package main

import (
	"context"
	"errors"
	"testing"
	"time"

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

	"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/lease"

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

// Two controllers at once (novox/hq to-be 45 §6, issue 204; the half of replay R1 that lives here): two
// serving controllers over one store and one bus. The second waits while the first holds the lease; on
// a handover it takes it at a higher epoch, the record says which held what and how each ended; and the
// one that lost it acts no more — no declaration composed, no plan and no condition written — the
// moment it lost it.
//
//	MESH_TEST_POSTGRES=… go test ./cmd/mesh-controller/ -run Controllers   (each test on a bus of its own: internal/testbus)

// aBusForTheLease is the test bus with the controller's lease bucket new.
func aBusForTheLease(t *testing.T) (string, jetstream.KeyValue) {
	t.Helper()
	url := testbus.URL(t)
	conn, err := nats.Connect(url)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(conn.Close)
	js, err := jetstream.New(conn)
	if err != nil {
		t.Fatal(err)
	}
	_ = js.DeleteKeyValue(t.Context(), broker.LeaseBucket)
	if err := broker.EnsureLeaseBucket(t.Context(), js); err != nil {
		t.Fatal(err)
	}
	kv, err := js.KeyValue(t.Context(), broker.LeaseBucket)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { _ = js.DeleteKeyValue(context.Background(), broker.LeaseBucket) })
	return url, kv
}

func TestTwoControllersOneActs(t *testing.T) {
	url, kv := aBusForTheLease(t)
	inv := inventory.ForTest(t)
	ctx := t.Context()

	// Controller A takes the lease.
	a := &actor{}
	aCtx, stopA := context.WithCancel(ctx)
	defer stopA()
	lostA, err := a.serveUnderTheLease(aCtx, inv, url)
	if err != nil {
		t.Fatal(err)
	}
	epochA, err := a.epoch(ctx)
	if err != nil || epochA == 0 {
		t.Fatalf("A holds no epoch: %d, %v", epochA, err)
	}

	// Controller B starts while A holds it, and waits — acting on nothing meanwhile.
	b := &actor{}
	bCtx, stopB := context.WithCancel(ctx)
	defer stopB()
	tookB := make(chan (<-chan struct{}), 1)
	go func() {
		lost, err := b.serveUnderTheLease(bCtx, inv, url)
		if err != nil {
			t.Errorf("B: %v", err)
			close(tookB)
			return
		}
		tookB <- lost
	}()
	select {
	case <-tookB:
		t.Fatal("B took the lease while A held it")
	case <-time.After(3 * time.Second):
	}
	if _, err := b.epoch(ctx); !errors.Is(err, lease.ErrNotHeld) {
		t.Fatalf("B, waiting, may act: %v", err)
	}

	// A hands over, as a controller being replaced does: B takes the lease at once, at a higher epoch.
	stopA()
	a.release()
	var lostB <-chan struct{}
	select {
	case lostB = <-tookB:
	case <-time.After(10 * time.Second):
		t.Fatal("B did not take the lease A gave back")
	}
	select {
	case <-lostA:
	default:
		t.Fatal("A, having given the lease back, is not told it no longer holds it")
	}
	epochB, err := b.epoch(ctx)
	if err != nil || epochB <= epochA {
		t.Fatalf("B acts as epoch %d after A's %d (%v): an epoch only grows", epochB, epochA, err)
	}
	if _, err := a.epoch(ctx); err == nil {
		t.Fatal("A acts after giving the lease back")
	}
	ea, _, _ := inv.EpochOf(ctx, epochA)
	eb, _, _ := inv.EpochOf(ctx, epochB)
	if ea.How != inventory.EpochReleased || eb.Ended != nil || eb.Instance != instance {
		t.Fatalf("the record of the handover reads %+v then %+v", ea, eb)
	}

	// Something else writes the lease's key — a third controller on a clock that read it as expired:
	// B's next renewal is refused, and B stops acting at once.
	if _, err := kv.Put(ctx, lease.Key, []byte(`{"instance":"a third controller","epoch":1}`)); err != nil {
		t.Fatal(err)
	}
	select {
	case <-lostB:
	case <-time.After(2 * lease.RenewEvery):
		t.Fatal("B was not told it lost the lease")
	}
	if _, err := b.epoch(ctx); !errors.Is(err, lease.ErrNotHeld) {
		t.Fatalf("B acts after losing the lease: %v", err)
	}
	// Nothing B does is written: a declaration's number is not taken, a plan is not saved, a condition
	// is not raised.
	inv.ActsUnder(b.epoch)
	if _, err := inv.AddNode(ctx, "anchor"); err != nil {
		t.Fatal(err)
	}
	saved := inventory.Plan{ID: "plan-after-loss", Repository: "novox/app", Commit: "c0ffee00", Created: time.Now(),
		State: inventory.PlanBuilding}
	if err := inv.SavePlan(ctx, &saved); err == nil {
		t.Fatal("B wrote a plan after losing the lease")
	}
	store := conditions.NewInMemory()
	keeper := conditions.NewKeeper(ctx, conditions.Options{Store: store, History: store,
		Epoch: func() (uint64, error) { return b.epoch(ctx) }})
	defer keeper.Close(context.Background())
	if _, err := keeper.Observe(ctx, conditions.Observation{Scope: conditions.ScopeCore, ID: "x", Kind: "x",
		Severity: conditions.Warning, Summary: "x", Source: "test"}); err == nil {
		t.Fatal("B raised a condition after losing the lease")
	}
	if ended, _, _ := inv.EpochOf(ctx, epochB); ended.How != inventory.EpochLost {
		t.Fatalf("B's epoch does not say it was lost: %+v", ended)
	}
}

// A controller whose bus refuses it the lease's key, with nobody holding it, serves without the lease:
// it acts with no epoch — refused by no node-engine — says so, and takes the lease once it can.
func TestAControllerTheBusRefusesTheLeaseServesUnleasedAndSaysSo(t *testing.T) {
	a := &actor{serving: true, unleased: "the bus refused the lease's key"}
	if epoch, err := a.epoch(context.Background()); err != nil || epoch != 0 {
		t.Fatalf("an unleased controller answers %d, %v: it acts, claiming no epoch", epoch, err)
	}
	if st := a.standing(); st.Unleased == "" || st.Held {
		t.Fatalf("its standing says %+v", st)
	}
	// One that neither holds nor is unleased — still waiting — acts on nothing.
	waiting := &actor{serving: true}
	if _, err := waiting.epoch(context.Background()); !errors.Is(err, lease.ErrNotHeld) {
		t.Fatalf("a controller waiting for the lease may act: %v", err)
	}
}