using System.IO;
using System.IO.Ports;
using System.Text;

namespace PamhagenSysCtrl.Helpers {
    public class T1 : IDisposable {

        public enum Mode { HALT = 1, RUN = 2, RUN_F = 3, HOLD = 4, ERROR = 6 }
        public readonly record struct Status(Mode Mode, int Flags);

        protected SerialPort Serial;
        protected Stream Stream;
        protected StreamReader Reader;

        public T1(string portName, Parity parity = Parity.Odd) {
            Serial = new SerialPort(portName, 9600, parity, 8, StopBits.One);
            Serial.Open();
            Stream = Serial.BaseStream ?? Stream.Null;
            Stream.ReadTimeout = 250;
            Stream.WriteTimeout = 250;
            Reader = new(Stream, Encoding.ASCII, false, 256);
        }

        public void Dispose() {
            Reader.Dispose();
            Stream.Dispose();
            Serial.Dispose();
            GC.SuppressFinalize(this);
        }

        protected async Task SendCommand(string cmd, string? data = null, bool checksum = true) {
            // max 255 bytes
            byte[] d = new byte[255];
            int n = Encoding.ASCII.GetBytes($"(A{1:00}{cmd}", d);
            if (data != null) {
                if (data.Length > 244) throw new ArgumentException("T1 playload too long");
                n += Encoding.ASCII.GetBytes(data, 0, data.Length, d, n);
            }
            if (checksum) {
                d[n++] = (byte)'&';
                byte chk = d.Take(n).Aggregate((s, c) => (byte)((s + c) & 0xFF));
                n += Encoding.ASCII.GetBytes($"{chk:X2}", 0, 2, d, n);
            }
            d[n++] = (byte)')';
            d[n++] = (byte)'\r';
            await Stream.WriteAsync(d.AsMemory(0, n));
        }

        protected async Task<(string, string)> ReceiveResponse(string? expectedCmd = null) {
            var line = await Reader.ReadUntilAsync('\r');
            if (line == null) {
                throw new IOException("Verbindung zu SPS (T1) verloren");
            } else if (line.Length < 9 || !line.StartsWith("(A") || !line.EndsWith(")\r") || line[^5] != '&') {
                throw new FormatException("Invalid response from PLC (T1)");
            }

            var chk1 = (byte)Convert.ToInt32(line[^4..^2], 16);
            var chk2 = Encoding.ASCII.GetBytes(line).SkipLast(4).Aggregate((s, c) => (byte)((s + c) & 0xFF));
            if (chk1 != chk2) {
                throw new IOException($"Ungültige Prüfsumme von SPS (T1)");
            }

            var (cmd, data) = (line[4..6], line[6..^5]);
            if (cmd == "ST" && data[3] == '6') {
                // TODO check for other error bits?
                await SendCommand("ER");
                var (_, res) = await ReceiveResponse("ER");
                int code = Convert.ToInt32(res);
                var error = Enum.IsDefined(typeof(T1Error), code) ? (T1Error)code : T1Error.UNKNOWN_ERROR;
                throw new T1Exception($"PLC Error ({data}): {error.GetName()}" + (error.GetDescription() != null ? $" ({error.GetDescription()})" : ""));
            } else if (cmd == expectedCmd) {
                return (cmd, data);
            } else if (cmd == "CE") {
                int code = Convert.ToInt32(data);
                throw code switch {
                    1 => new T1Exception($"Computer Link Error ({data}): Command error (Received command is illegal)"),
                    2 => new T1Exception($"Computer Link Error ({data}): Format error (Received message format is invalid)"),
                    3 => new T1Exception($"Computer Link Error ({data}): Checksum error (Checksum mismatch is detected)"),
                    _ => new T1Exception($"Computer Link Error ({data}): Unknown error"),
                };
            } else if (cmd == "EE") {
                int code = Convert.ToInt32(data);
                var error = Enum.IsDefined(typeof(T1Error), code) ? (T1Error)code : T1Error.UNKNOWN_ERROR;
                throw new T1Exception($"PLC Error ({data}): {error.GetName()}" + (error.GetDescription() != null ? $" ({error.GetDescription()})" : ""));
            } else if (expectedCmd != null) {
                throw new T1Exception($"Unexpected response from PLC (T1): {cmd} {data}");
            }

            return (cmd, data);
        }

        public async Task Test(string data = "PINGPONG") {
            await SendCommand("TS", data);
            var (_, res) = await ReceiveResponse("TS");
            if (data.Replace(" ", "") != res) throw new T1Exception("Wrong test response from PLC (T1)");
        }

        public async Task<Status> StatusRead() {
            await SendCommand("ST", checksum: false);
            var (_, res) = await ReceiveResponse("ST");
            return new Status((Mode)(res[3] - '0'), ((res[0] - '0') << 4) | (res[1] - '0'));
        }

        public async Task<T1Error> ErrorStatusRead() {
            await SendCommand("ER", checksum: false);
            var (_, res) = await ReceiveResponse("ER");
            var code = Convert.ToInt32(res, 10);
            return Enum.IsDefined(typeof(T1Error), code) ? (T1Error)code : T1Error.UNKNOWN_ERROR;
        }

        public Task<ushort[]> DataRead(string register, int length) {
            return DataRead((register, length));
        }

        public async Task<ushort[]> DataRead(params (string Register, int Length)[] registers) {
            await SendCommand("DR", string.Join(',', registers.Select(r => $"{r.Register},{r.Length}")));
            var (_, res) = await ReceiveResponse("DR");
            if (res.Length != registers.Sum(r => r.Length) * 4) throw new T1Exception("Invalid response length from PLC (T1)");
            return [.. Enumerable.Range(0, res.Length / 4).Select(i => Convert.ToUInt16(res.Substring(i * 4, 4), 16))];
        }

        public Task<Status> DataWrite(string register, params ushort[] values) {
            return DataWrite((register, values));
        }

        public async Task<Status> DataWrite(params (string Register, ushort[] Values)[] registers) {
            await SendCommand("DW", string.Join(',', registers.Select(r => $"{r.Register},{r.Values.Length}," + string.Join(',', r.Values.Select(v => $"{v:X4}")))));
            var (_, res) = await ReceiveResponse("ST");
            return new Status((Mode)(res[3] - '0'), ((res[0] - '0') << 4) | (res[1] - '0'));
        }
    }
}