package main

import (
	"sync"
	"time"
)

// The panel's recent-history ring: 18 slots of 5 seconds, sampled once a
// second from the same figures the console row prints. Slots are wall-time
// and survive a reset — recently is recently, whatever the counters were
// re-based to — while the since-reset aggregates and fault ages clear.
const (
	histSlots    = 18
	histSlotSpan = 5 * time.Second
	histSpan     = histSlots * histSlotSpan

	// Line rate is a verdict here, not a number: the headline is smeared and
	// briefly gated at startup, so anything close to the target counts.
	rateOKFrac = 0.98
)

var faultClasses = []struct {
	label string
	noun  string
	get   func(errs) uint64
}{
	{"lost", "loss", func(e errs) uint64 { return e.lost }},
	{"corrupt", "corrupt", func(e errs) uint64 { return e.corrupt }},
	{"link", "link fault", func(e errs) uint64 { return e.link }},
	{"internal", "internal", func(e errs) uint64 { return e.internal }},
}

type histSlot struct {
	seq       int64
	sampled   bool
	measuring bool
	faults    [4]uint64
	corrected uint64
	rateLow   bool
	haveSNR   bool
	snrMin    float64
	noiseOn   int
	noiseN    int
}

type history struct {
	mu    sync.Mutex
	start time.Time
	slots [histSlots]histSlot
	seq   int64

	prevValid     bool
	prevSince     errs
	prevCorrected uint64

	lastFault    [4]time.Time
	sinceRateLow bool
	sinceHaveSNR bool
	sinceSNRMin  float64
}

func newHistory(now time.Time) *history {
	return &history{start: now}
}

func (h *history) slot(seq int64) *histSlot {
	s := &h.slots[seq%histSlots]
	if s.seq != seq || !s.sampled {
		*s = histSlot{seq: seq, sampled: true}
	}
	return s
}

// Counters only move forward between samples except across a reset, where
// they re-base to zero; a backward step is that re-base, not negative faults.
func delta(now, prev uint64) uint64 {
	if now < prev {
		return 0
	}
	return now - prev
}

func (h *history) sample(now time.Time, v view, phy phyDisplay, nv noiseView,
	measuring bool, target float64) {
	h.mu.Lock()
	defer h.mu.Unlock()

	h.seq = int64(now.Sub(h.start) / histSlotSpan)
	s := h.slot(h.seq)

	if h.prevValid {
		for i, c := range faultClasses {
			d := delta(c.get(v.since), c.get(h.prevSince))
			s.faults[i] += d
			if d > 0 {
				h.lastFault[i] = now
			}
		}
		s.corrected += delta(phy.corrected, h.prevCorrected)
	}
	h.prevValid = true
	h.prevSince = v.since
	h.prevCorrected = phy.corrected

	if measuring {
		s.measuring = true
	} else {
		if v.rxGbps < rateOKFrac*target {
			s.rateLow = true
			h.sinceRateLow = true
		}
		if phy.haveSNR {
			if !s.haveSNR || phy.worstMargin < s.snrMin {
				s.haveSNR, s.snrMin = true, phy.worstMargin
			}
			if !h.sinceHaveSNR || phy.worstMargin < h.sinceSNRMin {
				h.sinceHaveSNR, h.sinceSNRMin = true, phy.worstMargin
			}
		}
	}
	s.noiseN++
	if nv.on {
		s.noiseOn++
	}
}

// The wall-time slots stay: recently is recently. Everything judged against
// the reset origin clears.
func (h *history) reset() {
	h.mu.Lock()
	h.prevValid = false
	h.lastFault = [4]time.Time{}
	h.sinceRateLow = false
	h.sinceHaveSNR = false
	h.sinceSNRMin = 0
	h.mu.Unlock()
}

type histView struct {
	// Oldest first; a slot that predates the ring or was never sampled has
	// sampled false and paints as unknown.
	slots        [histSlots]histSlot
	lastFault    [4]time.Time
	sinceRateLow bool
	sinceHaveSNR bool
	sinceSNRMin  float64
}

func (h *history) view() histView {
	h.mu.Lock()
	defer h.mu.Unlock()
	var out histView
	for k := 0; k < histSlots; k++ {
		seq := h.seq - int64(histSlots-1-k)
		if seq < 0 {
			continue
		}
		s := h.slots[seq%histSlots]
		if s.seq == seq && s.sampled {
			out.slots[k] = s
		}
	}
	out.lastFault = h.lastFault
	out.sinceRateLow = h.sinceRateLow
	out.sinceHaveSNR = h.sinceHaveSNR
	out.sinceSNRMin = h.sinceSNRMin
	return out
}

// The newest fault on record names the verdict; the cable's own verdict
// outranks traffic faults because it is the thing under test.
func (hv histView) newestFault(now time.Time) (i int, age time.Duration, ok bool) {
	best := -1
	for c, t := range hv.lastFault {
		if t.IsZero() {
			continue
		}
		if best < 0 || t.After(hv.lastFault[best]) {
			best = c
		}
	}
	if best < 0 {
		return 0, 0, false
	}
	return best, now.Sub(hv.lastFault[best]), true
}