//***********Selected as Spine, version 1
//this script will take the selected group of layers and from them create an animatable spine;
//  each vertebra is parented to the one below it, and each vertebra above the lowermost (base) vertebra
//  has an expression that is linked to the base vertebra's x rotation.
//***********//

function mainSpine()
{
	// make sure a comp is selected
	var activeItem = app.project.activeItem;
	if (activeItem == null || !(activeItem instanceof CompItem)){
		alert("You need to select some layers first.");
	} else {
      
		// make sure more than one layer is selected
		var s = activeItem.selectedLayers;
		var selNum = s.length;
		if (selNum < 2) {
			alert("You need to select at least two layers first.");
		} else {

			vn = selNum;
         gotANum = false;
         cancelledOut = false;
         while (! gotANum) {
            p = prompt("Enter overlap amount (in pixels. Zero means no overlap; negative number creates spacing):", "2");
            if (p == null) {
               cancelledOut = true;
               gotANum = true;//well, not really, but ...
            } else {
               if (! isNaN(p)) {
                  vOlap = parseFloat(p);
                  gotANum = true;
               }
            }
         }
         if (! cancelledOut) {
            app.beginUndoGroup("selection as spine");
            
            vNa = "vertabra";
            vShy = true;
            
            baseLayer = s[0];
            
            // (if not 3D layer, make it one)
            if (!baseLayer.threeDLayer) {baseLayer.threeDLayer = true} ;
            
            // rename to 'base vertebra'
            vZeroName = ("base " + vNa);
            baseLayer.name = vZeroName;
            
				lastLayer = baseLayer;
				lastLayerHtOffset = lastLayer.height;
				
				//change anchor point to bottom of layer
				ap = lastLayer.property("Anchor Point").value;
				lastLayer.property("Anchor Point").setValue( [ap[0], (lastLayerHtOffset), ap[2]] );
            
				for (i = 1; i < (vn); ++i) {
					/////LAYER ITEM ADJUSTMENTS/////
               
					newLayer = s[i];
					newLayer.name = (vNa + "_" + i);
					
					// (if not 3D layer, make it one)
					if (!newLayer.threeDLayer) {newLayer.threeDLayer = true} ;
               
					/////PROPERTY ADJUSTMENTS/////
               
					//change anchor point to bottom of layer
					ap = newLayer.property("Anchor Point").value;
					newLayer.property("Anchor Point").setValue( [ap[0], (newLayer.height), ap[2]] );
               
					p = lastLayer.property("Position").value;
               
					newLayer.property("Position").setValue([ p[0], (p[1] - lastLayerHtOffset + vOlap), p[2] ]);
					
					//add x rot expression to new layer
					newLayer.property("rotationX").expression = 'thisComp.layer("' + vZeroName + '").rotationX;';
					
					lastLayer = newLayer;  ///// now we have a reference to this layer to use at next iteration as last layer
					lastLayerHtOffset = lastLayer.height;
				}
            
				for (n = 0; n < (s.length-1); ++n) {
					childL = s[n + 1];
					parentL = s[n];
					childL.parent = parentL;
					if (vShy == true) {childL.shy = true} ;
				}
            
            app.endUndoGroup();
            alert("The base vertebra is the first layer selected.");
         }
      }
	}
}

mainSpine();