using System;
using System.Text;
using V2GDecoderNet.V2G;

namespace V2GDecoderNet.EXI
{
    /// <summary>
    /// EXI Encoder with exact C compatibility
    /// Matches iso1EXIDatatypesEncoder.c structure
    /// </summary>
    public static class EXIEncoderExact
    {
        public static byte[] EncodeV2GMessage(V2GMessageExact message)
        {
            try
            {
                var stream = new BitOutputStreamExact();
                
                // Write EXI header (0x80 0x98)
                stream.WriteNBitUnsignedInteger(16, 0x8098);
                
                // Write V2G message structure
                EncodeV2GMessageStructure(stream, message);
                
                return stream.ToArray();
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine($"EXI encoding error: {ex.Message}");
                throw new Exception($"Failed to encode V2G message: {ex.Message}", ex);
            }
        }
        
        private static void EncodeV2GMessageStructure(BitOutputStreamExact stream, V2GMessageExact message)
        {
            // Grammar state 0: Start with V2G_Message
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT({urn:iso:15118:2:2013:MsgDef}V2G_Message)
            
            // Grammar state 1: Header
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT({urn:iso:15118:2:2013:MsgHeader}Header)
            EncodeMessageHeader(stream, message.SessionID);
            
            // Grammar state 2: Body
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT({urn:iso:15118:2:2013:MsgDef}Body)
            EncodeBody(stream, message.Body);
            
            // End V2G_Message
            stream.WriteNBitUnsignedInteger(1, 0); // END_ELEMENT
        }
        
        private static void EncodeMessageHeader(BitOutputStreamExact stream, string sessionId)
        {
            // Grammar state for MessageHeaderType
            // START_ELEMENT({urn:iso:15118:2:2013:MsgHeader}SessionID)
            stream.WriteNBitUnsignedInteger(1, 0);
            
            // SessionID as hex binary
            stream.WriteNBitUnsignedInteger(1, 0); // CHARACTERS[BINARY_HEX]
            
            // Convert hex string to bytes
            byte[] sessionBytes = ConvertHexStringToBytes(sessionId);
            stream.WriteUnsignedInteger(sessionBytes.Length);
            WriteBytes(stream, sessionBytes);
            
            // End SessionID element
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // End Header (no Notification or Signature)
            stream.WriteNBitUnsignedInteger(1, 0); // EE
        }
        
        private static void EncodeBody(BitOutputStreamExact stream, BodyType body)
        {
            // Body type choice - CurrentDemandReq = 13 (6-bit)
            if (body.CurrentDemandReq_isUsed)
            {
                stream.WriteNBitUnsignedInteger(6, 13); // CurrentDemandReq choice
                EncodeCurrentDemandReqType(stream, body.CurrentDemandReq);
            }
            // Add other message types as needed
            else
            {
                throw new Exception("Unsupported message type for encoding");
            }
            
            // End Body
            stream.WriteNBitUnsignedInteger(1, 0); // EE
        }
        
        private static void EncodeCurrentDemandReqType(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // Grammar state 273: DC_EVStatus (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(DC_EVStatus)
            EncodeDC_EVStatusType(stream, req.DC_EVStatus);
            
            // Grammar state 274: EVTargetCurrent (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(EVTargetCurrent)
            EncodePhysicalValueType(stream, req.EVTargetCurrent);
            
            // Grammar state 275: Optional elements (3-bit choice)
            EncodeOptionalElements275(stream, req);
        }
        
        private static void EncodeOptionalElements275(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // Grammar state 275 - handle optional elements in sequence
            
            if (req.EVMaximumVoltageLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 0); // EVMaximumVoltageLimit choice
                EncodePhysicalValueType(stream, req.EVMaximumVoltageLimit);
                EncodeOptionalElements276(stream, req); // Continue to state 276
            }
            else if (req.EVMaximumCurrentLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 1); // EVMaximumCurrentLimit choice  
                EncodePhysicalValueType(stream, req.EVMaximumCurrentLimit);
                EncodeOptionalElements277(stream, req); // Continue to state 277
            }
            else if (req.EVMaximumPowerLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 2); // EVMaximumPowerLimit choice
                EncodePhysicalValueType(stream, req.EVMaximumPowerLimit);
                EncodeOptionalElements278(stream, req); // Continue to state 278
            }
            else if (req.BulkChargingComplete_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 3); // BulkChargingComplete choice
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.BulkChargingComplete ? 1u : 0u); // boolean value
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements279(stream, req); // Continue to state 279
            }
            else
            {
                // ChargingComplete (mandatory)
                stream.WriteNBitUnsignedInteger(3, 4); // ChargingComplete choice
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.ChargingComplete ? 1u : 0u); // boolean value
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements280(stream, req); // Continue to state 280
            }
        }
        
        private static void EncodeOptionalElements276(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // After EVMaximumVoltageLimit - states similar to 275 but different grammar
            if (req.EVMaximumCurrentLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 0); // EVMaximumCurrentLimit
                EncodePhysicalValueType(stream, req.EVMaximumCurrentLimit);
                EncodeOptionalElements277(stream, req);
            }
            else if (req.EVMaximumPowerLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 1); // EVMaximumPowerLimit
                EncodePhysicalValueType(stream, req.EVMaximumPowerLimit);
                EncodeOptionalElements278(stream, req);
            }
            else if (req.BulkChargingComplete_isUsed)
            {
                stream.WriteNBitUnsignedInteger(3, 2); // BulkChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.BulkChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements279(stream, req);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(3, 3); // ChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.ChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements280(stream, req);
            }
        }
        
        private static void EncodeOptionalElements277(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // After EVMaximumCurrentLimit
            if (req.EVMaximumPowerLimit_isUsed)
            {
                stream.WriteNBitUnsignedInteger(2, 0); // EVMaximumPowerLimit
                EncodePhysicalValueType(stream, req.EVMaximumPowerLimit);
                EncodeOptionalElements278(stream, req);
            }
            else if (req.BulkChargingComplete_isUsed)
            {
                stream.WriteNBitUnsignedInteger(2, 1); // BulkChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.BulkChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements279(stream, req);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(2, 2); // ChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.ChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements280(stream, req);
            }
        }
        
        private static void EncodeOptionalElements278(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // After EVMaximumPowerLimit
            if (req.BulkChargingComplete_isUsed)
            {
                stream.WriteNBitUnsignedInteger(1, 0); // BulkChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.BulkChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements279(stream, req);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(1, 1); // ChargingComplete
                stream.WriteNBitUnsignedInteger(1, 0); // boolean start
                stream.WriteNBitUnsignedInteger(1, req.ChargingComplete ? 1u : 0u);
                stream.WriteNBitUnsignedInteger(1, 0); // EE
                EncodeOptionalElements280(stream, req);
            }
        }
        
        private static void EncodeOptionalElements279(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // After BulkChargingComplete - must have ChargingComplete
            stream.WriteNBitUnsignedInteger(1, 0); // ChargingComplete
            stream.WriteNBitUnsignedInteger(1, 0); // boolean start
            stream.WriteNBitUnsignedInteger(1, req.ChargingComplete ? 1u : 0u);
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            EncodeOptionalElements280(stream, req);
        }
        
        private static void EncodeOptionalElements280(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // Grammar state 280: 2-bit choice for remaining optional elements
            if (req.RemainingTimeToFullSoC_isUsed)
            {
                stream.WriteNBitUnsignedInteger(2, 0); // RemainingTimeToFullSoC
                EncodePhysicalValueType(stream, req.RemainingTimeToFullSoC);
                EncodeOptionalElements281(stream, req);
            }
            else if (req.RemainingTimeToBulkSoC_isUsed)
            {
                stream.WriteNBitUnsignedInteger(2, 1); // RemainingTimeToBulkSoC
                EncodePhysicalValueType(stream, req.RemainingTimeToBulkSoC);
                EncodeOptionalElements282(stream, req);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(2, 2); // EVTargetVoltage (mandatory)
                EncodePhysicalValueType(stream, req.EVTargetVoltage);
                // End CurrentDemandReq
                stream.WriteNBitUnsignedInteger(1, 0); // EE
            }
        }
        
        private static void EncodeOptionalElements281(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // Grammar state 281: 2-bit choice after RemainingTimeToFullSoC
            if (req.RemainingTimeToBulkSoC_isUsed)
            {
                stream.WriteNBitUnsignedInteger(2, 0); // RemainingTimeToBulkSoC
                EncodePhysicalValueType(stream, req.RemainingTimeToBulkSoC);
                EncodeOptionalElements282(stream, req);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(2, 1); // EVTargetVoltage (mandatory)
                EncodePhysicalValueType(stream, req.EVTargetVoltage);
                // End CurrentDemandReq
                stream.WriteNBitUnsignedInteger(1, 0); // EE
            }
        }
        
        private static void EncodeOptionalElements282(BitOutputStreamExact stream, CurrentDemandReqType req)
        {
            // Grammar state 282: Must encode EVTargetVoltage
            stream.WriteNBitUnsignedInteger(1, 0); // EVTargetVoltage
            EncodePhysicalValueType(stream, req.EVTargetVoltage);
            // End CurrentDemandReq
            stream.WriteNBitUnsignedInteger(1, 0); // EE
        }
        
        private static void EncodeDC_EVStatusType(BitOutputStreamExact stream, DC_EVStatusType status)
        {
            // Grammar state for DC_EVStatusType
            
            // EVReady (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(EVReady)
            stream.WriteNBitUnsignedInteger(1, 0); // boolean start
            stream.WriteNBitUnsignedInteger(1, status.EVReady ? 1u : 0u); // boolean value
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // EVErrorCode (mandatory) 
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(EVErrorCode)
            stream.WriteNBitUnsignedInteger(1, 0); // enum start
            stream.WriteNBitUnsignedInteger(4, (uint)status.EVErrorCode); // 4-bit enum value
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // EVRESSSOC (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(EVRESSSOC)
            stream.WriteNBitUnsignedInteger(1, 0); // integer start
            stream.WriteNBitUnsignedInteger(7, (uint)status.EVRESSSOC); // 7-bit value (0-100)
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // End DC_EVStatus
            stream.WriteNBitUnsignedInteger(1, 0); // EE
        }
        
        private static void EncodePhysicalValueType(BitOutputStreamExact stream, PhysicalValueType value)
        {
            // Grammar state for PhysicalValueType
            
            // Multiplier (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(Multiplier)
            stream.WriteNBitUnsignedInteger(1, 0); // integer start
            EncodeInteger8(stream, value.Multiplier);
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // Unit (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(Unit)
            stream.WriteNBitUnsignedInteger(1, 0); // enum start
            stream.WriteNBitUnsignedInteger(3, (uint)value.Unit); // 3-bit enum
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // Value (mandatory)
            stream.WriteNBitUnsignedInteger(1, 0); // START_ELEMENT(Value)
            stream.WriteNBitUnsignedInteger(1, 0); // integer start
            EncodeInteger16(stream, value.Value);
            stream.WriteNBitUnsignedInteger(1, 0); // EE
            
            // End PhysicalValue
            stream.WriteNBitUnsignedInteger(1, 0); // EE
        }
        
        private static void EncodeInteger8(BitOutputStreamExact stream, sbyte value)
        {
            if (value >= 0)
            {
                stream.WriteNBitUnsignedInteger(1, 0); // positive sign bit
                stream.WriteUnsignedInteger((uint)value);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(1, 1); // negative sign bit
                stream.WriteUnsignedInteger((uint)(-(value + 1))); // magnitude
            }
        }
        
        private static void EncodeInteger16(BitOutputStreamExact stream, short value)
        {
            if (value >= 0)
            {
                stream.WriteNBitUnsignedInteger(1, 0); // positive sign bit
                stream.WriteUnsignedInteger((uint)value);
            }
            else
            {
                stream.WriteNBitUnsignedInteger(1, 1); // negative sign bit
                stream.WriteUnsignedInteger((uint)(-(value + 1))); // magnitude
            }
        }
        
        private static void WriteBytes(BitOutputStreamExact stream, byte[] bytes)
        {
            foreach (byte b in bytes)
            {
                stream.WriteNBitUnsignedInteger(8, b);
            }
        }
        
        private static byte[] ConvertHexStringToBytes(string hex)
        {
            if (hex.Length % 2 != 0)
                throw new ArgumentException("Hex string must have even length");
                
            byte[] bytes = new byte[hex.Length / 2];
            for (int i = 0; i < hex.Length; i += 2)
            {
                bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
            }
            return bytes;
        }
        
        public static byte[] EncodeCurrentDemandRes(CurrentDemandResType response)
        {
            try
            {
                var stream = new BitOutputStreamExact();
                
                // Write EXI header
                stream.WriteNBitUnsignedInteger(16, 0x8098);
                
                // Simple CurrentDemandRes encoding for testing
                // This is a placeholder - real implementation would need full grammar
                
                return stream.GetBytes();
            }
            catch (Exception ex)
            {
                throw new Exception($"Failed to encode CurrentDemandRes: {ex.Message}", ex);
            }
        }
    }
}