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use std::{
cmp, fmt,
io::{Error, ErrorKind, Read, Result, Write},
mem,
};
use super::VM;
impl VM {
/// Print directly to stdout, or buffer output internally.
///
/// Pass `true` to this method to buffer print output internally. This output can then be
/// accessed through this struct's [`Read`] implementation.
///
/// Pass `false` (the default mode) to sink all program output directly to [`Stdout`].
///
/// ### Example
///
/// ```
/// use std::io::Read;
///
/// let mut vm = lox_lang::VM::default();
/// vm.buffer_output(true);
///
/// vm.interpret("print nil == true;");
///
/// let mut buffer = String::new();
/// vm.read_to_string(&mut buffer).unwrap();
/// assert_eq!(buffer, "false\n");
///
/// vm.interpret("for (var a = 3; a < 12; a = a + 3) print a;");
///
/// buffer.clear();
/// vm.read_to_string(&mut buffer).unwrap();
/// assert_eq!(buffer, "3\n6\n9\n");
/// ```
///
/// [`Stdout`]: https://doc.rust-lang.org/std/io/struct.Stdout.html
/// [`Read`]: https://doc.rust-lang.org/std/io/trait.Read.html
pub fn buffer_output(&mut self, should_buffer: bool) {
if should_buffer && self.stdout.is_none() {
self.stdout = Some(Vec::new());
} else if !should_buffer && self.stdout.is_some() {
self.stdout = None;
}
}
pub(super) fn print(&mut self, args: fmt::Arguments) {
if let Some(ref mut out) = self.stdout {
out.write_fmt(args).unwrap();
} else {
print!("{}", args);
}
}
fn try_read_buf(&mut self) -> Result<&mut Vec<u8>> {
if let Some(ref mut my_buf) = &mut self.stdout {
Ok(my_buf)
} else {
Err(Error::new(
ErrorKind::Other,
"Currently logging directly to stdout.",
))
}
}
}
impl Read for VM {
fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
let my_buf = self.try_read_buf()?;
if my_buf.is_empty() {
return Ok(0);
}
let common_len = cmp::min(my_buf.len(), buf.len());
let new_vec = my_buf.split_off(common_len);
let old_vec = mem::replace(my_buf, new_vec);
buf[0..common_len].copy_from_slice(&old_vec);
Ok(common_len)
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize> {
let my_buf = self.try_read_buf()?;
if my_buf.is_empty() {
return Ok(0);
}
let len = my_buf.len();
buf.append(my_buf);
Ok(len)
}
}