package main

import (
	"fmt"
	"strings"
	"time"
)

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

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

	bcmPHYIDHi = 0x3590
	bcmPHYIDLo = 0x5081

	bcmCmdResidentTemp uint16 = 0x0031

	bcmReadDelayUs  = 3000
	bcmRetryDelayUs = 10000

	bcmWindow    = 3400 * time.Millisecond
	bcmWindowFit = 100 * time.Millisecond
	bcmFlipPoll  = 10 * time.Millisecond
	bcmFlipWait  = 5 * time.Second

	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
)

type bcm struct {
	*sff
	windowEnd time.Time
}

func newBCM(t *sff) *bcm {
	b := &bcm{sff: t}
	t.exec(func() { t.admit = b.window })
	return b
}

// The firmware's internal temp poll serves stale bridge reads for ~50 ms
// around it; work stays inside 3.4 s of an observed poll. A resident 0x0031 at
// expiry means the phase is unknown, so re-lock: arm, then take the true edge.
// Each taken edge immediately re-arms — the one CMD write per window lands at
// the start of the quiet period, maximally far from the next poll (writes near
// the poll are the µC-wedge risk), and every later expiry reads the phase
// without writing.
func (b *bcm) window() {
	if time.Now().Add(bcmWindowFit).Before(b.windowEnd) {
		return
	}
	armed := false
	deadline := time.Now().Add(bcmFlipWait)
	for {
		v, err := b.mdioRead(bcmMMDVendor, bcmRegCmd)
		if err != nil {
			panic(fmt.Sprintf("%s: heartbeat poll: %v", b.ifname, err))
		}
		if v == bcmCmdResidentTemp {
			if armed {
				b.windowEnd = time.Now().Add(bcmWindow)
				b.rearm()
				return
			}
			b.rearm()
			armed = true
			deadline = time.Now().Add(bcmFlipWait)
			continue
		}
		armed = true
		if time.Now().After(deadline) {
			b.windowEnd = time.Now().Add(bcmWindow)
			return
		}
		time.Sleep(bcmFlipPoll)
	}
}

func (b *bcm) rearm() {
	if _, err := b.waitStatus(func(st uint16) bool {
		return st != bcmStInProgress && st != bcmStBusy
	}); err != nil {
		panic(fmt.Sprintf("%s: rearm: %v", b.ifname, err))
	}
	if err := b.mdioWrite(bcmMMDVendor, bcmRegCmd, bcmCmdGetPairSwap); err != nil {
		panic(fmt.Sprintf("%s: rearm: %v", b.ifname, err))
	}
	if _, err := b.waitStatus(func(st uint16) bool {
		return st == bcmStPass || st == bcmStError
	}); err != nil {
		panic(fmt.Sprintf("%s: rearm: %v", b.ifname, err))
	}
}

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
}

// 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 write every DATA register (the handler
// executes stale DATA), so a partial parameter set is refused outright.
func (b *bcm) command(code uint16, params ...uint16) (data [5]uint16, err error) {
	if len(params) != 0 && len(params) != len(data) {
		panic(fmt.Sprintf("%s: command %#04x with %d params: a SET must write all %d DATA registers",
			b.ifname, code, len(params), len(data)))
	}
	b.exec(func() {
		if _, err = b.waitStatus(func(st uint16) bool {
			return st != bcmStInProgress && st != bcmStBusy
		}); err != nil {
			return
		}
		for i, p := range params {
			if err = b.mdioWrite(bcmMMDVendor, bcmRegData1+uint16(i), p); err != nil {
				return
			}
		}
		if err = b.mdioWrite(bcmMMDVendor, bcmRegCmd, code); err != nil {
			return
		}
		var st uint16
		if st, err = b.waitStatus(func(st uint16) bool {
			return st == bcmStPass || st == bcmStError
		}); err != nil {
			return
		}
		if st == bcmStError {
			err = fmt.Errorf("%s: command %#04x returned ERROR", b.ifname, code)
			return
		}
		if len(params) > 0 {
			return
		}
		for i := range data {
			if data[i], err = b.mdioRead(bcmMMDVendor, bcmRegData1+uint16(i)); err != nil {
				return
			}
		}
	})
	return
}

func (b *bcm) identify() (ident string, err error) {
	b.exec(func() {
		var hi, lo uint16
		if hi, err = b.mdioRead(1, 2); err != nil {
			return
		}
		if lo, err = b.mdioRead(1, 3); err != nil {
			return
		}
		if hi != bcmPHYIDHi || lo != bcmPHYIDLo {
			err = fmt.Errorf("%s: PHY ID %#04x:%#04x, want %#04x:%#04x",
				b.ifname, hi, lo, bcmPHYIDHi, bcmPHYIDLo)
			return
		}
		var sn []byte
		if sn, err = b.eeprom(68, 16); err != nil {
			return
		}
		ident = "BCM84891L sn " + strings.TrimSpace(string(sn))
	})
	return
}

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
}

// Left to AN, master/slave is a per-training lottery and each training's DSP
// convergence moves per-pair SNR by up to ~3.6 dB; pinned roles at least keep
// every session measured under identical conditions.
func (b *bcm) forceRole(master bool) (err error) {
	b.exec(func() {
		var v uint16
		if v, err = b.mdioRead(7, 32); err != nil {
			return
		}
		v |= 0x8000
		if master {
			v |= 0x4000
		} else {
			v &^= 0x4000
		}
		err = b.mdioWrite(7, 32, v)
	})
	return
}

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) cableDiag() (res ecdResult, err error) {
	b.exec(func() {
		var ctrl uint16
		if ctrl, err = b.mdioRead(bcmMMDVendor, bcmRegECDCtrl); err != nil {
			return
		}
		if err = b.mdioWrite(bcmMMDVendor, bcmRegECDCtrl, ctrl&^0xF400|0x8400); err != nil {
			return
		}
		deadline := time.Now().Add(ecdDeadline)
		for {
			if ctrl, err = b.mdioRead(bcmMMDVendor, bcmRegECDCtrl); err != nil {
				return
			}
			if ctrl&0x0800 == 0 {
				break
			}
			if time.Now().After(deadline) {
				err = fmt.Errorf("%s: cable diag still busy after %s", b.ifname, ecdDeadline)
				return
			}
			time.Sleep(ecdPoll)
		}
		b.window()
		var v uint16
		if v, err = b.mdioRead(1, bcmRegECDResult); err != nil {
			return
		}
		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))
			}
			var m uint16
			if m, err = b.mdioRead(1, bcmRegECDLen+uint16(i)); err != nil {
				return
			}
			res.metres[i] = int(m)
		}
	})
	return
}