// +build linux

package cpu

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"

	"github.com/pkg/errors"
)

const nanoSecondsPerSecond = 1e9

// ErrNoCFSLimit is no quota limit
var ErrNoCFSLimit = errors.Errorf("no quota limit")

var clockTicksPerSecond = uint64(GetClockTicks())

// systemCPUUsage returns the host system's cpu usage in
// nanoseconds. An error is returned if the format of the underlying
// file does not match.
//
// Uses /proc/stat defined by POSIX. Looks for the cpu
// statistics line and then sums up the first seven fields
// provided. See man 5 proc for details on specific field
// information.
func systemCPUUsage() (usage uint64, err error) {
	var (
		line string
		f    *os.File
	)
	if f, err = os.Open("/proc/stat"); err != nil {
		return
	}
	bufReader := bufio.NewReaderSize(nil, 128)
	defer func() {
		bufReader.Reset(nil)
		f.Close()
	}()
	bufReader.Reset(f)
	for err == nil {
		if line, err = bufReader.ReadString('\n'); err != nil {
			err = errors.WithStack(err)
			return
		}
		parts := strings.Fields(line)
		switch parts[0] {
		case "cpu":
			if len(parts) < 8 {
				err = errors.WithStack(fmt.Errorf("bad format of cpu stats"))
				return
			}
			var totalClockTicks uint64
			for _, i := range parts[1:8] {
				var v uint64
				if v, err = strconv.ParseUint(i, 10, 64); err != nil {
					err = errors.WithStack(fmt.Errorf("error parsing cpu stats"))
					return
				}
				totalClockTicks += v
			}
			usage = (totalClockTicks * nanoSecondsPerSecond) / clockTicksPerSecond
			return
		}
	}
	err = errors.Errorf("bad stats format")
	return
}

func totalCPUUsage() (usage uint64, err error) {
	var cg *cgroup
	if cg, err = currentcGroup(); err != nil {
		return
	}
	return cg.CPUAcctUsage()
}

func perCPUUsage() (usage []uint64, err error) {
	var cg *cgroup
	if cg, err = currentcGroup(); err != nil {
		return
	}
	return cg.CPUAcctUsagePerCPU()
}

func cpuSets() (sets []uint64, err error) {
	var cg *cgroup
	if cg, err = currentcGroup(); err != nil {
		return
	}
	return cg.CPUSetCPUs()
}

func cpuQuota() (quota int64, err error) {
	var cg *cgroup
	if cg, err = currentcGroup(); err != nil {
		return
	}
	return cg.CPUCFSQuotaUs()
}

func cpuPeriod() (peroid uint64, err error) {
	var cg *cgroup
	if cg, err = currentcGroup(); err != nil {
		return
	}
	return cg.CPUCFSPeriodUs()
}

func cpuFreq() uint64 {
	lines, err := readLines("/proc/cpuinfo")
	if err != nil {
		return 0
	}
	for _, line := range lines {
		fields := strings.Split(line, ":")
		if len(fields) < 2 {
			continue
		}
		key := strings.TrimSpace(fields[0])
		value := strings.TrimSpace(fields[1])
		if key == "cpu MHz" || key == "clock" {
			// treat this as the fallback value, thus we ignore error
			if t, err := strconv.ParseFloat(strings.Replace(value, "MHz", "", 1), 64); err == nil {
				return uint64(t * 1000.0 * 1000.0)
			}
		}
	}
	return 0
}

func cpuMaxFreq() uint64 {
	feq := cpuFreq()
	data, err := readFile("/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq")
	if err != nil {
		return feq
	}
	// override the max freq from /proc/cpuinfo
	cfeq, err := parseUint(data)
	if err == nil {
		feq = cfeq
	}
	return feq
}