'use strict';

// t: current time, b: beginning value, _c: final value, d: total duration
var tweenFunctions = {
  linear: function(t, b, _c, d) {
    var c = _c - b;
    return c * t / d + b;
  },
  easeInQuad: function(t, b, _c, d) {
    var c = _c - b;
    return c * (t /= d) * t + b;
  },
  easeOutQuad: function(t, b, _c, d) {
    var c = _c - b;
    return -c * (t /= d) * (t - 2) + b;
  },
  easeInOutQuad: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d / 2) < 1) {
      return c / 2 * t * t + b;
    } else {
      return -c / 2 * ((--t) * (t - 2) - 1) + b;
    }
  },
  easeInCubic: function(t, b, _c, d) {
    var c = _c - b;
    return c * (t /= d) * t * t + b;
  },
  easeOutCubic: function(t, b, _c, d) {
    var c = _c - b;
    return c * ((t = t / d - 1) * t * t + 1) + b;
  },
  easeInOutCubic: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d / 2) < 1) {
      return c / 2 * t * t * t + b;
    } else {
      return c / 2 * ((t -= 2) * t * t + 2) + b;
    }
  },
  easeInQuart: function(t, b, _c, d) {
    var c = _c - b;
    return c * (t /= d) * t * t * t + b;
  },
  easeOutQuart: function(t, b, _c, d) {
    var c = _c - b;
    return -c * ((t = t / d - 1) * t * t * t - 1) + b;
  },
  easeInOutQuart: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d / 2) < 1) {
      return c / 2 * t * t * t * t + b;
    } else {
      return -c / 2 * ((t -= 2) * t * t * t - 2) + b;
    }
  },
  easeInQuint: function(t, b, _c, d) {
    var c = _c - b;
    return c * (t /= d) * t * t * t * t + b;
  },
  easeOutQuint: function(t, b, _c, d) {
    var c = _c - b;
    return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
  },
  easeInOutQuint: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d / 2) < 1) {
      return c / 2 * t * t * t * t * t + b;
    } else {
      return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
    }
  },
  easeInSine: function(t, b, _c, d) {
    var c = _c - b;
    return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
  },
  easeOutSine: function(t, b, _c, d) {
    var c = _c - b;
    return c * Math.sin(t / d * (Math.PI / 2)) + b;
  },
  easeInOutSine: function(t, b, _c, d) {
    var c = _c - b;
    return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
  },
  easeInExpo: function(t, b, _c, d) {
    var c = _c - b;
    return (t==0) ? b : c * Math.pow(2, 10 * (t/d - 1)) + b;
  },
  easeOutExpo: function(t, b, _c, d) {
    var c = _c - b;
    return (t==d) ? b+c : c * (-Math.pow(2, -10 * t/d) + 1) + b;
  },
  easeInOutExpo: function(t, b, _c, d) {
    var c = _c - b;
    if (t === 0) {
      return b;
    }
    if (t === d) {
      return b + c;
    }
    if ((t /= d / 2) < 1) {
      return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
    } else {
      return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
    }
  },
  easeInCirc: function(t, b, _c, d) {
    var c = _c - b;
    return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
  },
  easeOutCirc: function(t, b, _c, d) {
    var c = _c - b;
    return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
  },
  easeInOutCirc: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d / 2) < 1) {
      return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
    } else {
      return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
    }
  },
  easeInElastic: function(t, b, _c, d) {
    var c = _c - b;
    var a, p, s;
    s = 1.70158;
    p = 0;
    a = c;
    if (t === 0) {
      return b;
    } else if ((t /= d) === 1) {
      return b + c;
    }
    if (!p) {
      p = d * 0.3;
    }
    if (a < Math.abs(c)) {
      a = c;
      s = p / 4;
    } else {
      s = p / (2 * Math.PI) * Math.asin(c / a);
    }
    return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
  },
  easeOutElastic: function(t, b, _c, d) {
    var c = _c - b;
    var a, p, s;
    s = 1.70158;
    p = 0;
    a = c;
    if (t === 0) {
      return b;
    } else if ((t /= d) === 1) {
      return b + c;
    }
    if (!p) {
      p = d * 0.3;
    }
    if (a < Math.abs(c)) {
      a = c;
      s = p / 4;
    } else {
      s = p / (2 * Math.PI) * Math.asin(c / a);
    }
    return a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b;
  },
  easeInOutElastic: function(t, b, _c, d) {
    var c = _c - b;
    var a, p, s;
    s = 1.70158;
    p = 0;
    a = c;
    if (t === 0) {
      return b;
    } else if ((t /= d / 2) === 2) {
      return b + c;
    }
    if (!p) {
      p = d * (0.3 * 1.5);
    }
    if (a < Math.abs(c)) {
      a = c;
      s = p / 4;
    } else {
      s = p / (2 * Math.PI) * Math.asin(c / a);
    }
    if (t < 1) {
      return -0.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
    } else {
      return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * 0.5 + c + b;
    }
  },
  easeInBack: function(t, b, _c, d, s) {
    var c = _c - b;
    if (s === void 0) {
      s = 1.70158;
    }
    return c * (t /= d) * t * ((s + 1) * t - s) + b;
  },
  easeOutBack: function(t, b, _c, d, s) {
    var c = _c - b;
    if (s === void 0) {
      s = 1.70158;
    }
    return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
  },
  easeInOutBack: function(t, b, _c, d, s) {
    var c = _c - b;
    if (s === void 0) {
      s = 1.70158;
    }
    if ((t /= d / 2) < 1) {
      return c / 2 * (t * t * (((s *= 1.525) + 1) * t - s)) + b;
    } else {
      return c / 2 * ((t -= 2) * t * (((s *= 1.525) + 1) * t + s) + 2) + b;
    }
  },
  easeInBounce: function(t, b, _c, d) {
    var c = _c - b;
    var v;
    v = tweenFunctions.easeOutBounce(d - t, 0, c, d);
    return c - v + b;
  },
  easeOutBounce: function(t, b, _c, d) {
    var c = _c - b;
    if ((t /= d) < 1 / 2.75) {
      return c * (7.5625 * t * t) + b;
    } else if (t < 2 / 2.75) {
      return c * (7.5625 * (t -= 1.5 / 2.75) * t + 0.75) + b;
    } else if (t < 2.5 / 2.75) {
      return c * (7.5625 * (t -= 2.25 / 2.75) * t + 0.9375) + b;
    } else {
      return c * (7.5625 * (t -= 2.625 / 2.75) * t + 0.984375) + b;
    }
  },
  easeInOutBounce: function(t, b, _c, d) {
    var c = _c - b;
    var v;
    if (t < d / 2) {
      v = tweenFunctions.easeInBounce(t * 2, 0, c, d);
      return v * 0.5 + b;
    } else {
      v = tweenFunctions.easeOutBounce(t * 2 - d, 0, c, d);
      return v * 0.5 + c * 0.5 + b;
    }
  }
};

module.exports = tweenFunctions;