package utils

import (
	"sync"
	"testing"
)

func TestNew(t *testing.T) {
	q := New[int](5)
	if q.capacity != 5 {
		t.Errorf("expected capacity 5, got %d", q.capacity)
	}
	if q.Len() != 0 {
		t.Errorf("expected empty queue, got len %d", q.Len())
	}
}

func TestPushPop(t *testing.T) {
	q := New[int](3)

	q.Push(1)
	q.Push(2)
	q.Push(3)

	if q.Len() != 3 {
		t.Errorf("expected len 3, got %d", q.Len())
	}

	val, ok := q.Pop()
	if !ok || val != 1 {
		t.Errorf("expected (1, true), got (%d, %v)", val, ok)
	}

	val, ok = q.Pop()
	if !ok || val != 2 {
		t.Errorf("expected (2, true), got (%d, %v)", val, ok)
	}

	val, ok = q.Pop()
	if !ok || val != 3 {
		t.Errorf("expected (3, true), got (%d, %v)", val, ok)
	}

	val, ok = q.Pop()
	if ok {
		t.Errorf("expected (_, false), got (%d, %v)", val, ok)
	}
}

func TestPushDropsOldest(t *testing.T) {
	q := New[int](3)

	q.Push(1)
	q.Push(2)
	q.Push(3)
	q.Push(4) // should drop 1

	if q.Len() != 3 {
		t.Errorf("expected len 3, got %d", q.Len())
	}

	val, ok := q.Pop()
	if !ok || val != 2 {
		t.Errorf("expected (2, true), got (%d, %v)", val, ok)
	}

	val, ok = q.Pop()
	if !ok || val != 3 {
		t.Errorf("expected (3, true), got (%d, %v)", val, ok)
	}

	val, ok = q.Pop()
	if !ok || val != 4 {
		t.Errorf("expected (4, true), got (%d, %v)", val, ok)
	}
}

func TestPeek(t *testing.T) {
	q := New[string](2)

	_, ok := q.Peek()
	if ok {
		t.Error("expected Peek on empty queue to return false")
	}

	q.Push("a")
	q.Push("b")

	val, ok := q.Peek()
	if !ok || val != "a" {
		t.Errorf("expected (a, true), got (%s, %v)", val, ok)
	}

	// Peek should not remove
	if q.Len() != 2 {
		t.Errorf("Peek should not modify queue, len is %d", q.Len())
	}
}

func TestIsEmpty(t *testing.T) {
	q := New[int](2)

	if !q.IsEmpty() {
		t.Error("new queue should be empty")
	}

	q.Push(1)
	if q.IsEmpty() {
		t.Error("queue with item should not be empty")
	}

	q.Pop()
	if !q.IsEmpty() {
		t.Error("queue after pop should be empty")
	}
}

func TestConcurrentAccess(t *testing.T) {
	q := New[int](100)
	var wg sync.WaitGroup

	// Concurrent pushes
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(n int) {
			defer wg.Done()
			for j := 0; j < 20; j++ {
				q.Push(n*20 + j)
			}
		}(i)
	}

	// Concurrent pops
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for j := 0; j < 10; j++ {
				q.Pop()
			}
		}()
	}

	wg.Wait()

	// Should not panic and queue should be in valid state
	_ = q.Len()
	_ = q.IsEmpty()
}

func TestCapacityOne(t *testing.T) {
	q := New[int](1)

	q.Push(1)
	q.Push(2) // drops 1

	if q.Len() != 1 {
		t.Errorf("expected len 1, got %d", q.Len())
	}

	val, ok := q.Pop()
	if !ok || val != 2 {
		t.Errorf("expected (2, true), got (%d, %v)", val, ok)
	}
}

func TestNewNonPositiveCapacityUsesMinimum(t *testing.T) {
	tests := []struct {
		name         string
		capacity     int
		wantCapacity int
	}{
		{name: "zero", capacity: 0, wantCapacity: 1},
		{name: "negative", capacity: -5, wantCapacity: 1},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			q := New[int](tc.capacity)
			if q.capacity != tc.wantCapacity {
				t.Fatalf("expected capacity %d, got %d", tc.wantCapacity, q.capacity)
			}

			q.Push(42)
			if got := q.Len(); got != 1 {
				t.Fatalf("expected len 1 after push, got %d", got)
			}

			val, ok := q.Pop()
			if !ok || val != 42 {
				t.Fatalf("expected (42, true), got (%d, %v)", val, ok)
			}
		})
	}
}

func TestPushNormalizesInvalidCapacityState(t *testing.T) {
	q := &Queue[int]{capacity: 0}

	q.Push(1)
	q.Push(2)

	if q.Len() != 0 {
		t.Errorf("expected len 0, got %d", q.Len())
	}

	if _, ok := q.Pop(); ok {
		t.Error("expected pop on zero-capacity queue to return false")
	}
}

func TestItems(t *testing.T) {
	q := New[int](5)
	q.Push(10)
	q.Push(20)
	q.Push(30)

	items := q.Items()
	if len(items) != 3 {
		t.Fatalf("expected 3 items, got %d", len(items))
	}
	if items[0] != 10 || items[1] != 20 || items[2] != 30 {
		t.Fatalf("unexpected items: %v", items)
	}

	// Verify Items returns a copy (doesn't drain the queue)
	if q.Len() != 3 {
		t.Fatalf("Items should not drain the queue, len=%d", q.Len())
	}
}

func TestItems_Empty(t *testing.T) {
	q := New[int](5)
	items := q.Items()
	if items != nil {
		t.Fatalf("expected nil for empty queue, got %v", items)
	}
}