package util

import (
	"math/rand"
	"strconv"
	"time"
	"unicode"
)

const alphabet = "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

func init() {
	rand.Seed(time.Now().UnixNano())
}

func GenerateRandomString(n int) string {
	b := make([]byte, n)

	for i := range b {
		b[i] = alphabet[rand.Intn(len(alphabet))]
	}

	return string(b)
}

func IsWhitespaceFree(s string) bool {
	for _, r := range s {
		if unicode.IsSpace(r) {
			return false
		}
	}

	return true
}

func AtoiInto(s string, into *int) error {
	num, err := strconv.Atoi(s)
	if err != nil {
		return err
	}

	*into = num
	return nil
}

func RepeatedSlice[T any](value T, n int) []T {
	arr := make([]T, n)
	for i := 0; i < n; i++ {
		arr[i] = value
	}
	return arr
}

func Shuffle[T any](slice []T) {
	rand.Shuffle(len(slice), func(i, j int) {
		slice[i], slice[j] = slice[j], slice[i]
	})
}

func Sample[T any](vs []T, count int) []T {
	buffer := append([]T{}, vs...)
	result := make([]T, count)

	for i := 0; i < count; i++ {
		n := rand.Intn(len(buffer))
		result[i], buffer = buffer[n], append(buffer[:n], buffer[n+1:]...)
	}

	return result
}

func GroupBy[K comparable, V any](vs []V, keyFn func(V) K) map[K][]V {
	r := map[K][]V{}
	for _, v := range vs {
		key := keyFn(v)
		group, ok := r[key]
		if !ok {
			group = []V{}
		}

		r[key] = append(group, v)
	}

	return r
}