"""
1. How the Gas Sensor Works
🔸 The MQ-2 sensor detect gases like: 
- Methane (CH₄)
- Propane (C₃H₈)
- LPG
- Smoke
- CO₂, NH₃, Alcohol etc.

🧠 Working Principle
- Inside the sensor is a heater coil and a semiconductor material (SnO₂) whose resistance changes in the presence of gases.
- When gas concentration increases, the resistance drops, which changes the voltage output on the AO pin (Analog Output).

🔧 Circuit Configuration
The gas sensor has:
- VCC: Power (Often 3.3V can be used for some sensors with reduced range)
- GND: Ground
- AO: Analog Output → Connects to ADC pin on Raspberry Pi Pico
    → The AO pin is connected in a voltage divider configuration inside the sensor. 
    → As gas concentration changes, so does the voltage on AO.
- DOUT: Normally Not connected in many applications 
    → Digital output (HIGH/LOW if threshold crossed based on an Internal Trimpot/Potentiometer)

📈 Output Behavior
- Clean air → Higher resistance → Lower voltage
- Gas presence → Lower resistance → Higher voltage
- You read this analog voltage with ADC.read_u16() and convert it to a float voltage using:
    → V = (ADC_value / 65535 ) x 3.3

===================================================================================================================

🖥️ 2. How the I2C LCD Works
🔸 What Is an I2C LCD?
It's a regular 16x2 character LCD (based on the HD44780 chip) with an I2C adapter board (usually a PCF8574 I/O expander) soldered at the back.

🧠 How I2C LCD Displays Data
- The I2C LCD driver chip (PCF8574) receives commands over I2C.
- It converts I2C messages to parallel commands for the actual LCD controller (HD44780).
- You send strings like lcd.putstr("Hello"), and the display lights up each character in the grid of 16 columns x 2 rows.

🔧 Wiring with I2C
- Instead of using 6-8 GPIO pins (as with parallel LCDs), this LCD uses just 2 lines:
    → SDA: Serial Data (e.g., GP0)
    → SCL: Serial Clock (e.g., GP1)
- These are I²C lines that let the Pi-Pico talk to the display using only 2 pins, leaving others free for sensors.

🧪 Communication Flow
    MicroPython Code
        │
        ▼
    Pi Pico I2C (GP0, GP1)
        │
        ▼
    PCF8574 (I2C Expander on LCD)\
        │                         \______ Requires i2c_lcd.py and lcd_api.py files as libraries
        ▼                         /
    HD44780 LCD Controller ______/
        │
        ▼
    Characters appear on screen!

"""

from machine import ADC, Pin, I2C           # Import hardware-related classes: ADC for analog input, Pin for GPIO, I2C for I2C communication
from i2c_lcd import I2cLcd                  # Import the custom I2C LCD class from your i2c_lcd.py file
import time                                 # Import time module for using delays

# --- LCD Configuration ---
i2c = I2C(0, sda=Pin(0), scl=Pin(1), freq=400000)  # Initialize I2C interface (I2C0) on GP0 (SDA) and GP1 (SCL) with 400kHz frequency
lcd = I2cLcd(i2c, 0x27, 2, 16)                     # Initialize the 16x2 I2C LCD display at address 0x27 (2 rows, 16 columns)

# --- Gas Sensor Configuration ---
gas_sensor = ADC(26)              # Set up ADC on GP26 (ADC0) to read analog voltage from gas sensor
VREF = 3.3                        # Reference voltage (3.3V on Pi Pico)
ADC_RES = 65535                   # Maximum ADC reading for 16-bit resolution (0 to 65535)
DOLLAR_RATE = 2.50                # Cost rate per volt: $2.50 per volt of gas reading

# --- Display Startup Message ---
lcd.clear()                       # Clear the LCD screen
lcd.putstr("Gas Sensor")          # Print "Gas Sensor" on the top row
lcd.move_to(0, 1)                 # Move cursor to beginning of second row
lcd.putstr("Meter Reading")       # Print "Meter Reading" on the second row
time.sleep(2)                     # Wait for 2 seconds to show startup message

while True:
    # Read analog value and convert to voltage
    raw_value = gas_sensor.read_u16()                    # Read raw 16-bit ADC value from gas sensor (0–65535)
    print(raw_value)                                     # Print raw value to serial terminal for debugging
    voltage = (raw_value / ADC_RES) * VREF               # Convert raw ADC value to actual voltage (0.0V to 3.3V)
    bill = voltage * DOLLAR_RATE                         # Calculate billing amount based on voltage

    # Display on LCD
    lcd.clear()                                          # Clear LCD screen
    lcd.move_to(0, 0)                                    # Move to beginning of first row
    lcd.putstr("Raw: {}".format(raw_value))              # Show raw ADC value
    lcd.move_to(0, 1)                                    # Move to beginning of second row
    lcd.putstr("Voltage: {:.1f} V".format(voltage))      # Show measured voltage (rounded to 1 decimal)

    time.sleep(2)                                        # Wait 1 second before switching screen

    lcd.clear()                                          # Clear LCD again for new screen
    lcd.move_to(0, 0)                                    # Move to top row
    lcd.putstr("Bill Charge:")                           # Display label for billing
    lcd.move_to(0, 1)                                    # Move to second row
    lcd.putstr("$ {:.4f}".format(bill))                  # Display calculated billing amount (rounded to 4 decimal places)

    time.sleep(2)                                        # Wait 1 second before repeating the loop