package main

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"sync"
	"time"

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

// `status` answered from a summary the serving controller keeps current (novox/hq to-be 45 Phase 0,
// §4's D9 and §8's health of the controller).
//
// **Asked, it was composed: every machine resolved, twice, while its caller waited.** On 2026-10-06
// the verb took eighteen seconds on a mesh of four machines, so its caller read "still running" and
// had to ask `calls` for the answer to "is the mesh alright" — the one question that must answer at
// once, and the one a self-check and a rollout gate will ask every few minutes. So the serving
// controller composes it in the background — at its start, after anything that changes what it says
// (a machine's report, a build, a verb that acts), and every minute regardless — and the verb answers
// the last composition at once, saying when it was composed and how long that took. A caller who
// needs it newer than that reads the time and asks again; nothing is answered as current that is not.

// statusEvery is how often the summary is composed with nothing having nudged it; statusSettle how
// long a nudge waits for the next, so a push answered by four machines is composed once.
var (
	statusEvery  = time.Minute
	statusSettle = 2 * time.Second
	// statusComposeWithin bounds one composition, so a store that hangs cannot stop the summary for
	// good; the attempt is said as failed, and the last summary stands with its age.
	statusComposeWithin = 2 * time.Minute
)

// statusSummary is the last composed `status --json`, and when.
type statusSummary struct {
	compose func(context.Context) ([]byte, error)
	// every, settle and within are the clocks above, read once when it is made.
	every, settle, within time.Duration

	mu         sync.Mutex
	body       []byte
	composedAt time.Time
	took       time.Duration
	failed     string
	failedAt   time.Time
	started    time.Time
	first      chan struct{} // closed when the first attempt ends, either way

	nudged chan struct{}
}

func newStatusSummary(compose func(context.Context) ([]byte, error)) *statusSummary {
	return &statusSummary{compose: compose, started: time.Now(), first: make(chan struct{}),
		nudged: make(chan struct{}, 1), every: statusEvery, settle: statusSettle, within: statusComposeWithin}
}

// statusFrom is the serving controller's summary; nil in any other process, where `status` is
// composed when asked, as at a shell.
var statusFrom *statusSummary

// nudge asks for a composition soon. Never blocks: one pending is as good as many.
func (s *statusSummary) nudge() {
	if s == nil {
		return
	}
	select {
	case s.nudged <- struct{}{}:
	default:
	}
}

// keep composes until ctx ends: now, on a nudge once things settle, and every statusEvery.
func (s *statusSummary) keep(ctx context.Context) {
	once := sync.Once{}
	for {
		s.composeOnce(ctx)
		once.Do(func() { close(s.first) })
		timer := time.NewTimer(s.every)
		select {
		case <-ctx.Done():
			timer.Stop()
			return
		case <-timer.C:
		case <-s.nudged:
			timer.Stop()
			// Let what else is arriving arrive, then compose once for all of it.
			select {
			case <-ctx.Done():
				return
			case <-time.After(s.settle):
			}
			select {
			case <-s.nudged:
			default:
			}
		}
	}
}

func (s *statusSummary) composeOnce(ctx context.Context) {
	start := time.Now()
	asking, cancel := context.WithTimeout(ctx, s.within)
	body, err := s.compose(asking)
	cancel()
	took := time.Since(start)
	s.mu.Lock()
	defer s.mu.Unlock()
	if err != nil {
		s.failed, s.failedAt = err.Error(), time.Now()
		fmt.Printf("status could not be composed (after %s): %v — `status` answers the last summary, "+
			"with its age\n", took.Round(time.Millisecond), err)
		return
	}
	s.body, s.composedAt, s.took, s.failed = body, start, took, ""
}

// answer is what the `status` verb answers: the last summary at once, the same document `status
// --json` prints, with when it was composed. Before the first composition has ended it waits for it,
// but never past the caller's window; a controller that has none says so and why, rather than
// answering an empty mesh as a well one.
func (s *statusSummary) answer(ctx context.Context) (any, error) {
	wait := time.NewTimer(link.AnswerWithin - time.Second)
	defer wait.Stop()
	select {
	case <-s.first:
	case <-wait.C:
	case <-ctx.Done():
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.body == nil {
		why := "its first composition has not finished"
		if s.failed != "" {
			why = "it could not be composed: " + s.failed
		}
		return nil, fmt.Errorf("this controller started %s ago and has no status to answer yet — %s. "+
			"Ask again shortly", time.Since(s.started).Round(time.Second), why)
	}
	var parsed any
	_ = json.Unmarshal(s.body, &parsed)
	out := map[string]any{
		"output": string(s.body), "ok": true, "answer": parsed,
		"composed":   s.composedAt.UTC().Format(time.RFC3339),
		"age":        time.Since(s.composedAt).Round(time.Second).String(),
		"composedIn": s.took.Round(time.Millisecond).String(),
		"note": "composed by the serving controller at its start, after each report, build or act, and " +
			"every minute; answered at once from the last composition",
	}
	if s.failed != "" && s.failedAt.After(s.composedAt) {
		out["lastAttemptFailed"] = fmt.Sprintf("%s: %s — this summary is the last that could be composed",
			s.failedAt.UTC().Format(time.RFC3339), s.failed)
	}
	return out, nil
}

// composeStatus is `status --json`, composed in this process against its stores.
func composeStatus(open *stores) func(context.Context) ([]byte, error) {
	return func(ctx context.Context) ([]byte, error) {
		asked, err := theThreeQuestions(ctx, open)
		if err != nil {
			return nil, err
		}
		return statusAsJSON(asked)
	}
}

// readingVerbs are the verbs that only read; after any other, what `status` says may have changed, so the summary is
// composed again; a verb that only reads leaves it alone, or a console polling `nodes` would keep the
// controller composing for ever.
var readingVerbs = map[string]bool{
	"tools": true, "calls": true, "status": true, "nodes": true, "node": true, "modules": true,
	"seats": true, "builds": true, "plan": true, "queue": true, "durations": true, "hand-acts": true,
	"doctor": true, "conditions": true, "healers": true,
}

// nudgingListener is the enrolment, nudging the summary when a machine said something new.
type nudgingListener struct {
	link.Enrolment
	summary *statusSummary
	// open is the serving controller's stores, for replacing a given value after a module's first
	// good start (novox/hq ADR 0228).
	open *stores
}

func (l nudgingListener) Heard(ctx context.Context, report link.Report) (bool, error) {
	// A declaration refused as older than the one the machine holds is counted by its writer — the
	// controller epoch it claimed (novox/hq to-be 45 §6, S13) — and so is what the machine's own count
	// says it refused beyond the refusals heard.
	now := time.Now()
	if report.StaleRefusalOf() {
		link.StaleRefusals.Refused(link.Refusal{Writer: link.WriterEpoch(report.Epoch), Epoch: report.Epoch,
			Receiver: report.Node, At: now})
	}
	if report.Ordered() {
		link.StaleRefusals.Lifetime(report.Node, report.RefusedOlder, now)
	}
	// A send refused for the generation it was composed from is kept on the send it refused, so S20 names
	// its sender (novox/hq issue 234).
	if report.OlderGeneration != nil {
		heardGenerationRefusal(ctx, l.Enrolment.Inventory, report)
	}
	// What the machine's witnesses put back and stand by (novox/hq ADR 0236): read by the gate and its
	// probe. Only from an account of the machine — not a word that a declaration was set aside, nor a rekey.
	if report.Superseded == "" && report.Rekey == nil && report.Node != "" {
		witnessed.heard(report.Node, report.Rollbacks, now)
	}
	news, err := l.Enrolment.Heard(ctx, report)
	if news {
		l.summary.nudge()
	}
	// What it says of its long-running resources (novox/hq ADR 0240): kept, and its modules' conditions
	// raised or cleared from it. Only from an account of the machine the store took.
	if err == nil && report.Health != nil && report.Superseded == "" && report.Rekey == nil && report.Node != "" &&
		l.Enrolment.Inventory != nil {
		if herr := stateHealth(ctx, l.Enrolment.Inventory, conditionsFrom, report.Node, *report.Health, now); herr != nil {
			fmt.Fprintf(os.Stderr, "mesh-controller: could not keep what %s says of its resources' health: %v\n",
				report.Node, herr)
		}
	}
	if err == nil && l.open != nil && startedWell(report) {
		// Off the report's path: replacing a given value sends the machine, and a report waits for
		// nothing it caused (novox/hq ADR 0228).
		go replaceGiven(context.WithoutCancel(ctx), l.open, report)
	}
	return news, err
}