package main

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"time"

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

const (
	bcmI2CWrite = 0xAC
	bcmI2CRead  = 0xAD

	bcmMMDVendor uint16 = 0x1E
	bcmRegCmd    uint16 = 0x4005
	bcmRegStatus uint16 = 0x4037
	bcmRegData1  uint16 = 0x4038

	bcmStInProgress uint16 = 0x0002
	bcmStPass       uint16 = 0x0004
	bcmStError      uint16 = 0x0008
	bcmStBusy       uint16 = 0xBBBB

	bcmCmdGetPairSwap uint16 = 0x8000
	bcmCmdSetEEEMode  uint16 = 0x8009
	bcmCmdSetJumbo    uint16 = 0x801C
	bcmCmdGetSNR      uint16 = 0x8030

	bcmRegECDCtrl   uint16 = 0x4006
	bcmRegECDResult uint16 = 0xA896
	bcmRegECDLen    uint16 = 0xA897

	bcmPHYIDHi = 0x3590
	bcmPHYIDLo = 0x5081

	bcmReadDelayUs  = 3000
	bcmRetryDelayUs = 10000

	bcmStatusPoll = 100 * time.Millisecond
	// Covers the handler's documented 2 s freeze during 10GBASE-T training.
	bcmStatusTimeout = 3 * time.Second

	ecdPoll     = 200 * time.Millisecond
	ecdDeadline = 50 * time.Second

	pairIdentityMap = 0xE4
)

const (
	pairOK    = 1
	pairOpen  = 2
	pairShort = 3
	pairXtalk = 4
)

var pairVerdicts = map[int]string{
	pairOK: "ok", pairOpen: "OPEN", pairShort: "SHORT", pairXtalk: "XTALK",
}

type bcm struct {
	ifname string
	path   string

	// Every method holds it for its whole logical operation: exactly one
	// host-side conversation with the module at a time, by construction.
	mu sync.Mutex
}

func openBCM(ifname string) (*bcm, error) {
	devLink, err := os.Readlink("/sys/class/net/" + ifname + "/device")
	if err != nil {
		return nil, fmt.Errorf("%s: %w", ifname, err)
	}
	drv, err := ifDriver(ifname)
	if err != nil {
		return nil, fmt.Errorf("%s: %w", ifname, err)
	}
	if drv != "ixgbe" {
		return nil, fmt.Errorf("%s: no module I2C transport for driver %s", ifname, drv)
	}
	b := &bcm{
		ifname: ifname,
		path:   "/sys/kernel/debug/ixgbe/" + filepath.Base(devLink) + "/sff_i2c",
	}
	if _, err := os.Stat(b.path); err != nil {
		return nil, fmt.Errorf("%s: %w (patched ixgbe?)", ifname, err)
	}
	return b, nil
}

func (b *bcm) op(cmd string) (string, error) {
	fd, err := unix.Open(b.path, unix.O_RDWR, 0)
	if err != nil {
		return "", fmt.Errorf("%s: %w", b.path, err)
	}
	defer unix.Close(fd)
	if _, err := unix.Write(fd, []byte(cmd)); err != nil {
		return "", fmt.Errorf("%s %q: %w", b.ifname, cmd, err)
	}
	buf := make([]byte, 256)
	n, err := unix.Read(fd, buf)
	if err != nil {
		return "", fmt.Errorf("%s %q: %w", b.ifname, cmd, err)
	}
	resp := strings.TrimSpace(string(buf[:n]))
	if !strings.HasPrefix(resp, "ok") {
		return "", fmt.Errorf("%s %q: %s", b.ifname, cmd, resp)
	}
	return strings.TrimSpace(resp[2:]), nil
}

func parseHexBytes(s string, n int) ([]byte, error) {
	fields := strings.Fields(s)
	if len(fields) != n {
		return nil, fmt.Errorf("want %d bytes, got %q", n, s)
	}
	out := make([]byte, n)
	for i, f := range fields {
		var v byte
		if _, err := fmt.Sscanf(f, "%x", &v); err != nil {
			return nil, fmt.Errorf("byte %q in %q", f, s)
		}
		out[i] = v
	}
	return out, nil
}

// A single bus hold; split write/read ops would let the driver's own SFP
// traffic consume the bridge's pending read.
func (b *bcm) compound(waddr, raddr byte, delayUs, n int, wdata []byte) ([]byte, error) {
	var sb strings.Builder
	fmt.Fprintf(&sb, "x %02x %02x %d %x", waddr, raddr, delayUs, n)
	for _, v := range wdata {
		fmt.Fprintf(&sb, " %02x", v)
	}
	resp, err := b.op(sb.String())
	if err != nil {
		return nil, err
	}
	return parseHexBytes(resp, n)
}

func (b *bcm) mdioReadDelay(devad, reg uint16, delayUs int) (uint16, error) {
	d, err := b.compound(bcmI2CWrite, bcmI2CRead, delayUs, 2,
		[]byte{0x20 | byte(devad), byte(reg >> 8), byte(reg)})
	if err != nil {
		return 0, err
	}
	return uint16(d[0])<<8 | uint16(d[1]), nil
}

// 0x0000 is also the bridge's not-ready signature, so a zero is read again at
// a longer delay before being believed.
func (b *bcm) mdioRead(devad, reg uint16) (uint16, error) {
	v, err := b.mdioReadDelay(devad, reg, bcmReadDelayUs)
	if err != nil || v != 0 {
		return v, err
	}
	return b.mdioReadDelay(devad, reg, bcmRetryDelayUs)
}

func (b *bcm) mdioWrite(devad, reg, val uint16) error {
	_, err := b.op(fmt.Sprintf("w %02x %02x %02x %02x %02x %02x",
		bcmI2CWrite, byte(devad), byte(reg>>8), byte(reg), byte(val>>8), byte(val)))
	return err
}

func (b *bcm) eeprom(off byte, n int) ([]byte, error) {
	return b.compound(0xA0, 0xA1, 500, n, []byte{off})
}

// The datasheet's completion handshake: poll STATUS on its 100 ms cadence
// until the wanted state, bounded by a deadline.
func (b *bcm) waitStatus(want func(uint16) bool) (uint16, error) {
	deadline := time.Now().Add(bcmStatusTimeout)
	for {
		st, err := b.mdioRead(bcmMMDVendor, bcmRegStatus)
		if err != nil {
			return 0, err
		}
		if want(st) {
			return st, nil
		}
		if time.Now().After(deadline) {
			return 0, fmt.Errorf("%s: command handler stuck, status %#04x", b.ifname, st)
		}
		time.Sleep(bcmStatusPoll)
	}
}

// GETs must be invoked bare (pre-writing any DATA register leaves the handler
// executing as a no-op); SETs must pass their full parameter set (the handler
// executes stale DATA).
func (b *bcm) command(code uint16, params ...uint16) ([5]uint16, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	var data [5]uint16
	if _, err := b.waitStatus(func(st uint16) bool {
		return st != bcmStInProgress && st != bcmStBusy
	}); err != nil {
		return data, err
	}
	for i, p := range params {
		if err := b.mdioWrite(bcmMMDVendor, bcmRegData1+uint16(i), p); err != nil {
			return data, err
		}
	}
	if err := b.mdioWrite(bcmMMDVendor, bcmRegCmd, code); err != nil {
		return data, err
	}
	st, err := b.waitStatus(func(st uint16) bool {
		return st == bcmStPass || st == bcmStError
	})
	if err != nil {
		return data, err
	}
	if st == bcmStError {
		return data, fmt.Errorf("%s: command %#04x returned ERROR", b.ifname, code)
	}
	if len(params) > 0 {
		return data, nil
	}
	for i := range data {
		if data[i], err = b.mdioRead(bcmMMDVendor, bcmRegData1+uint16(i)); err != nil {
			return data, err
		}
	}
	return data, nil
}

func (b *bcm) identify() (string, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	hi, err := b.mdioRead(1, 2)
	if err != nil {
		return "", err
	}
	lo, err := b.mdioRead(1, 3)
	if err != nil {
		return "", err
	}
	if hi != bcmPHYIDHi || lo != bcmPHYIDLo {
		return "", fmt.Errorf("%s: PHY ID %#04x:%#04x, want %#04x:%#04x",
			b.ifname, hi, lo, bcmPHYIDHi, bcmPHYIDLo)
	}
	sn, err := b.eeprom(68, 16)
	if err != nil {
		return "", err
	}
	return "BCM84891L sn " + strings.TrimSpace(string(sn)), nil
}

// PMA 1.1 latches low, so the first read reports any drop since it was last
// read and the second reports the wire as it is now.
func (b *bcm) linkUp() (bool, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	if _, err := b.mdioRead(1, 1); err != nil {
		return false, err
	}
	v, err := b.mdioRead(1, 1)
	if err != nil {
		return false, err
	}
	return v&0x0004 != 0, nil
}

func (b *bcm) forceEEEOff() error {
	_, err := b.command(bcmCmdSetEEEMode, 0x0000, 0x0000, 0x7A12, 0x0480, 0x0000)
	return err
}

func (b *bcm) forceJumbo() error {
	_, err := b.command(bcmCmdSetJumbo, 1, 0, 0, 0, 0)
	return err
}

func (b *bcm) restartAN() error {
	b.mu.Lock()
	defer b.mu.Unlock()
	v, err := b.mdioRead(7, 0)
	if err != nil {
		return err
	}
	return b.mdioWrite(7, 0, v|0x0200)
}

func (b *bcm) eeeAdvert() (uint16, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.mdioRead(7, 60)
}

func (b *bcm) pairMap() (byte, error) {
	d, err := b.command(bcmCmdGetPairSwap)
	if err != nil {
		return 0, err
	}
	return byte(d[1]), nil
}

func (b *bcm) snr() ([4]float64, error) {
	var out [4]float64
	d, err := b.command(bcmCmdGetSNR)
	if err != nil {
		return out, err
	}
	for i := range out {
		out[i] = float64(d[i+1]) / 10
	}
	return out, nil
}

func (b *bcm) pcsLatch() (blocks, ber uint64, err error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	v, err := b.mdioRead(3, 33)
	if err != nil {
		return 0, 0, err
	}
	return uint64(v & 0xFF), uint64((v >> 8) & 0x3F), nil
}

func (b *bcm) fastRetrainCount() (uint16, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	v, err := b.mdioRead(1, 147)
	if err != nil {
		return 0, err
	}
	return v >> 11, nil
}

type ecdResult struct {
	verdicts [4]int
	metres   [4]int
}

func (b *bcm) cableDiag() (ecdResult, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	var res ecdResult
	ctrl, err := b.mdioRead(bcmMMDVendor, bcmRegECDCtrl)
	if err != nil {
		return res, err
	}
	if err := b.mdioWrite(bcmMMDVendor, bcmRegECDCtrl, ctrl&^0xF400|0x8400); err != nil {
		return res, err
	}
	deadline := time.Now().Add(ecdDeadline)
	for {
		ctrl, err = b.mdioRead(bcmMMDVendor, bcmRegECDCtrl)
		if err != nil {
			return res, err
		}
		if ctrl&0x0800 == 0 {
			break
		}
		if time.Now().After(deadline) {
			return res, fmt.Errorf("%s: cable diag still busy after %s", b.ifname, ecdDeadline)
		}
		time.Sleep(ecdPoll)
	}
	v, err := b.mdioRead(1, bcmRegECDResult)
	if err != nil {
		return res, err
	}
	for i := range res.verdicts {
		res.verdicts[i] = int(v>>(4*i)) & 0xF
		if res.verdicts[i] > pairXtalk {
			panic(fmt.Sprintf("%s: ghost ECD verdict %#04x", b.ifname, v))
		}
		m, err := b.mdioRead(1, bcmRegECDLen+uint16(i))
		if err != nil {
			return res, err
		}
		res.metres[i] = int(m)
	}
	return res, nil
}

const (
	phyInterval  = time.Second
	phyStale     = 5 * time.Second
	phyMaxDark   = 30
	linkWaitSpan = 25 * time.Second
	linkWaitPoll = time.Second

	snrOperatingPoint = 26.5
	snrGoodMargin     = 3.0
	snrWarnMargin     = 1.0

	// No trained link produces SNR outside this; readings there are another
	// register's data (die temp ≈ 8, handler status ≈ 0.4) and the run dies.
	snrGhostLow  = 15.0
	snrGhostHigh = 50.0
)

type phyModule struct {
	bcm  *bcm
	busy atomic.Bool

	mu           sync.Mutex
	sampled      bool
	lastOK       time.Time
	link         bool
	haveSNR      bool
	snr          [4]float64
	blocks       uint64
	ber          uint64
	retrains     uint64
	recentDelta  uint64
	primed       bool
	retrainCount uint16
}

// Silent while a measure owns the module.
func (m *phyModule) poll() error {
	if m.busy.Load() {
		return nil
	}
	link, err := m.bcm.linkUp()
	if err != nil {
		return err
	}
	var snr [4]float64
	if link {
		if snr, err = m.bcm.snr(); err != nil {
			return err
		}
		for _, s := range snr {
			if s < snrGhostLow || s > snrGhostHigh {
				panic(fmt.Sprintf("%s: ghost SNR %.1f dB", m.bcm.ifname, s))
			}
		}
	}
	blocks, ber, err := m.bcm.pcsLatch()
	if err != nil {
		return err
	}
	count, err := m.bcm.fastRetrainCount()
	if err != nil {
		return err
	}

	m.mu.Lock()
	m.sampled = true
	m.lastOK = time.Now()
	m.link = link
	m.haveSNR = link
	m.snr = snr
	// The first poll after a baseline drains latches from the bringup/diag
	// retrain era, so it only sets the origin; the retrain counter is 5 bits.
	if m.primed {
		delta := blocks + ber + uint64((count-m.retrainCount)&0x1F)
		m.blocks += blocks
		m.ber += ber
		m.retrains += uint64((count - m.retrainCount) & 0x1F)
		m.recentDelta = delta
	} else {
		m.recentDelta = 0
		m.primed = true
	}
	m.retrainCount = count
	m.mu.Unlock()
	return nil
}

func (m *phyModule) run(done *atomic.Bool) {
	tick := time.NewTicker(phyInterval)
	defer tick.Stop()

	dark := 0
	var lastErr error
	for !done.Load() {
		<-tick.C
		if err := m.poll(); err != nil {
			dark++
			lastErr = err
			if dark >= phyMaxDark {
				panic(fmt.Sprintf("module diagnostics dark for %d polls: %v", dark, lastErr))
			}
			continue
		}
		dark = 0
	}
}

func (m *phyModule) reset() {
	m.mu.Lock()
	m.blocks, m.ber, m.retrains, m.recentDelta = 0, 0, 0, 0
	m.primed = false
	m.mu.Unlock()
}

type phyModView struct {
	fresh   bool
	link    bool
	margins [4]float64
	blocks  uint64
	ber     uint64
	retrain uint64
	recent  uint64
}

func (m *phyModule) view() phyModView {
	m.mu.Lock()
	defer m.mu.Unlock()
	v := phyModView{
		fresh:   m.sampled && time.Since(m.lastOK) < phyStale,
		link:    m.link && m.haveSNR,
		blocks:  m.blocks,
		ber:     m.ber,
		retrain: m.retrains,
	}
	if v.fresh {
		v.recent = m.recentDelta
	}
	for i, s := range m.snr {
		v.margins[i] = s - snrOperatingPoint
	}
	return v
}

type cableInfo struct {
	ecd  ecdResult
	maps [2]byte
}

func (c cableInfo) metresString() string {
	sum, n := 0, 0
	for i, v := range c.ecd.verdicts {
		if v == pairOK {
			sum += c.ecd.metres[i]
			n++
		}
	}
	if n == 0 {
		return "-"
	}
	return fmt.Sprintf("%d", (sum+n/2)/n)
}

const (
	clsNone = iota
	clsGood
	clsWarn
	clsBad
)

func snrClass(margin float64) int {
	switch {
	case margin >= snrGoodMargin:
		return clsGood
	case margin >= snrWarnMargin:
		return clsWarn
	default:
		return clsBad
	}
}

type phyDisplay struct {
	haveSNR     bool
	worstMargin float64
	corrected   uint64
	recent      uint64
	metres      string
	metresClass int
}

func pairLetter(i int) string { return string(rune('A' + i)) }

// Each end resolves MDI on its own, so a swap at either end counts.
func pairSwapped(i int, maps [2]byte) bool {
	return int(maps[0]>>(2*i))&3 != i || int(maps[1]>>(2*i))&3 != i
}

func cableSummary(cable cableInfo, measuring bool) (string, int) {
	if measuring {
		return "...", clsNone
	}
	anyData, anyFault, anySwap := false, false, false
	for i, v := range cable.ecd.verdicts {
		if v != 0 {
			anyData = true
		}
		if v != 0 && v != pairOK {
			anyFault = true
		}
		if pairSwapped(i, cable.maps) {
			anySwap = true
		}
	}
	s := cable.metresString()
	switch {
	case !anyData:
		return "-", clsNone
	case anyFault:
		return s, clsBad
	case anySwap:
		return s, clsWarn
	}
	return s, clsGood
}

func phyDisplayFrom(cable cableInfo, measuring bool, a, b phyModView) phyDisplay {
	d := phyDisplay{
		haveSNR:   a.fresh && b.fresh && a.link && b.link,
		corrected: a.blocks + a.ber + a.retrain + b.blocks + b.ber + b.retrain,
		recent:    a.recent + b.recent,
	}
	if d.haveSNR {
		d.worstMargin = min(a.margins[0], b.margins[0])
		for i := range a.margins {
			if m := min(a.margins[i], b.margins[i]); m < d.worstMargin {
				d.worstMargin = m
			}
		}
	}
	d.metres, d.metresClass = cableSummary(cable, measuring)
	return d
}

// The pollers are held silent throughout; pair maps are read after the
// relink, so the MDI resolution is the fresh one.
func measureCable(mods []*phyModule, waitRelink bool, done *atomic.Bool) (cableInfo, bool, error) {
	for _, m := range mods {
		m.busy.Store(true)
	}
	defer func() {
		for _, m := range mods {
			m.busy.Store(false)
		}
	}()

	var c cableInfo
	var err error
	c.ecd, err = mods[0].bcm.cableDiag()
	if err != nil {
		return c, false, err
	}
	relinked := false
	if waitRelink {
		names := [2]string{mods[0].bcm.ifname, mods[1].bcm.ifname}
		_, relinked = waitCarrier(names, done)
	}
	for i, m := range mods {
		if c.maps[i], err = m.bcm.pairMap(); err != nil {
			return c, false, err
		}
	}
	return c, relinked, nil
}

type cableDiag struct {
	mods      []*phyModule
	completed chan error

	mu      sync.Mutex
	info    cableInfo
	running bool
}

func newCableDiag(mods []*phyModule, info cableInfo) *cableDiag {
	return &cableDiag{mods: mods, completed: make(chan error, 1), info: info}
}

func (c *cableDiag) snapshot() (cableInfo, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.info, c.running
}

func (c *cableDiag) kick(done *atomic.Bool) bool {
	c.mu.Lock()
	if c.running {
		c.mu.Unlock()
		return false
	}
	c.running = true
	c.mu.Unlock()

	go func() {
		defer holdPanic()
		info, _, err := measureCable(c.mods, true, done)
		if err != nil {
			info = cableInfo{}
		}
		c.mu.Lock()
		c.info = info
		c.running = false
		c.mu.Unlock()
		select {
		case c.completed <- err:
		default:
		}
	}()
	return true
}

func mapString(m byte) string {
	if m == pairIdentityMap {
		return "straight"
	}
	out := make([]string, 4)
	for i := range out {
		out[i] = pairLetter(int(m>>(2*i)) & 3)
	}
	return "swapped to " + strings.Join(out, "")
}

func verdictString(r ecdResult) string {
	bad := []string{}
	for i, v := range r.verdicts {
		if v != pairOK {
			s, ok := pairVerdicts[v]
			if !ok {
				s = fmt.Sprintf("%d", v)
			}
			bad = append(bad, fmt.Sprintf("%s %s at %dm", pairLetter(i), s, r.metres[i]))
		}
	}
	if len(bad) > 0 {
		return strings.Join(bad, ", ")
	}
	return fmt.Sprintf("all pairs ok, %d/%d/%d/%d m",
		r.metres[0], r.metres[1], r.metres[2], r.metres[3])
}

func openModules(names [2]string) ([]*phyModule, [2]string, error) {
	mods := make([]*phyModule, 0, 2)
	var idents [2]string
	for i, name := range names {
		b, err := openBCM(name)
		if err != nil {
			return nil, idents, err
		}
		idents[i], err = b.identify()
		if err != nil {
			return nil, idents, err
		}
		m := &phyModule{bcm: b}
		// Born busy: the pollers stay silent through bringup's SETs and
		// retrains until the first measure completes and lifts the gate.
		m.busy.Store(true)
		mods = append(mods, m)
	}
	return mods, idents, nil
}

func waitCarrier(names [2]string, done *atomic.Bool) (time.Duration, bool) {
	start := time.Now()
	deadline := start.Add(linkWaitSpan)
	for {
		if carrierUp(names[0]) && carrierUp(names[1]) {
			return time.Since(start), true
		}
		if time.Now().After(deadline) || (done != nil && done.Load()) {
			return time.Since(start), false
		}
		time.Sleep(linkWaitPoll)
	}
}

// No trustworthy config readback exists (DATA1 is firmware scratch) and no
// cable is guaranteed at bringup, so both settings are forced every boot: the
// one deterministic assurance. The handler freezes during training, so the
// carrier settles — the host checks just reset the links — before any command.
// Never waits for a link: there may be no cable, and forcing config needs
// none — the AN restart applies it whenever training next happens.
func moduleChecks(mods []*phyModule, names [2]string) []checkResult {
	var out []checkResult
	fail := func(item string, err error) []checkResult {
		return append(out, checkResult{item: item, err: err})
	}

	for i, m := range mods {
		res := checkResult{item: names[i] + " eee", state: "forced off"}
		if err := m.bcm.forceEEEOff(); err != nil {
			return fail(res.item, err)
		}
		out = append(out, res)

		res = checkResult{item: names[i] + " jumbo", state: "forced on"}
		if err := m.bcm.forceJumbo(); err != nil {
			return fail(res.item, err)
		}
		out = append(out, res)

		if err := m.bcm.restartAN(); err != nil {
			return fail(names[i]+" retrain", err)
		}
	}

	res := checkResult{item: "eee advert"}
	var adv [2]string
	for i, m := range mods {
		v, err := m.bcm.eeeAdvert()
		if err != nil {
			return fail(res.item, err)
		}
		adv[i] = fmt.Sprintf("%#04x", v)
		if v != 0 {
			res.err = fmt.Errorf("%s still advertises EEE %#04x", names[i], v)
		}
	}
	res.state = adv[0] + "/" + adv[1]
	return append(out, res)
}

func cableLine(c cableInfo) string {
	return fmt.Sprintf("%s; map %s / %s",
		verdictString(c.ecd), mapString(c.maps[0]), mapString(c.maps[1]))
}