messy method

Game_AI.prototype.executeSlideHorizontaly = function(a,b) {
    // a = speed
    // b = total time
    var initialPos = -400;
    var finalPos = this._personality.xOffset;
    this._value = 0;
// begin loop
    if(this._value < b ){
        this._value ++
    // first condition : if x is inferior than the finalPos
        if(this.aiSprite.x < finalPos){
            this.aiSprite.x += a;
        // second condition : if value is reaching is limit
         if(this._value >= b){
          this.aiSprite.x = finalPos;
         }
        }
    // third condition : if the x = finalPos AND time value is not b
    // return the sprite to his initiat position if asked.
        if(this.aiSprite.x >= finalPos && !this._value >= b){
            this.aiSprite.x -= a;
        // last condition : if the pose is inferior or equal to initial pos
        // or time limit is reached.
            if(this.aiSprite.x <= initialPos || this._value >= b){
                this.aiSprite.x = initialPos;
            }
        }
    }
// deactivate the flag when finish
    this.setEffectFlag(false);
};