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

fn main() {
    // If these env variables exist then we are building on nix, use them as hash
    // and tag.
    if let (Some(hash), Some(tag)) = (option_env!("NIX_GIT_HASH"), option_env!("NIX_GIT_TAG")) {
        create_hash_file(hash);
        create_tag_file(tag);
    } else {
        // Get the current githash
        // Note: It will compare commits. As long as the commits do not diverge from the
        // server no version change will be detected.
        match Command::new("git")
            .args(&[
                "log",
                "-n",
                "1",
                "--pretty=format:%h/%cd",
                "--date=format:%Y-%m-%d-%H:%M",
                "--abbrev=8",
            ])
            .output()
        {
            Ok(output) => match String::from_utf8(output.stdout) {
                Ok(hash) => {
                    create_hash_file(&hash);
                },
                Err(e) => panic!("failed to convert git output to UTF-8: {}", e),
            },
            Err(e) => panic!("failed to retrieve current git commit hash: {}", e),
        }

        // Get the current githash
        // Note: It will compare commits. As long as the commits do not diverge from the
        // server no version change will be detected.
        match Command::new("git")
            .args(&["describe", "--exact-match", "--tags", "HEAD"])
            .output()
        {
            Ok(output) => match String::from_utf8(output.stdout) {
                Ok(tag) => {
                    create_tag_file(&tag);
                },
                Err(e) => panic!("failed to convert git output to UTF-8: {}", e),
            },
            Err(e) => panic!("failed to retrieve current git commit hash: {}", e),
        }
    }

    // Check if git-lfs is working
    if std::env::var("DISABLE_GIT_LFS_CHECK").is_err() && cfg!(not(feature = "no-assets")) {
        let asset_path: PathBuf = ["..", "assets", "voxygen", "background", "bg_main.png"]
            .iter()
            .collect();
        let asset_file = match File::open(&asset_path) {
            Ok(file) => file,
            Err(e) => panic!(
                "failed to open asset file {}: {}",
                asset_path.to_str().unwrap(),
                e
            ),
        };
        const LFS_MARKER: &[u8] = b"version https://git-lfs.github.com/spec/";
        let mut buffer = Vec::new();
        let bytes_read = asset_file
            .take(LFS_MARKER.len() as u64)
            .read_to_end(&mut buffer)
            .expect("failed to read asset file");

        if bytes_read == LFS_MARKER.len() && buffer == LFS_MARKER {
            panic!(
                "\n\nGit Large File Storage (git-lfs) has not been set up correctly.\n\
                 Most common reasons:\n\
                 \t- git-lfs was not installed before cloning this repository\n\
                 \t- this repository was not cloned from the primary gitlab mirror.\n\
                 \t  The github mirror does not support lfs.\n\
                 See the book at https://book.veloren.net/ for details.\n\n"
            );
        }
    }
}

fn create_hash_file(hash: &str) {
    let mut target = File::create(
        Path::new(&env::var("OUT_DIR").expect("failed to query OUT_DIR environment variable"))
            .join("githash"),
    )
    .expect("failed to create git hash file!");
    target
        .write_all(hash.trim().as_bytes())
        .expect("failed to write to file!");
}

fn create_tag_file(tag: &str) {
    let mut target = File::create(
        Path::new(&env::var("OUT_DIR").expect("failed to query OUT_DIR environment variable"))
            .join("gittag"),
    )
    .expect("failed to create git tag file!");
    target
        .write_all(tag.trim().as_bytes())
        .expect("failed to write to file!");
}
