/*
  oktween.add({
    obj: el.style,
    units: "px",
    from: { left: 0 },
    to: { left: 100 },
    duration: 1000,
    easing: oktween.easing.circ_out,
    update: function(obj){
      console.log(obj.left)
    }
    finished: function(){
      console.log("done")
    }
  })
*/

import { lerp } from '../../util/math'

const oktween = {}
let tweens = []

let last_t = 0
let id = 0

oktween.speed = 1
oktween.add = (tween) => {
  tween.id = id++
  tween.obj = tween.obj || {}
  if (tween.easing) {
    if (typeof tween.easing === "string") {
      tween.easing = oktween.easing[tween.easing]
    }
  } else {
    tween.easing = oktween.easing.linear
  }
  if (!('from' in tween) && !('to' in tween)) {
    tween.keys = []
  } else if (!('from' in tween)) {
    tween.from = {}
    tween.keys = Object.keys(tween.to)
    tween.keys.forEach(function(prop) {
      tween.from[prop] = parseFloat(tween.obj[prop])
    })
  } else {
    tween.keys = Object.keys(tween.from)
  }
  tween.delay = tween.delay || 0
  tween.start = last_t + tween.delay
  tween.done = false
  tween.after = tween.after || []
  tween.then = (fn) => { tween.after.push(fn); return tween }
  tween.tick = 0
  tween.skip = tween.skip || 1
  tween.dt = 0
  tweens.push(tween)
  return tween
}
oktween.update = (t) => {
  let done = false
  requestAnimationFrame(oktween.update)
  last_t = t * oktween.speed
  if (tweens.length === 0) return
  tweens.forEach((tween, i) => {
    const dt = Math.min(1.0, (t - tween.start) / tween.duration)
    tween.tick++
    if (dt < 0 || (dt < 1 && (tween.tick % tween.skip != 0))) return
    const ddt = tween.easing(dt)
    tween.dt = ddt
    tween.keys.forEach((prop) => {
      let val = lerp(ddt, tween.from[prop], tween.to[prop])
      if (tween.round) val = Math.round(val)
      if (tween.units) val = (Math.round(val)) + tween.units
      tween.obj[prop] = val
    })
    if (tween.update) {
      tween.update(tween.obj, dt)
    }
    if (dt === 1) {
      if (tween.finished) {
        tween.finished(tween)
      }
      if (tween.after.length) {
        const twn = tween.after.shift()
        twn.obj = twn.obj || tween.obj
        twn.after = tween.after
        oktween.add(twn)
      }
      if (tween.loop) {
        tween.start = t + tween.delay
      }
      else {
        done = true
        tween.done = true
      }
    }
  })
  if (done) {
    tweens = tweens.filter(tween => !tween.done)
  }
}

requestAnimationFrame(oktween.update)

oktween.easing = {
  linear: (t) => {
    return t
  },
  circ_out: (t) => {
    return Math.sqrt(1 - (t = t - 1) * t)
  },
  circ_in: (t) => {
    return -(Math.sqrt(1 - (t * t)) - 1)
  },
  circ_in_out: (t) => {
    return ((t*=2) < 1) ? -0.5 * (Math.sqrt(1 - t * t) - 1) : 0.5 * (Math.sqrt(1 - (t -= 2) * t) + 1)
  },
  quad_in: (n) => {
    return Math.pow(n, 2)
  },
  quad_out: (n) => {
    return n * (n - 2) * -1
  },
  quad_in_out: (n) => {
    n = n * 2
    if (n < 1) { return Math.pow(n, 2) / 2 }
    return -1 * ((--n) * (n - 2) - 1) / 2
  },
  cubic_bezier: (mX1, mY1, mX2, mY2) => {
    function A(aA1, aA2) { return 1.0 - 3.0 * aA2 + 3.0 * aA1 }
    function B(aA1, aA2) { return 3.0 * aA2 - 6.0 * aA1 }
    function C(aA1)      { return 3.0 * aA1 }

    // Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
    function CalcBezier(aT, aA1, aA2) {
      return ((A(aA1, aA2)*aT + B(aA1, aA2))*aT + C(aA1))*aT
    }

    // Returns dx/dt given t, x1, and x2, or dy/dt given t, y1, and y2.
    function GetSlope(aT, aA1, aA2) {
      return 3.0 * A(aA1, aA2)*aT*aT + 2.0 * B(aA1, aA2) * aT + C(aA1)
    }

    function GetTForX(aX) {
      // Newton raphson iteration
      let aGuessT = aX
      for (let i = 0; i < 10; ++i) {
        const currentSlope = GetSlope(aGuessT, mX1, mX2)
        if (currentSlope == 0.0) return aGuessT
        const currentX = CalcBezier(aGuessT, mX1, mX2) - aX
        aGuessT -= currentX / currentSlope
      }
      return aGuessT
    }

    return function (aX) {
      if (mX1 == mY1 && mX2 == mY2) return aX // linear
      return CalcBezier(aX, mY1, mY2)
    }
  }
}

export default oktween