use std::fmt;
pub struct Indented<'a, D: ?Sized> {
inner: &'a mut D,
level: usize,
indent_required: bool,
}
pub fn indented<D: ?Sized>(f: &mut D, level: usize) -> Indented<'_, D> {
Indented {
inner: f,
level,
indent_required: true,
}
}
impl<T> fmt::Write for Indented<'_, T>
where
T: fmt::Write + ?Sized,
{
fn write_str(&mut self, s: &str) -> fmt::Result {
for (ind, line) in s.split('\n').enumerate() {
if ind > 0 {
self.inner.write_char('\n')?;
self.indent_required = true;
}
if self.indent_required && !line.is_empty() {
write!(self.inner, "{:indent$}{}", "", line, indent = self.level)?;
self.indent_required = false;
} else if !line.is_empty() {
write!(self.inner, "{}", line)?;
}
}
Ok(())
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::fmt::Write;
#[test]
fn test_simple() {
let output = &mut String::new();
let input = "Hello!";
let expected = " Hello!";
write!(indented(output, 4), "{}", input).unwrap();
assert_eq!(output, expected);
}
#[test]
fn test_multi_line() {
let output = &mut String::new();
let input = "Hello!\nThere!";
let expected = " Hello!\n There!";
write!(indented(output, 4), "{}", input).unwrap();
assert_eq!(output, expected);
}
#[test]
fn test_multi_write() {
let output = &mut String::new();
let input = "Hello!\nThere!";
let expected = " Hello!\n There!\n Hello!\n There!\n";
writeln!(indented(output, 4), "{}", input).unwrap();
writeln!(indented(output, 4), "{}", input).unwrap();
assert_eq!(output, expected);
}
#[test]
fn test_nested_indents() {
let output = &mut String::new();
let input = "Hello!\nThere!";
let mut level1 = indented(output, 2);
writeln!(level1, "{}", input).unwrap();
let mut level2 = indented(&mut level1, 2);
writeln!(level2, "{}", input).unwrap();
assert_eq!(output, " Hello!\n There!\n Hello!\n There!\n")
}
}