OneRepMaxCalculator.ts

export class OneRepMaxCalculator {
  private readonly weight: number
  private readonly repetitions: number
  private readonly smallestPlate: number

  constructor(weight: number, repetitions: number, smallestPlate: number = 5) {
    this.weight = weight
    this.repetitions = repetitions
    this.smallestPlate = smallestPlate
  }

  private toSmallestPlate(weight: number): number {
    const roundedWeight = Math.round(weight)
    const { smallestPlate } = this
    if (roundedWeight % smallestPlate === 0) {
      return roundedWeight
    }
    const fullSmallestPlate = Math.floor(roundedWeight / smallestPlate)
    const differenceA = roundedWeight - fullSmallestPlate * smallestPlate
    const differenceB = smallestPlate - differenceA
    if (differenceA < smallestPlate / 2) {
      return roundedWeight - differenceA
    } else {
      return roundedWeight + differenceB
    }
  }

  epley(): number {
    return this.toSmallestPlate(this.weight * (1 + this.repetitions / 30))
  }

  brzycki(): number {
    return this.toSmallestPlate(this.weight * (36 / (37 - this.repetitions)))
  }

  mcGlothin(): number {
    return this.toSmallestPlate((100 * this.weight) / (101.3 - 2.67123 * this.repetitions))
  }

  lombardi(): number {
    return this.toSmallestPlate(this.weight * Math.pow(this.repetitions, 0.1))
  }

  oConner(): number {
    return this.toSmallestPlate(this.weight * (1 + this.repetitions / 40))
  }

  average(): number {
    return this.toSmallestPlate(
      (this.epley() + this.brzycki() + this.mcGlothin() + this.lombardi() + this.oConner()) / 5
    )
  }
}

const calc = new OneRepMaxCalculator(100, 6)

console.log('epley', calc.epley())
console.log('brzycki', calc.brzycki())
console.log('mcGlothin', calc.mcGlothin())
console.log('lombardi', calc.lombardi())
console.log('oConner', calc.oConner())
console.log('average', calc.average())