package beerpongelo

import (
	"math"
)

func winProbPlayer(p, e1, e2 float64) float64 {
	const MAGIC float64 = 500

	lhs := 1 / (1 + math.Pow(10., (p-e1)/MAGIC))
	rhs := 1 / (1 + math.Pow(10., (p-e2)/MAGIC))
	return (lhs + rhs) / 2.
}

func NewRating(t0p0, t0p1, t1p0, t1p1 float64, score int) (float64, float64, float64, float64) {
	const K float64 = 50
	const SCORE_BIAS float64 = 1
	const SCORE_SCALE float64 = 0.4
	const MAX_SCORE float64 = 10

	et0p0 := winProbPlayer(t0p0, t1p0, t1p1)
	et0p1 := winProbPlayer(t0p1, t1p0, t1p1)
	et1p0 := winProbPlayer(t1p0, t0p0, t0p1)
	et1p1 := winProbPlayer(t1p1, t0p0, t0p1)

	et0 := (et0p0 + et0p1) / 2.
	et1 := (et1p0 + et1p1) / 2.

	ct0p0 := t0p0 / (t0p0 + t0p1)
	ct0p1 := t0p1 / (t0p0 + t0p1)
	ct1p0 := t1p0 / (t1p0 + t1p1)
	ct1p1 := t1p1 / (t1p0 + t1p1)

	var st0 float64
	var st1 float64
	if score > 0 {
		st0 = 1
		st1 = 0
	} else {
		st0 = 0
		st1 = 1
	}

	scoreMod := SCORE_SCALE * math.Log(math.Abs(float64(score))+SCORE_BIAS) / (math.Log(MAX_SCORE) + SCORE_BIAS)

	newt0p0 := t0p0 + K*scoreMod*((st0*ct0p0)-(et0*ct0p0))
	newt0p1 := t0p1 + K*scoreMod*((st0*ct0p1)-(et0*ct0p1))
	newt1p0 := t1p0 + K*scoreMod*((st1*ct1p0)-(et1*ct1p0))
	newt1p1 := t1p1 + K*scoreMod*((st1*ct1p1)-(et1*ct1p1))

	return newt0p0, newt0p1, newt1p0, newt1p1
}