#include "SoftwareServo.h"

SoftwareServo *SoftwareServo::first;

#define NO_ANGLE (0xff)

SoftwareServo::SoftwareServo() : pin(0),angle(NO_ANGLE),pulse0(0),min16(34),max16(150),next(0)
{}

void SoftwareServo::setMinimumPulse(uint16_t t)
{
  min16 = t/16;
}

void SoftwareServo::setMaximumPulse(uint16_t t)
{
  max16 = t/16;
}

uint8_t SoftwareServo::attach(int pinArg)
{
  pin = pinArg;
  angle = NO_ANGLE;
  pulse0 = 0;
  next = first;
  first = this;
  digitalWrite(pin,0);
  pinMode(pin,OUTPUT);
  return 1;
}

void SoftwareServo::detach()
{
  for ( SoftwareServo **p = &first; *p != 0; p = &((*p)->next) ) {
    if ( *p == this) {
      *p = this->next;
      this->next = 0;
      return;
    }
  }
}

void SoftwareServo::write(int angleArg)
{
  if ( angleArg < 0) angleArg = 0;
  if ( angleArg > 180) angleArg = 180;
  angle = angleArg;
  // bleh, have to use longs to prevent overflow, could be tricky if always a 16MHz clock, but not true
  // That 64L on the end is the TCNT0 prescaler, it will need to change if the clock's prescaler changes,
  // but then there will likely be an overflow problem, so it will have to be handled by a human.
  pulse0 = (min16*16L*clockCyclesPerMicrosecond() + (max16-min16)*(16L*clockCyclesPerMicrosecond())*angle/180L)/64L;
}

uint8_t SoftwareServo::read()
{
  return angle;
}

uint8_t SoftwareServo::attached()
{
  for ( SoftwareServo *p = first; p != 0; p = p->next ) {
    if ( p == this) return 1;
  }
  return 0;
}

void SoftwareServo::refresh()
{
  uint8_t count = 0, i = 0;
  uint16_t base = 0;
  SoftwareServo *p;
  static unsigned long lastRefresh = 0;
  unsigned long m = millis();

  // if we haven't wrapped millis, and 20ms have not passed, then don't do anything
  if ( m >= lastRefresh && m < lastRefresh + 20) return;
  lastRefresh = m;

  for ( p = first; p != 0; p = p->next ) if ( p->pulse0) count++;
  if ( count == 0) return;
  
  // gather all the servos in an array
  SoftwareServo *s[count];
  for ( p = first; p != 0; p = p->next ) if ( p->pulse0) s[i++] = p;

  // bubblesort the servos by pulse time, ascending order
  for(;;) {
    uint8_t moved = 0;
    for ( i = 1; i < count; i++) {
      if ( s[i]->pulse0 < s[i-1]->pulse0) {
        SoftwareServo *t = s[i];
        s[i] = s[i-1];
        s[i-1] = t;
        moved = 1;
      }
    }
    if ( !moved) break;
  }
  
  // turn on all the pins
  // Note the timing error here... when you have many servos going, the
  // ones at the front will get a pulse that is a few microseconds too long.
  // Figure about 4uS/servo after them. This could be compensated, but I feel
  // it is within the margin of error of software servos that could catch
  // an extra interrupt handler at any time.
  for ( i = 0; i < count; i++) digitalWrite( s[i]->pin, 1);

  uint8_t start = TCNT0;
  uint8_t now = start;
  uint8_t last = now;
  
  // Now wait for each pin's time in turn..
  for ( i = 0; i < count; i++) {
    uint16_t go = start + s[i]->pulse0;
    
    // loop until we reach or pass 'go' time
    for (;;) {
      now = TCNT0;
      if ( now < last) base += 256;
      last = now;
  
      if ( base+now > go) {
        digitalWrite( s[i]->pin,0);
        break;
      }
    }
  }
}