using System;
using WIDESEAWCS_S7Simulator.Core.Interfaces;

namespace WIDESEAWCS_S7Simulator.Core.Memory
{
    /// <summary>
    /// T区（定时器区/Timer）实现
    /// 用于模拟西门子S7 PLC的定时器区域
    /// 每个定时器占用2字节，存储定时器的时间值（毫秒）
    /// </summary>
    public class TRegion : MemoryRegion, IMemoryRegion
    {
        /// <summary>
        /// 区域类型
        /// </summary>
        public override string RegionType => "T";

        /// <summary>
        /// 每个定时器占用的字节数（S7定时器为2字节）
        /// </summary>
        private const int TimerSize = 2;

        /// <summary>
        /// 定时器数量
        /// </summary>
        public int TimerCount => Size / TimerSize;

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

            // 验证没有溢出
            if (timerCount > Size / TimerSize)
                throw new OverflowException($"定时器数量{timerCount}过大，超出内存限制");
        }

        /// <summary>
        /// 读取定时器值
        /// </summary>
        /// <param name="timerNumber">定时器号（从1开始）</param>
        /// <returns>定时器值（毫秒）</returns>
        /// <exception cref="ArgumentOutOfRangeException">当timerNumber为0或超出定时器数量时抛出</exception>
        public ushort ReadTimer(ushort timerNumber)
        {
            if (timerNumber == 0)
                throw new ArgumentOutOfRangeException(nameof(timerNumber), "定时器号必须大于0（从1开始）");

            if (timerNumber > TimerCount)
                throw new ArgumentOutOfRangeException(nameof(timerNumber),
                    $"定时器号{timerNumber}超出范围，当前定时器总数为{TimerCount}");

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

        /// <summary>
        /// 写入定时器值
        /// </summary>
        /// <param name="timerNumber">定时器号（从1开始）</param>
        /// <param name="value">定时器值（毫秒）</param>
        /// <exception cref="ArgumentOutOfRangeException">当timerNumber为0或超出定时器数量时抛出</exception>
        public void WriteTimer(ushort timerNumber, ushort value)
        {
            if (timerNumber == 0)
                throw new ArgumentOutOfRangeException(nameof(timerNumber), "定时器号必须大于0（从1开始）");

            if (timerNumber > TimerCount)
                throw new ArgumentOutOfRangeException(nameof(timerNumber),
                    $"定时器号{timerNumber}超出范围，当前定时器总数为{TimerCount}");

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