// =====================================================
//  PROJECT 1 — Temperature & Humidity Monitor
// =====================================================

// ─── PART 1: LIBRARIES ────────────────────────────
// Bring in all the tools we need

#include <Arduino.h>          // Main Arduino library - always first
#include "DHT.h"              // DHT22 sensor library
#include <Wire.h>             // I2C communication library
#include <Adafruit_GFX.h>     // Graphics library for display
#include <Adafruit_SSD1306.h> // OLED display driver library

// ─── PART 2: PIN DEFINITIONS ──────────────────────
// Give nicknames to pin numbers

#define DHT_PIN       15   // DHT22 data wire connected to GPIO 15
#define DHT_TYPE      DHT22 // We are using DHT22 type sensor
#define SCREEN_WIDTH  128  // OLED display width in pixels
#define SCREEN_HEIGHT 64   // OLED display height in pixels
#define OLED_RESET    -1   // No reset pin needed, so -1

// ─── PART 3: CREATE OBJECTS ───────────────────────
// Create sensor and display so we can use them in code

DHT dht(DHT_PIN, DHT_TYPE);
// This creates a DHT sensor object
// DHT_PIN = which pin to read from (GPIO 15)
// DHT_TYPE = what type of sensor (DHT22)

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
// This creates a display object
// SCREEN_WIDTH, SCREEN_HEIGHT = size of display (128x64)
// &Wire = use I2C communication
// OLED_RESET = no reset pin (-1)

// ─── PART 4: VARIABLES ────────────────────────────
// Boxes to store our data while program runs

float temperature = 0.0; // stores temperature value  (float = decimal number)
float humidity    = 0.0; // stores humidity value
int   readCount   = 0;   // counts how many readings done (int = whole number)

// ─── PART 5: TIMING VARIABLES ─────────────────────
unsigned long lastReadTime = 0;    // stores last time we read sensor
const int READ_INTERVAL    = 2000; // read every 2000 milliseconds = 2 seconds
// unsigned long = big number that stores milliseconds since ESP32 started
// const = this value never changes during the program

// =====================================================
//  SETUP — runs ONCE when ESP32 starts or resets
// =====================================================
void setup() {

  // Start Serial Monitor
  // This opens a communication channel between ESP32 and your laptop
  // 115200 is the speed (baud rate) - both sides must use same speed
  Serial.begin(115200);

  // Print a welcome message to Serial Monitor
  Serial.println("=============================");
  Serial.println("  Project 1 - Temp Monitor  ");
  Serial.println("=============================");

  // Start the DHT22 sensor
  dht.begin();
  Serial.println("DHT22 sensor started");

  // Start the OLED display
  // 0x3C is the I2C address of display - like a house address
  // Every I2C device has a unique address so ESP32 knows who to talk to
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    // If display fails to start, print error and stop program
    Serial.println("ERROR: Display not found! Check wiring.");
    while (true); // stop here forever
  }
  Serial.println("OLED display started");

  // Show welcome screen on display
  display.clearDisplay();           // clear any old data
  display.setTextColor(SSD1306_WHITE); // set text colour to white
  display.setTextSize(1);           // text size 1 = small
  display.setCursor(20, 10);        // set position x=20, y=10 pixels
  display.println("Project 1");
  display.setCursor(5, 30);
  display.println("Temp & Humidity");
  display.setCursor(20, 50);
  display.println("Starting...");
  display.display(); // IMPORTANT - this line actually sends to screen
                     // without this line nothing shows on display

  delay(2000); // wait 2 seconds showing welcome screen

  // Print table header to Serial Monitor
  Serial.println("Count | Temp C | Humidity % | Status");
  Serial.println("--------------------------------------");
}

// =====================================================
//  LOOP — runs FOREVER after setup finishes
// =====================================================
void loop() {

  // millis() returns how many milliseconds have passed since ESP32 started
  // We use this instead of delay() because delay() freezes the entire ESP32
  // With millis() the ESP32 keeps running and just checks if enough time passed
  if (millis() - lastReadTime >= READ_INTERVAL) {

    lastReadTime = millis(); // save current time for next comparison
    readCount++;             // add 1 to read counter

    // Read temperature and humidity from DHT22 sensor
    temperature = dht.readTemperature(); // reads Celsius value
    humidity    = dht.readHumidity();    // reads humidity percentage

    // isnan() means "is not a number"
    // If sensor gives bad reading it returns NaN (not a number)
    // We check for this so we do not show garbage values
    if (isnan(temperature) || isnan(humidity)) {
      Serial.println("ERROR: Sensor read failed!");
      showError();
      return; // skip rest of loop and start again
    }

    // Get status based on temperature value
    // This calls our function below and stores the result
    String status = getStatus(temperature);

    // Print reading to Serial Monitor in neat format
    // %d = integer, %.1f = float with 1 decimal, %s = string
    Serial.printf("%d | %.1f | %.1f | %s\n",
      readCount, temperature, humidity, status.c_str());

    // Show reading on OLED display
    showOnDisplay(temperature, humidity, status, readCount);
  }
}

// =====================================================
//  FUNCTION 1 — getStatus()
//  Takes temperature value and returns a status word
//  INPUT:  float temp (the temperature number)
//  OUTPUT: String (the status word)
// =====================================================
String getStatus(float temp) {
  if (temp < 20.0) {
    return "COLD";           // below 20 degrees
  } else if (temp < 30.0) {
    return "NORMAL";         // 20 to 29 degrees
  } else if (temp < 40.0) {
    return "WARM";           // 30 to 39 degrees
  } else {
    return "HOT!";           // 40 and above
  }
}
// NOTE: This exact same pattern is used in welding project
// if (current > 5.0) { arcActive = true; touchCount++; }

// =====================================================
//  FUNCTION 2 — showOnDisplay()
//  Takes all readings and shows them on OLED screen
//  INPUT:  temp, hum, status, count values
//  OUTPUT: nothing (void) - just updates screen
// =====================================================
void showOnDisplay(float temp, float hum, String status, int count) {

  display.clearDisplay(); // always clear first before drawing new data

  // ROW 1 - Title at top
  display.setTextSize(1);      // small text
  display.setCursor(0, 0);     // top left corner x=0, y=0
  display.println("-- Temp Monitor --");

  // ROW 2 - Temperature in big text
  display.setTextSize(2);      // bigger text
  display.setCursor(0, 14);    // move down 14 pixels
  display.print("T:");
  display.print(temp, 1);      // print temp with 1 decimal place
  display.println("C");

  // ROW 3 - Humidity in small text
  display.setTextSize(1);      // back to small text
  display.setCursor(0, 36);    // move down to y=36
  display.print("Hum: ");
  display.print(hum, 1);
  display.println("%");

  // ROW 4 - Status and count at bottom
  display.setCursor(0, 50);    // bottom of screen y=50
  display.print(status);
  display.print("  #");
  display.println(count);

  display.display(); // send everything to screen - never forget this line!
}

// =====================================================
//  FUNCTION 3 — showError()
//  Shows error message on display when sensor fails
// =====================================================
void showError() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(15, 20);
  display.println("SENSOR ERROR!");
  display.setCursor(10, 40);
  display.println("Check wiring...");
  display.display();
}