//
// UART 外设实现
// 基于 UART 规格,包含完整的 FIFO、中断和调制解调器控制功能
//

using System;
using System.Collections.Generic;
using Antmicro.Renode.Core;
using Antmicro.Renode.Logging;
using Antmicro.Renode.Peripherals.Bus;
using Antmicro.Renode.Peripherals.UART;
using Antmicro.Renode.Utilities;
using Antmicro.Renode.Time;
using Antmicro.Migrant;

namespace Antmicro.Renode.Peripherals.CustomPeripherals
{
    /// <summary>
    /// UART_771_RUHW_2CFG 控制器：同步串口、遥测、有中断
    /// 接收缓存0B，发送缓存2048B，输入时钟24MHz
    /// </summary>
    public class UART_771_RUHW_2CFG6 : IDoubleWordPeripheral, IKnownSize
    {
        private readonly IMachine machine;          
        private readonly object txFifoLock = new object();
        private readonly object rxFifoLock = new object();

        public UART_771_RUHW_2CFG6(IMachine machine)    
        {
            this.clockFrequency = 24000000;
            this.machine = machine;     
            transmissionGeneration = 0;

            // 创建 FIFO
            txFifo = new Queue<byte>();
            rxFifo = new Queue<byte>();

            // 创建中断线
            IRQ = new GPIO();

            // 初始化寄存器
            DefineRegisters();
            Reset();

            this.Log(LogLevel.Info, "771 UART initialized, clock: {0} Hz", clockFrequency);
        }

        public void Reset()
        {
            lock(txFifoLock)
            {
                txFifo.Clear();
            }
            lock(rxFifoLock)
            {
                rxFifo.Clear();
            }

            fsta = FSTA_TEMP;        // FIFO状态寄存器
            frm_cnt = 0;        // 帧计数
            byte_cnt = 0;
            tbr = 0;        // 发送FIFO剩余字节数 
            currentBaudRate = 16384;    // 时钟配置缺省为16384Hz
            clk_set = (ushort)(clockFrequency / (2 * currentBaudRate) - 1);
            scramble_ctrl = 0x00;    // 加解扰使能禁止
            rstr = 0x00;        // 复位/使能寄存器

            RxfifoEnabled = true;
            TxfifoEnabled = true;       //发送fifo使能

            transmissionScheduled = false;
            transmissionGeneration++;
            InterruptTriggerCondition = false;      //重置后不满足条件

            IRQ.Set(false);
            UpdateInterrupts();

            this.Log(LogLevel.Info, "TX_FIFO_SIZE reset");
        }

        
        private void DefineRegisters()
        {
            // 寄存器访问通过 ReadDoubleWord/WriteDoubleWord 实现

        }


        // ========================================
        // IBusPeripheral 接口实现
        // ========================================
        public uint ReadDoubleWord(long offset)
        {
            return ReadRegisters(offset);
        }

        public void WriteDoubleWord(long offset, uint value)
        {
            WriteRegisters(offset, value);
        }


        // ========================================
        // 自定义
        // ========================================
        public uint ReadRegisters(long offset)
        {
            uint value = 0;

            switch (offset)
            {

                case (long)Registers.FSTA:      // FIFO状态寄存器
                    value = (byte)(fsta & 0xFF);
                    this.Log(LogLevel.Info, "Read FSTA: 0x{0:X2}", value);
                    break; 

                case (long)Registers.FRM_CNT:      //帧计数，待定
                    value = (uint)frm_cnt;
                    this.Log(LogLevel.Info, "Read TBR_FreeBytes: {0}", value);
                    break;

                case (long)Registers.TBR_FreeBytes:      //发送FIFO剩余字节数
                    lock(txFifoLock)
                    {
                        tbr = (ushort)txFifo.Count;
                    }
                    value = (uint)tbr;
                    this.Log(LogLevel.Info, "Read TBR_FreeBytes: {0}", value);
                    break;
              
                case (long)Registers.CLK_SET:       //时钟配置，暂无读操作
                    value = (uint)clk_set;
                    this.Log(LogLevel.Info, "Read CLK_SET: {0}", value);
                    break;

                case (long)Registers.SCRAMBLE_CTRL:       //加解扰使能禁止，暂无读操作
                    value = (uint)(scramble_ctrl & 0xFF);
                    this.Log(LogLevel.Info, "Read SCRAMBLE_CTRL: 0x{0}", value);
                    break;

                case (long)Registers.RSTR:      // 复位/使能,暂无读操作
                    value = (uint)(rstr & 0xFF);
                    this.Log(LogLevel.Info, "Read RSTR: 0x{0}", value);
                    break;

                default:
                    this.Log(LogLevel.Warning, "Read to unknown offset: 0x{0:X} = 0x{1:X2}", offset, value);
                    break;
            }
            
            return value;
        }


        public void WriteRegisters(long offset, uint value)
        {

            switch (offset)
            {

                case (long)Registers.TBR_RBR:      // 发送FIFO
                    WriteTBR(value);      
                    //this.Log(LogLevel.Info, "Write TBR_RBR: {0}", value);  
                    break; 

                case (long)Registers.CLK_SET:      // 时钟配置
                    clk_set = (ushort)value;
                    currentBaudRate = (ushort)(clockFrequency / 2 / (1 + value));      
                    this.Log(LogLevel.Info, "Write CLK_SET: {0}, currentBaudRate: {1}", value, currentBaudRate);  
                    // 计算传输速率
                    ComputeTransRate();
                    break; 

                case (long)Registers.SCRAMBLE_CTRL:      // 加解扰使能禁止
                    scramble_ctrl = (byte)(value & 0xFF);      
                    this.Log(LogLevel.Info, "Write SCRAMBLE_CTRL: 0x{0:X2}", value);  
                    break;

                case (long)Registers.RSTR:      // 复位/使能
                    rstr = (byte)(value & 0xFF);
                    this.Log(LogLevel.Info, "Write RSTR: 0x{0:X2}", rstr);
                    if ((rstr & 0XFF) == RSTR_RES)
                    {
                        Reset();
                    }
                    break;

                default:
                    this.Log(LogLevel.Warning, "Write to unknown offset: 0x{0:X} = 0x{1:X2}", offset, value);
                    break;
            }
        }


        // ========================================
        // 按波特率计算传输速率，同步串口无起始位、停止位、奇偶校验位
        // ========================================
        public void ComputeTransRate()
        {
            // 计算传输时间
            int bitsPerByte = 8;  // 数据位
            
            // 计算传输时间（秒）,16384hz->488.24us
            if(currentBaudRate == 0)
            {
                return;
            }
            double secondsPerByte = (double)bitsPerByte / currentBaudRate;
            microsecondsPerByte = (ulong)(secondsPerByte * 1000000);
            
            this.Log(LogLevel.Debug, 
                "Scheduling byte transmission: {0} bits @ {1} bps = {2}μs", 
                bitsPerByte, currentBaudRate, microsecondsPerByte);
        }

        private void UpdateInterrupts()
        {
            if(InterruptTriggerCondition == false)
            {
                // FIFO空 → 必须先写满>64，期间绝对不触发中断
                IRQ.Set(false);
                return;
            }

            lock(txFifoLock)
            {
                // <64 中断，>96 清除，中间保持
                if (txFifo.Count < IRQ_MINBYTES)
                {
                    IRQ.Set(true);
                    this.Log(LogLevel.Info, "Interrupt asserted");
                }
                else if (txFifo.Count > IRQ_MAXBYTES)
                {
                    IRQ.Set(false);
                }                
            }
            
        }


        public void WriteTBR(uint value)
        {
            // 从星务接收数据 ，操作txFifo
            // value 低16位有效
            this.Log(LogLevel.Info, "Write TBR: 0x{0:X2}", value);

            lock(txFifoLock)
            {
                if (TxfifoEnabled)
                {
                    if ((txFifo.Count + 2) <= TX_FIFO_SIZE)
                    {
                        bool wasEmpty = (txFifo.Count == 0);

                        byte tmp = (byte)(value >> 8);
                        txFifo.Enqueue(tmp);
                        tmp = (byte)value;
                        txFifo.Enqueue(tmp);
                        fsta = (byte)(fsta & (~FSTA_TEMP));     // 发送缓冲区不为空，D0置0

                        // 更新帧计数
                        byte_cnt += 2;
                        frm_cnt = (ushort)(byte_cnt / FRAME_LONG);    // 遥测帧固定1024字节

                        // FIFO从空变为非空
                        if(wasEmpty)
                        {
                            this.Log(LogLevel.Info, "FIFO: Empty->NonEmpty");
                            // 启动传输调度（事件驱动）
                            ScheduleNextByteTransmit();
                        }

                        if (txFifo.Count >= (TX_FIFO_SIZE / 2))
                        {
                            // 置半满标志
                            fsta = (byte)(fsta | FSTA_TLHF);     // 发送FIFO半满,D2置1
                        }

                        if((InterruptTriggerCondition == false) && (txFifo.Count > IRQ_MINBYTES))
                        {
                            InterruptTriggerCondition = true;
                            UpdateInterrupts();
                        }
                    }
                    else
                    {
                        fsta = (byte)(fsta | FSTA_TFUL);     // 发送FIFO满
                        this.Log(LogLevel.Warning, "TX FIFO overflow");
                    }
                }
                else
                {
                    // 非 FIFO 模式，待定
                    txFifo.Clear();
                    txFifo.Enqueue((byte)value);
                    fsta = (byte)(fsta & (~FSTA_TEMP));     // 发送缓冲区不为空，D0置0              
                }
            }
       
        }


        // ========================================
        // 核心：按波特率调度发送（事件驱动）
        // ========================================
        private void ScheduleNextByteTransmit()
        {
            lock(txFifoLock)
            {
                // 防止重复调度
                if (transmissionScheduled)
                {
                    return;
                }
                
                if (txFifo.Count == 0)
                {
                    // FIFO空
                    fsta = (byte)((fsta & 0xF0) | FSTA_TEMP);     
                    fsta |= FSTA_THHF;   //空闲置1                                   
                    this.Log(LogLevel.Info, "TX FIFO empty");
                    InterruptTriggerCondition = false;
                    return;
                }

                if (txFifo.Count < (TX_FIFO_SIZE / 2))
                {
                    // 清半满标志
                    fsta = (byte)(fsta & (~FSTA_TLHF));     // 发送FIFO非半满，D2清0
                }              
                
                transmissionScheduled = true;
                fsta = (byte)(fsta & (~FSTA_THHF));       //正在发送，置0   
                var currentGeneration = transmissionGeneration;
                
                // 使用Renode虚拟时间调度
                machine.ScheduleAction(
                    TimeInterval.FromMicroseconds(microsecondsPerByte),
                    _ => TransmitOneByte(currentGeneration)
                );
            }
        }

        private void TransmitOneByte(ulong generation)
        {
            lock(txFifoLock)
            {
                transmissionScheduled = false;
                
                // 检查是否被Reset取消
                if (generation != transmissionGeneration)
                {
                    this.Log(LogLevel.Debug, "Transmission cancelled (reset)");
                    return;
                }
                
                if (txFifo.Count > 0)
                {
                    byte data = txFifo.Dequeue();
                    
                    // 触发CharReceived事件（外部Backend可订阅 网络中间层改为订阅这个事件的方式）
                    TransmitCharacter(data);
                    
                    this.Log(LogLevel.Info, 
                        "Transmitted: 0x{0:X2} ('{1}'), Remaining: {2}", 
                        data, 
                        (data >= 32 && data < 127) ? (char)data : '.', 
                        txFifo.Count);
                    
                    // 继续调度下一个字节
                    UpdateInterrupts();
                    ScheduleNextByteTransmit();
                }
            }
        }        




        public string GetTXFIFODataString()
        {
            string data = "0x";
            byte tmp;

            // 从 TX FIFO 发送数据，中间层获取txfifo接口

            if(txFifo.Count == 0)
            {
                this.Log(LogLevel.Info, "TXFIFO Null");
                return "0x00";
            }

            while (txFifo.Count > 0)
            {
                tmp = txFifo.Dequeue();
                data += tmp.ToString("X2");  // 转换为16进制字符串                
            }

            this.Log(LogLevel.Info, "Transmitted: 0x{0}, TXFIFO Null", data);

      
            UpdateInterrupts();     

            return data;
        }

        // ========================================
        // 同步串口属性
        // ========================================       
        public uint BaudRate => 0;
        public enum Bits { None }
        public Bits StopBits => Bits.None;
        public enum Parity { None }
        public Parity ParityBit => Parity.None;

        public uint GetFSTA() => fsta;
        public uint GetByteCount() => byte_cnt;
        public ushort GetFrameCount() => frm_cnt;

        public event Action<byte> CharReceived;

        private void TransmitCharacter(byte data) 
        {
            CharReceived?.Invoke(data);
        }


        public long Size => 0x80;   //uart地址长度总空间

        public GPIO IRQ { get; }

        // ========================================
        // 寄存器定义
        // ========================================

        private enum Registers : long
        {
            TBR_RBR = 0x00,          // TBR发送FIFO
            FSTA = 0x04,             // FIFO状态寄存器
            FRM_CNT = 0x08,          // 帧计数
            TBR_FreeBytes = 0x0C,    // 发送FIFO剩余字节数
            CLK_SET = 0x10,          // 时钟配置
            SCRAMBLE_CTRL = 0x14,    // 加解扰使能禁止
            RSTR = 0x7C              // 复位/使能 x55复位；其他使能
        }


        // FSTA FIFO状态寄存器
        private const byte FSTA_TEMP = 0x01;  // 发送FIFO空
        private const byte FSTA_TLHF= 0x02;  // 发送FIFO半满
        private const byte FSTA_TFUL = 0x04;  // 发送FIFO满
        private const byte FSTA_THHF = 0x08;  // 1为空闲；0为正在发送
        

        // RSTR 复位/使能寄存器
        private const byte RSTR_RES = 0x55;  // 0x55复位，其他使能

        private const byte SCRAMBLE_CTRL_ENABLE = 0x55;    // 0x55加解扰使能，其他禁止

        // 常量
        private const int RX_FIFO_SIZE = 0;        // 接收FIFO_SIZE
        private const int TX_FIFO_SIZE = 2048;        // 发送FIFO_SIZE
        private const int FRAME_LONG = 1024;    // 帧长固定为1024B
        private const int IRQ_MINBYTES = 64;    // FIFO中的字节数小于64字节时会产生中断
        private const int IRQ_MAXBYTES = 96;    // FIFO中的字节数大于96字节时会清中断



        // ========================================
        // 私有字段
        // ========================================

        private readonly uint clockFrequency;
        private uint currentBaudRate; 
        private uint byte_cnt;   // 字节计数，计算帧计数

        // 寄存器
        private byte fsta;        // FIFO状态寄存器
        private ushort frm_cnt;   // 帧计数
        private ushort tbr;       // 发送FIFO剩余字节数
        private ushort clk_set;   // 时钟配置
        private byte scramble_ctrl;          // 加解扰使能禁止
        private byte rstr;          // 复位/使能
        

        // FIFO
        private readonly Queue<byte> rxFifo;
        private readonly Queue<byte> txFifo;
        private bool RxfifoEnabled;
        private bool TxfifoEnabled;
        private bool transmissionScheduled;
        private ulong transmissionGeneration;
        private ulong microsecondsPerByte;
        private bool InterruptTriggerCondition;     //FIFO为空后写入64字节才允许触发中断


        
    }
}