/** This file is part of natlib.
 * https://github.com/mvasilkov/natlib
 * @license MIT | Copyright (c) 2022, 2023, 2024 Mark Vasilkov
 */
'use strict'

import { UINT32_MAX } from '../prelude.js'
import { register0, type IVec3, type Vec3 } from '../Vec3.js'
import type { IPrng32 } from './prng'

/** Return a pseudorandom number in the range [-1, 1]. */
export const randomClosedUnit1Ball = (prng: IPrng32): number => (2 * prng.randomUint32() - UINT32_MAX) / UINT32_MAX

/** Return a pseudorandom number in the range (-1, 1). */
export const randomOpenUnit1Ball = (prng: IPrng32): number => (2 * prng.randomUint32() - UINT32_MAX) / (UINT32_MAX + 1)

/** Get a pseudorandom point on the unit sphere. */
export const uniformSampleSphere = (prng: IPrng32): Vec3 => {
    // Algorithm by George Marsaglia (1972)
    let u: number, v: number, n: number

    do {
        u = randomOpenUnit1Ball(prng)
        v = randomOpenUnit1Ball(prng)
        n = u ** 2 + v ** 2
    }
    while (n >= 1)

    const a = 2 * (1 - n) ** 0.5

    return register0.set(a * u, a * v, 1 - 2 * n)
}

/** Get a pseudorandom point on the unit hemisphere. */
export const uniformSampleHemisphere = (prng: IPrng32, normal: Readonly<IVec3>): Vec3 =>
    uniformSampleSphere(prng).dot(normal) < 0 ? register0.scale(-1) : register0