package virtqueue

import (
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestUsedRing_MemoryLayout(t *testing.T) {
	const queueSize = 2

	memory := make([]byte, usedRingSize(queueSize))
	r := newUsedRing(queueSize, memory)

	*r.flags = 0x01ff
	*r.ringIndex = 1
	r.ring[0] = UsedElement{
		DescriptorIndex: 0x0123,
		Length:          0x4567,
	}
	r.ring[1] = UsedElement{
		DescriptorIndex: 0x89ab,
		Length:          0xcdef,
	}

	assert.Equal(t, []byte{
		0xff, 0x01,
		0x01, 0x00,
		0x23, 0x01, 0x00, 0x00,
		0x67, 0x45, 0x00, 0x00,
		0xab, 0x89, 0x00, 0x00,
		0xef, 0xcd, 0x00, 0x00,
		0x00, 0x00,
	}, memory)
}

func TestUsedRing_Take(t *testing.T) {
	const queueSize = 8

	tests := []struct {
		name      string
		ring      []UsedElement
		ringIndex uint16
		lastIndex uint16
		expected  []UsedElement
	}{
		{
			name: "nothing new",
			ring: []UsedElement{
				{DescriptorIndex: 1},
				{DescriptorIndex: 2},
				{DescriptorIndex: 3},
				{DescriptorIndex: 4},
				{},
				{},
				{},
				{},
			},
			ringIndex: 4,
			lastIndex: 4,
			expected:  nil,
		},
		{
			name: "no overflow",
			ring: []UsedElement{
				{DescriptorIndex: 1},
				{DescriptorIndex: 2},
				{DescriptorIndex: 3},
				{DescriptorIndex: 4},
				{},
				{},
				{},
				{},
			},
			ringIndex: 4,
			lastIndex: 1,
			expected: []UsedElement{
				{DescriptorIndex: 2},
				{DescriptorIndex: 3},
				{DescriptorIndex: 4},
			},
		},
		{
			name: "ring overflow",
			ring: []UsedElement{
				{DescriptorIndex: 9},
				{DescriptorIndex: 10},
				{DescriptorIndex: 3},
				{DescriptorIndex: 4},
				{DescriptorIndex: 5},
				{DescriptorIndex: 6},
				{DescriptorIndex: 7},
				{DescriptorIndex: 8},
			},
			ringIndex: 10,
			lastIndex: 7,
			expected: []UsedElement{
				{DescriptorIndex: 8},
				{DescriptorIndex: 9},
				{DescriptorIndex: 10},
			},
		},
		{
			name: "index overflow",
			ring: []UsedElement{
				{DescriptorIndex: 9},
				{DescriptorIndex: 10},
				{DescriptorIndex: 3},
				{DescriptorIndex: 4},
				{DescriptorIndex: 5},
				{DescriptorIndex: 6},
				{DescriptorIndex: 7},
				{DescriptorIndex: 8},
			},
			ringIndex: 2,
			lastIndex: 65535,
			expected: []UsedElement{
				{DescriptorIndex: 8},
				{DescriptorIndex: 9},
				{DescriptorIndex: 10},
			},
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			memory := make([]byte, usedRingSize(queueSize))
			r := newUsedRing(queueSize, memory)

			copy(r.ring, tt.ring)
			*r.ringIndex = tt.ringIndex
			r.lastIndex = tt.lastIndex

			assert.Equal(t, tt.expected, r.take())
		})
	}
}