using System;
using System.Text;

namespace XP.Hardware.PLC.Helpers
{
    /// <summary>
    /// PLC 数据块解析器 | PLC data block parser
    /// 将批量读取的 byte[] 按偏移量解析为各种数据类型，避免多次单点读取的通讯开销
    /// S7 PLC 使用大端字节序（Big-Endian）
    /// </summary>
    public class PlcDataBlock
    {
        private readonly byte[] _data;
        private readonly int _baseAddress;

        /// <summary>
        /// 原始字节数据 | Raw byte data
        /// </summary>
        public byte[] RawData => _data;

        /// <summary>
        /// 数据块起始地址 | Data block base address
        /// </summary>
        public int BaseAddress => _baseAddress;

        /// <summary>
        /// 数据长度（字节数）| Data length in bytes
        /// </summary>
        public int Length => _data?.Length ?? 0;

        /// <summary>
        /// 构造函数 | Constructor
        /// </summary>
        /// <param name="data">批量读取的字节数据 | Batch read byte data</param>
        /// <param name="baseAddress">数据块起始地址 | Data block base address</param>
        public PlcDataBlock(byte[] data, int baseAddress = 0)
        {
            _data = data ?? throw new ArgumentNullException(nameof(data));
            _baseAddress = baseAddress;
        }

        /// <summary>
        /// 获取相对于 baseAddress 的实际偏移量 | Get actual offset relative to baseAddress
        /// </summary>
        /// <param name="absoluteAddress">绝对地址 | Absolute address</param>
        /// <returns>数组内偏移量 | Array offset</returns>
        private int ToOffset(int absoluteAddress)
        {
            int offset = absoluteAddress - _baseAddress;
            if (offset < 0 || offset >= _data.Length)
                throw new ArgumentOutOfRangeException(nameof(absoluteAddress),
                    $"地址 {absoluteAddress} 超出数据范围 [{_baseAddress}, {_baseAddress + _data.Length - 1}] | " +
                    $"Address {absoluteAddress} out of range [{_baseAddress}, {_baseAddress + _data.Length - 1}]");
            return offset;
        }

        /// <summary>
        /// 检查偏移量和长度是否在范围内 | Check if offset and length are within range
        /// </summary>
        private void CheckRange(int offset, int requiredBytes)
        {
            if (offset + requiredBytes > _data.Length)
                throw new ArgumentOutOfRangeException(
                    $"地址 {_baseAddress + offset} 需要 {requiredBytes} 字节，但剩余仅 {_data.Length - offset} 字节 | " +
                    $"Address {_baseAddress + offset} requires {requiredBytes} bytes, but only {_data.Length - offset} remaining");
        }

        /// <summary>
        /// 读取 Bool 值（按位寻址）| Read Bool value (bit addressing)
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <param name="bitIndex">位索引 (0-7) | Bit index (0-7)</param>
        /// <returns>布尔值 | Boolean value</returns>
        public bool GetBool(int address, int bitIndex)
        {
            if (bitIndex < 0 || bitIndex > 7)
                throw new ArgumentOutOfRangeException(nameof(bitIndex),
                    $"位索引必须在 0-7 之间 | Bit index must be between 0-7");
            int offset = ToOffset(address);
            return (_data[offset] & (1 << bitIndex)) != 0;
        }

        /// <summary>
        /// 读取 Byte 值 | Read Byte value
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>字节值 | Byte value</returns>
        public byte GetByte(int address)
        {
            int offset = ToOffset(address);
            return _data[offset];
        }

        /// <summary>
        /// 读取 Int16 (Short) 值，大端字节序 | Read Int16 (Short) value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>Int16 值 | Int16 value</returns>
        public short GetInt16(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 2);
            return (short)((_data[offset] << 8) | _data[offset + 1]);
        }

        /// <summary>
        /// 读取 UInt16 (UShort) 值，大端字节序 | Read UInt16 (UShort) value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>UInt16 值 | UInt16 value</returns>
        public ushort GetUInt16(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 2);
            return (ushort)((_data[offset] << 8) | _data[offset + 1]);
        }

        /// <summary>
        /// 读取 Int32 (Int) 值，大端字节序 | Read Int32 (Int) value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>Int32 值 | Int32 value</returns>
        public int GetInt32(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 4);
            return (_data[offset] << 24) | (_data[offset + 1] << 16) |
                   (_data[offset + 2] << 8) | _data[offset + 3];
        }

        /// <summary>
        /// 读取 UInt32 值，大端字节序 | Read UInt32 value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>UInt32 值 | UInt32 value</returns>
        public uint GetUInt32(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 4);
            return (uint)((_data[offset] << 24) | (_data[offset + 1] << 16) |
                          (_data[offset + 2] << 8) | _data[offset + 3]);
        }

        /// <summary>
        /// 读取 Float (Single) 值，大端字节序 | Read Float (Single) value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>Float 值 | Float value</returns>
        public float GetFloat(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 4);
            // S7 大端：需要反转为小端后转换 | S7 Big-Endian: reverse to Little-Endian for conversion
            byte[] temp = new byte[4];
            temp[0] = _data[offset + 3];
            temp[1] = _data[offset + 2];
            temp[2] = _data[offset + 1];
            temp[3] = _data[offset];
            return BitConverter.ToSingle(temp, 0);
        }

        /// <summary>
        /// 读取 Double 值，大端字节序 | Read Double value, Big-Endian
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <returns>Double 值 | Double value</returns>
        public double GetDouble(int address)
        {
            int offset = ToOffset(address);
            CheckRange(offset, 8);
            // S7 大端：需要反转为小端后转换 | S7 Big-Endian: reverse to Little-Endian for conversion
            byte[] temp = new byte[8];
            for (int i = 0; i < 8; i++)
                temp[i] = _data[offset + 7 - i];
            return BitConverter.ToDouble(temp, 0);
        }

        /// <summary>
        /// 读取 ASCII 字符串 | Read ASCII string
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <param name="length">字符串长度（字节数）| String length in bytes</param>
        /// <returns>字符串值 | String value</returns>
        public string GetString(int address, int length)
        {
            if (length <= 0)
                throw new ArgumentOutOfRangeException(nameof(length),
                    $"字符串长度必须大于 0 | String length must be greater than 0");
            int offset = ToOffset(address);
            CheckRange(offset, length);
            // 去除尾部空字符 | Trim trailing null characters
            return Encoding.ASCII.GetString(_data, offset, length).TrimEnd('\0');
        }

        /// <summary>
        /// 读取指定范围的原始字节 | Read raw bytes from specified range
        /// </summary>
        /// <param name="address">绝对字节地址 | Absolute byte address</param>
        /// <param name="length">字节数 | Number of bytes</param>
        /// <returns>字节数组 | Byte array</returns>
        public byte[] GetBytes(int address, int length)
        {
            int offset = ToOffset(address);
            CheckRange(offset, length);
            byte[] result = new byte[length];
            Array.Copy(_data, offset, result, 0, length);
            return result;
        }
    }
}