package udp

import (
	"crypto/rc4"
	"errors"
	"fmt"
)

// CRC32 lookup table for polynomial 0xEDB88320 (IEEE 802.3 standard)
var crcTable = [256]uint32{
	0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
	0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
	0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
	0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
	0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
	0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
	0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
	0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
	0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
	0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
	0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
	0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
	0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
	0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
	0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
	0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
	0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
	0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
	0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
	0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
	0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
	0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
	0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
	0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
	0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
	0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
	0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
	0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
	0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
	0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
	0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
	0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D,
}

// CRC16 computes CRC32 checksum with custom key initialization for EQ2 protocol
// This function implements the reverse-engineered CRC calculation used in EQ2
// despite being named CRC16, it actually performs 32-bit CRC calculation
func CRC16(buf []byte, key uint32) uint32 {
	crc := key // Initialize with provided key

	// Pre-process the key through multiple CRC table lookups
	// This mirrors the original assembly implementation's key initialization
	crc = ^crc             // Invert initial key
	crc &= 0xFF            // Mask to lowest byte
	crc = crcTable[crc]    // First table lookup
	crc ^= 0x00FFFFFF      // XOR with mask

	// Process second byte of original key
	temp := key >> 8         // Shift key right 8 bits
	temp ^= crc              // XOR with current CRC
	crc >>= 8                // Shift CRC right 8 bits
	temp &= 0xFF             // Mask to byte
	crc &= 0x00FFFFFF        // Mask CRC to 24 bits
	crc ^= crcTable[temp]    // Second table lookup

	// Process third byte of original key
	temp = key >> 16                 // Shift key right 16 bits
	temp ^= crc                      // XOR with current CRC
	crc >>= 8                        // Shift CRC right 8 bits
	temp &= 0xFF                     // Mask to byte
	temp2 := crcTable[temp]          // Third table lookup
	crc &= 0x00FFFFFF                // Mask CRC to 24 bits
	crc ^= temp2                     // XOR with lookup result

	// Process fourth byte of original key
	fourthByte := key >> 24      // Extract highest byte
	fourthByte ^= crc            // XOR with current CRC
	fourthByte &= 0xFF           // Mask to byte
	temp2 = crcTable[fourthByte] // Fourth table lookup
	crc >>= 8                    // Shift CRC right 8 bits
	crc &= 0x00FFFFFF            // Mask CRC to 24 bits
	crc ^= temp2                 // XOR with lookup result

	// Process each byte in the input buffer
	for _, b := range buf {
		byteVal := uint32(b) & 0xFF      // Extract current byte
		byteVal ^= crc                   // XOR byte with current CRC
		crc >>= 8                        // Shift CRC right 8 bits
		byteVal &= 0xFF                  // Ensure byte is masked
		lookup := crcTable[byteVal]      // Table lookup for this byte
		crc &= 0x00FFFFFF                // Mask CRC to 24 bits
		crc ^= lookup                    // XOR with lookup result
	}

	return ^crc // Return inverted final CRC
}

// ValidateCRCWithKey checks if packet has valid CRC using the provided key
// Expects CRC to be the last 2 bytes of data
func ValidateCRCWithKey(data []byte, key uint32) bool {
	if len(data) < 4 { // Need at least [header][opcode][data][CRC][CRC]
		return false
	}

	// The CRC should be calculated on the serialized packet (opcode + data), excluding header and CRC
	// EQ2 packet format: [header][opcode][data...][CRC16]
	// CRC covers: [opcode][data...] (starting from byte 1, excluding header and CRC)
	payload := data[1 : len(data)-2] // Skip header, include opcode, exclude CRC
	expectedCRC := uint16(data[len(data)-1])<<8 | uint16(data[len(data)-2]) // Big-endian CRC

	// Calculate and compare
	actualCRC := uint16(CRC16(payload, key))
	
	// Debug output
	fmt.Printf("CRC Debug - Key: 0x%08X, Expected: 0x%04X, Actual: 0x%04X, Match: %v\n", 
		key, expectedCRC, actualCRC, expectedCRC == actualCRC)
	fmt.Printf("CRC payload (%d bytes): ", len(payload))
	for i, b := range payload {
		fmt.Printf("%02X ", b)
		if i > 0 && (i+1)%16 == 0 {
			fmt.Printf("\n                        ")
		}
	}
	fmt.Printf("\n")
	
	return expectedCRC == actualCRC
}

// ValidateCRC checks if packet has valid CRC using default key (0)
// Expects CRC to be the last 2 bytes of data
func ValidateCRC(data []byte) bool {
	return ValidateCRCWithKey(data, 0)
}

// AppendCRCWithKey adds 16-bit CRC to the end of data using the provided key
func AppendCRCWithKey(data []byte, key uint32) []byte {
	crc := uint16(CRC16(data, key))
	result := make([]byte, len(data)+2)
	copy(result, data)

	// Append CRC in big-endian format (as per C++ htons)
	result[len(data)] = byte(crc)
	result[len(data)+1] = byte(crc >> 8)

	return result
}

// AppendCRC adds 16-bit CRC to the end of data using default key (0)
func AppendCRC(data []byte) []byte {
	return AppendCRCWithKey(data, 0)
}

// ValidateAndStrip validates CRC and returns data without CRC suffix
func ValidateAndStrip(data []byte) ([]byte, bool) {
	if !ValidateCRC(data) {
		return nil, false
	}
	return data[:len(data)-2], true
}

// Crypto handles RC4 encryption/decryption for EQ2EMu protocol
type Crypto struct {
	clientCipher *rc4.Cipher // Cipher for decrypting client data
	serverCipher *rc4.Cipher // Cipher for encrypting server data
	key          []byte      // Encryption key
	encrypted    bool        // Whether encryption is active
}

// NewCrypto creates a new crypto instance with encryption disabled
func NewCrypto() *Crypto {
	return &Crypto{}
}

// SetKey initializes RC4 encryption with the given key
// Creates separate ciphers for client and server with 20-byte priming
func (c *Crypto) SetKey(key []byte) error {
	if len(key) == 0 {
		return errors.New("encryption key cannot be empty")
	}

	// Create separate RC4 ciphers for bidirectional communication
	clientCipher, err := rc4.NewCipher(key)
	if err != nil {
		return err
	}

	serverCipher, err := rc4.NewCipher(key)
	if err != nil {
		return err
	}

	// Prime both ciphers with 20 dummy bytes per EQ2EMu protocol
	dummy := make([]byte, 20)
	clientCipher.XORKeyStream(dummy, dummy)
	serverCipher.XORKeyStream(dummy, dummy)

	c.clientCipher = clientCipher
	c.serverCipher = serverCipher
	c.key = make([]byte, len(key))
	copy(c.key, key)
	c.encrypted = true

	return nil
}

// IsEncrypted returns whether encryption is currently active
func (c *Crypto) IsEncrypted() bool {
	return c.encrypted
}

// Encrypt encrypts data for transmission to client
func (c *Crypto) Encrypt(data []byte) []byte {
	if !c.encrypted || c.serverCipher == nil {
		return data
	}

	encrypted := make([]byte, len(data))
	copy(encrypted, data)
	c.serverCipher.XORKeyStream(encrypted, encrypted)
	return encrypted
}

// Decrypt decrypts data received from client
func (c *Crypto) Decrypt(data []byte) []byte {
	if !c.encrypted || c.clientCipher == nil {
		return data
	}

	decrypted := make([]byte, len(data))
	copy(decrypted, data)
	c.clientCipher.XORKeyStream(decrypted, decrypted)
	return decrypted
}

// GetKey returns a copy of the encryption key
func (c *Crypto) GetKey() []byte {
	if c.key == nil {
		return nil
	}
	keyCopy := make([]byte, len(c.key))
	copy(keyCopy, c.key)
	return keyCopy
}

// Reset disables encryption and clears keys
func (c *Crypto) Reset() {
	c.clientCipher = nil
	c.serverCipher = nil
	c.key = nil
	c.encrypted = false
}