prepare-commit-msg.rs

use std::env;
use std::ops::Deref;
use std::io::prelude::*;
use std::fs::File;
use std::process::Command;

fn main() {
    let args = env::args().skip(1).take(3).collect::<Vec<_>>();

    match args.get(1).map_or("", Deref::deref) {
        "" | "message" => {
            let mut branch = Command::new("git")
                .arg("rev-parse")
                .arg("--symbolic-full-name")
                .arg("--abbrev-ref")
                .arg("HEAD")
                .output()
                .unwrap()
                .stdout;

            branch.retain(|&b| b != b' ' && b != b'\n');

            if !branch.is_empty() {
                let message = File::open(&args[0]).and_then(|mut f| {
                    let mut buf = Vec::new();
                    f.read_to_end(&mut buf).map(|_| buf)
                }).unwrap();

                if !message.starts_with(&branch) {
                    File::create(&args[0]).and_then(|mut f| {
                        f.write_all(&branch).and_then(|_|
                        f.write(b" ")).and_then(|_|
                        f.write_all(&message))
                    }).unwrap();
                }
            }
        }
        _ => ()
    }
}