#include <WiFi.h>
#include <WiFiManager.h>
#include <Wire.h>
#include <SensirionI2cSht4x.h>
#include <Adafruit_NeoPixel.h>
#include <math.h>

// --- Pin Definitions ---
#define PIN_NEOPIXEL 0
#define NUM_LEDS     9
#define PIN_FAN_PWM  4

// SHT40 Inside (Hardware I2C)
#define SDA_IN 8
#define SCL_IN 9

// SHT40 Outside (Software I2C)
#define SDA_OUT 5
#define SCL_OUT 6

// --- Global Objects ---
Adafruit_NeoPixel strip(NUM_LEDS, PIN_NEOPIXEL, NEO_GRB + NEO_KHZ800);
TwoWire BusIn = TwoWire(0);
TwoWire BusOut = TwoWire(1);
SensirionI2cSht4x shtIn;
SensirionI2cSht4x shtOut;

// PWM Settings for 120mm Fan
const int fanChannel = 0;
const int freq = 25000;
const int resolution = 8;

// --- Logic Constants ---
const float HUM_TARGET_MIN = 50.0; // Don't vent if inside is already dry (<50%)
const float AH_MARGIN = 0.5;      // Inside must be at least 0.5g/m3 wetter than outside
const int   MIN_FAN_PWM = 100;    // Minimum torque to spin the fan

// --- Helper: Absolute Humidity Calculation (g/m3) ---
float calculateAH(float t, float rh) {
  // Magnus-Tetens formula for Saturation Vapor Pressure
  float svp = 6.112 * exp((17.67 * t) / (t + 243.5));
  float vp = svp * (rh / 100.0);
  return (vp * 216.74) / (t + 273.15);
}

void setup() {
  // 1. Power Stability Delay
  delay(500); 
  Serial.begin(115200);

  // 2. Initialize LEDs (Yellow = WiFi Setup Mode)
  strip.begin();
  strip.setBrightness(40); 
  for(int i=0; i<NUM_LEDS; i++) strip.setPixelColor(i, 255, 150, 0);
  strip.show();

  // 3. WiFi Manager (AP Mode: "ESP32_Venting_Setup")
  WiFiManager wm;
  if(!wm.autoConnect("ESP32_Venting_Setup")) {
      Serial.println("WiFi Timeout - Continuing Offline");
  } else {
      Serial.println("WiFi Connected!");
  }

  // 4. Initialize Sensors
  // Boot indoor and outdoor SHT40 on separate I2C buses to avoid address conflict
  BusIn.begin(SDA_IN, SCL_IN);
  BusOut.begin(SDA_OUT, SCL_OUT);
  shtIn.begin(BusIn, 0x44);
  shtOut.begin(BusOut, 0x44);

  // 5. Initialize PWM Fan
  ledcSetup(fanChannel, freq, resolution);
  ledcAttachPin(PIN_FAN_PWM, fanChannel);

  Serial.println("System Ready.");
}

void loop() {
  float tIn, hIn, tOut, hOut;
  uint16_t error;

  // Read Sensors
  shtIn.measureHighPrecision(tIn, hIn);
  shtOut.measureHighPrecision(tOut, hOut);

  // Calculate Absolute Humidity
  float ahIn = calculateAH(tIn, hIn);
  float ahOut = calculateAH(tOut, hOut);

  int pwmValue = 0;
  int litPixels = 0;

  // --- VENTING LOGIC ---
  // If Inside > 50% RH AND Inside has more water mass than Outside
  if (hIn > HUM_TARGET_MIN && ahIn > (ahOut + AH_MARGIN)) {
    float diff = ahIn - ahOut;
    // Map water difference (0.5g to 5.0g) to PWM (100 to 255)
    pwmValue = map(constrain(diff, 0.5, 5.0), 0.5, 5.0, MIN_FAN_PWM, 255);
    // Map PWM to number of LEDs (1 to 10)
    litPixels = map(pwmValue, MIN_FAN_PWM, 255, 1, NUM_LEDS);
  } else {
    pwmValue = 0;
    litPixels = 0;
  }

  ledcWrite(fanChannel, pwmValue);

  // --- NEOPIXEL UI ---
  // Color based on INSIDE Relative Humidity
  uint8_t r, g, b;
  if (hIn < 45) {
    r = 0; g = 255; b = 200; // Cyan: Dry
  } else if (hIn < 60) {
    r = 0; g = 50; b = 255;  // Blue: Good
  } else {
    r = 255; g = 0; b = 150; // Magenta: Humid
  }

  strip.clear();
  if (litPixels > 0) {
    for(int i = 0; i < litPixels; i++) {
      strip.setPixelColor(i, r, g, b);
    }
  } else {
    // System heartbeat: 1 dim pixel showing current humidity color
    strip.setPixelColor(0, r/6, g/6, b/6);
  }
  strip.show();

  // Debug Output
  Serial.printf("IN: %.1fC %.1f%% (%.2fg) | OUT: %.1fC %.1f%% (%.2fg) | PWM: %d\n", 
                tIn, hIn, ahIn, tOut, hOut, ahOut, pwmValue);

  delay(5000); // 5-second update interval
}