//! Ely's Git: where it is and how it runs (§13.1).

use std::{
    io,
    path::{Path, PathBuf},
    process::Command,
};

use crate::AppId;

/// ElyTree's setting naming a system Git; empty is Ely's own.
pub const PROGRAM: &str = "git";

/// The oldest system Git counted as verified (user decision).
pub const LEAST: (u32, u32) = (2, 40);

/// `ELY_GIT`, ElyTree's setting, else Ely's own Git.
pub fn locate() -> io::Result<(PathBuf, bool)> {
    if let Some(path) = std::env::var_os("ELY_GIT") {
        return Ok((PathBuf::from(path), false));
    }
    let set = crate::settings::Store::app(AppId::Tree)?.read()?;
    match set.get(PROGRAM) {
        None => {}
        Some(serde_json::Value::String(path)) if path.is_empty() => {}
        Some(serde_json::Value::String(path)) => return Ok((PathBuf::from(path), false)),
        Some(other) => return Err(io::Error::new(io::ErrorKind::InvalidData, format!("settings: git cannot be {other}"))),
    }
    let exe = std::env::current_exe()?;
    Ok((own(exe.parent().unwrap_or(Path::new("."))), true))
}

/// `git version 2.56.0…` as (2, 56); None for anything else.
pub fn parse_version(text: &str) -> Option<(u32, u32)> {
    let number = text.trim().strip_prefix("git version ")?;
    let mut parts = number.split(|c: char| !c.is_ascii_digit());
    Some((parts.next()?.parse().ok()?, parts.next()?.parse().ok()?))
}

/// What `git --version` says, once it succeeds.
pub fn version_of(path: &Path) -> io::Result<(String, (u32, u32))> {
    let output = Command::new(path).arg("--version").output()?;
    if !output.status.success() {
        let said = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(io::Error::other(format!("{} --version failed ({}): {said}", path.display(), output.status)));
    }
    let version = String::from_utf8_lossy(&output.stdout).trim().to_string();
    let number = parse_version(&version).ok_or_else(|| io::Error::other(format!("{} is no Git: {version:?}", path.display())))?;
    Ok((version, number))
}

/// A system Git's version, if 2.40 or later.
pub fn system_version(path: &Path) -> io::Result<String> {
    let (version, number) = version_of(path)?;
    if number < LEAST {
        let message = format!("{version} at {} is older than {}.{}", path.display(), LEAST.0, LEAST.1);
        return Err(io::Error::new(io::ErrorKind::Unsupported, message));
    }
    Ok(version)
}

/// Beside `dir`, in its bundle, in ElyTree's, or built.
fn own(dir: &Path) -> PathBuf {
    // ElyTree carries Git; the other apps use its copy.
    let tree = format!("../../../{}.app/Contents/Resources/git/bin/git", AppId::Tree.name());
    let built = Path::new(env!("CARGO_MANIFEST_DIR")).join("../../engines/git/bin/git");
    [
        dir.join("git/bin/git"),
        dir.join("../Resources/git/bin/git"),
        dir.join(tree),
    ]
    .into_iter()
    .find(|path| path.is_file())
    .unwrap_or(built)
}

/// Git at `git` in `dir`, as Ely runs it.
pub fn command(git: &Path, dir: &Path, args: &[&str]) -> Command {
    let mut command = Command::new(git);
    command
        .args(args)
        .current_dir(dir)
        // Reads never take the index lock from an outside Git.
        .env("GIT_OPTIONAL_LOCKS", "0")
        // A path is a path, never a pattern.
        .env("GIT_LITERAL_PATHSPECS", "1")
        .env("GIT_TERMINAL_PROMPT", "0")
        // No terminal for an editor; Git's own message stands.
        .env("GIT_EDITOR", "true")
        .env("GIT_SEQUENCE_EDITOR", "true");
    command
}

#[cfg(test)]
mod tests {
    #[cfg(unix)]
    #[test]
    fn a_failing_version_query_is_no_version() {
        use std::os::unix::fs::PermissionsExt as _;
        let dir = tempfile::tempdir().unwrap();
        let fake = dir.path().join("git");
        std::fs::write(&fake, "#!/bin/sh\necho 'git version 2.56.0'\necho 'fatal: version query failed' >&2\nexit 7\n").unwrap();
        std::fs::set_permissions(&fake, std::fs::Permissions::from_mode(0o755)).unwrap();
        let error = super::system_version(&fake).expect_err("a failed run");
        assert!(error.to_string().contains("version query failed"), "{error}");
        assert!(super::version_of(&fake).is_err());
    }

    #[test]
    fn versions_read_as_major_and_minor() {
        assert_eq!(super::parse_version("git version 2.56.0\n"), Some((2, 56)));
        assert_eq!(super::parse_version("git version 2.54.0 (Apple Git-157)"), Some((2, 54)));
        assert_eq!(super::parse_version("hello"), None);
    }

    use super::own;

    #[test]
    fn apps_beside_elytree_use_its_git() {
        let apps = tempfile::tempdir().expect("a temp dir");
        let mark = apps.path().join("ElyMark.app/Contents/MacOS");
        let git = apps.path().join("ElyTree.app/Contents/Resources/git/bin");
        std::fs::create_dir_all(&mark).expect("ElyMark");
        assert!(own(&mark).ends_with("engines/git/bin/git"));
        std::fs::create_dir_all(&git).expect("ElyTree's Git");
        std::fs::write(git.join("git"), "").expect("git");
        assert_eq!(own(&mark), mark.join("../../../ElyTree.app/Contents/Resources/git/bin/git"));
    }
}