#include "U8glib.h"

#define ECHO_PIN 6
#define TRIG_PIN 7

U8GLIB_SSD1306_128X64 u8g; // create an instant of OLED display

void setup() {
  Serial.begin(115200);
  u8g.setFont(u8g_font_7x13); // set the font for text
  //u8g.setColorIndex(1); set the display colour can be done outside picture loop
}

float readDistanceCM() {
  unsigned long timestart = millis();
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
  unsigned long timeend = millis();
  Serial.println("----");
  Serial.println(timeend - timestart);

}


void loop() {

  float distance = readDistanceCM();
  Serial.println(distance);

  //delay(50);


  u8g.firstPage(); //marks the beginning of the picture loop.
  do {
    u8g.setColorIndex(1); // set the colour to white

    //note (X,Y) position is the lower left corner of the first character of the string

    u8g.drawFrame(4, 10, 128, 20); //draw frame at (0,10) with width = 128, height = 20

    if (distance < 108) {
      u8g.drawBox(10, 15, distance, 10);
    }//draw box at (10,15) with width = x, height = 10

    else if (distance >= 108) {
      u8g.drawBox(10, 15, 108, 10);
    }

    if (distance >= 200) {
      u8g.drawStr(0, 50, "safe");
    }

    else if (80 <= distance <= 200) {
      u8g.drawStr(0, 50, "Careful");
    }

    else if (distance <= 80) {
      u8g.drawStr(0, 50, "Too close");
    }

    u8g.setColorIndex(0); //change the colour back to black

  } while ( u8g.nextPage() ); //marks the end of the body of the picture loop

  u8g.setColorIndex(1);
  u8g.drawStr(0, 20, "outside");
  //drawing function must use inside the picture loop.
  delay(500);
}