using System;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections.Generic;

namespace V2GProtocol
{
    public class V2GDecoder
    {
        private const byte V2G_TP_VERSION = 0x01;
        private const byte V2G_TP_INVERSE_VERSION = 0xFE;
        
        public enum V2GPayloadType : ushort
        {
            EXI_Encoded_V2G_Message = 0x8001,
            DIN_Message = 0x9000,
            SAP_Message = 0x9001
        }

        public class V2GMessage
        {
            public byte Version { get; set; }
            public byte InverseVersion { get; set; }
            public V2GPayloadType PayloadType { get; set; }
            public uint PayloadLength { get; set; }
            public byte[] Payload { get; set; }
            public bool IsValid { get; set; }
            public string DecodedContent { get; set; }
        }

        public static V2GMessage DecodeMessage(byte[] data)
        {
            var message = new V2GMessage();
            
            if (data.Length < 8)
            {
                message.IsValid = false;
                return message;
            }

            int offset = 0;
            
            // V2G Transfer Protocol Header (8 bytes)
            message.Version = data[offset++];
            message.InverseVersion = data[offset++];
            message.PayloadType = (V2GPayloadType)((data[offset] << 8) | data[offset + 1]);
            offset += 2;
            message.PayloadLength = (uint)((data[offset] << 24) | (data[offset + 1] << 16) | (data[offset + 2] << 8) | data[offset + 3]);
            offset += 4;

            // Validate header
            message.IsValid = (message.Version == V2G_TP_VERSION && message.InverseVersion == V2G_TP_INVERSE_VERSION);

            if (message.IsValid && offset + message.PayloadLength <= data.Length)
            {
                message.Payload = new byte[message.PayloadLength];
                Array.Copy(data, offset, message.Payload, 0, (int)message.PayloadLength);
                
                // Try to decode payload based on type
                message.DecodedContent = DecodePayload(message.Payload, message.PayloadType);
            }

            return message;
        }

        private static string DecodePayload(byte[] payload, V2GPayloadType payloadType)
        {
            var sb = new StringBuilder();
            
            switch (payloadType)
            {
                case V2GPayloadType.EXI_Encoded_V2G_Message:
                    sb.AppendLine("EXI Encoded V2G Message:");
                    sb.AppendLine(DecodeEXI(payload));
                    break;
                case V2GPayloadType.DIN_Message:
                    sb.AppendLine("DIN Message:");
                    sb.AppendLine(DecodeDIN(payload));
                    break;
                case V2GPayloadType.SAP_Message:
                    sb.AppendLine("SAP Message:");
                    sb.AppendLine(DecodeSAP(payload));
                    break;
                default:
                    sb.AppendLine($"Unknown payload type: 0x{(ushort)payloadType:X4}");
                    sb.AppendLine("Raw payload:");
                    sb.AppendLine(BytesToHex(payload));
                    break;
            }
            
            return sb.ToString();
        }

        private static string DecodeEXI(byte[] payload)
        {
            var sb = new StringBuilder();
            
            // EXI 매직 바이트 체크 ($EXI)
            if (payload.Length >= 4 && payload[0] == 0x24 && payload[1] == 0x45 && payload[2] == 0x58 && payload[3] == 0x49)
            {
                sb.AppendLine("EXI Magic Cookie found: $EXI");
                
                // EXI 헤더 파싱 시도
                int offset = 4;
                if (offset < payload.Length)
                {
                    byte distinguishingBits = payload[offset++];
                    sb.AppendLine($"EXI Distinguishing Bits: 0x{distinguishingBits:X2}");
                    
                    // EXI 바디 데이터
                    if (offset < payload.Length)
                    {
                        sb.AppendLine("EXI Body:");
                        sb.AppendLine(TryDecodeXMLContent(payload, offset));
                    }
                }
            }
            else
            {
                // EXI 매직 바이트가 없으면 직접 EXI 디코딩 시도
                sb.AppendLine("No EXI magic cookie, attempting direct EXI decode:");
                sb.AppendLine(TryDecodeXMLContent(payload, 0));
            }
            
            sb.AppendLine("\nRaw EXI Data:");
            sb.AppendLine(BytesToHex(payload));
            
            return sb.ToString();
        }

        private static string DecodeDIN(byte[] payload)
        {
            var sb = new StringBuilder();
            sb.AppendLine("DIN SPEC 70121 Message");
            sb.AppendLine(TryDecodeXMLContent(payload, 0));
            sb.AppendLine("\nRaw DIN Data:");
            sb.AppendLine(BytesToHex(payload));
            return sb.ToString();
        }

        private static string DecodeSAP(byte[] payload)
        {
            var sb = new StringBuilder();
            sb.AppendLine("SAP Message");
            
            if (payload.Length >= 20)
            {
                // SAP 헤더 파싱
                sb.AppendLine("SAP Header:");
                sb.AppendLine($"  Message Type: 0x{payload[0]:X2}");
                sb.AppendLine($"  Session ID: {BitConverter.ToUInt64(payload, 1)}");
                sb.AppendLine($"  Protocol: 0x{payload[9]:X2}");
            }
            
            sb.AppendLine("\nRaw SAP Data:");
            sb.AppendLine(BytesToHex(payload));
            return sb.ToString();
        }

        private static string TryDecodeXMLContent(byte[] payload, int offset)
        {
            var sb = new StringBuilder();
            
            // ASCII 텍스트로 디코드 시도
            try
            {
                string asciiText = Encoding.ASCII.GetString(payload, offset, payload.Length - offset);
                if (ContainsXMLLikeContent(asciiText))
                {
                    sb.AppendLine("Possible XML content (ASCII):");
                    sb.AppendLine(asciiText);
                }
            }
            catch { }
            
            // UTF-8 디코드 시도
            try
            {
                string utf8Text = Encoding.UTF8.GetString(payload, offset, payload.Length - offset);
                if (ContainsXMLLikeContent(utf8Text))
                {
                    sb.AppendLine("Possible XML content (UTF-8):");
                    sb.AppendLine(utf8Text);
                }
            }
            catch { }
            
            // V2G 메시지 키워드 검색
            sb.AppendLine(SearchV2GKeywords(payload, offset));
            
            return sb.ToString();
        }

        private static bool ContainsXMLLikeContent(string text)
        {
            return text.Contains("<") && text.Contains(">") || 
                   text.Contains("SessionSetup") || 
                   text.Contains("ChargeParameter") ||
                   text.Contains("PowerDelivery") ||
                   text.Contains("V2G_Message");
        }

        private static string SearchV2GKeywords(byte[] payload, int offset)
        {
            var sb = new StringBuilder();
            var keywords = new string[]
            {
                "SessionSetupReq", "SessionSetupRes", 
                "ServiceDiscoveryReq", "ServiceDiscoveryRes",
                "ServiceDetailReq", "ServiceDetailRes",
                "PaymentServiceSelectionReq", "PaymentServiceSelectionRes",
                "ChargeParameterDiscoveryReq", "ChargeParameterDiscoveryRes",
                "PowerDeliveryReq", "PowerDeliveryRes",
                "ChargingStatusReq", "ChargingStatusRes",
                "MeteringReceiptReq", "MeteringReceiptRes",
                "SessionStopReq", "SessionStopRes",
                "V2G_Message", "Header", "Body"
            };

            var found = new List<string>();
            string dataAsString = Encoding.ASCII.GetString(payload, offset, payload.Length - offset);
            
            foreach (var keyword in keywords)
            {
                if (dataAsString.Contains(keyword, StringComparison.OrdinalIgnoreCase))
                {
                    found.Add(keyword);
                }
            }
            
            if (found.Any())
            {
                sb.AppendLine("Found V2G keywords:");
                foreach (var keyword in found)
                {
                    sb.AppendLine($"  - {keyword}");
                }
            }
            
            return sb.ToString();
        }

        public static string BytesToHex(byte[] bytes)
        {
            var sb = new StringBuilder();
            for (int i = 0; i < bytes.Length; i += 16)
            {
                sb.Append($"{i:X4}   ");
                
                // Hex bytes
                for (int j = 0; j < 16; j++)
                {
                    if (i + j < bytes.Length)
                        sb.Append($"{bytes[i + j]:X2} ");
                    else
                        sb.Append("   ");
                }
                
                sb.Append("  ");
                
                // ASCII representation
                for (int j = 0; j < 16 && i + j < bytes.Length; j++)
                {
                    byte b = bytes[i + j];
                    sb.Append(b >= 32 && b <= 126 ? (char)b : '.');
                }
                
                sb.AppendLine();
            }
            return sb.ToString();
        }

        public static byte[] ParseHexFile(string filePath)
        {
            var bytes = new List<byte>();
            
            foreach (string line in File.ReadAllLines(filePath))
            {
                var parts = line.Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries);
                
                foreach (var part in parts)
                {
                    // Skip line numbers and ASCII part
                    if (part.Contains("→") || part.Length != 2)
                        continue;
                        
                    if (byte.TryParse(part, System.Globalization.NumberStyles.HexNumber, null, out byte b))
                    {
                        bytes.Add(b);
                    }
                }
            }
            
            return bytes.ToArray();
        }
    }
}