// This software implements an Apple ADB interface for a trackball. It uses a  
// Teensy 3.2 and is based on the code from this Imgur post https://imgur.com/a/BQjt9le
// 
// Revision History
// Initial Release Aug 3, 2021
// 
#define ADB_DATA_PIN 5 // TB bidirectional data pin
//
// TB Constants
int ADB_TIMEOUT = 10000;
// TB Functions
static void send_0bit() {
 digitalWrite(ADB_DATA_PIN, LOW);
 delayMicroseconds(65);
 digitalWrite(ADB_DATA_PIN, HIGH);
 delayMicroseconds(35);
}

static void send_1bit() {
 digitalWrite(ADB_DATA_PIN, LOW);
 delayMicroseconds(35);
 digitalWrite(ADB_DATA_PIN, HIGH);
 delayMicroseconds(65);
}

static void attn() {
  //delay(1);
  digitalWrite(ADB_DATA_PIN, LOW);
  delayMicroseconds(800-35);
  send_0bit();
}

void send_talk_command() {
 //attn
 pinMode(ADB_DATA_PIN, OUTPUT);
 attn();
 //address (3) 0011
 //0
  send_0bit();
  send_0bit();
  send_1bit();
  send_1bit();
 //talk 11
  send_1bit();
  send_1bit();
 //register 00
  send_0bit();
  send_0bit();
 //stop bit
  send_0bit();
 //start to stop time
 delayMicroseconds(140);

}
int receive_data_packet() {
 pinMode(ADB_DATA_PIN, INPUT);
 int data_time = 0;
 bool command_stop = false;
 int adb_data = 0;
 //begin reading ADB datapin
 
 while(digitalRead(ADB_DATA_PIN)!=LOW && data_time < ADB_TIMEOUT){
  //wait for beginning of start bit
  data_time+=1;
  delayMicroseconds(1);
 }

  while(digitalRead(ADB_DATA_PIN)!=HIGH && data_time < ADB_TIMEOUT){
  //wait for end of start bit
  data_time+=1;
  delayMicroseconds(1);
 }

 while(digitalRead(ADB_DATA_PIN)!=LOW && data_time < ADB_TIMEOUT){
  //wait for beginning of first data bit
  data_time+=1;
  delayMicroseconds(1);
 }

 //data packet
 data_time = 0;
 while(!command_stop && data_time < ADB_TIMEOUT) {
  int low = 0;
  int high = 0;
  bool bit_stop = false;
  while(!bit_stop && data_time < ADB_TIMEOUT) {
    
    int adb_stream = digitalRead(ADB_DATA_PIN);
    if(adb_stream == LOW) low+=1;
    if(adb_stream == HIGH) high+=1;
    if(adb_stream == LOW && high > 0) bit_stop = true;
    if(high > 240){
      bit_stop = true;
      break;
    }
    data_time+=1;
    delayMicroseconds(1);
  }
  if(high > 240){
    command_stop = true;
  }
  //append the new data bit to adb_data
  if(high > low && !command_stop) adb_data = (adb_data << 1) + 1;
  if(low > high && !command_stop) adb_data = adb_data << 1;
  
 }
 //stop bit 
 return adb_data;
}

void parse_data(int data) {
      if(data !=0) {
       int mousex = data & 0b0000000001111111;
       int mousey = (data >> 8) & 0b01111111;
       //the mouse value is
        //7 bit two's complement
       if((mousey & 0b1000000) != 0) {
          mousey =  ((~mousey + 1) & 0b01111111) * -1;
       }
       if((mousex & 0b1000000) != 0) {
          mousex =  ((~mousex + 1) & 0b01111111) * -1;
       }
       Mouse.move(mousex, mousey);
       Mouse.move(mousex, mousey);

      int mouseClick = data & 0b1000000000000000;
      
      if(mouseClick == 0) {
        Mouse.set_buttons(1,0,0);
      }
      else if(mouseClick != 0) {
        Mouse.set_buttons(0,0,0);
      }
     }
}

//
//----------------------------------Setup-------------------------------------------
void setup() {
  
}
//
//---------------------------------Main Loop---------------------------------------------
//
void loop() {   
   send_talk_command();
   parse_data(receive_data_packet());
//
  delay(20); // 
}