go-sprout/sprout

package random

import (
    cryptorand "crypto/rand"
    "math/big"
    "strings"
)

// randomString generates a random string of a given length using specified options.
// It supports a flexible character set based on the provided options.
//
// Parameters:
//
//    count int - the length of the string to generate.
//    opts *randomOpts - options specifying character sets to include in the string.
//
// Returns:
//
//    string - the randomly generated string.
//
// Usage:
//
//    opts := &randomOpts{withLetters: true, withNumbers: true}
//    randomStr := rr.randomString(10, opts) // Generates a 10-character alphanumeric string.
func (rr *RandomRegistry) randomString(count int, opts *randomOpts) string {
    if count <= 0 {
        return ""
    }

    if len(opts.withChars) == 0 {
        if opts.withAscii {
            opts.withChars = make([]rune, 95) // 95 printable ASCII characters
            for i := 32; i <= 126; i++ {
                opts.withChars[i-32] = rune(i)
            }
        } else {
            var buffer []rune
            if opts.withLetters {
                buffer = make([]rune, 52) // 26 lowercase + 26 uppercase letters
                for i := 0; i < 26; i++ {
                    buffer[i] = 'a' + rune(i)
                    buffer[i+26] = 'A' + rune(i)
                }
            }
            if opts.withNumbers {
                if buffer == nil {
                    buffer = make([]rune, 10) // 10 digits
                } else {
                    buffer = append(buffer, make([]rune, 10)...)
                }
                for i := 0; i < 10; i++ {
                    buffer[len(buffer)-10+i] = '0' + rune(i)
                }
            }
            opts.withChars = buffer
        }
    }

    var builder strings.Builder
    builder.Grow(count)

    maxIndex := big.NewInt(int64(len(opts.withChars)))
    for i := 0; i < count; i++ {
        index, _ := cryptorand.Int(cryptorand.Reader, maxIndex)
        builder.WriteRune(opts.withChars[index.Int64()])
    }

    return builder.String()
}