//go:build linux

package processor

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"regexp"
	"strconv"
	"strings"
)

var numberRegex *regexp.Regexp = regexp.MustCompile(`\d+`)

func getLinuxCpuInfo() (ProcessorInformation, error) {
	procFile, err := os.Open("/proc/stat")
	if err != nil {
		return ProcessorInformation{}, fmt.Errorf("Could not find /proc/stat. Are you sure you are on linux?")
	}
	defer procFile.Close()

	fileReader := bufio.NewScanner(procFile)

	var idleTime uint64
	var nice uint64
	var kernelTime uint64
	var userTime uint64
	var iowait uint64
	var irq uint64
	var softirq uint64

	for linesExtracted := 0; fileReader.Scan(); linesExtracted++ {
		line := fileReader.Text()

		if strings.HasPrefix(line, "cpu ") {
			/*
			* fields[0] name of the core, we are extracting the first row so "total cpu", we don't care about subsequent cores (yet?)
			* fields[1] a useless space to skip
			* fields[2] cpu ticks spent on user processes
			* fields[3] cpu ticks spent on low priority processes
			* fields[4] cpu ticks spent on kernel processes
			* fields[5] idle time measured in cpu ticks
			* fields[6] cpu ticks spent on iowait (disk/network)
			* fields[7] irq (hardware interrupt)
			* fields[8] softirq (software interrupt)
			* fields[9] steal < for virtualization
			* fields[10] guest < for virtualization
			* fields[11] guest_nice < for virtualization
			 */
			fields := strings.Split(line, " ")

			userTime, _ = strconv.ParseUint(fields[2], 10, 64)
			nice, _ = strconv.ParseUint(fields[3], 10, 64)
			kernelTime, _ = strconv.ParseUint(fields[4], 10, 64)
			idleTime, _ = strconv.ParseUint(fields[5], 10, 64)
			iowait, _ = strconv.ParseUint(fields[6], 10, 64)  // a type of idle time
			irq, _ = strconv.ParseUint(fields[7], 10, 64)     // active time
			softirq, _ = strconv.ParseUint(fields[8], 10, 64) // active time
		}

		// ? Possibly extract more rows later on, for example breaking down each core and not just the combined value
		if linesExtracted >= 1 {
			break
		}
	}

	if fileReader.Err() != nil {
		return ProcessorInformation{}, fmt.Errorf("There was an error while reading /proc/stat. Error: %v", fileReader.Err())
	}

	return ProcessorInformation{
		IdleTimeSinceBoot:   idleTime + iowait,
		KernelTimeSinceBoot: kernelTime + irq + softirq,
		UserTimeSinceBoot:   userTime + nice,
	}, nil
}

func GetCPUInformation() ProcessorInformation {
	info, err := getLinuxCpuInfo()
	if err != nil {
		log.Printf("Could not read processor info. Error: %v", err)
		return ProcessorInformation{}
	}
	return info
}