namespace ErvProtocol
{
    public static class StatusDecoder
    {
        public const byte STATUS = 0x81;   // ERV→PC 상태
        public const byte ACK    = 0x82;   // ERV→PC 제어 응답
        public const int  STATUS_LEN  = 240;  // 238 + 2((꺼짐)예약 잔여초 u16)
        public const int  THR_OFF     = 134;  // 모드별 오염단계 임계표 시작 오프셋
        public const int  TEMPHUMI_OFF = 230; // 각실 온도/습도 블록 시작 (4실 × [Temp,Humi])
        public const int  RESERVE_OFF  = 238; // (꺼짐)예약 잔여초 u16

        static int U16(byte[] p, int off) => (p[off] << 8) | p[off + 1];  // 빅엔디안

        // STATUS(0x81) payload(73B) → StatusRecord. 길이 부족 시 null.
        public static StatusRecord? Decode(byte[] p)
        {
            if (p.Length < STATUS_LEN) return null;

            var s = new StatusRecord
            {
                Power      = p[0],
                RunMode    = p[1],
                AutoState  = p[2],
                FanMode    = p[3],
                SubMode    = p[4],
                Hood       = p[5],
                HystPreset = p[6],
                HystPm25   = U16(p, 7),
                HystPm10   = U16(p, 9),
                HystVoc    = U16(p, 11),
                HystCo2    = U16(p, 13),
                ErrorCode  = U16(p, 15),
            };

            const int baseOff = 17;
            for (int r = 0; r < 4; r++)
            {
                int o = baseOff + r * 14;
                var room = s.Rooms[r];
                room.Damper      = p[o + 0];
                room.Pm25        = U16(p, o + 1);
                room.Pm10        = U16(p, o + 3);
                room.Voc         = U16(p, o + 5);
                room.Co2         = U16(p, o + 7);
                room.AirQuality  = p[o + 9];
                room.LedDim      = p[o + 10];
                room.LoadScore   = U16(p, o + 11);
                room.FinalVolume = p[o + 13];
            }

            // ERV 리셋 (offset 73)
            s.Reset = p[73];

            // 풍량 VSP 블록 (offset 74~, 9엔트리 × u16 SA·EA)
            const int vspOff = 74;
            for (int i = 0; i < 9; i++)
            {
                int o = vspOff + i * 4;
                s.Vsp[i].Sa = U16(p, o);
                s.Vsp[i].Ea = U16(p, o + 2);
            }

            // 히스테리시스 프리셋 테이블 (offset 110~, 3프리셋 × PM2.5/PM10/VOC/CO2 u16)
            const int hystOff = 110;
            for (int i = 0; i < 3; i++)
            {
                int o = hystOff + i * 8;
                s.HystTable[i].Pm25 = U16(p, o);
                s.HystTable[i].Pm10 = U16(p, o + 2);
                s.HystTable[i].Voc  = U16(p, o + 4);
                s.HystTable[i].Co2  = U16(p, o + 6);
            }

            // 모드별 오염단계 임계표 (offset 134~, 3프리셋 × [CO2,PM2.5,PM10,VOC] × L1~L4 u16)
            for (int i = 0; i < 3; i++)
            {
                int o = THR_OFF + i * 32;
                for (int k = 0; k < 4; k++) s.ThrTable[i].Co2[k]  = U16(p, o + 0 + k * 2);
                for (int k = 0; k < 4; k++) s.ThrTable[i].Pm25[k] = U16(p, o + 8 + k * 2);
                for (int k = 0; k < 4; k++) s.ThrTable[i].Pm10[k] = U16(p, o + 16 + k * 2);
                for (int k = 0; k < 4; k++) s.ThrTable[i].Voc[k]  = U16(p, o + 24 + k * 2);
            }

            // 각실 온도/습도 (offset 230~, 4실 × [Temp, Humi])
            for (int r = 0; r < 4; r++)
            {
                int o = TEMPHUMI_OFF + r * 2;
                s.Rooms[r].Temp = p[o + 0];
                s.Rooms[r].Humi = p[o + 1];
            }

            // (꺼짐)예약 잔여초 (offset 238, u16)
            s.ReserveRemainSec = U16(p, RESERVE_OFF);
            return s;
        }
    }
}