//go:build darwin || linux

package gateway

import (
	"io"
	"net"
	"os"
	"runtime"
	"strconv"
	"strings"
	"syscall"
)

func qualificationProcessCPUSeconds() float64 {
	var usage syscall.Rusage
	if syscall.Getrusage(syscall.RUSAGE_SELF, &usage) != nil {
		return -1
	}
	return float64(usage.Utime.Sec+usage.Stime.Sec) +
		float64(usage.Utime.Usec+usage.Stime.Usec)/1_000_000
}

func qualificationProviderVideoSocketDiagnostics(connection *net.UDPConn) (receiveBuffer int, receiveBufferAvailable bool, kernelDrops uint64, kernelDropsAvailable bool) {
	if connection == nil {
		return 0, false, 0, false
	}
	raw, err := connection.SyscallConn()
	if err != nil {
		return 0, false, 0, false
	}
	var inode uint64
	var socketErr error
	if err := raw.Control(func(descriptor uintptr) {
		receiveBuffer, socketErr = syscall.GetsockoptInt(int(descriptor), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
		if runtime.GOOS == "linux" {
			var stat syscall.Stat_t
			if statErr := syscall.Fstat(int(descriptor), &stat); statErr == nil {
				inode = stat.Ino
			}
		}
	}); err != nil || socketErr != nil {
		return 0, false, 0, false
	}
	receiveBufferAvailable = true
	if runtime.GOOS == "linux" {
		kernelDrops, kernelDropsAvailable = qualificationLinuxUDPDrops(inode)
	}
	return receiveBuffer, receiveBufferAvailable, kernelDrops, kernelDropsAvailable
}

func qualificationLinuxUDPDrops(inode uint64) (uint64, bool) {
	if inode == 0 {
		return 0, false
	}
	inodeText := strconv.FormatUint(inode, 10)
	for _, path := range []string{"/proc/net/udp", "/proc/net/udp6"} {
		file, err := os.Open(path)
		if err != nil {
			continue
		}
		raw, readErr := io.ReadAll(io.LimitReader(file, 1<<20))
		closeErr := file.Close()
		if readErr != nil || closeErr != nil {
			continue
		}
		for _, line := range strings.Split(string(raw), "\n") {
			fields := strings.Fields(line)
			if len(fields) < 11 || fields[9] != inodeText {
				continue
			}
			drops, err := strconv.ParseUint(fields[len(fields)-1], 10, 64)
			if err != nil {
				return 0, false
			}
			return drops, true
		}
	}
	return 0, false
}