package admission

import (
	"context"
	"errors"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

func TestFixedWindowEnforcesGlobalAndPerKeyLimits(t *testing.T) {
	now := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
	limiter, err := NewFixedWindow(FixedWindowConfig{
		Window: time.Minute,
		Global: 3,
		PerKey: 2,
		Now:    func() time.Time { return now },
	})
	if err != nil {
		t.Fatalf("NewFixedWindow(): %v", err)
	}

	if err := limiter.Admit(context.Background(), "client-a"); err != nil {
		t.Fatalf("Admit(a1): %v", err)
	}
	if err := limiter.Admit(context.Background(), "client-a"); err != nil {
		t.Fatalf("Admit(a2): %v", err)
	}
	if err := limiter.Admit(context.Background(), "client-a"); !errors.Is(err, ErrPerKeyLimit) {
		t.Fatalf("Admit(a3) error = %v, want ErrPerKeyLimit", err)
	}
	if err := limiter.Admit(context.Background(), "client-b"); err != nil {
		t.Fatalf("Admit(b1): %v", err)
	}
	if err := limiter.Admit(context.Background(), "client-c"); !errors.Is(err, ErrGlobalLimit) {
		t.Fatalf("Admit(c1) error = %v, want ErrGlobalLimit", err)
	}
}

func TestFixedWindowResetsAndIsConcurrencySafe(t *testing.T) {
	var current atomic.Int64
	base := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
	limiter, err := NewFixedWindow(FixedWindowConfig{
		Window: time.Minute,
		Global: 10,
		PerKey: 10,
		Now: func() time.Time {
			return base.Add(time.Duration(current.Load()))
		},
	})
	if err != nil {
		t.Fatalf("NewFixedWindow(): %v", err)
	}

	var accepted atomic.Int64
	var wg sync.WaitGroup
	for range 100 {
		wg.Add(1)
		go func() {
			defer wg.Done()
			if limiter.Admit(context.Background(), "client-a") == nil {
				accepted.Add(1)
			}
		}()
	}
	wg.Wait()
	if got := accepted.Load(); got != 10 {
		t.Fatalf("accepted = %d, want 10", got)
	}

	current.Store(int64(time.Minute))
	if err := limiter.Admit(context.Background(), "client-a"); err != nil {
		t.Fatalf("Admit(after reset): %v", err)
	}
}

func TestFixedWindowRejectsNilContextAndEmptyIdentity(t *testing.T) {
	t.Parallel()
	limiter, err := NewFixedWindow(FixedWindowConfig{
		Window: time.Minute,
		Global: 1,
	})
	if err != nil {
		t.Fatalf("NewFixedWindow(): %v", err)
	}

	if err := limiter.Admit(nil, "client-a"); !errors.Is(err, ErrInvalidIdentity) {
		t.Fatalf("Admit(nil context) error = %v, want ErrInvalidIdentity", err)
	}
	if err := limiter.Admit(context.Background(), ""); !errors.Is(err, ErrInvalidIdentity) {
		t.Fatalf("Admit(empty identity) error = %v, want ErrInvalidIdentity", err)
	}
}

func TestAdmitterImplementations(t *testing.T) {
	t.Parallel()
	var _ Admitter = (*FixedWindow)(nil)
	var _ Admitter = AllowAll{}
}