using System;
using WIDESEAWCS_S7Simulator.Core.Interfaces;

namespace WIDESEAWCS_S7Simulator.Core.Memory
{
    /// <summary>
    /// C区（计数器区/Counter）实现
    /// 用于模拟西门子S7 PLC的计数器区域
    /// 每个计数器占用2字节，存储计数器的当前值
    /// </summary>
    public class CRegion : MemoryRegion, IMemoryRegion
    {
        /// <summary>
        /// 区域类型
        /// </summary>
        public override string RegionType => "C";

        /// <summary>
        /// 每个计数器占用的字节数（S7计数器为2字节）
        /// </summary>
        private const int CounterSize = 2;

        /// <summary>
        /// 计数器数量
        /// </summary>
        public int CounterCount => Size / CounterSize;

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="counterCount">计数器数量</param>
        /// <exception cref="ArgumentOutOfRangeException">当counterCount小于或等于0时抛出</exception>
        /// <exception cref="OverflowException">当counterCount * CounterSize超出int范围时抛出</exception>
        public CRegion(int counterCount) : base(counterCount * CounterSize)
        {
            if (counterCount <= 0)
                throw new ArgumentOutOfRangeException(nameof(counterCount), "计数器数量必须大于0");

            // 验证没有溢出
            if (counterCount > Size / CounterSize)
                throw new OverflowException($"计数器数量{counterCount}过大，超出内存限制");
        }

        /// <summary>
        /// 读取计数器值
        /// </summary>
        /// <param name="counterNumber">计数器号（从1开始）</param>
        /// <returns>计数器值</returns>
        /// <exception cref="ArgumentOutOfRangeException">当counterNumber为0或超出计数器数量时抛出</exception>
        public ushort ReadCounter(ushort counterNumber)
        {
            if (counterNumber == 0)
                throw new ArgumentOutOfRangeException(nameof(counterNumber), "计数器号必须大于0（从1开始）");

            if (counterNumber > CounterCount)
                throw new ArgumentOutOfRangeException(nameof(counterNumber),
                    $"计数器号{counterNumber}超出范围，当前计数器总数为{CounterCount}");

            ushort offset = (ushort)((counterNumber - 1) * CounterSize);
            var data = Read(offset, CounterSize);
            return (ushort)((data[0] << 8) | data[1]);
        }

        /// <summary>
        /// 写入计数器值
        /// </summary>
        /// <param name="counterNumber">计数器号（从1开始）</param>
        /// <param name="value">计数器值</param>
        /// <exception cref="ArgumentOutOfRangeException">当counterNumber为0或超出计数器数量时抛出</exception>
        public void WriteCounter(ushort counterNumber, ushort value)
        {
            if (counterNumber == 0)
                throw new ArgumentOutOfRangeException(nameof(counterNumber), "计数器号必须大于0（从1开始）");

            if (counterNumber > CounterCount)
                throw new ArgumentOutOfRangeException(nameof(counterNumber),
                    $"计数器号{counterNumber}超出范围，当前计数器总数为{CounterCount}");

            ushort offset = (ushort)((counterNumber - 1) * CounterSize);
            var data = new byte[] { (byte)(value >> 8), (byte)(value & 0xFF) };
            Write(offset, data);
        }
    }
}