package main

import (
	"sync"
	"time"
)

// The panel's recent-history ring: 18 slots of 5 seconds. Fault and corrected
// deltas arrive straight from the layers below the moment they clear the mask,
// and the per-frame judgments — measure state, rate, SNR — from the draw loop,
// so a slot has data within one tick of being born. Slots are wall-time and
// survive a reset — recently is recently, whatever the aggregates were
// re-based to — while the fault ages and since-reset extremes 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
}

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

	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
}

// Bucketing sits above the mask: only fault deltas that survived it arrive
// here, already flattened, so a slot is a plain sum.
func (h *history) addFaults(now time.Time, e errs) {
	h.mu.Lock()
	defer h.mu.Unlock()
	s := h.slot(int64(now.Sub(h.start) / histSlotSpan))
	for i, c := range faultClasses {
		if d := c.get(e); d > 0 {
			s.faults[i] += d
			h.lastFault[i] = now
		}
	}
}

func (h *history) addCorrected(now time.Time, d uint64) {
	h.mu.Lock()
	h.slot(int64(now.Sub(h.start)/histSlotSpan)).corrected += d
	h.mu.Unlock()
}

// The per-frame judgments, from the same figures the panel paints.
func (h *history) sample(now time.Time, v view, phy phyDisplay,
	measuring bool, target float64) {
	h.mu.Lock()
	defer h.mu.Unlock()

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

	if measuring {
		s.measuring = true
		return
	}
	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
		}
	}
}

// The wall-time slots stay: recently is recently. Everything judged against
// the reset origin clears.
func (h *history) reset() {
	h.mu.Lock()
	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
}

// The window's newest column is the slot containing now, taken from the draw
// clock rather than the last sample, so the grid rolls on the slot boundary
// itself.
func (h *history) view(now time.Time) histView {
	h.mu.Lock()
	defer h.mu.Unlock()
	newest := int64(now.Sub(h.start) / histSlotSpan)
	var out histView
	for k := 0; k < histSlots; k++ {
		seq := newest - 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
}