import prand from 'pure-rand'

export default class NumberGenerator {
    private generator: prand.RandomGenerator
    public seed: number

    constructor(seed?: number) {
        this.seed = seed ?? Date.now() ^ (Math.random() * 0x100000000)
        this.generator = prand.xoroshiro128plus(this.seed)
    }

    /**
     * Returns a uniformly distributed random integer between min and max
     */
    public uniformInt(min: number, max: number): number {
        const [value, rng] = prand.uniformIntDistribution(min, max)(this.generator)
        this.generator = rng
        return value
    }

    /*
    * Returns a uniformly distributed random float between min and max
    */
    public uniformFloat(min: number, max: number) {
        const [value, rng] = prand.uniformIntDistribution(min * 1000, max * 1000)(this.generator)
        this.generator = rng
        return value / 1000
    }

    /**
     * Returns a normally distributed random number with mean mu and standard deviation sigma.
     */
    public normalFloat(mu: number, sigma: number): number {
        let u = 0, v = 0
        while(u === 0) u = 1 - this.uniformFloat(0, 1)
        while(v === 0) v = this.uniformFloat(0, 1)
        return sigma * Math.sqrt( -2.0 * Math.log( u ) ) * Math.cos( 2.0 * Math.PI * v ) + mu
    }

    /**
     * Picks a single random element from the array.
     * Returns undefined if the array is empty.
     */
    public pickRandom<T>(array: T[]): T | undefined {
        if (array.length === 0) {
            return undefined
        }
        return array[this.uniformInt(0, array.length - 1)]
    }

    /**
     * Picks a random subset of the array without replacement.
     * Returns an empty array if the array is empty.
     */
    public pickRandomArray<T>(array: T[], size: number): T[] {
        if (array.length === 0) {
            return []
        }
        const result: T[] = []
        const copy = array.slice()
        const limit = Math.min(size, copy.length)

        for (let i = 0; i < limit; i++) {
            const index = this.uniformInt(0, copy.length - 1)
            result.push(copy[index])
            copy.splice(index, 1)
        }
        return result
    }
}