# Copyright 2012 United States Government, as represented by the Secretary of Defense, Under
# Secretary of Defense (Personnel & Readiness).
# 
# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
# in compliance with the License. You may obtain a copy of the License at
# 
#   http://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing, software distributed under the License
# is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
# or implied. See the License for the specific language governing permissions and limitations under
# the License.

## The component representation of a path following behavior
## 
## @name followPath.vwf
## @namespace

--- 
extends:
  http://vwf.example.com/node3.vwf
properties:

  ## Whether the component is following a path
  ## 
  ## @name followPath.vwf#followPath-following
  ## @property

  followPath-following:
    set: |
      if ( value && ! this["followPath-following"] ) {  // starting
        if ( this["followPath-path"] ) {
          if ( this["followPath-path"] instanceof Array ) {
            if ( this["followPath-path"].length > 1 ) {
              this["followPath-following"] = true;  // set the internal value
              this.future(this["followPath-tickRate"]).followPath();  // run the first step and schedule the next one
              this.translation = [ this["followPath-path"][0].translation[0], this["followPath-path"][0].translation[1], this["followPath-height"] ];
              this["followPath-lastTime"] = this.time;
            }
          }
        }
      } else if ( ! value && this["followPath-following"] ) { // stopping
        this["followPath-following"] = false;  // set the internal value
      }
    value: false

  ## Path to follow
  ## 
  ## @name followPath.vwf#followPath-path
  ## @property

  followPath-path:

  ## Index of the last path point achieved.
  ## 
  ## @name followPath.vwf#followPath-lastPathIndex
  ## @property

  followPath-lastPathIndex:
    set: |
      if ( value >= 0 ) {
        if ( this["followPath-path"] && value < this["followPath-path"].length ) {
          this["followPath-lastPathIndex"] = value;
          this["followPath-nextPathIndex"] = value+1;
          if ( this["followPath-nextPathIndex"] == this["followPath-path"].length ) {
            this["followPath-nextPathIndex"] = 0;
          }
        } else {
          this["followPath-lastPathIndex"] = 0;
          this["followPath-nextPathIndex"] = 1;              
        }
      }
    value: 0

  ## Index of the next path point to achieve.
  ## 
  ## @name followPath.vwf#followPath-nextPathIndex
  ## @property

  followPath-nextPathIndex: 1

  ## Should the path loop.
  ## 
  ## @name followPath.vwf#followPath-looping
  ## @property

  followPath-looping: true

  ## Height to follow path at
  ## 
  ## @name followPath.vwf#followPath-height
  ## @property

  followPath-height: 1200

  ## Last time that followPath 'ticked.'
  ## 
  ## @name followPath.vwf#followPath-lastTime
  ## @property

  followPath-lastTime: 0
  
  ## How often follow path will tick.
  ## 
  ## @name followPath.vwf#followPath-tickRate
  ## @property

  followPath-tickRate: 1

methods:

  ## Follow Path function. Updates component position and calls vwf future followPath call
  ## 
  ## @name followPath.vwf#followPath
  ## @function
  ##
  ## @returns undefined

  followPath:
scripts:
- |
  this.followPath = function()  {  // when following path ...
    var time = this.time;
    var len = this["followPath-path"].length;
    var timeElasped = time - this["followPath-lastTime"];
    var lastPathPoint = this["followPath-path"][ this["followPath-lastPathIndex"] ];
    var nextPathPoint = this["followPath-path"][ this["followPath-nextPathIndex"] ];
    var goalPointIndex = this["followPath-nextPathIndex"] + 1;
    if ( goalPointIndex >= this["followPath-path"].length ) {
      goalPointIndex = 0;
    }
    var goalPathPoint = this["followPath-path"][ goalPointIndex ];
      
    var percentDone = timeElasped / nextPathPoint.time;
    if ( percentDone > 0.975 ) {
      percentDone = 1;
    }


    if ( ( goalPointIndex == 0 ) && ( this["followPath-looping"] == false ) ) {
      goalPathPoint = nextPathPoint + ( nextPathPoint - lastPathPoint );
      if ( percentDone == 1 ) {
        this[ "followPath-following" ] = false;
      }
    }

    
    function interpolate( beforeCoord, afterCoord, percent ) {
      return beforeCoord + percent * (afterCoord - beforeCoord);
    }
        
    var newX = interpolate( nextPathPoint.translation[0], goalPathPoint.translation[0], percentDone );
    var newY = interpolate( nextPathPoint.translation[1], goalPathPoint.translation[1], percentDone );
    var goal = [ newX, newY, this["followPath-height"] ];
        
    newX = interpolate( lastPathPoint.translation[0], nextPathPoint.translation[0], percentDone );
    newY = interpolate( lastPathPoint.translation[1], nextPathPoint.translation[1], percentDone );
        
    var zRot = [ goalPathPoint.translation[0] - newX, goalPathPoint.translation[1] - newY, 0 ];

    var rotation = Math.atan2( zRot[1], zRot[0] )-(Math.PI*0.5);
    var sinRot = Math.sin(rotation);
    var cosRot = Math.cos(rotation);

    this.transformTo([ cosRot, sinRot, 0, 0, -sinRot, cosRot, 0, 0, 0, 0, 1, 0, newX, newY, this["followPath-height"], 1], this["followPath-tickRate"]);
        
    if ( percentDone == 1 ) {
      this["followPath-lastPathIndex"] = this["followPath-lastPathIndex"] + 1;
      this["followPath-lastTime"] =  time;
    }
    
    if ( this[ "followPath-following" ] ) {
      this.future( this["followPath-tickRate"] ).followPath( );
    }
  }  //@ sourceURL=fly.vwf