package main

import (
	"context"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"slices"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/nats-io/nats.go"

	"github.com/novox/mesh-controller/internal/broker"
	"github.com/novox/mesh-controller/internal/conditions"
	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// The healers (novox/hq to-be 45 §7, ADR 0227 rule 7, Phase 3).
//
// **A known failure heals itself, under a brake, and every repair is said.** Research 031 counted the
// repairs people made by hand in six days: a push to unstick a plan waiting on a report (four times),
// a controller restarted to make an object again (twice), a plan closed (twice), a consumer re-made from
// now (once). Each was the ordinary path, taken again by a person who noticed. A healer is that act,
// registered against the one condition kind it answers, so the mesh takes it itself:
//
//   - **its repair is the ordinary path again** — the send a push makes, the plan's own close, the
//     assertion every send makes, the consumer reset the verb makes — never a withdrawal, a deletion of
//     data or a recreation of it;
//   - **its budget** is how many acts it may take against one thing in a window, and **its settle** how
//     long after an act it leaves the observation to say whether it worked;
//   - **success is never the healer's to say.** The condition clears when the watchdog or the probe that
//     raised it no longer sees it. A healer marking its own work done would be the second opinion of a
//     fact that rule 1 forbids;
//   - **a spent budget stops it**: the condition is the operator's, urgent, with every attempt in
//     `tried`, and no healer touches it again until observation clears it;
//   - **every act is said**: begun in the store before it is made (so a controller dying mid-act has
//     still spent it), kept in the condition's `tried` as `healer Hn`, and said on the bus as the
//     controller seat's `healer-acted`. A heal is not a hand act and is never in the hand-act log —
//     which is how S15 can tell a repair the mesh made from one a person had to.
//
// **And the mesh-wide brake**: more than healBrakeLimit acts in an hour, all healers together, and every
// healer stops — an urgent condition says so — until an hour has passed with none. A healer looping is
// then at most a dozen acts, said, and never the incident itself.
//
// Only the controller holding the lease heals, under its epoch: a controller serving without the lease
// (S12) heals nothing, because a repair is the one act that can always wait for the lease.

// The mesh-wide brake (to-be 45 §7): how many acts all healers together may take in an hour.
const (
	healBrakeLimit  = 12
	healBrakeWindow = time.Hour
)

// healEvery is how often the healers look at what is open.
var healEvery = 30 * time.Second

// What raises the healers' own conditions, and their kinds.
const (
	sourceHealers      = "healers"
	kindHealersBraked  = "healers-braked"
	kindConsumerBehind = "consumer-behind"
	kindHealersBlind   = "probe-failed"
)

// healerRow is one row of the registry.
type healerRow struct {
	ID string
	// Kinds are the condition kinds it answers: from the signals table, the probe registry, or an event.
	Kinds []string
	// Condition, Repair, Then, From are the row in words, as to-be 45 §7 and `healers` say it.
	Condition string
	Repair    string
	Then      string
	From      string
	// Budget acts against one budget key within Window; Settle after an act before the next, or the
	// escalation, so the observation has had its turn to say whether it worked.
	Budget int
	Window time.Duration
	Settle time.Duration
	// ActsIn is where the repair runs: the controller, or a module that repairs its own (H5).
	ActsIn string
	// Event is what each act is said as.
	Event string
	// applies says whether this condition is one the healer may act on, and what its budget is
	// counted against; why when it is not. Reads, never acts. Nil where the repair is a module's.
	applies func(ctx context.Context, h *healing, c conditions.Condition) (budget string, ok bool, why string, err error)
	// repair is the act: what it did in words, what came of it, or an error when it could not be done.
	repair func(ctx context.Context, h *healing, c conditions.Condition) (act, said string, err error)
}

// actsInController is a healer whose repair the controller makes.
const actsInController = "controller"

// healerRegistry is to-be 45 §7's table, compiled in. **The registry is the design's live form**: a
// test generated from it holds every row to a condition kind the mesh raises, a budget, a brake and its
// event (healers_test.go).
var healerRegistry = []healerRow{
	{ID: "H1", Kinds: []string{"sent-not-reported"},
		Condition: "a machine was sent a declaration and has not reported it (S2)",
		Repair: "ask the machine's node-engine to say again what it last applied (the `report` verb); if what " +
			"comes back is not the declaration it was sent, or nothing comes, send it its current declaration " +
			"again — what a push of that one machine does, never moving a build a policy or a plan holds back",
		Then: "resolver operator, urgent", From: "a push by hand to unstick a plan waiting on a report (230, 257, 264, 267)",
		Budget: 2, Window: 6 * time.Hour, Settle: 3 * time.Minute, ActsIn: actsInController, Event: link.KeyHealerActed,
		applies: appliesToAMachine, repair: repairReport},
	{ID: "H2", Kinds: []string{"stalled"},
		Condition: "a plan stalled on a wait that is superseded — a newer plan of its repository and branch " +
			"exists — or already finished — every module of every tier built or failed, and every one that " +
			"rolls out sent (S3); or a delivery held past its state's bound where mesh-delivery's table lets H2 " +
			"take a transition (D14, novox/hq ADR 0239)",
		Repair: "close the plan with its note, as `plans close` does: superseded, naming the newer plan, or " +
			"done; what it asked still builds and registers — or, for a delivery, mesh-delivery's `close`, which " +
			"reads its walk again and takes only the transition its table names",
		Then: "resolver operator, urgent", From: "a stuck plan closed by hand (214, 254)",
		Budget: 1, Window: 24 * time.Hour, Settle: 2 * time.Minute, ActsIn: actsInController, Event: link.KeyHealerActed,
		applies: appliesToAStalePlan, repair: repairPlan},
	{ID: "H3", Kinds: []string{"holder-silent", "consumer-lost"},
		Condition: "a seat's holder that does not answer (D3), or a durable consumer the mesh expects and the " +
			"bus does not hold (D6, S9)",
		Repair: "assert the bus's streams, consumers and seat workers again — the assertion every send makes " +
			"(issue 208)",
		Then: "resolver operator, urgent", From: "a controller restarted to make a missing object again (208, 248)",
		Budget: 1, Window: time.Hour, Settle: 6 * time.Minute, ActsIn: actsInController, Event: link.KeyHealerActed,
		applies: appliesToAnObject, repair: repairObjects},
	{ID: "H4", Kinds: []string{kindConsumerBehind},
		Condition: "a durable consumer far behind its stream's head (D6) that the stream table marks resettable",
		Repair: "re-make the consumer to deliver from now — `broker consumer-reset` (issue 248); what it drops " +
			"is caught up where the table says",
		Then: "resolver operator, urgent", From: "a consumer re-made from now by hand (248)",
		Budget: 1, Window: 24 * time.Hour, Settle: 6 * time.Minute, ActsIn: actsInController, Event: link.KeyHealerActed,
		applies: appliesToAResettableConsumer, repair: repairConsumer},
	{ID: "H5", Kinds: []string{kindProviderFailing},
		Condition: "the identity provider's administrator refusing the mesh's secret (provider-failing, " +
			"credentials-rejected)",
		Repair: "the provider repairs it itself through the server's own bootstrap command, checks again and " +
			"says what it did (ADR 0224 §5); the controller keeps its word as the condition",
		Then: "announced failing by the provider, braked from ten minutes doubling to six hours (ADR 0224 §5)",
		From: "the identity provider's admin reset through its bootstrap command (179)",
		// Its budget and brake are the module's own: ten minutes, doubling, to six hours.
		Budget: 1, Window: 10 * time.Minute, Settle: 10 * time.Minute,
		ActsIn: "the provider module (keycloak), ADR 0224 §5", Event: "provisioner.failing, provisioner.recovered"},
}

// healerFor is the healer registered for a kind, and false when none acts in the controller.
func healerFor(kind string) (healerRow, bool) {
	for _, r := range healerRegistry {
		if r.repair != nil && slices.Contains(r.Kinds, kind) {
			return r, true
		}
	}
	return healerRow{}, false
}

// healerNamedFor is any healer registered for a kind, wherever it acts: what S15 says beside a cause.
func healerNamedFor(kind string) string {
	for _, r := range healerRegistry {
		if slices.Contains(r.Kinds, kind) {
			return r.ID
		}
	}
	return ""
}

// healing is the healers' runner and what their repairs reach.
type healing struct {
	open   *stores
	keeper *conditions.Keeper
	teller conditions.Teller
	// js is the bus, for the repairs that assert or reset its objects; nil where there is none.
	js *broker.JetStream
	// epoch is the lease's gate; acting says this controller is the one acting, not one standing by.
	epoch  func(ctx context.Context) (uint64, error)
	acting func() bool
	now    func() time.Time
	say    func(format string, args ...any)

	// The acts, as seams a test replaces: asking a machine to report, sending it again, asserting the
	// bus's objects, resetting a consumer.
	askReport     func(ctx context.Context, node string) error
	sendAgain     func(ctx context.Context, node string) error
	assertObjects func(ctx context.Context) error
	resetConsumer func(stream, name string) (string, error)
	// reportWait is how long H1 waits for the machine's report after asking.
	reportWait time.Duration

	mu sync.Mutex
	// declined is why each condition was last passed over, so it is said once and `healers` can show it.
	declined map[string]string
	paused   string
}

// newHealing is the serving controller's runner, its acts the real ones.
func newHealing(open *stores, keeper *conditions.Keeper, teller conditions.Teller, js *broker.JetStream) *healing {
	h := &healing{open: open, keeper: keeper, teller: teller, js: js, acting: link.Holding,
		epoch: func(ctx context.Context) (uint64, error) { return theLease.epoch(ctx) },
		now:   time.Now, say: func(format string, args ...any) { fmt.Printf(format+"\n", args...) },
		reportWait: 45 * time.Second, declined: map[string]string{}}
	h.askReport = func(ctx context.Context, node string) error {
		if h.js == nil {
			return errors.New("this controller is not on the bus")
		}
		return askToReport(ctx, h.js.Conn(), node)
	}
	h.sendAgain = func(ctx context.Context, node string) error {
		// **Never what a policy or a plan holds back** (ADR 0221): a send by the mesh itself is a push
		// that did not name the machine — a person's word sends a held build, a healer's does not.
		held, err := heldMachines(ctx, open, []string{node})
		if err != nil {
			return err
		}
		if why := held[node]; len(why) > 0 {
			return fmt.Errorf("not sent again: it would move what a policy or a plan holds back (ADR 0221) — %s; "+
				"`push %s` sends it, on a person's word", strings.Join(why, "; "), node)
		}
		return sendTo(ctx, open, []string{node})
	}
	h.assertObjects = func(ctx context.Context) error {
		if h.js == nil {
			return errors.New("this controller is not on the bus")
		}
		return assertOnSend(ctx, open.inventory, h.js, "  ")
	}
	h.resetConsumer = func(stream, name string) (string, error) {
		if h.js == nil {
			return "", errors.New("this controller is not on the bus")
		}
		before, after, err := h.js.ResetConsumer(stream, name)
		if err != nil {
			return "", err
		}
		return fmt.Sprintf("it was %d behind with %d unacknowledged; it delivers from now, %d pending", before.Pending,
			before.AckPending, after.Pending), nil
	}
	return h
}

// askToReport asks one machine's node-engine to say again what it last applied (to-be 45 §6). On core
// NATS, fired and flushed: the answer is the machine's ordinary report, read from the store.
func askToReport(ctx context.Context, conn *nats.Conn, node string) error {
	body, err := json.Marshal(map[string]any{"asked": time.Now().UTC(), "by": "the controller's healer H1"})
	if err != nil {
		return err
	}
	if err := conn.Publish(broker.AskReportSubject(node), body); err != nil {
		return err
	}
	flushing, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	return conn.FlushWithContext(flushing)
}

// keep runs the healers until ctx ends.
func (h *healing) keep(ctx context.Context) {
	tick := time.NewTicker(healEvery)
	defer tick.Stop()
	for {
		h.tick(ctx)
		select {
		case <-ctx.Done():
			return
		case <-tick.C:
		}
	}
}

// tick is one look at what is open, and every act it calls for.
func (h *healing) tick(ctx context.Context) {
	if h.acting != nil && !h.acting() {
		return
	}
	epoch, err := h.epoch(ctx)
	switch {
	case err != nil:
		h.pause(fmt.Sprintf("this controller may not act: %v", err))
		return
	case epoch == 0:
		h.pause("this controller serves without the lease (S12): a repair waits for it")
		return
	}
	inv := h.open.inventory
	now := h.now()
	heals, err := inv.HealsSince(ctx, now.Add(-24*time.Hour))
	if err != nil {
		// Blind: nothing is done, and that is said — never read as "no heals, budgets whole".
		h.reconcile(ctx, []conditions.Observation{{Scope: conditions.ScopeProbe, ID: "healers", Token: "failed",
			Kind: kindHealersBlind, Severity: conditions.Warning,
			Summary: "the healers cannot read what they did, so they count no budget and act on nothing",
			Said:    firstLine(err.Error())}})
		return
	}
	open, err := h.keeper.Open(ctx)
	if err != nil {
		h.say("the healers cannot read the open conditions, and act on nothing: %v", err)
		return
	}
	acts := actsWithin(heals, now.Add(-healBrakeWindow))
	if braked, said := brakeHolds(acts, open, now); braked {
		h.reconcile(ctx, []conditions.Observation{brakeObservation(acts, said)})
		h.pause("the mesh-wide brake holds: " + said)
		return
	}
	h.reconcile(ctx, nil)
	h.resume()
	for _, c := range open {
		row, ok := healerFor(c.Kind)
		if !ok || c.Escalated() {
			continue
		}
		budget, applies, why, err := row.applies(ctx, h, c)
		if err != nil {
			h.decline(c.Key, row.ID, "could not tell whether it applies: "+err.Error())
			continue
		}
		if !applies {
			h.decline(c.Key, row.ID, why)
			continue
		}
		h.forget(c.Key)
		spent := spentOn(heals, row, budget, now)
		if n := len(spent); n > 0 && now.Sub(spent[n-1].At) < row.Settle {
			continue // its last act is still the observation's to judge
		}
		if len(spent) >= row.Budget {
			h.escalate(ctx, row, c, budget, spent)
			continue
		}
		if len(acts) >= healBrakeLimit {
			return // the brake takes hold on the next look, said there
		}
		if h.act(ctx, row, c, budget, len(spent)) {
			acts = append(acts, inventory.Heal{At: now})
		}
	}
}

// act is one healer's act on one condition: begun in the store, made, finished, kept in the
// condition's tried and said. False when it could not even be begun.
func (h *healing) act(ctx context.Context, row healerRow, c conditions.Condition, budget string, spent int) bool {
	inv := h.open.inventory
	begun, err := inv.BeginHeal(ctx, inventory.Heal{Healer: row.ID, ConditionKey: c.Key, Kind: c.Kind,
		BudgetKey: budget, Act: row.Repair, At: h.now()})
	if err != nil {
		h.say("healer %s did not act on %s: %v", row.ID, c.Key, err)
		return false
	}
	act, said, err := row.repair(ctx, h, c)
	outcome := inventory.HealActed
	if err != nil {
		outcome, said = inventory.HealFailed, err.Error()
	}
	if act == "" {
		act = row.Repair
	}
	finishing, cancel := context.WithTimeout(context.WithoutCancel(ctx), 10*time.Second)
	defer cancel()
	if ferr := inv.FinishHeal(finishing, begun.ID, outcome, act+" — "+said); ferr != nil {
		h.say("healer %s acted on %s and could not record what came of it: %v", row.ID, c.Key, ferr)
	}
	budgetWords := fmt.Sprintf("act %d of %d within %s", spent+1, row.Budget, row.Window)
	attempt := conditions.Attempt{What: act, Outcome: outcome + ": " + said + " (" + budgetWords + ")",
		By: "healer " + row.ID}
	if _, _, terr := h.keeper.Tried(finishing, c.Key, attempt, conditions.ResolverHealer(row.ID)); terr != nil {
		h.say("healer %s acted on %s and could not keep it in the condition: %v", row.ID, c.Key, terr)
	}
	h.tell(finishing, healerActed{Healer: row.ID, Condition: c.Key, Kind: c.Kind, Act: act, Outcome: outcome,
		Said: said, Budget: budgetWords, Epoch: begun.Epoch})
	h.say("healer %s %s %s: %s — %s (%s)", row.ID, outcome, c.Key, act, said, budgetWords)
	return true
}

// escalate is a spent budget: the condition is the operator's now, urgent, with what was tried. Said
// once: an escalated condition is passed over by every healer until observation clears it.
func (h *healing) escalate(ctx context.Context, row healerRow, c conditions.Condition, budget string, spent []inventory.Heal) {
	var tried []string
	for _, s := range spent {
		tried = append(tried, fmt.Sprintf("%s at %s (%s)", s.Outcome, s.At.UTC().Format("15:04 MST"), firstLine(s.Said)))
	}
	said := fmt.Sprintf("its budget of %d act(s) within %s is spent and %s is still open: %s", row.Budget, row.Window,
		c.Key, strings.Join(tried, "; "))
	if _, err := h.open.inventory.BeginHeal(ctx, inventory.Heal{Healer: row.ID, ConditionKey: c.Key, Kind: c.Kind,
		BudgetKey: budget, Act: "handed the condition to the operator", Outcome: inventory.HealEscalated, Said: said,
		At: h.now()}); err != nil {
		h.say("healer %s could not record handing %s to the operator, and does not: %v", row.ID, c.Key, err)
		return
	}
	attempt := conditions.Attempt{What: "handed to the operator: nothing in the mesh will repair it now",
		Outcome: inventory.HealEscalated + ": " + said, By: "healer " + row.ID}
	if _, _, err := h.keeper.Escalate(ctx, c.Key, attempt); err != nil {
		h.say("healer %s could not hand %s to the operator: %v", row.ID, c.Key, err)
	}
	h.tell(ctx, healerActed{Healer: row.ID, Condition: c.Key, Kind: c.Kind, Act: "handed to the operator",
		Outcome: inventory.HealEscalated, Said: said, Budget: fmt.Sprintf("%d of %d within %s", len(spent), row.Budget, row.Window)})
	h.say("healer %s handed %s to the operator: %s", row.ID, c.Key, said)
}

// healerActed is the body of `healer-acted` (to-be 45 §7): the healer, the condition, the act and its
// outcome, and where the budget stands. **A contract**, like a condition's events: the operator-channel's
// holder may say it.
type healerActed struct {
	Event     string    `json:"event"`
	At        time.Time `json:"at"`
	Healer    string    `json:"healer"`
	By        string    `json:"by"`
	Condition string    `json:"condition"`
	Kind      string    `json:"kind"`
	Act       string    `json:"act"`
	// Outcome is acted, failed or escalated. Acted says the act was made, not that it worked: the
	// condition clearing says that.
	Outcome string `json:"outcome"`
	Said    string `json:"said"`
	Budget  string `json:"budget"`
	Epoch   uint64 `json:"epoch,omitempty"`
	Show    string `json:"show"`
}

// tell says a heal on the bus. Not said is said in the log: the act and the condition's tried still
// hold it.
func (h *healing) tell(ctx context.Context, e healerActed) {
	e.Event, e.At, e.By = link.KeyHealerActed, h.now().UTC(), "healer "+e.Healer
	e.Show = "mesh-controller.conditions key=" + e.Condition
	if h.teller == nil {
		return
	}
	body, err := json.Marshal(e)
	if err != nil {
		return
	}
	saying, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	if err := h.teller.PublishSeatEvent(saying, conditions.Seat, link.KeyHealerActed, body); err != nil {
		h.say("healer %s %s %s, and that could NOT be said on the bus: %v", e.Healer, e.Outcome, e.Condition, err)
	}
}

// reconcile keeps the healers' own conditions: the brake, and their being blind.
func (h *healing) reconcile(ctx context.Context, observed []conditions.Observation) {
	if err := h.keeper.Reconcile(ctx, sourceHealers, observed); err != nil {
		h.say("the healers' own conditions could not be kept: %v", err)
	}
}

func (h *healing) pause(why string) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.paused != why {
		h.say("the healers act on nothing: %s", why)
	}
	h.paused = why
}

func (h *healing) resume() {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.paused != "" {
		h.say("the healers act again")
	}
	h.paused = ""
}

// decline remembers why a healer passed a condition over, said once.
func (h *healing) decline(key, healer, why string) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.declined[key] != why {
		h.say("healer %s leaves %s alone: %s", healer, key, why)
	}
	h.declined[key] = why
}

func (h *healing) forget(key string) {
	h.mu.Lock()
	defer h.mu.Unlock()
	delete(h.declined, key)
}

// actsWithin are the heals since a moment that were acts — begun, made or failed; an escalation is a
// saying, not an act, and the brake does not count it.
func actsWithin(heals []inventory.Heal, since time.Time) []inventory.Heal {
	var out []inventory.Heal
	for _, h := range heals {
		if !h.At.Before(since) && h.Outcome != inventory.HealEscalated {
			out = append(out, h)
		}
	}
	return out
}

// spentOn is one healer's acts against one budget key within its window, oldest first.
func spentOn(heals []inventory.Heal, row healerRow, budget string, now time.Time) []inventory.Heal {
	var out []inventory.Heal
	for _, h := range actsWithin(heals, now.Add(-row.Window)) {
		if h.Healer == row.ID && h.BudgetKey == budget {
			out = append(out, h)
		}
	}
	return out
}

// brakeHolds says whether the mesh-wide brake holds: the limit reached within the hour, or the brake
// already said and an act within the hour still — it lets go an hour after the last act, not the first.
func brakeHolds(acts []inventory.Heal, open []conditions.Condition, now time.Time) (bool, string) {
	said := fmt.Sprintf("%d act(s) by the healers in the last %s, the limit %d", len(acts), healBrakeWindow, healBrakeLimit)
	if len(acts) >= healBrakeLimit {
		return true, said
	}
	held := slices.ContainsFunc(open, func(c conditions.Condition) bool { return c.Kind == kindHealersBraked })
	if held && len(acts) > 0 {
		last := acts[len(acts)-1].At
		return true, fmt.Sprintf("%s; held until an hour after the last, at %s", said,
			last.Add(healBrakeWindow).UTC().Format("15:04 MST"))
	}
	return false, said
}

// brakeObservation is the brake, as the urgent condition that says it.
func brakeObservation(acts []inventory.Heal, said string) conditions.Observation {
	counts := map[string]int{}
	for _, a := range acts {
		if a.Healer != "" {
			counts[a.Healer+" on "+a.ConditionKey]++
		}
	}
	var most []string
	for what, n := range counts {
		most = append(most, fmt.Sprintf("%s ×%d", what, n))
	}
	sort.Strings(most)
	return conditions.Observation{Scope: conditions.ScopeMesh, ID: "healers", Token: "braked", Kind: kindHealersBraked,
		Severity: conditions.Urgent,
		Summary: "every healer has stopped: the healers acted more often in an hour than the mesh allows, which is a " +
			"healer looping, not repairing — " + said,
		Said: strings.Join(most, ", ")}
}

// --- H1 ----------------------------------------------------------------------------------------------

// appliesToAMachine is H1's: a machine named, its budget counted against the condition.
func appliesToAMachine(_ context.Context, _ *healing, c conditions.Condition) (string, bool, string, error) {
	if c.Subject.Machine == "" {
		return "", false, "it names no machine", nil
	}
	return c.Key, true, "", nil
}

// repairReport is H1: ask the machine to report; if what comes back is not what it was sent, or nothing
// comes, send it again.
func repairReport(ctx context.Context, h *healing, c conditions.Condition) (string, string, error) {
	node := c.Subject.Machine
	inv := h.open.inventory
	// The store's clock, as the report's time is: not the runner's, which a test moves by hand.
	asked := time.Now()
	askErr := h.askReport(ctx, node)
	current, heard := false, false
	if askErr == nil {
		deadline := time.Now().Add(h.reportWait)
		for {
			r, found, err := lastReportOf(ctx, inv, node)
			if err != nil {
				return "", "", err
			}
			if found && r.At != nil && r.At.After(asked) {
				heard, current = true, r.Current
				if current {
					break
				}
			}
			if time.Now().After(deadline) {
				break
			}
			select {
			case <-ctx.Done():
				return "", "", ctx.Err()
			case <-time.After(min(2*time.Second, h.reportWait/4+time.Millisecond)):
			}
		}
	}
	if current {
		return "asked " + node + "'s node-engine to say again what it last applied",
			"it reported the declaration it was sent: its report had not reached the mesh", nil
	}
	why := "it said nothing within " + h.reportWait.String() + " — its node-engine may be older than the report verb"
	switch {
	case askErr != nil:
		why = "it could not be asked: " + askErr.Error()
	case heard:
		why = "it reported a declaration other than the one it was sent"
	}
	if err := h.sendAgain(ctx, node); err != nil {
		return "asked " + node + " to report, then sent it its current declaration again", why + "; the send failed",
			err
	}
	return "asked " + node + " to report, then sent it its current declaration again", why + "; sent again", nil
}

// lastReportOf is one machine's last report beside its last send.
func lastReportOf(ctx context.Context, inv *inventory.Inventory, node string) (inventory.Reported, bool, error) {
	reports, err := inv.LastReports(ctx)
	if err != nil {
		return inventory.Reported{}, false, err
	}
	for _, r := range reports {
		if r.Node == node {
			return r, true, nil
		}
	}
	return inventory.Reported{}, false, nil
}

// --- H2 ----------------------------------------------------------------------------------------------

// planStale is why a plan's wait is superseded or finished, and the state closing it leaves it in; empty
// when it is neither, which is not H2's to repair.
func planStale(ctx context.Context, inv *inventory.Inventory, p inventory.Plan) (state, why string, err error) {
	if p.Release != nil {
		return "", "", nil // a release plan walks machines, and its own gate says when it is done (ADR 0236)
	}
	recent, err := inv.RecentPlans(ctx, 50)
	if err != nil {
		return "", "", err
	}
	for _, newer := range recent {
		if newer.ID == p.ID || !newer.Created.After(p.Created) || !repositoryMatches(newer.Repository, p.Repository) ||
			newer.Branch != p.Branch || newer.State == inventory.PlanSuperseded {
			continue
		}
		return inventory.PlanSuperseded, fmt.Sprintf("superseded by %s (%s %s), a newer merge of the same repository "+
			"and branch", newer.ID, newer.Repository, short(newer.Commit)), nil
	}
	for _, tier := range p.Tiers {
		for _, m := range tier {
			s := p.Modules[m]
			if s == nil || (s.State != "built" && s.State != "failed") {
				return "", "", nil
			}
			if s.State == "built" && s.SentAt == nil {
				u, err := inv.UpgradeOf(ctx, m)
				if err != nil {
					return "", "", err
				}
				if u.RollOut {
					return "", "", nil
				}
			}
		}
	}
	return inventory.PlanDone, "finished: every module of every tier is built or failed, and every one that rolls " +
		"out was sent — nothing is left to wait on", nil
}

// appliesToAStalePlan is H2's: the plan is open, and its wait is superseded or finished.
func appliesToAStalePlan(ctx context.Context, h *healing, c conditions.Condition) (string, bool, string, error) {
	if c.Subject.Scope == conditions.ScopeDelivery {
		return appliesToAStalledDelivery(ctx, h, c)
	}
	p, err := h.open.inventory.PlanByID(ctx, c.Subject.ID)
	if err != nil {
		return "", false, "", err
	}
	if !p.Open() {
		return "", false, "the plan is " + p.State + " already: its condition clears on the next look", nil
	}
	state, _, err := planStale(ctx, h.open.inventory, p)
	if err != nil {
		return "", false, "", err
	}
	if state == "" {
		return "", false, "its wait is neither superseded nor finished: it waits on something still to come, " +
			"which its own signal says", nil
	}
	return c.Key, true, "", nil
}

// repairPlan is H2: the plan closed with its note, under the plans' hold, by compare-and-set.
func repairPlan(ctx context.Context, h *healing, c conditions.Condition) (string, string, error) {
	if c.Subject.Scope == conditions.ScopeDelivery {
		return repairDelivery(ctx, h, c)
	}
	inv := h.open.inventory
	release, err := inv.HoldPlans(ctx, true)
	if err != nil {
		return "", "", err
	}
	defer release()
	p, err := inv.PlanByID(ctx, c.Subject.ID)
	if err != nil {
		return "", "", err
	}
	if !p.Open() {
		return "closed nothing", "the plan is " + p.State + " already", nil
	}
	state, why, err := planStale(ctx, inv, p)
	if err != nil {
		return "", "", err
	}
	if state == "" {
		return "closed nothing", "its wait is no longer superseded or finished", nil
	}
	p.State = state
	p.Note = fmt.Sprintf("closed by healer H2 at tier %d: %s", p.Tier, why)
	if state != inventory.PlanDone {
		sayUnsent(&p, func(m string) bool {
			u, err := inv.UpgradeOf(ctx, m)
			return err == nil && u.RollOut
		})
	}
	if err := inv.SavePlan(ctx, &p); err != nil {
		return "", "", err
	}
	return "closed the plan " + p.ID + " (" + state + ")", why, nil
}

// --- H3 ----------------------------------------------------------------------------------------------

// appliesToAnObject is H3's: every holder or consumer the probe or the bus names, its budget per object.
func appliesToAnObject(_ context.Context, h *healing, c conditions.Condition) (string, bool, string, error) {
	if h.assertObjects == nil {
		return "", false, "this controller is not on the bus", nil
	}
	return c.Key, true, "", nil
}

// repairObjects is H3: the send's own assertion of every stream, consumer and seat worker.
func repairObjects(ctx context.Context, h *healing, _ conditions.Condition) (string, string, error) {
	if err := h.assertObjects(ctx); err != nil {
		return "", "", err
	}
	return "asserted the bus's streams, consumers and seat workers again",
		"every object the mesh defines is asserted; the probe that raised it says on its next run whether it is there", nil
}

// --- H4 ----------------------------------------------------------------------------------------------

// resettable is why a consumer may be reset by the mesh itself, from the stream table; empty when not.
func resettable(stream, name string) string {
	for _, c := range broker.MeshConsumers() {
		if c.Stream == stream && c.Name == name {
			return c.Resettable
		}
	}
	return ""
}

// consumerOf is the stream and consumer a bus condition names: `<stream>.<consumer>`.
func consumerOf(c conditions.Condition) (string, string, bool) {
	stream, name, found := strings.Cut(c.Subject.ID, ".")
	return stream, name, found && stream != "" && name != ""
}

// appliesToAResettableConsumer is H4's: only a consumer the stream table marks resettable.
func appliesToAResettableConsumer(_ context.Context, _ *healing, c conditions.Condition) (string, bool, string, error) {
	stream, name, ok := consumerOf(c)
	if !ok {
		return "", false, "it names no consumer", nil
	}
	if resettable(stream, name) == "" {
		return "", false, fmt.Sprintf("%s on %s is not marked resettable in the stream table: what a reset drops, "+
			"nothing would catch up", name, stream), nil
	}
	return c.Key, true, "", nil
}

// repairConsumer is H4: `broker consumer-reset`, made by the mesh.
func repairConsumer(_ context.Context, h *healing, c conditions.Condition) (string, string, error) {
	stream, name, _ := consumerOf(c)
	said, err := h.resetConsumer(stream, name)
	if err != nil {
		return "", "", err
	}
	return fmt.Sprintf("re-made %s on %s to deliver from now", name, stream),
		said + "; " + resettable(stream, name), nil
}

// --- the verb ----------------------------------------------------------------------------------------

// healersCommand is `healers`: the registry, what the healers did lately, and the brake.
func healersCommand(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("healers", flag.ContinueOnError)
	daysFlag := set.Int("days", 7, "how many days of acts back")
	jsonFlag := set.Bool("json", false, "as data")
	if rest, err := parseAround(set, args); err != nil {
		return err
	} else if len(rest) > 0 {
		return errors.New("healers [--days N] [--json]")
	}
	days, asJSON := *daysFlag, *jsonFlag
	if days <= 0 {
		return fmt.Errorf("healers --days takes a number of days, not %d", days)
	}
	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	now := time.Now()
	heals, err := open.inventory.HealsSince(ctx, now.Add(-time.Duration(days)*24*time.Hour))
	if err != nil {
		return fmt.Errorf("what the healers did cannot be read: %w", err)
	}
	conds, condErr := openConditions(ctx)
	braked, said := brakeHolds(actsWithin(heals, now.Add(-healBrakeWindow)), conds, now)
	brake := map[string]any{"holds": braked, "said": said, "limit": healBrakeLimit, "window": healBrakeWindow.String()}
	if condErr != nil {
		brake["conditions"] = "the open conditions could not be read, so whether the brake was said is not known: " +
			condErr.Error()
	}
	var rows []map[string]any
	for _, r := range healerRegistry {
		rows = append(rows, map[string]any{"id": r.ID, "kinds": r.Kinds, "condition": r.Condition, "repair": r.Repair,
			"budget": fmt.Sprintf("%d act(s) within %s, %s apart at least", r.Budget, r.Window, r.Settle),
			"then":   r.Then, "acts-in": r.ActsIn, "event": r.Event, "from": r.From})
	}
	if heals == nil {
		heals = []inventory.Heal{}
	}
	if asJSON {
		return printJSON(map[string]any{"healers": rows, "heals": heals, "brake": brake, "days": days,
			"note": "a heal is never a hand act; whether it repaired anything is the condition's clearing to say"})
	}
	for _, r := range healerRegistry {
		fmt.Printf("%s  %s\n    → %s\n    budget %d within %s; then %s (in %s)\n", r.ID, r.Condition, r.Repair, r.Budget,
			r.Window, r.Then, r.ActsIn)
	}
	fmt.Printf("\nthe brake: %s — %s\n\n", map[bool]string{true: "HOLDS, every healer has stopped", false: "off"}[braked], said)
	if len(heals) == 0 {
		fmt.Printf("no healer acted in the last %d day(s)\n", days)
		return nil
	}
	for i := len(heals) - 1; i >= 0; i-- {
		x := heals[i]
		fmt.Printf("%s  %s %-9s %s\n    %s\n", x.At.Local().Format("2006-01-02 15:04"), x.Healer, x.Outcome, x.ConditionKey,
			firstLine(x.Said))
	}
	return nil
}

// forgettingOldHeals removes heals past their keeping once a day, by the controller acting only.
func forgettingOldHeals(ctx context.Context, inv *inventory.Inventory) {
	for {
		if link.Holding() {
			if n, err := inv.ForgetOldHeals(ctx); err != nil {
				fmt.Printf("heals older than %s could not be removed: %v\n", inventory.HealsKeptFor, err)
			} else if n > 0 {
				fmt.Printf("removed %d heal(s) older than %s\n", n, inventory.HealsKeptFor)
			}
		}
		select {
		case <-ctx.Done():
			return
		case <-time.After(24 * time.Hour):
		}
	}
}

// healsCount is what the healers did, counted for `status`.
type healsCount struct {
	Acts      int `json:"acts"`
	Escalated int `json:"escalated"`
}

// countHeals counts acts and escalations.
func countHeals(heals []inventory.Heal) *healsCount {
	out := &healsCount{}
	for _, h := range heals {
		if h.Outcome == inventory.HealEscalated {
			out.Escalated++
		} else {
			out.Acts++
		}
	}
	return out
}