botfights/server/src/engine/odds.test.ts

import { describe, it, expect } from 'vitest'
import {
  eloProbability,
  calculateOdds,
  oddsToFractional,
  oddsToAmerican,
  calculatePayout,
  validateBet,
} from './odds.js'

describe('eloProbability', () => {
  it('equal ELO gives 50/50', () => {
    expect(eloProbability(1200, 1200)).toBeCloseTo(0.5, 5)
  })

  it('higher ELO favored', () => {
    expect(eloProbability(1400, 1200)).toBeGreaterThan(0.7)
  })

  it('lower ELO underdog', () => {
    expect(eloProbability(1000, 1400)).toBeLessThan(0.15)
  })

  it('probabilities are complementary', () => {
    const pA = eloProbability(1300, 1100)
    const pB = eloProbability(1100, 1300)
    expect(pA + pB).toBeCloseTo(1, 5)
  })

  it('extreme ELO difference stays finite', () => {
    const p = eloProbability(100, 2500)
    expect(p).toBeGreaterThan(0)
    expect(p).toBeLessThan(0.001)
    expect(isFinite(p)).toBe(true)
  })
})

describe('calculateOdds', () => {
  it('equal ELO gives near-even odds', () => {
    const odds = calculateOdds(1200, 1200)
    expect(odds.botAWinProb).toBeCloseTo(0.5, 1)
    expect(odds.botBWinProb).toBeCloseTo(0.5, 1)
    expect(odds.botADecimalOdds).toBeCloseTo(2.0, 0)
  })

  it('house edge reduces payout below fair odds', () => {
    const odds = calculateOdds(1200, 1200, { houseEdge: 0.05 })
    expect(odds.botAPayoutMultiplier).toBeLessThan(odds.botADecimalOdds)
    expect(odds.botBPayoutMultiplier).toBeLessThan(odds.botBDecimalOdds)
  })

  it('favorite has lower payout multiplier', () => {
    const odds = calculateOdds(1500, 1200)
    expect(odds.botAPayoutMultiplier).toBeLessThan(odds.botBPayoutMultiplier)
  })

  it('streak adjusts probability', () => {
    const noStreak = calculateOdds(1200, 1200)
    const withStreak = calculateOdds(1200, 1200, { streakA: 5 })
    expect(withStreak.botAWinProb).toBeGreaterThan(noStreak.botAWinProb)
  })

  it('probabilities always sum to 1', () => {
    const odds = calculateOdds(1600, 1000, { streakA: 3, streakB: 1 })
    expect(odds.botAWinProb + odds.botBWinProb).toBeCloseTo(1, 2)
  })

  it('probabilities capped between 2% and 98%', () => {
    const odds = calculateOdds(3000, 500, { streakA: 5 })
    expect(odds.botAWinProb).toBeLessThanOrEqual(0.98)
    expect(odds.botBWinProb).toBeGreaterThanOrEqual(0.02)
  })

  it('spread reflects ELO difference', () => {
    const odds = calculateOdds(1500, 1200)
    expect(odds.spread).toBe(300)
  })
})

describe('oddsToFractional', () => {
  it('even money', () => {
    expect(oddsToFractional(2.0)).toBe('1/1')
  })

  it('3/1', () => {
    expect(oddsToFractional(4.0)).toBe('3/1')
  })

  it('1/2', () => {
    expect(oddsToFractional(1.5)).toBe('1/2')
  })
})

describe('oddsToAmerican', () => {
  it('underdog shows positive', () => {
    expect(oddsToAmerican(3.0)).toBe('+200')
  })

  it('favorite shows negative', () => {
    expect(oddsToAmerican(1.5)).toBe('-200')
  })

  it('even money', () => {
    expect(oddsToAmerican(2.0)).toBe('+100')
  })
})

describe('calculatePayout', () => {
  it('100 sats at 2x = 200', () => {
    expect(calculatePayout(100, 2.0)).toBe(200)
  })

  it('floors to integer sats', () => {
    expect(calculatePayout(100, 1.94)).toBe(194)
  })
})

describe('validateBet', () => {
  it('valid bet', () => {
    expect(validateBet(1000).valid).toBe(true)
  })

  it('below minimum', () => {
    const r = validateBet(50)
    expect(r.valid).toBe(false)
    expect(r.error).toContain('Minimum')
  })

  it('above maximum', () => {
    const r = validateBet(200_000)
    expect(r.valid).toBe(false)
    expect(r.error).toContain('Maximum')
  })

  it('zero is invalid', () => {
    expect(validateBet(0).valid).toBe(false)
  })

  it('negative is invalid', () => {
    expect(validateBet(-100).valid).toBe(false)
  })

  it('non-integer is invalid', () => {
    expect(validateBet(100.5).valid).toBe(false)
  })

  it('custom limits', () => {
    expect(validateBet(50, 10, 100).valid).toBe(true)
    expect(validateBet(5, 10, 100).valid).toBe(false)
  })
})