// check if browser supports everything needed
function SLIDE_general_support() {
  var d = document;
  var b = d.body;
  if (!b) return 1;
  if (!d.getElementById) return 2;
}

// check if named element supports everything needed
function SLIDE_element_support(elementName, checkLevel) {
  var d = document;
  var e = d.getElementById(elementName);
  if (!e) return 1;
  if (checkLevel=='basic') return 0;
  if (typeof(e.offsetTop)!='number') return 2;
  if (typeof(e.offsetHeight)!='number') return 3;
  if (checkLevel=='position') return 0;
  if (!e.style) return 4;
  if (typeof(e.style.top)!='string') return 5;
  if (typeof(e.style.position)!='string') return 6;
  return 0;
}

// how much window has scrolled
// courtesy of www.quirksmode.org
function SLIDE_scrollTop() {
  var d = document;
  if (self.pageYOffset) {
    // all except IE
    return self.pageYOffset;
  }
  else if (d.documentElement && d.documentElement.scrollTop) {
    // Explorer 6 Strict
    return d.documentElement.scrollTop;
  }
  else {
    // all other Explorers
    var b = d.body;
    return b.scrollTop;
  }
}

// viewport height
// courtesy of www.quirksmode.org
function SLIDE_clientHeight() {
  var d = document;
  if (self.innerHeight) {
    // all except Explorer
    return self.innerHeight;
  }
  else if (d.documentElement && d.documentElement.clientHeight) {
    // Explorer 6 Strict Mode
    return d.documentElement.clientHeight;
  }
  else {
    // other Explorers
    var b = d.body;
    return b.clientHeight;
  }
}

// function that updates the slider position
function SLIDE_update(sliderName, containerName, slideSpeed, updateInterval, breakerName, cDelta) {
  // grab elements
  var d = document;
  var slider = d.getElementById(sliderName);
  var container = d.getElementById(containerName);
  if (breakerName) var breaker = d.getElementById(breakerName);
  // init slider position
  var topStopper = container.offsetTop + cDelta;
  var wantedPosition = topStopper;
  // determine would-be position in regard to viewport
  var clientHeight = SLIDE_clientHeight();
  var scrollTop = SLIDE_scrollTop();
  // if element is shorter than or equal with the viewport
  if (slider.offsetHeight <= clientHeight) {
    // align element top margin with viewport top margin
    wantedPosition = scrollTop;
  }
  // if element is bigger than the viewport
  else {
    // if element top margin is lower than the viewport top margin
    if (scrollTop < slider.offsetTop) {
      // align element top margin with top viewport margin
      wantedPosition = scrollTop;
    }
    // if element bottom margin is higher than the bottom viewport margin
    else if (scrollTop + clientHeight > slider.offsetTop + slider.offsetHeight) {
      // align element bottom margin with bottom viewport margin
      wantedPosition = scrollTop + clientHeight - slider.offsetHeight;
    }
    else {
      // we're in the middle, and the element is taller than the viewport, leave as it is
      wantedPosition = slider.offsetTop;
    }
  }
  // next, we have to adjust position in regard to container
  // did the slider go up past the top of the container?
  if (wantedPosition < topStopper) {
    wantedPosition = topStopper;
  }
  else {
    // did the slider go down past the bottom of the container?
    if (wantedPosition + slider.offsetHeight >= topStopper + container.offsetHeight) {
      wantedPosition = topStopper + container.offsetHeight - slider.offsetHeight;
    }
    else {
      // slider is in the visible area with either both margins or none
      // no adjustment needed, let user scroll it normally
    }
  }
  // if there's a breaker, use it
  if (breaker) {
    if (wantedPosition + slider.offsetHeight > breaker.offsetTop) {
      wantedPosition = breaker.offsetTop - slider.offsetHeight;
    }
  }
  // adjust jump according to requested speed
  if (slideSpeed != 0) {
    var delta = Math.ceil(Math.abs(slider.offsetTop - wantedPosition) * slideSpeed);
    wantedPosition = (slider.offsetTop > wantedPosition) ? slider.offsetTop - delta : slider.offsetTop + delta;
  }
  // ** SWITCH FROM ABSOLUTE (PAGE VALUE) TO RELATIVE (INSIDE CONTAINER) VALUE **
  var wPold = wantedPosition;
  relativePosition = wantedPosition - topStopper;
  // sanity checks
  // did it pass over the top margin of the container?
  if (relativePosition < 0)  {
    relativePosition = 0;
  }
  // did it pass over the lower margin of the container?
  if (relativePosition + slider.offsetHeight > container.offsetHeight) {
    relativePosition = container.offsetHeight - slider.offsetHeight;
  }
  // set the new position
  slider.style.top = relativePosition + 'px';
  // detect anomalies; most likely user resized fonts
  if (wantedPosition != slider.offsetTop) {
    // recalculate cDelta
    cDelta = slider.offsetTop - container.offsetTop;
    // force a reset jump
    slider.style.top = '0px'; 
  }
  //debugging
  /*window.status=
  'rP='+relativePosition
  +', wP='+wantedPosition
  +(wantedPosition!=slider.offsetTop?'*':'')
  +', c.oT='+container.offsetTop
  +', s.oT='+slider.offsetTop
  +', s.oH='+slider.offsetHeight
  +', tS='+topStopper
  +', cH='+clientHeight
  +', sT='+scrollTop
  +', cD='+cDelta
  ;*/
  // set hook to call myself again later; this is better than calling myself directly,
  // because the used memory is freed and reallocated, rather than allocated over and over
  setTimeout("SLIDE_update('"+sliderName+"','"+containerName+"',"+slideSpeed+","+updateInterval+",'"+breakerName+"',"+cDelta+")", updateInterval);
}

// function that tests slider data and launches it if it checks out
function SLIDE_launch_slider(sInfo) {
  // init vars
  var d = document;
  var er = 0;
  // test and init slider
  er = SLIDE_element_support(sInfo[0], 'style');
  if (er) return 0;
  s = d.getElementById(sInfo[0]);
  // test and init container
  er = SLIDE_element_support(sInfo[1], 'position');
  if (er) return 0;
  var c = d.getElementById(sInfo[1]);
  // test and init breaker
  if (sInfo[4]) {
    er = SLIDE_element_support(sInfo[4], 'position');
    if (er) return 0;
    var b = d.getElementById(sInfo[4]);
  }
  else {
    var b = false;
  }
  // force relative positioning
  s.style.position = 'relative';
  // launch slider
  SLIDE_update(sInfo[0], sInfo[1], sInfo[2], sInfo[3], sInfo[4], s.offsetTop - c.offsetTop);
}