package util

import (
	"bytes"
	"io"
	"math"
	"math/rand/v2"
	"runtime"
	"strings"
	"testing"
	"time"
)

func TestBufferReadWrite(t *testing.T) {
	buf := NewBuffer()

	buf.WriteBool(true)
	buf.WriteInt(42)
	buf.WriteFloat64(3.14)
	buf.WriteString("Testing, 1, 2, 3!")

	readBuf := NewBufferFromBytes(buf.Bytes())

	boolVal := readBuf.ReadBool()
	intVal := readBuf.ReadInt()
	floatVal := readBuf.ReadFloat64()
	stringVal := readBuf.ReadString()

	if boolVal != true {
		t.Errorf("Expected bool value to be true, got %v", boolVal)
	}
	if intVal != 42 {
		t.Errorf("Expected int value to be 42, got %v", intVal)
	}
	if floatVal != 3.14 {
		t.Errorf("Expected float value to be 3.14, got %v", floatVal)
	}
	if stringVal != "Testing, 1, 2, 3!" {
		t.Errorf("Expected string value to be 'Hello, World!', got %v", stringVal)
	}
}

func TestBufferWriteReadBytes(t *testing.T) {
	buf := NewBuffer()

	bytesToWrite := []byte{0x01, 0x02, 0x03, 0x04}
	buf.WriteBytes(bytesToWrite)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readBytes := readBuf.ReadBytes(len(bytesToWrite))

	if !bytes.Equal(readBytes, bytesToWrite) {
		t.Errorf("Expected bytes to be %v, got %v", bytesToWrite, readBytes)
	}
}

func TestBufferWriteReadUInt64(t *testing.T) {
	buf := NewBuffer()

	uint64Val := uint64(1234567890)
	buf.WriteUInt64(uint64Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readUInt64 := readBuf.ReadUInt64()

	if readUInt64 != uint64Val {
		t.Errorf("Expected uint64 value to be %v, got %v", uint64Val, readUInt64)
	}
}

func TestBufferWriteReadFloat32(t *testing.T) {
	buf := NewBuffer()

	float32Val := float32(3.14159)
	buf.WriteFloat32(float32Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readFloat32 := readBuf.ReadFloat32()

	if readFloat32 != float32Val {
		t.Errorf("Expected float32 value to be %v, got %v", float32Val, readFloat32)
	}
}

func TestBufferWriteReadInt8(t *testing.T) {
	buf := NewBuffer()

	int8Val := int8(-42)
	buf.WriteInt8(int8Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readInt8 := readBuf.ReadInt8()

	if readInt8 != int8Val {
		t.Errorf("Expected int8 value to be %v, got %v", int8Val, readInt8)
	}
}

func TestBufferWriteReadUInt16(t *testing.T) {
	buf := NewBuffer()

	uint16Val := uint16(65535)
	buf.WriteUInt16(uint16Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readUInt16 := readBuf.ReadUInt16()

	if readUInt16 != uint16Val {
		t.Errorf("Expected uint16 value to be %v, got %v", uint16Val, readUInt16)
	}
}

func TestBufferWriteReadInt32(t *testing.T) {
	buf := NewBuffer()

	int32Val := int32(-1234567890)
	buf.WriteInt32(int32Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readInt32 := readBuf.ReadInt32()

	if readInt32 != int32Val {
		t.Errorf("Expected int32 value to be %v, got %v", int32Val, readInt32)
	}
}

func TestBufferWriteReadUInt8(t *testing.T) {
	buf := NewBuffer()

	uint8Val := uint8(255)
	buf.WriteUInt8(uint8Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readUInt8 := readBuf.ReadUInt8()

	if readUInt8 != uint8Val {
		t.Errorf("Expected uint8 value to be %v, got %v", uint8Val, readUInt8)
	}
}

func TestBufferWriteReadInt16(t *testing.T) {
	buf := NewBuffer()

	int16Val := int16(-32768)
	buf.WriteInt16(int16Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readInt16 := readBuf.ReadInt16()

	if readInt16 != int16Val {
		t.Errorf("Expected int16 value to be %v, got %v", int16Val, readInt16)
	}
}

func TestBufferWriteReadUInt32(t *testing.T) {
	buf := NewBuffer()

	uint32Val := uint32(4294967295)
	buf.WriteUInt32(uint32Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readUInt32 := readBuf.ReadUInt32()

	if readUInt32 != uint32Val {
		t.Errorf("Expected uint32 value to be %v, got %v", uint32Val, readUInt32)
	}
}

func TestBufferWriteReadInt64(t *testing.T) {
	buf := NewBuffer()

	int64Val := int64(-9223372036854775808)
	buf.WriteInt64(int64Val)

	readBuf := NewBufferFromBytes(buf.Bytes())
	readInt64 := readBuf.ReadInt64()

	if readInt64 != int64Val {
		t.Errorf("Expected int64 value to be %v, got %v", int64Val, readInt64)
	}
}

func TestBufferBytes(t *testing.T) {
	buf := NewBuffer()

	buf.WriteInt(-42)
	buf.WriteFloat64(-3.14)

	unreadBytes := buf.Bytes()

	newBuf := NewBufferFromBytes(unreadBytes)

	intVal := newBuf.ReadInt()
	floatVal := newBuf.ReadFloat64()

	if intVal != -42 {
		t.Errorf("Expected int value to be -42, got %v", intVal)
	}
	if floatVal != -3.14 {
		t.Errorf("Expected float value to be -3.14, got %v", floatVal)
	}
}

func TestBufferNewBufferFrom(t *testing.T) {
	buf := NewBuffer()

	buf.WriteInt(42)
	buf.WriteFloat64(3.14)

	newBuf := NewBufferFrom(buf)

	intVal := newBuf.ReadInt()
	floatVal := newBuf.ReadFloat64()

	if intVal != 42 {
		t.Errorf("Expected int value to be 42, got %v", intVal)
	}
	if floatVal != 3.14 {
		t.Errorf("Expected float value to be 3.14, got %v", floatVal)
	}
}

const letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

func generateRandomString(ln int) string {
	b := make([]byte, ln)
	for i := range b {
		b[i] = letters[rand.IntN(len(letters))]
	}
	return string(b)
}

func memMib() float64 {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	return float64(m.Alloc) / 1024.0 / 1024.0
}

func TestStringBytes(t *testing.T) {
	baselineMem := memMib()

	b := make([]byte, 10<<20)

	afterMem := memMib()
	delta := afterMem - baselineMem
	t.Logf("Allocated %v MiB, Delta: %v MiB", afterMem, delta)

	s := "Hello World!"
	sl := b[512 : 512+len(s)]
	copy(sl, stringToBytes(s))

	afterMem = memMib()
	delta = afterMem - baselineMem
	t.Logf("Allocated %v MiB, Delta: %v MiB", afterMem, delta)

	// this should pin the large backing array in memory, preventing it from being GC'd
	newS := bytesToString(sl)

	runtime.GC()
	time.Sleep(time.Second)

	afterMem = memMib()
	delta = afterMem - baselineMem
	t.Logf("S: %s, Allocated %v MiB, Delta: %v MiB", newS, afterMem, delta)

	// copy the string into a new string and clear out pinned string
	sCopy := strings.Clone(newS)
	newS = ""

	// Now that we've dropped the reference to the pinned backing array, it should be GC'd
	runtime.GC()
	time.Sleep(time.Second)

	afterMem = memMib()
	delta = afterMem - baselineMem
	t.Logf("S: %s, Allocated %v MiB, Delta: %v MiB", sCopy, afterMem, delta)

	if sCopy != s {
		t.Errorf("Expected string to be %v, got %v", s, sCopy)
	}

	if delta > 0.5 {
		t.Errorf("Expected memory delta to be less than 0.5 MiB, got %v MiB", delta)
	}
}

type randomByteReader struct {
	bytes []byte
	pos   int
}

func newRandomByteReader(bytes []byte) *randomByteReader {
	return &randomByteReader{
		bytes: bytes,
		pos:   0,
	}
}

// reads a random number of bytes from 1-4 each time Read is called.
// simulates partial buffered reads
func (sbr *randomByteReader) Read(b []byte) (int, error) {
	if sbr.pos >= len(sbr.bytes) {
		return 0, io.EOF
	}

	toCopy := rand.IntN(4) + 1
	if toCopy > len(b) {
		toCopy = len(b)
	}

	var err error
	remaining := len(sbr.bytes) - sbr.pos
	if toCopy > remaining {
		err = io.EOF
		toCopy = remaining
	}

	bytesCopied := copy(b, sbr.bytes[sbr.pos:sbr.pos+toCopy])
	sbr.pos += bytesCopied

	return bytesCopied, err
}

func TestBufferReaderSupport(t *testing.T) {
	buf := NewBuffer()
	buf.WriteBool(true)
	buf.WriteInt(42)
	buf.WriteFloat64(3.14)
	buf.WriteString("Testing, 1, 2, 3!")
	buf.WriteUInt64(uint64(123456))
	buf.WriteInt16(44)
	buf.WriteFloat32(float32(5.0))

	reader := newRandomByteReader(buf.Bytes())
	readerBuff := NewBufferFromReader(reader)

	b := readerBuff.ReadBool()
	i := readerBuff.ReadInt()
	f := readerBuff.ReadFloat64()
	s := readerBuff.ReadString()
	ui64 := readerBuff.ReadUInt64()
	i16 := readerBuff.ReadInt16()
	f32 := readerBuff.ReadFloat32()

	if !b {
		t.Errorf("expected true, got: false")
	}
	if i != 42 {
		t.Errorf("expected 42, got: %d", i)
	}
	if f != 3.14 {
		t.Errorf("expected 3.14, got: %f", f)
	}
	if s != "Testing, 1, 2, 3!" {
		t.Errorf("expected 'Testing, 1, 2, 3!', got: '%s'", s)
	}
	if ui64 != uint64(123456) {
		t.Errorf("expected 123456, got: %d", ui64)
	}
	if i16 != int16(44) {
		t.Errorf("expected 44, got: %d", i16)
	}
	if f32 != float32(5.0) {
		t.Errorf("expected 5.0, got: %f", f32)
	}
}

func TestTooLargeStringTruncate(t *testing.T) {
	normalStr := generateRandomString(100)
	bigStr := generateRandomString(math.MaxUint16 + (math.MaxUint16 / 2))
	expectedBigStrRead := bigStr[:math.MaxUint16]

	otherBigStr := generateRandomString(math.MaxUint16)
	plusOne := generateRandomString(math.MaxUint16 + 1)
	expectedPlusOne := plusOne[:math.MaxUint16]

	buf := NewBuffer()

	buf.WriteInt(42)
	buf.WriteFloat64(3.14)
	buf.WriteString(normalStr)
	buf.WriteString(bigStr)
	buf.WriteString(otherBigStr)
	buf.WriteString(plusOne)

	readBuf := NewBufferFromBytes(buf.Bytes())

	intVal := readBuf.ReadInt()
	floatVal := readBuf.ReadFloat64()
	normalStrRead := readBuf.ReadString()
	bigStrRead := readBuf.ReadString()
	otherBigStrRead := readBuf.ReadString()
	plusOneRead := readBuf.ReadString()

	if intVal != 42 {
		t.Errorf("Expected int value to be 42, got %v", intVal)
	}
	if floatVal != 3.14 {
		t.Errorf("Expected float value to be 3.14, got %v", floatVal)
	}
	if normalStrRead != normalStr {
		t.Errorf("Expected string value to be %v, got %v", normalStr, normalStrRead)
	}
	if bigStrRead != expectedBigStrRead {
		t.Errorf("Expected large string values to be equivalent!")
	}
	if otherBigStrRead != otherBigStr {
		t.Errorf("Expected large string values to be equivalent!")
	}
	if plusOneRead != expectedPlusOne {
		t.Errorf("Expected large string values to be equivalent!")
	}
}