package link

import (
	"context"
	"encoding/json"
	"io"
	"log"
	"os"
	"sync"
	"testing"
	"time"

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

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

// A build, end to end, against a real server.
//
// The claim worth checking is the one ADR 0121 rests on: **one publish reaches three audiences**.
// Whoever asked matches the outcome by the id their request carried; the controller records it; the
// catalogue places it. On the old bus that fan-out came from a shared exchange, and it would be easy
// to write a version where only the asker hears it and nobody notices for weeks.
//
//	docker run -d --rm --name t -p 14230:4222 nats:2.10-alpine -js
//	MESH_TEST_NATS=nats://127.0.0.1:14230 go test ./internal/link/ -run TestNatsABuild

func aBusWithTheBuildRole(t *testing.T) *broker.JetStream {
	t.Helper()
	url := os.Getenv("MESH_TEST_NATS")
	if url == "" {
		t.Skip("MESH_TEST_NATS unset")
	}
	js, err := broker.Dial(url)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(js.Close)

	seats := []broker.DeclaredSeat{{Name: TheBuildMachine, Accepts: []string{"build"},
		Emits: []string{"built"}}}
	if err := broker.AssertMeshStreams(js); err != nil {
		t.Fatal(err)
	}
	if err := broker.RaiseSeats(js, seats, map[string]broker.Holder{
		TheBuildMachine: {Node: "anchor", Module: "builder"},
	}); err != nil {
		t.Fatal(err)
	}
	clean := func() {
		_ = js.Context().DeleteStream("SEAT_MESH_BUILD_MACHINE")
		for _, s := range broker.MeshStreams() {
			_ = js.Context().PurgeStream(s.Name)
		}
	}
	t.Cleanup(clean)
	return js
}

// The whole round trip: asked, taken, built, and the outcome heard by the asker and by a consumer of
// the role's event who never asked for anything.
func TestNatsABuildIsTakenAndItsOutcomeReachesEverybody(t *testing.T) {
	js := aBusWithTheBuildRole(t)
	ctx, stop := context.WithCancel(context.Background())
	defer stop()

	// A third party on the role's event — what the catalogue is. Subscribed first, so nothing is
	// missed.
	heard := make(chan BuildResult, 4)
	watching, err := js.Conn().Subscribe(BuildOutcome(), func(msg *nats.Msg) {
		var r BuildResult
		if json.Unmarshal(msg.Data, &r) == nil {
			heard <- r
		}
	})
	if err != nil {
		t.Fatal(err)
	}
	defer func() { _ = watching.Unsubscribe() }()
	_ = js.Conn().Flush()

	// A build machine holding the role.
	machine := MachineOverNATS(js, "anchor")
	defer machine.Close()
	failed := make(chan error, 1)
	go func() {
		failed <- machine.Take(ctx, func(ctx context.Context, work Build) {
			r := work.Request()
			_ = work.Announce(ctx, BuildResult{
				ID: r.ID, Repository: r.Repository, On: "anchor", Commit: "abc1234",
				Manifest: json.RawMessage(`{"module":"shop"}`),
			})
			_ = work.Done()
		})
	}()

	ask := &natsBuilds{js: js}
	result, err := ask.Submit(ctx, BuildRequest{ID: "b-1", Repository: "/r"}, 15*time.Second)
	if err != nil {
		select {
		case why := <-failed:
			t.Fatalf("the machine could not take work: %v", why)
		default:
		}
		t.Fatalf("the asker never got an outcome: %v", err)
	}
	if result.ID != "b-1" || result.Commit != "abc1234" {
		t.Fatalf("the asker got %+v", result)
	}
	// Named in the outcome, because only the manifest says what was built and the catalogue reading
	// this event needs to know.
	if result.Module != "shop" {
		t.Errorf("the outcome names module %q, so a catalogue reading it cannot place the build",
			result.Module)
	}

	select {
	case also := <-heard:
		if also.ID != "b-1" {
			t.Fatalf("a third party heard %+v", also)
		}
	case <-time.After(5 * time.Second):
		t.Fatal("nobody but the asker heard the outcome, so the catalogue would never place the build")
	}

	// And the work left the queue: a request a machine took and settled must not be given to another.
	deadline := time.Now().Add(5 * time.Second)
	for time.Now().Before(deadline) {
		info, err := js.Context().StreamInfo("SEAT_MESH_BUILD_MACHINE")
		if err == nil && info.State.Msgs == 0 {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}
	t.Fatal("the request is still queued after being settled, so another machine would build it again")
}

// Work submitted with no machine holding the role waits rather than failing, and is done when one
// arrives. **That is what a queue is for**, and the alternative — refusing because nobody is there
// yet — would make installing a build machine an ordering problem.
func TestNatsABuildWaitsForAMachineRatherThanFailing(t *testing.T) {
	js := aBusWithTheBuildRole(t)

	body, _ := json.Marshal(BuildRequest{ID: "b-2", Repository: "/r"})
	if _, err := js.Context().Publish(BuildWork(), body); err != nil {
		t.Fatal(err)
	}
	info, err := js.Context().StreamInfo("SEAT_MESH_BUILD_MACHINE")
	if err != nil || info.State.Msgs != 1 {
		t.Fatalf("the work did not queue: %+v %v", info, err)
	}

	// Now a machine arrives and finds it waiting.
	ctx, stop := context.WithCancel(context.Background())
	defer stop()
	took := make(chan string, 1)
	machine := MachineOverNATS(js, "anchor")
	defer machine.Close()
	go func() {
		_ = machine.Take(ctx, func(ctx context.Context, work Build) {
			took <- work.Request().ID
			_ = work.Announce(ctx, BuildResult{ID: work.Request().ID, On: "anchor", Failed: "no"})
			_ = work.Done()
		})
	}()
	select {
	case id := <-took:
		if id != "b-2" {
			t.Fatalf("the machine took %q", id)
		}
	case <-time.After(10 * time.Second):
		t.Fatal("a machine that arrived after the work did never got it, so the backlog was lost")
	}
}

// A machine that dies before saying anything leaves the work for another.
func TestNatsWorkAMachineDidNotAnswerGoesBackToTheQueue(t *testing.T) {
	js := aBusWithTheBuildRole(t)
	ctx, stop := context.WithCancel(context.Background())
	defer stop()

	body, _ := json.Marshal(BuildRequest{ID: "b-3", Repository: "/r"})
	if _, err := js.Context().Publish(BuildWork(), body); err != nil {
		t.Fatal(err)
	}

	var once sync.Once
	handed := make(chan struct{}, 2)
	machine := MachineOverNATS(js, "anchor")
	defer machine.Close()
	go func() {
		_ = machine.Take(ctx, func(ctx context.Context, work Build) {
			handed <- struct{}{}
			// The first time, hand it straight back — a machine that stopped mid-build.
			var settled bool
			once.Do(func() { _ = work.Hold(200 * time.Millisecond); settled = true })
			if !settled {
				_ = work.Announce(ctx, BuildResult{ID: work.Request().ID, On: "anchor"})
				_ = work.Done()
			}
		})
	}()

	for i := 0; i < 2; i++ {
		select {
		case <-handed:
		case <-time.After(10 * time.Second):
			t.Fatalf("the work was handed over %d time(s); unanswered work must come back", i)
		}
	}
}

func quietLog() *log.Logger { return log.New(io.Discard, "", 0) }

var _ = quietLog