use std::env;
use std::fs::File;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::process::Command;

fn main() {
 // Only check .git/HEAD dirty status if it exists - doing so when
 // building dependent crates may lead to false positives and rebuilds
 if Path::new(".git/HEAD").exists() {
 println!("cargo:rerun-if-changed=.git/HEAD");
 }

 println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");

 let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());

 File::create(out_dir.join("commit-info.txt"))
 .unwrap()
 .write_all(commit_info().as_bytes())
 .unwrap();
}

// Try to get hash and date of the last commit on a best effort basis. If anything goes wrong
// (git not installed or if this is not a git repository) just return an empty string.
fn commit_info() -> String {
 match (channel(), commit_hash(), commit_date()) {
 (channel, Some(hash), Some(date)) => format!("{} ({} {})", channel, hash.trim_end(), date),
 _ => String::new(),
 }
}

fn channel() -> String {
 if let Ok(channel) = env::var("CFG_RELEASE_CHANNEL") {
 channel
 } else {
 "nightly".to_owned()
 }
}

fn commit_hash() -> Option<String> {
 Command::new("git")
 .args(&["rev-parse", "--short", "HEAD"])
 .output()
 .ok()
 .and_then(|r| String::from_utf8(r.stdout).ok())
}

fn commit_date() -> Option<String> {
 Command::new("git")
 .args(&["log", "-1", "--date=short", "--pretty=format:%cd"])
 .output()
 .ok()
 .and_then(|r| String::from_utf8(r.stdout).ok())
}