// Package webrtc is the datarhei Core subsystem that turns WebRTC into
// a first-class output alongside RTMP, SRT, and HLS. It owns the WHEP
// HTTP handler, wires FFmpeg's RTP output into per-process Pion
// Sources, and tracks active peer connections.
//
// See docs/design/2026-04-17-datarhei-dragon-fork-m2-webrtc-core-integration.md
// for the full design.
package webrtc

import (
	"fmt"
	"net"
)

// Alloc binds :0 on loopback UDPv4, records the port the kernel assigned,
// closes the socket, and returns the port number.
//
// The caller is expected to re-bind that exact port via
// core/webrtc.NewSourceOn immediately. There is a microsecond-sized race
// window where another process on the host could grab the port; if that
// happens, the caller's rebind will fail and the error should be
// propagated. In practice this is rare enough that a retry loop would be
// unnecessary churn.
func Alloc() (int, error) {
	c, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 0})
	if err != nil {
		return 0, fmt.Errorf("webrtc: portalloc: %w", err)
	}
	defer c.Close()
	return c.LocalAddr().(*net.UDPAddr).Port, nil
}