package lobby

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

	"github.com/google/uuid"
	"go.uber.org/zap"

	"scrabble/backend/internal/engine"
	"scrabble/backend/internal/game"
)

// fakeCreator records the games a matchmaker asks it to start.
type fakeCreator struct {
	created []game.CreateParams
	err     error
}

func (f *fakeCreator) Create(_ context.Context, p game.CreateParams) (game.Game, error) {
	if f.err != nil {
		return game.Game{}, f.err
	}
	f.created = append(f.created, p)
	return game.Game{ID: uuid.New(), Players: len(p.Seats)}, nil
}

// fakeRobots is a RobotProvider returning a fixed robot id, or an error to model
// an empty pool.
type fakeRobots struct {
	id  uuid.UUID
	err error
}

func (f *fakeRobots) Pick() (uuid.UUID, error) {
	if f.err != nil {
		return uuid.Nil, f.err
	}
	return f.id, nil
}

// testWaitDelay is long enough that the reaper never fires in the pairing tests
// (which do not run it); the substitution tests drive reap directly.
const testWaitDelay = 10 * time.Second

func newTestMatchmaker(creator GameCreator, robotID uuid.UUID) *Matchmaker {
	return NewMatchmaker(creator, &fakeRobots{id: robotID}, testWaitDelay, zap.NewNop())
}

func seatsContain(seats []uuid.UUID, want ...uuid.UUID) bool {
	for _, w := range want {
		found := false
		for _, s := range seats {
			if s == w {
				found = true
				break
			}
		}
		if !found {
			return false
		}
	}
	return true
}

func TestMatchmakerPairsTwoHumans(t *testing.T) {
	creator := &fakeCreator{}
	mm := newTestMatchmaker(creator, uuid.New())
	ctx := context.Background()
	a, b := uuid.New(), uuid.New()

	r1, err := mm.Enqueue(ctx, a, engine.VariantEnglish)
	if err != nil {
		t.Fatalf("enqueue a: %v", err)
	}
	if r1.Matched {
		t.Fatal("first enqueue must wait, not match")
	}
	if mm.QueueLen(engine.VariantEnglish) != 1 {
		t.Fatalf("queue len = %d, want 1", mm.QueueLen(engine.VariantEnglish))
	}

	r2, err := mm.Enqueue(ctx, b, engine.VariantEnglish)
	if err != nil {
		t.Fatalf("enqueue b: %v", err)
	}
	if !r2.Matched {
		t.Fatal("second enqueue must match")
	}
	if mm.QueueLen(engine.VariantEnglish) != 0 {
		t.Fatalf("queue len = %d, want 0 after match", mm.QueueLen(engine.VariantEnglish))
	}
	if len(creator.created) != 1 {
		t.Fatalf("created %d games, want 1", len(creator.created))
	}
	p := creator.created[0]
	if len(p.Seats) != 2 || !seatsContain(p.Seats, a, b) {
		t.Errorf("seats = %v, want both %s and %s", p.Seats, a, b)
	}
	if p.TurnTimeout != game.DefaultTurnTimeout || !p.HintsAllowed || p.HintsPerPlayer != autoMatchHintsPerPlayer {
		t.Errorf("auto-match defaults not applied: %+v", p)
	}

	// The waiting opponent learns of the match through Poll, exactly once.
	got, err := mm.Poll(ctx, a)
	if err != nil {
		t.Fatalf("poll a: %v", err)
	}
	if !got.Matched || got.Game.ID != r2.Game.ID {
		t.Errorf("poll a = %+v, want the matched game %s", got, r2.Game.ID)
	}
	if again, _ := mm.Poll(ctx, a); again.Matched {
		t.Error("poll result must drain after the first read")
	}
}

func TestMatchmakerAlreadyQueued(t *testing.T) {
	mm := newTestMatchmaker(&fakeCreator{}, uuid.New())
	ctx := context.Background()
	a := uuid.New()
	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue: %v", err)
	}
	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); !errors.Is(err, ErrAlreadyQueued) {
		t.Fatalf("second enqueue err = %v, want ErrAlreadyQueued", err)
	}
}

func TestMatchmakerCancel(t *testing.T) {
	mm := newTestMatchmaker(&fakeCreator{}, uuid.New())
	ctx := context.Background()
	a := uuid.New()
	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue: %v", err)
	}
	if !mm.Cancel(ctx, a) {
		t.Fatal("cancel of a queued account must report true")
	}
	if mm.QueueLen(engine.VariantEnglish) != 0 {
		t.Fatalf("queue len = %d, want 0 after cancel", mm.QueueLen(engine.VariantEnglish))
	}
	if mm.Cancel(ctx, a) {
		t.Fatal("cancel of an unqueued account must report false")
	}
}

func TestMatchmakerVariantsAreSeparate(t *testing.T) {
	creator := &fakeCreator{}
	mm := newTestMatchmaker(creator, uuid.New())
	ctx := context.Background()
	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue en: %v", err)
	}
	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble); err != nil {
		t.Fatalf("enqueue ru: %v", err)
	}
	if len(creator.created) != 0 {
		t.Fatalf("different variants must not match; created %d", len(creator.created))
	}
	if mm.QueueLen(engine.VariantEnglish) != 1 || mm.QueueLen(engine.VariantRussianScrabble) != 1 {
		t.Errorf("each variant pool should hold one waiter")
	}
}

func TestMatchmakerFIFO(t *testing.T) {
	creator := &fakeCreator{}
	mm := newTestMatchmaker(creator, uuid.New())
	ctx := context.Background()
	a, b, c := uuid.New(), uuid.New(), uuid.New()
	for _, id := range []uuid.UUID{a, b, c} {
		if _, err := mm.Enqueue(ctx, id, engine.VariantEnglish); err != nil {
			t.Fatalf("enqueue %s: %v", id, err)
		}
	}
	// a waited, b matched a (oldest), c waits.
	if len(creator.created) != 1 {
		t.Fatalf("created %d games, want 1", len(creator.created))
	}
	if !seatsContain(creator.created[0].Seats, a, b) {
		t.Errorf("FIFO match should pair a and b, got %v", creator.created[0].Seats)
	}
	if mm.QueueLen(engine.VariantEnglish) != 1 {
		t.Errorf("c should remain queued; len = %d", mm.QueueLen(engine.VariantEnglish))
	}
}

func TestMatchmakerReaperSubstitutesRobot(t *testing.T) {
	creator := &fakeCreator{}
	robotID := uuid.New()
	mm := newTestMatchmaker(creator, robotID)
	base := time.Now()
	mm.clock = func() time.Time { return base }
	ctx := context.Background()
	a := uuid.New()

	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue: %v", err)
	}

	mm.Reap(ctx, base.Add(5*time.Second)) // before the wait window
	if len(creator.created) != 0 || mm.QueueLen(engine.VariantEnglish) != 1 {
		t.Fatalf("must not substitute before the wait: created=%d queued=%d", len(creator.created), mm.QueueLen(engine.VariantEnglish))
	}

	mm.Reap(ctx, base.Add(testWaitDelay+time.Second)) // past the wait window
	if len(creator.created) != 1 {
		t.Fatalf("created %d games, want 1 after substitution", len(creator.created))
	}
	if !seatsContain(creator.created[0].Seats, a, robotID) {
		t.Errorf("substituted game seats = %v, want human %s and robot %s", creator.created[0].Seats, a, robotID)
	}
	if mm.QueueLen(engine.VariantEnglish) != 0 {
		t.Errorf("waiter should be dequeued after substitution")
	}
	got, err := mm.Poll(ctx, a)
	if err != nil || !got.Matched {
		t.Errorf("poll after substitution = %+v err=%v, want matched", got, err)
	}
}

func TestMatchmakerReaperSkipsCancelled(t *testing.T) {
	creator := &fakeCreator{}
	mm := newTestMatchmaker(creator, uuid.New())
	base := time.Now()
	mm.clock = func() time.Time { return base }
	ctx := context.Background()
	a := uuid.New()

	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue: %v", err)
	}
	mm.Cancel(ctx, a)
	mm.Reap(ctx, base.Add(testWaitDelay+time.Second))
	if len(creator.created) != 0 {
		t.Errorf("a cancelled waiter must not be substituted; created %d", len(creator.created))
	}
}

func TestMatchmakerReaperDefersWithoutRobot(t *testing.T) {
	creator := &fakeCreator{}
	mm := NewMatchmaker(creator, &fakeRobots{err: errors.New("empty pool")}, testWaitDelay, zap.NewNop())
	base := time.Now()
	mm.clock = func() time.Time { return base }
	ctx := context.Background()
	a := uuid.New()

	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
		t.Fatalf("enqueue: %v", err)
	}
	mm.Reap(ctx, base.Add(testWaitDelay+time.Second))
	if len(creator.created) != 0 {
		t.Errorf("no robot available: must not create a game; created %d", len(creator.created))
	}
	if mm.QueueLen(engine.VariantEnglish) != 1 {
		t.Errorf("waiter must stay queued when substitution is deferred; len %d", mm.QueueLen(engine.VariantEnglish))
	}
}