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/* SuperSimpleIR -
 * Bare-minimum no-frills code to interpret input from an IR decoder, using pin change interrupts.
 * Does no fancy decoding - it's up to you to figure out which button corresponds with the
 * output from this snippet. The provided message codes work with an Apple remote, but this is by
 * no means limited to such remotes (for instance, my Yamaha receiver's remote works fine with this).
 * Possible improvements:
 * - Use a timer interrupt instead of timeToCommitMessage. I didn't bother
 *   implementing this as the project I developed this for will need the timer for other tasks.
 * - The message commit code is (barely) vulnerable to concurrency issues if a pulse comes in while
 *   we try to commit a message. In practice I don't think this matters.
 * - It gets confused easily if the signal gets weak and corrupted.
 */

// From the Tiny core.
#include <TinyDebugSerial.h>

TinyDebugSerial mySerial;

// Pin defs.
#define IN_IR 4 // If this is changed, change the code that enables interrupts.

#define IR_MSG_PLUS               2011287570
#define IR_MSG_MINUS              2011279378
#define IR_MSG_REW                2011238418
#define IR_MSG_FFWD               2011291666
#define IR_MSG_PLAYPAUSE          2011242514
#define IR_MSG_MENU               2011250706
#define IR_MSG_REPEAT_LAST_BUTTON 0

// After this much time has elapsed after the last transition, consider the
// message complete.
#define MSG_COMMIT_TIME_MICROSEC 30000

enum IRProtocolState { Idle, Building };

unsigned long timeOfLastIRPinChange;  // Time when the last pin change happened on the IR decoder.
unsigned long timeToCommitMessage;    // Time after which we should consider the message complete.
unsigned long message;                // Workspace where the message is built up.
IRProtocolState irProtocolState;      // What our protocol decoder is doing.

void processIRMessage(long message);

ISR(PCINT0_vect) {
  boolean isPinHigh = digitalRead(IN_IR);
  long currentTime = micros();
  long microsSinceLastChange = (currentTime - timeOfLastIRPinChange);
  timeOfLastIRPinChange = currentTime;

  // Bump up the commit time, since we got a level change.
  timeToCommitMessage = MSG_COMMIT_TIME_MICROSEC + timeOfLastIRPinChange;

  if (!isPinHigh)
  {
     // Going low.
    if (microsSinceLastChange < 700)
    {
      // Space
      message = message << 1;
    }
    else if (microsSinceLastChange < 2000)
    {
      // Mark.
      message = message << 1;
      message |= 1;
    }
    else if (microsSinceLastChange < 20000)
    {
      // First LOW.
      message = 0;
      irProtocolState = Building;
    }
  }

}

void setup()
{ 
  mySerial.begin(9600);
  mySerial.println("IR test up.");

  timeOfLastIRPinChange = micros();
  timeToCommitMessage = -1;
  irProtocolState = Idle;

  GIMSK = _BV(PCIE);    // Enable pin change interrupt
  PCMSK = _BV(PCINT4);  // Enable the interrupt for only pin 4.
}

void loop() {
  // Check to see if we can commit a message. If so, process it.
  if (micros() >= timeToCommitMessage && irProtocolState == Building)
  {
    long localMessage = message;
    message = 0;
    irProtocolState = Idle;
    processIRMessage(localMessage);
  }
}

void processIRMessage(long message)
{
  switch (message)
    {
      case IR_MSG_PLUS: mySerial.println("Plus"); break;
      case IR_MSG_MINUS: mySerial.println("Minus"); break;
      case IR_MSG_REW: mySerial.println("REW"); break;
      case IR_MSG_FFWD: mySerial.println("FFWD"); break;
      case IR_MSG_PLAYPAUSE: mySerial.println("Play/Pause"); break;
      case IR_MSG_MENU: mySerial.println("Menu"); break;
      case IR_MSG_REPEAT_LAST_BUTTON: mySerial.println("(repeat last)"); break;
      default: mySerial.print("Unknown code: "); mySerial.println(message); break;
    }
}