/*
  ESP32-C3 (Xiao) + HC-SR04 Ultrasonic + 1.3" OLED I2C
  -------------------------------------------------------
  Board   : Seeed Studio XIAO ESP32-C3
  Sensor  : HC-SR04 Ultrasonic Distance Sensor
  Display : 1.3" OLED SH1106 I2C

  HC-SR04 Wiring:
    HC-SR04 VCC  → 5V
    HC-SR04 GND  → GND
    HC-SR04 TRIG → D3 (GPIO3)
    HC-SR04 ECHO → D2 (GPIO2)  via voltage divider (see below!)

  !! HC-SR04 ECHO outputs 5V — ESP32-C3 is NOT 5V tolerant !!
  !! Use a voltage divider on ECHO pin:                       !!
  !!   ECHO → 1kΩ → D2 (GPIO2)                               !!
  !!                       └── 2kΩ → GND                     !!

  OLED I2C Wiring:
    OLED VCC → 3.3V
    OLED GND → GND
    OLED SDA → D4 (GPIO4)
    OLED SCL → D5 (GPIO5)

  Libraries needed:
    - U8g2  by oliver
*/

#include <U8g2lib.h>
#include <Wire.h>

// ── Pin config ────────────────────────────────────────────────────────────────
#define TRIG_PIN  D3    // D3 / GPIO3
#define ECHO_PIN  D2    // D2 / GPIO2 (via voltage divider)

#define MAX_DISTANCE_CM  400   // HC-SR04 max reliable range

// ── Objects ───────────────────────────────────────────────────────────────────
U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);

// ── Helper: measure distance ───────────────────────────────────────────────────
float measureDistanceCM() {
  // Send 10us trigger pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure echo pulse duration (timeout = max range in us)
  long duration = pulseIn(ECHO_PIN, HIGH, 30000);

  if (duration == 0) return -1;  // No echo = out of range

  float distanceCM = (duration * 0.0343) / 2.0;

  if (distanceCM > MAX_DISTANCE_CM) return -1;
  return distanceCM;
}

// ── Setup ─────────────────────────────────────────────────────────────────────
void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  Serial.println("=== XIAO ESP32-C3 + HC-SR04 + 1.3 OLED ===");

  u8g2.begin();
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_ncenB08_tr);
  u8g2.drawStr(10, 30, "Initialising...");
  u8g2.sendBuffer();

  delay(500);
}

// ── Main Loop ─────────────────────────────────────────────────────────────────
void loop() {
  float distCM = measureDistanceCM();
  float distIN = distCM / 2.54;

  // ── Serial output ──
  if (distCM < 0) {
    Serial.println("Distance : out of range");
  } else {
    Serial.print("Distance : ");
    Serial.print(distCM, 1);
    Serial.print(" cm  /  ");
    Serial.print(distIN, 1);
    Serial.println(" in");
  }

  // ── OLED display ──
  u8g2.clearBuffer();

  // Title
  u8g2.setFont(u8g2_font_ncenB08_tr);
  u8g2.drawStr(18, 12, "HC-SR04 Distance Fab");
  u8g2.drawHLine(0, 15, 128);

  if (distCM < 0) {
    u8g2.setFont(u8g2_font_ncenB12_tr);
    u8g2.drawStr(10, 42, "Out of range");
  } else {
    char lineCM[20], lineIN[20];
    snprintf(lineCM, sizeof(lineCM), "%.1f cm", distCM);
    snprintf(lineIN, sizeof(lineIN), "%.1f in", distIN);

    u8g2.setFont(u8g2_font_ncenB18_tr);   // big font for cm
    u8g2.drawStr(0, 42, lineCM);

    u8g2.setFont(u8g2_font_ncenB12_tr);   // smaller for inches
    u8g2.drawStr(0, 62, lineIN);
  }

  u8g2.sendBuffer();

  delay(200);  // update 5x per second for smooth readings
}