zff 2.0.1

This crate is a library to interact with zff, a file format for forensic images.
Documentation 
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use crate::{
	Result,
	ZffError,
	ZffErrorKind,
	FILE_EXTENSION_START,
	FILE_EXTENSION_PARSER_ERROR,
};

/// Returns the next file extension value.
/// # Example
/// ```
/// use zff::*;
/// 
/// let file_extension = "z01";
/// assert_eq!(file_extension_next_value(file_extension).unwrap(), "z02");
/// ```
/// # Error
/// fails if the file-extension is in an unsuitable format.
pub fn file_extension_next_value<V: Into<String>>(value: V) -> Result<String> {
	let value = value.into();

	let mut chars = value.chars();
	match chars.next() {
		Some(FILE_EXTENSION_START) => (),
		_ => return Err(ZffError::new(ZffErrorKind::FileExtensionParserError, FILE_EXTENSION_PARSER_ERROR)),
	};
	let mut next_value: u64 = match chars.as_str().parse() {
		Ok(val) => val,
		Err(e) => return Err(ZffError::new(ZffErrorKind::FileExtensionParserError, e.to_string())),
	};
	next_value += 1;
	if next_value <= 9 {
		Ok(String::from("z0") + &next_value.to_string())
	} else {
		Ok(String::from("z") + &next_value.to_string())
	}
}

/// Returns the previous file extension value.
/// # Example
/// ```
/// use zff::*;
/// 
/// let file_extension = "z05";
/// assert_eq!(file_extension_previous_value(file_extension).unwrap(), "z04");
/// ```
/// # Error
/// fails if the file-extension is in an unsuitable format or if the previous value is < 0.
pub fn file_extension_previous_value<V: Into<String>>(value: V) -> Result<String> {
	let value = value.into();

	let mut chars = value.chars();
	match chars.next() {
		Some(FILE_EXTENSION_START) => (),
		_ => return Err(ZffError::new(ZffErrorKind::FileExtensionParserError, FILE_EXTENSION_PARSER_ERROR)),
	};
	let mut previous_value: u64 = match chars.as_str().parse() {
		Ok(val) => val,
		Err(e) => return Err(ZffError::new(ZffErrorKind::FileExtensionParserError, e.to_string())),
	};
	previous_value -= 1;
	if previous_value <= 9 {
		Ok(String::from("z0") + &previous_value.to_string())
	} else {
		Ok(String::from("z") + &previous_value.to_string())
	}
}