#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_SSD1306 display(128, 64, &Wire, -1);
const int EYE_Y = 20;
const int EYE_W = 16;
const int GAP = 16;
const unsigned long BLINK_PERIOD_MS = 2000;
const unsigned long CLOSED_MS = 120;
const unsigned long MOVE_MS = 70;
unsigned long lastMove = 0;
int gaze = 0;
int direction = 1;

void face(bool closed, int offset, int jump, bool smile) {
  display.clearDisplay();
  int left = 64 - GAP / 2 - EYE_W + offset;
  int right = 64 + GAP / 2 + offset;
  int y = EYE_Y - jump;
  int height = closed ? 2 : 16;
  display.fillRoundRect(left, y, EYE_W, height, closed ? 0 : 4, SSD1306_WHITE);
  display.fillRoundRect(right, y, EYE_W, height, closed ? 0 : 4, SSD1306_WHITE);

  if (smile) {
    display.drawLine(54, 43 - jump, 59, 48 - jump, SSD1306_WHITE);
    display.drawLine(59, 48 - jump, 69, 48 - jump, SSD1306_WHITE);
    display.drawLine(69, 48 - jump, 74, 43 - jump, SSD1306_WHITE);
  }

  display.display();
}

void setup() {
  Serial.begin(115200);

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("OLED init failed"));
    while (true) { delay(100); }
  }

  Serial.println(F("OLED ready"));
}

void loop() {
  unsigned long now = millis();

  if (now - lastMove >= MOVE_MS) {
    lastMove = now;
    gaze += direction;

    if (gaze >= 10 || gaze <= -10) {
      direction = -direction;
    }

  }

  face(now % BLINK_PERIOD_MS < CLOSED_MS, gaze, 0, true);
}