private var mouseButton1DownPoint : Vector2;
private var mouseButton1UpPoint : Vector2;
private var mouseButton1DownTerrainHitPoint : Vector3;
private var mouseButton2DownPoint : Vector2;
private var mouseButton2UpPoint : Vector2;
private var selectionPointStart : Vector3;
private var selectionPointEnd : Vector3;
private var mouseLeftDrag : boolean = false;
private var terrainLayerMask = 1 << 8;
private var nonTerrainLayerMask = ~terrainLayerMask;
private var raycastLength : float = 200.0;
// semi transparent texture for the selection rectangle
var selectionTexture : Texture;
// range in which a mouse down and mouse up event will be treated as "the same location" on the map.
private var mouseButtonReleaseBlurRange : int = 20;

function OnGUI() {
  if (mouseLeftDrag) {
    
   var width : int = mouseButton1UpPoint.x - mouseButton1DownPoint.x;
   var height : int = (Screen.height - mouseButton1UpPoint.y) - (Screen.height - mouseButton1DownPoint.y);
   var rect : Rect = Rect(mouseButton1DownPoint.x, Screen.height - mouseButton1DownPoint.y, width, height);
   GUI.DrawTexture (rect, selectionTexture, ScaleMode.StretchToFill, true);
  }
}

function Update ()
{
  // Left mouse button
  if (Input.GetButtonDown("Fire1")) {
    Mouse1Down(Input.mousePosition);
  }
   
  if (Input.GetButtonUp("Fire1")) {
    Mouse1Up(Input.mousePosition);
  }
   
  if (Input.GetButton("Fire1")) {
   // Used to determine if there is some mouse drag operation going on.  
   Mouse1DownDrag(Input.mousePosition);
  }
   
  // Right mouse button
  if (Input.GetButtonDown("Fire2")) {
   mouseButton2DownPoint = Input.mousePosition;
  }
   
  if (Input.GetButtonUp("Fire2")) {
   mouseButton2UpPoint = Input.mousePosition;
   // De-selection if right mouse button is pressed at the same point (more or less) where it was clicked down.
   // Use this inRange with a slight offset so if right mb was not released _exactly_ at the button down position, but with a slight offset.
   if (IsInRange(mouseButton2DownPoint, mouseButton2UpPoint)) {
    UnitManager.GetInstance().ClearSelectedUnitsList();
   }
  }
}

function Mouse1DownDrag(screenPosition : Vector2) {
  // Only show the drag selection texture if the mouse has been moved and not if the user made only a single left mouse click
  if (screenPosition != mouseButton1DownPoint) {
   mouseLeftDrag = true;
   // while dragging, update the current mouse pos for the selection rectangle.
   mouseButton1UpPoint = screenPosition;
    
   var hit : RaycastHit;
   ray = Camera.main.ScreenPointToRay (screenPosition);    
   if ( Physics.Raycast (ray, hit, raycastLength, terrainLayerMask) )
   {  
    //print ("Hit Terrain 2 " + hit.point);
    selectionPointEnd = hit.point;
    UnitManager.GetInstance().ClearSelectedUnitsList();
    UnitManager.GetInstance().SelectUnitsInArea(selectionPointStart, selectionPointEnd);
   }  
  }
}

function Mouse1Down(screenPosition : Vector2) {
    
   mouseButton1DownPoint = screenPosition;
    
   var hit : RaycastHit;
   var ray = Camera.main.ScreenPointToRay (mouseButton1DownPoint);  
   //Debug.DrawRay (ray.origin, ray.direction * 100.0, Color.green);  
   if ( Physics.Raycast (ray, hit, raycastLength) ) // terrainLayerMask
   {  
    if (hit.collider.name == "Terrain")
    {
     mouseButton1DownTerrainHitPoint = hit.point;
     selectionPointStart = hit.point;
    }  
    else
    {
     //print ("Mouse Down Hit something: " + hit.collider.name);

     // Ray hit a unit, not the terrain. Deselect all units as the fire 1 up  
     // event will then select that just recently clicked unit!
     UnitManager.GetInstance().ClearSelectedUnitsList();
    }
    //Debug.DrawRay (ray.origin, ray.direction * 100.0, Color.green);   
   }
}

function Mouse1Up(screenPosition : Vector2) {
   
  mouseButton1UpPoint = screenPosition;
  var hit : RaycastHit;
   
  //print("currently selected units: " + UnitManager.GetInstance().GetSelectedUnitsCount());  
  mouseLeftDrag = false;
   
  if (IsInRange(mouseButton1DownPoint, mouseButton1UpPoint)) {
   // user just did a click, no dragging. mouse 1 down and up pos are equal.
   // if units are selected, move them. If not, select that unit.
   if (UnitManager.GetInstance().GetSelectedUnitsCount() == 0) {
    // no units selected, select the one we clicked - if any.
    ray = Camera.main.ScreenPointToRay (mouseButton1DownPoint);
    if ( Physics.Raycast (ray, hit, raycastLength, nonTerrainLayerMask) )
    {  
     // Ray hit something. Try to select that hit target.  
     //print ("Hit something: " + hit.collider.name);
     hit.collider.gameObject.SendMessage("SetSelected");
    }
         
   } else {
    // untis are selected, move them. Unit Manager's unit count is > 0!
    UnitManager.GetInstance().MoveSelectedUnitsToPoint(mouseButton1DownTerrainHitPoint);
   }  
  }  
}

function IsInRange(v1 : Vector2, v2 : Vector2) : boolean {
  var dist = Vector2.Distance(v1, v2);
  print("Right click release button distance: " + dist);
  if (Vector2.Distance(v1, v2) < mouseButtonReleaseBlurRange) {
   return true;
  }
  return false;
}

// the one and only instance for the unit manager
private static var instance : UnitManager;
private var allUnitsList = new Array();
private var selectedUnitsList = new Array();
private var debugMode = false;

// accessor that delivers always the one and only instance of the UnitManager
// Use it like this: UnitManager.GetInstance().<function name>
static function GetInstance() : UnitManager {
  if (instance == null) {
   instance =  FindObjectOfType(UnitManager);
  }
  return instance;
}

function GetSelectedUnitsCount() {
  return selectedUnitsList.length;
}

function AddUnit(go : GameObject) {
  allUnitsList.Add(go);
   
  if (debugMode) {
   print("UnitManager: added unit: " + go.name);
  }
}

function AddSelectedUnit(go : GameObject) {
  selectedUnitsList.Push(go);
  go.SendMessage("SetUnitSelected", true);
   
  if (debugMode) {
   print("UnitManager: added selected unit: " + go.name);
  }
}

function ClearSelectedUnitsList() {
  if (debugMode) {
   print("ClearSelectedUnitsList");
  }
   
  for (var go : GameObject in allUnitsList) {
   go.SendMessage("SetUnitSelected", false);
  }
  selectedUnitsList.Clear();
}

function MoveSelectedUnitsToPoint(destinationPoint : Vector3) {
  for (var go : GameObject in selectedUnitsList) {
   if (debugMode) {
    print("MoveSelectedUnits: Moving unit " + go.name);
   }
   go.SendMessage("MoveToPoint", destinationPoint);
  }
}

function SelectUnitsInArea(point1 : Vector3, point2 : Vector3) {
  if (debugMode) {
   print("Select Units in area...");
  }
   
  if (point2.x < point1.x) {
   // swap x positions. Selection rectangle is beeing drawn from right to left
   var x1 = point1.x;
   var x2 = point2.x;
   point1.x = x2;
   point2.x = x1;
  }
   
  if (point2.z > point1.z) {
   // swap z positions. Selection rectangle is beeing drawn from bottom to top
   var z1 = point1.z;
   var z2 = point2.z;
   point1.z = z2;
   point2.z = z1;
  }
   
  for (var go : GameObject in allUnitsList) {
   var goPos : Vector3 = go.transform.position;
   //print("goPos:" + goPos + " 1:" + point1 + " 2:" + point2);
   if (goPos.x > point1.x && goPos.x < point2.x && goPos.z < point1.z && goPos.z > point2.z) {
    selectedUnitsList.Push(go);
   
    if (debugMode)
     print("Unit inside: " + go.name);
      
    go.SendMessage("SetUnitSelected", true);
   }
  }
}  

function Test() {
  print("UnitManager: Test!");
}

function OnApplicationQuit() {
  instance = null;
}