package link

import (
	"context"
	"crypto/ed25519"
	"encoding/json"
	"errors"
	"reflect"
	"sync"
	"testing"
	"time"
)

// A report of an apply reaches the mesh even when the apply ended the link, and one lost anyway is
// said again the next time the node is linked (novox/hq issue 264).

// quietLink is a link with no broker behind it. A report is refused once the context it is
// published on is cancelled, as the bus's is ("reporting: context canceled"), or while refusing.
type quietLink struct {
	mu        sync.Mutex
	reports   []Report
	refusing  bool
	delivered chan Declaration
	lost      chan error
}

func newQuietLink(arriving ...Declaration) *quietLink {
	l := &quietLink{delivered: make(chan Declaration, len(arriving)), lost: make(chan error, 1)}
	for _, d := range arriving {
		l.delivered <- d
	}
	return l
}

func (l *quietLink) Report(ctx context.Context, _ string, body []byte) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	l.mu.Lock()
	defer l.mu.Unlock()
	if l.refusing {
		return errors.New("refused")
	}
	var r Report
	if err := json.Unmarshal(body, &r); err != nil {
		return err
	}
	l.reports = append(l.reports, r)
	return nil
}
func (l *quietLink) Alive(context.Context, string, []byte) error { return nil }
func (l *quietLink) Declarations() <-chan Declaration            { return l.delivered }
func (l *quietLink) Lost() <-chan error                          { return l.lost }
func (l *quietLink) Close()                                      {}

func (l *quietLink) said() []Report {
	l.mu.Lock()
	defer l.mu.Unlock()
	return append([]Report(nil), l.reports...)
}

// keptInMemory is Unsaid without a disk.
type keptInMemory struct {
	report *Report
}

func (k *keptInMemory) Keep(r Report) error {
	if r.Declared == "" {
		k.report = nil
		return nil
	}
	k.report = &r
	return nil
}
func (k *keptInMemory) Said(declared string) error {
	if k.report != nil && k.report.Declared == declared {
		k.report = nil
	}
	return nil
}
func (k *keptInMemory) Pending() (Report, bool, error) {
	if k.report == nil {
		return Report{}, false, nil
	}
	return *k.report, true, nil
}

func aMember(t *testing.T) (Membership, ed25519.PrivateKey) {
	t.Helper()
	public, private, err := ed25519.GenerateKey(nil)
	if err != nil {
		t.Fatal(err)
	}
	return Membership{Node: "n1", Signer: public}, private
}

// Measured on the anchor: a declaration carried a new controller and a new host, the host applied
// it, stood aside for its successor — which cancels the link — and the report of that apply failed
// with "context canceled". The plan waited on it until somebody pushed by hand.
func TestAnApplyThatEndsTheLinkIsStillReported(t *testing.T) {
	m, key := aMember(t)
	declaration := &said{body: signedBy(t, key, []byte(`{"declaration":1}`))}
	l := newQuietLink(declaration)
	kept := &keptInMemory{}

	ctx, standAside := context.WithCancel(context.Background())
	defer standAside()
	apply := func(context.Context, []byte, []byte) Report {
		standAside() // the host delivered its successor, and stands aside for it
		return Report{Declared: "d1", Applied: []string{"a"}}
	}

	done := make(chan error, 1)
	go func() { done <- serve(ctx, l, m, apply, nil, time.Second, nil, kept) }()
	select {
	case err := <-done:
		if err != nil {
			t.Fatal(err)
		}
	case <-time.After(5 * time.Second):
		t.Fatal("the link did not end after the apply stood aside")
	}

	reports := l.said()
	if len(reports) != 1 || reports[0].Declared != "d1" || !reflect.DeepEqual(reports[0].Applied, []string{"a"}) {
		t.Fatalf("the apply's report did not reach the mesh: %+v", reports)
	}
	if !declaration.handled {
		t.Fatal("the declaration was not settled after its report")
	}
	if _, ok, _ := kept.Pending(); ok {
		t.Fatal("a report the mesh took is still kept to be said again")
	}
}

// A report that did not reach the mesh — the host died between applying and publishing, or the
// broker refused it — is said on the next link, before anything else, and exactly as it was made.
func TestAReportLostAfterTheApplyIsSaidOnTheNextLink(t *testing.T) {
	m, key := aMember(t)
	made := Report{Declared: "d1", Applied: []string{"a"}, Failed: map[string]string{"b": "no room"}}
	kept := &keptInMemory{}

	// The apply happens and its report is lost.
	first := newQuietLink(&said{body: signedBy(t, key, []byte(`{"declaration":1}`))})
	first.refusing = true
	ctx, stop := context.WithCancel(context.Background())
	apply := func(context.Context, []byte, []byte) Report { stop(); return made }
	if err := serve(ctx, first, m, apply, nil, time.Second, nil, kept); err != nil {
		t.Fatal(err)
	}
	if len(first.said()) != 0 {
		t.Fatal("the broker refused the report and it counted as said")
	}

	// The next host links. It is stopped at once, so all it does is what it does on linking.
	next := newQuietLink()
	gone, cancel := context.WithCancel(context.Background())
	cancel()
	never := func(context.Context, []byte, []byte) Report {
		t.Fatal("nothing was delivered, and something was applied")
		return Report{}
	}
	if err := serve(gone, next, m, never, nil, time.Second, nil, kept); err != nil {
		t.Fatal(err)
	}
	reports := next.said()
	made.Node = m.Node
	if len(reports) != 1 || !reflect.DeepEqual(reports[0], made) {
		t.Fatalf("the lost report was not said again as it was made: %+v", reports)
	}
	if _, ok, _ := kept.Pending(); ok {
		t.Fatal("a report said again is still kept")
	}
}

// A node that never applied anything, or whose last report was taken, says nothing on linking.
func TestNothingIsSaidAgainWhenNothingWasLost(t *testing.T) {
	m, _ := aMember(t)
	l := newQuietLink()
	gone, cancel := context.WithCancel(context.Background())
	cancel()
	if err := serve(gone, l, m, nil, nil, time.Second, nil, &keptInMemory{}); err != nil {
		t.Fatal(err)
	}
	if err := serve(gone, l, m, nil, nil, time.Second, nil, nil); err != nil {
		t.Fatal(err)
	}
	if reports := l.said(); len(reports) != 0 {
		t.Fatalf("a node with nothing lost reported %+v", reports)
	}
}