Add pager if output exceeds 50 lines

src/cli.rs

@@ -1,15 +1,18 @@
 use std::ffi::{c_int, OsString};
 use std::fmt::Debug;
-use std::io::Error;
+use std::io::{Error, Write};
 use std::os::unix::io::AsRawFd;
 
 use crate::output::{Color, OutputWriter, Style};
 use crate::{add, commit, diff, init, log, restore, rm, status, workspace::Repository};
 use std::io;
 use std::path::{Path, PathBuf};
+use std::process::{Child, Command, Stdio};
 
 use clap::{Parser, Subcommand};
 
+const PRE_PAGER_BUFFER_SIZE: usize = 50;
+
 #[derive(Parser, Debug)]
 struct Args {
  #[command(subcommand)]
@@ -123,6 +126,8 @@ pub fn run_command<P: AsRef<Path>, S: Into<OsString> + Clone>(
 
 pub struct StdoutWriter {
  isatty: bool,
+ pager: Option<Child>,
+ pre_pager_buffer: Option<Vec<String>>,
 }
 
 extern "C" {
@@ -133,21 +138,68 @@ impl StdoutWriter {
  pub fn new() -> Self {
  let stdout_fd = io::stdout().as_raw_fd();
  let isatty = unsafe { isatty(stdout_fd) } != 0;
- Self { isatty }
+ Self { isatty, pager: None, pre_pager_buffer: Some(vec![]) }
  }
 
- fn print_ansi_code(&mut self, ansi_code: &str) {
+ fn print_ansi_code(&mut self, ansi_code: &str) -> io::Result<&mut dyn OutputWriter> {
  if !self.isatty {
- return;
+ return Ok(self);
+ }
+
+ self.write(format!("\x1b[{}m", ansi_code))
+ }
+
+ fn attach_pager(&mut self) -> &mut Self {
+ self.pager = Some(
+ Command::new("less")
+ .arg("-R")
+ .stdin(Stdio::piped())
+ .spawn()
+ .unwrap(),
+ );
+ return self;
+ }
+
+ fn flush_buffer(&mut self) {
+ let buffer = self.pre_pager_buffer.take().unwrap();
+ if self.isatty && buffer.len() > PRE_PAGER_BUFFER_SIZE {
+ self.attach_pager();
+ }
+
+ for line in buffer {
+ self.write(line).unwrap();
  }
+ }
+}
 
- print!("\x1b[{}m", ansi_code);
+impl Drop for StdoutWriter {
+ fn drop(&mut self) {
+ if self.pre_pager_buffer.is_some() {
+ self.flush_buffer();
+ }
+ if let Some(ref mut pager) = self.pager {
+ pager.wait().unwrap();
+ }
  }
 }
 
 impl OutputWriter for StdoutWriter {
  fn write(&mut self, content: String) -> io::Result<&mut dyn OutputWriter> {
- print!("{}", content);
+ if let Some(ref mut buffer) = self.pre_pager_buffer {
+ buffer.push(content);
+ if buffer.len() > PRE_PAGER_BUFFER_SIZE {
+ self.flush_buffer();
+ }
+ } else if let Some(ref mut pager) = self.pager {
+ pager
+ .stdin
+ .as_mut()
+ .unwrap()
+ .write_all(content.as_bytes())
+ .unwrap();
+ } else {
+ print!("{}", content);
+ }
  Ok(self)
  }
 
@@ -158,22 +210,19 @@ impl OutputWriter for StdoutWriter {
  Color::Cyan => "36",
  Color::Brown => "38;5;130",
  };
- self.print_ansi_code(ansi_code);
- Ok(self)
+ self.print_ansi_code(ansi_code)
  }
 
  fn set_style(&mut self, style: Style) -> io::Result<&mut dyn OutputWriter> {
  let ansi_code = match style {
  Style::Bold => "1",
  Style::Normal => "22",
  };
- self.print_ansi_code(ansi_code);
- Ok(self)
+ self.print_ansi_code(ansi_code)
  }
 
  fn reset_formatting(&mut self) -> io::Result<&mut dyn OutputWriter> {
- self.print_ansi_code("0");
- Ok(self)
+ self.print_ansi_code("0")
  }
 }