import prand from 'pure-rand'

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

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

    public jump(): void {
        this.generator =  this.generator.jump()
    }

    /**
     * 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 an array of uniformly distributed random integers between min and max
     */
    public uniformIntArray(min: number, max: number, size: number): number[] {
        const result: number[] = []
        for (let i = 0; i < size; i++) {
            result.push(this.uniformInt(min, max))
        }
        return result
    }

    /*
    * 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 an array of uniformly distributed random floats between min and max.
     */
    public uniformFloatArray(min: number, max: number, size: number): number[] {
        const result: number[] = []
        for (let i = 0; i < size; i++) {
            result.push(this.uniformFloat(min, max))
        }
        return result
    }

    /**
     * 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
    }

    /**
     * Returns an array of normally distributed random numbers with mean mu and standard deviation sigma.
     */
    public normalFloatArray(mu: number, sigma: number, size: number): number[] {
        const result: number[] = []
        for (let i = 0; i < size; i++) {
            result.push(this.normalFloat(mu, sigma))
        }
        return result
    }


    /**
     * Returns a Poisson distributed random number with mean lambda. 
     */
    public poissonInt(lambda: number): number {
        const L = Math.exp(-lambda)
        let k = 0
        let p = 1
        do {
            k++
            p *= this.uniformFloat(0, 1)
        } while (p > L)
        return k - 1
    }

    /**
     * Returns an array of Poisson distributed random numbers with mean lambda.
     */
    public poissonIntArray(lambda: number, size: number): number[] {
        const result: number[] = []
        for (let i = 0; i < size; i++) {
            result.push(this.poissonInt(lambda))
        }
        return result
    }

    /**
     * Picks a single random element from the array.
     * Returns undefined if the array is empty.
     */
    public pickRandom<T>(array: T[]): T {
        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()
        for (let i = 0; i < size; i++) {
            const index = this.uniformInt(0, copy.length - 1)
            result.push(copy[index])
            copy.splice(index, 1)
        }
        return result
    }

    public shuffle<T>(array: T[]): T[] {
        const result = array.slice()
        for (let i = result.length - 1; i > 0; i--) {
            const j = this.uniformInt(0, i)
            const temp = result[i]
            result[i] = result[j]
            result[j] = temp
        }
        return result
    }

}