// Author: NithinU2802

// Hexadecimal to Octal Converter: Converts Hexadecimal to Octal

// Wikipedia References:

// 1. https://en.wikipedia.org/wiki/Hexadecimal

// 2. https://en.wikipedia.org/wiki/Octal

pub fn hexadecimal_to_octal(hex_str: &str) -> Result<String, &'static str> {

let hex_str = hex_str.trim();

if hex_str.is_empty() {

return Err("Empty string");

}

// Validate hexadecimal string

if !hex_str.chars().all(|c| c.is_ascii_hexdigit()) {

return Err("Invalid hexadecimal string");

}

// Convert hex to decimal first

let decimal = u64::from_str_radix(hex_str, 16).map_err(|_| "Conversion error")?;

// Then convert decimal to octal

if decimal == 0 {

return Ok("0".to_string());

}

let mut num = decimal;

let mut octal = String::new();

while num > 0 {

let remainder = num % 8;

octal.push_str(&remainder.to_string());

num /= 8;

}

// Reverse the string to get the correct octal representation

Ok(octal.chars().rev().collect())

}

#[cfg(test)]

mod tests {

use super::*;

#[test]

fn test_hexadecimal_to_octal() {

assert_eq!(hexadecimal_to_octal("A"), Ok("12".to_string()));

assert_eq!(hexadecimal_to_octal("FF"), Ok("377".to_string()));

assert_eq!(hexadecimal_to_octal("64"), Ok("144".to_string()));

assert_eq!(hexadecimal_to_octal("0"), Ok("0".to_string()));

}

#[test]

fn test_invalid_input() {

assert_eq!(hexadecimal_to_octal(""), Err("Empty string"));

assert_eq!(

hexadecimal_to_octal("GG"),

Err("Invalid hexadecimal string")

);

assert_eq!(

hexadecimal_to_octal("XYZ"),

Err("Invalid hexadecimal string")

);

}

}