package main

import (
	"fmt"
	"net"
	"os"
	"path/filepath"
	"strings"
	"time"
	"unsafe"

	"golang.org/x/sys/unix"
)

type ethtoolIfreq struct {
	name [unix.IFNAMSIZ]byte
	data unsafe.Pointer
	_    [16]byte
}

type flagsIfreq struct {
	name  [unix.IFNAMSIZ]byte
	flags uint16
	_     [22]byte
}

type ethtoolRingparam struct {
	cmd               uint32
	rxMaxPending      uint32
	rxMiniMaxPending  uint32
	rxJumboMaxPending uint32
	txMaxPending      uint32
	rxPending         uint32
	rxMiniPending     uint32
	rxJumboPending    uint32
	txPending         uint32
}

type ethtoolCoalesce struct {
	cmd                      uint32
	rxCoalesceUsecs          uint32
	rxMaxCoalescedFrames     uint32
	rxCoalesceUsecsIrq       uint32
	rxMaxCoalescedFramesIrq  uint32
	txCoalesceUsecs          uint32
	txMaxCoalescedFrames     uint32
	txCoalesceUsecsIrq       uint32
	txMaxCoalescedFramesIrq  uint32
	statsBlockCoalesceUsecs  uint32
	useAdaptiveRxCoalesce    uint32
	useAdaptiveTxCoalesce    uint32
	pktRateLow               uint32
	rxCoalesceUsecsLow       uint32
	rxMaxCoalescedFramesLow  uint32
	txCoalesceUsecsLow       uint32
	txMaxCoalescedFramesLow  uint32
	pktRateHigh              uint32
	rxCoalesceUsecsHigh      uint32
	rxMaxCoalescedFramesHigh uint32
	txCoalesceUsecsHigh      uint32
	txMaxCoalescedFramesHigh uint32
	rateSampleInterval       uint32
}

const (
	wantGovernor      = "performance"
	wantCoalesceUsecs = 25
	wantRxRing        = 8160
	wantTxRing        = 4096
)

type checkResult struct {
	item  string
	state string
	fixed bool
	fatal bool
	err   error
}

func (r checkResult) status() string {
	switch {
	case r.err != nil:
		return paint("FAIL", cRed)
	case r.fixed:
		return paint("FIXED", cYellow)
	default:
		return paint("ok", cGreen)
	}
}

func (r checkResult) detail() string {
	if r.err != nil {
		if r.state == "" {
			return r.err.Error()
		}
		return fmt.Sprintf("%s: %v", r.state, r.err)
	}
	return r.state
}

func ethtoolCall(fd int, ifname string, data unsafe.Pointer) error {
	var ifr ethtoolIfreq
	if len(ifname) >= unix.IFNAMSIZ {
		return fmt.Errorf("interface name %q too long", ifname)
	}
	copy(ifr.name[:], ifname)
	ifr.data = data
	_, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(fd),
		uintptr(unix.SIOCETHTOOL), uintptr(unsafe.Pointer(&ifr)))
	if errno != 0 {
		return errno
	}
	return nil
}

func getRings(fd int, ifname string) (ethtoolRingparam, error) {
	rp := ethtoolRingparam{cmd: unix.ETHTOOL_GRINGPARAM}
	err := ethtoolCall(fd, ifname, unsafe.Pointer(&rp))
	return rp, err
}

func getCoalesce(fd int, ifname string) (ethtoolCoalesce, error) {
	ec := ethtoolCoalesce{cmd: unix.ETHTOOL_GCOALESCE}
	err := ethtoolCall(fd, ifname, unsafe.Pointer(&ec))
	return ec, err
}

func checkGovernor(want string) checkResult {
	res := checkResult{item: "cpu governor"}
	paths, err := filepath.Glob("/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor")
	if err != nil || len(paths) == 0 {
		res.err = fmt.Errorf("no cpufreq governors found")
		return res
	}
	var wrong []string
	counts := map[string]int{}
	for _, p := range paths {
		b, err := os.ReadFile(p)
		if err != nil {
			res.err = err
			return res
		}
		got := strings.TrimSpace(string(b))
		counts[got]++
		if got != want {
			wrong = append(wrong, p)
		}
	}
	if len(wrong) == 0 {
		res.state = fmt.Sprintf("%s on all %d cpus", want, len(paths))
		return res
	}
	var found []string
	for k, v := range counts {
		found = append(found, fmt.Sprintf("%s:%d", k, v))
	}
	for _, p := range wrong {
		if err := os.WriteFile(p, []byte(want), 0o644); err != nil {
			res.err = err
			res.state = fmt.Sprintf("could not set %s", p)
			return res
		}
	}
	res.fixed = true
	res.state = fmt.Sprintf("was %s, now %s on all %d cpus", strings.Join(found, " "), want, len(paths))
	return res
}

func checkLinkUp(fd int, ifname string) checkResult {
	res := checkResult{item: ifname + " link up"}
	var ifr flagsIfreq
	copy(ifr.name[:], ifname)
	_, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(fd),
		uintptr(unix.SIOCGIFFLAGS), uintptr(unsafe.Pointer(&ifr)))
	if errno != 0 {
		res.err = errno
		res.fatal = true
		return res
	}
	if ifr.flags&unix.IFF_UP != 0 {
		res.state = "up"
		return res
	}
	ifr.flags |= unix.IFF_UP
	_, _, errno = unix.Syscall(unix.SYS_IOCTL, uintptr(fd),
		uintptr(unix.SIOCSIFFLAGS), uintptr(unsafe.Pointer(&ifr)))
	if errno != 0 {
		res.err = errno
		res.state = "could not set IFF_UP"
		res.fatal = true
		return res
	}
	res.fixed = true
	res.state = "was down, now up"
	return res
}

func checkCarrier(ifname string, wait time.Duration) checkResult {
	res := checkResult{item: ifname + " carrier"}
	deadline := time.Now().Add(wait)
	for {
		v, ok := readUint("/sys/class/net/" + ifname + "/carrier")
		if ok && v == 1 {
			res.state = "present"
			return res
		}
		if time.Now().After(deadline) {
			res.err = fmt.Errorf("no carrier after %s", wait)
			res.fatal = true
			return res
		}
		time.Sleep(100 * time.Millisecond)
	}
}

func checkCoalesce(fd int, ifname string, rxUsecs, txUsecs uint32) checkResult {
	res := checkResult{item: ifname + " coalesce"}
	ec, err := getCoalesce(fd, ifname)
	if err != nil {
		res.err = err
		return res
	}
	desc := func(e ethtoolCoalesce) string {
		return fmt.Sprintf("adaptive rx=%d tx=%d rx-usecs=%d tx-usecs=%d",
			e.useAdaptiveRxCoalesce, e.useAdaptiveTxCoalesce, e.rxCoalesceUsecs, e.txCoalesceUsecs)
	}
	if ec.useAdaptiveRxCoalesce == 0 && ec.useAdaptiveTxCoalesce == 0 &&
		ec.rxCoalesceUsecs == rxUsecs && ec.txCoalesceUsecs == txUsecs {
		res.state = desc(ec)
		return res
	}
	was := desc(ec)
	ec.cmd = unix.ETHTOOL_SCOALESCE
	ec.useAdaptiveRxCoalesce = 0
	ec.useAdaptiveTxCoalesce = 0
	ec.rxCoalesceUsecs = rxUsecs
	ec.txCoalesceUsecs = txUsecs
	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&ec)); err != nil {
		res.err = err
		res.state = "could not set"
		return res
	}
	res.fixed = true
	res.state = fmt.Sprintf("was %s, now adaptive off rx-usecs=%d tx-usecs=%d", was, rxUsecs, txUsecs)
	return res
}

func checkRings(fd int, ifname string, rxWant, txWant uint32) (checkResult, bool) {
	res := checkResult{item: ifname + " rings"}
	rp, err := getRings(fd, ifname)
	if err != nil {
		res.err = err
		return res, false
	}
	rx := min(rxWant, rp.rxMaxPending)
	tx := min(txWant, rp.txMaxPending)
	if rp.rxPending == rx && rp.txPending == tx {
		res.state = fmt.Sprintf("rx=%d tx=%d", rp.rxPending, rp.txPending)
		return res, false
	}
	was := fmt.Sprintf("rx=%d tx=%d", rp.rxPending, rp.txPending)
	rp.cmd = unix.ETHTOOL_SRINGPARAM
	rp.rxPending = rx
	rp.txPending = tx
	if err := ethtoolCall(fd, ifname, unsafe.Pointer(&rp)); err != nil {
		res.err = err
		res.state = "could not set"
		return res, false
	}
	res.fixed = true
	res.state = fmt.Sprintf("was %s, now rx=%d tx=%d (link reset)", was, rx, tx)
	return res, true
}

func checkNoAddrs(ifname string) checkResult {
	res := checkResult{item: ifname + " unmanaged"}
	ifi, err := net.InterfaceByName(ifname)
	if err != nil {
		res.err = err
		return res
	}
	addrs, err := ifi.Addrs()
	if err != nil {
		res.err = err
		return res
	}
	var routable []string
	for _, a := range addrs {
		ipn, ok := a.(*net.IPNet)
		if !ok || ipn.IP.IsLinkLocalUnicast() {
			continue
		}
		routable = append(routable, a.String())
	}
	if len(routable) == 0 {
		res.state = "no routable addresses"
		return res
	}
	res.err = fmt.Errorf("has %s; NetworkManager or DHCP is configuring this interface",
		strings.Join(routable, ","))
	return res
}

func withIoctlSocket(fn func(fd int) []checkResult) []checkResult {
	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
	if err != nil {
		return []checkResult{{item: "ioctl socket", err: err, fatal: true}}
	}
	defer unix.Close(fd)
	return fn(fd)
}

func configureSystem(ifnames []string) []checkResult {
	return withIoctlSocket(func(fd int) []checkResult {
		out := []checkResult{checkGovernor(wantGovernor)}
		for _, ifname := range ifnames {
			out = append(out, checkLinkUp(fd, ifname))
			out = append(out, checkCoalesce(fd, ifname, wantCoalesceUsecs, wantCoalesceUsecs))

			carrierWait := 3 * time.Second
			r, reset := checkRings(fd, ifname, wantRxRing, wantTxRing)
			out = append(out, r)
			if reset {
				carrierWait = 10 * time.Second
			}
			out = append(out, checkCarrier(ifname, carrierWait))
			out = append(out, checkNoAddrs(ifname))
		}
		return out
	})
}