import serial
import struct
import time

class SCD30_HIL_Lib:
    def __init__(self, emulator_port='/dev/i2c_emulator', target_port='/dev/esp_sensor_test', baud=921600):
        # High speed for the bridge to minimize I2C latency
        self.emulator = serial.Serial(emulator_port, baud, timeout=0.05)
        # Standard speed for the Target application logs
        self.target = serial.Serial(target_port, 115200, timeout=0.1)
        
    def _calculate_crc8(self, data):
        """SCD30 specific CRC-8 (Polynomial 0x31)"""
        crc = 0xFF
        for byte in data:
            crc ^= byte
            for _ in range(8):
                if crc & 0x80:
                    crc = (crc << 1) ^ 0x31
                else:
                    crc <<= 1
                crc &= 0xFF
        return crc

    def _pack_float(self, value):
        """Converts float to [MSB, LSB, CRC, MSB2, LSB2, CRC]"""
        b = struct.pack('>f', value) # Big-endian IEEE754
        w1, w2 = [b[0], b[1]], [b[2], b[3]]
        return w1 + [self._calculate_crc8(w1)] + w2 + [self._calculate_crc8(w2)]

    def process_bridge(self, co2_val, temp_val, hum_val):
        """
        Listens for 'CMD:' from Emulator and replies with 'DATA:'
        Returns True if a measurement was successfully served.
        """
        line = self.emulator.readline().decode('utf-8', errors='ignore').strip()
        
        if line.startswith("CMD:"):
            cmd = line[4:]
            
            if "0202" in cmd: # Data Ready Status request
                resp = [0x00, 0x01, self._calculate_crc8([0x00, 0x01])]
                self.emulator.write(f"DATA:{''.join(f'{b:02X}' for b in resp)}\n".encode())
                
            elif "0300" in cmd: # Read Measurement request
                payload = self._pack_float(co2_val) + \
                          self._pack_float(temp_val) + \
                          self._pack_float(hum_val)
                hex_data = "".join(f"{b:02X}" for b in payload)
                self.emulator.write(f"DATA:{hex_data}\n".encode())
                return True # Measurement cycle complete
        return False

    def get_target_reading(self):
        """Captures the output from the Target ESP32 Serial Monitor"""
        return self.target.readline().decode('utf-8', errors='ignore').strip()

    def close(self):
        self.emulator.close()
        self.target.close()