package mock

import (
	"math/big"
	"math/rand"

	sdk "github.com/cosmos/cosmos-sdk/types"
)

// BigInterval is a representation of the interval [lo, hi), where
// lo and hi are both of type sdk.Int
type BigInterval struct {
	lo sdk.Int
	hi sdk.Int
}

// RandFromBigInterval chooses an interval uniformly from the provided list of
// BigIntervals, and then chooses an element from an interval uniformly at random.
func RandFromBigInterval(r *rand.Rand, intervals []BigInterval) sdk.Int {
	if len(intervals) == 0 {
		return sdk.ZeroInt()
	}

	interval := intervals[r.Intn(len(intervals))]

	lo := interval.lo
	hi := interval.hi

	diff := hi.Sub(lo)
	result := sdk.NewIntFromBigInt(new(big.Int).Rand(r, diff.BigInt()))
	result = result.Add(lo)

	return result
}

// shamelessly copied from https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang#31832326

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const (
	letterIdxBits = 6                    // 6 bits to represent a letter index
	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
)

func RandStringOfLength(r *rand.Rand, n int) string {
	b := make([]byte, n)
	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
	for i, cache, remain := n-1, r.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = r.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			b[i] = letterBytes[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}
	return string(b)
}