status}")
    
    def get_marker_history(self) -> list[SCTE35Marker]:
        """Return all markers in history as a copy."""
        return list(self._marker_history)
    
    def clear_history(self) -> None:
        """Clear the marker history."""
        self._marker_history.clear()