package utils

import (
	"crypto/rand"
	"fmt"
	"io"
)

func GenerateSecure6DigitNumber() (string, error) {
	// Generate a random number between 0 and 999999 (inclusive)
	// This ensures we get a 6-digit number, including those starting with 0
	max := 1000000 // Upper bound (exclusive)
	b := make([]byte, 4) // A 4-byte slice is sufficient for a 32-bit integer

	if _, err := io.ReadFull(rand.Reader, b); err != nil {
		return "", fmt.Errorf("failed to read random bytes: %w", err)
	}

	// Convert bytes to an integer
	// We use a simple modulo operation to get a number within our desired range.
	// While this introduces a slight bias for very large ranges, for 1,000,000
	// it's negligible and simpler than more complex methods like rejection sampling.
	num := int(uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])) % max

	return fmt.Sprintf("%06d", num), nil
}