//! Binary installer: download a precompiled binary (direct URL or GitHub
//! Releases asset), verify its checksum, extract it if needed, and install
//! it into the global bin directory.

use super::*;

pub fn install(
    app: &App,
    agent: &AgentDef,
    method: &MethodSpec,
    runner: &dyn Runner,
) -> Result<InstallOutcome> {
    let root = install_root(app, &agent.name);
    let dist = root.join("dist");
    let bindir = bin_dir(app);
    ensure_dir(app, &root)?;
    ensure_dir(app, &dist)?;
    ensure_dir(app, &bindir)?;

    // Resolve the download URL (direct or GitHub release asset).
    let (url, tag): (String, Option<String>) = if let Some(u) = &method.url {
        (u.clone(), None)
    } else if let Some(repo) = &method.repo {
        let release = crate::download::latest_release(repo)?;
        let picked = crate::download::pick_asset(
            &release,
            &method.asset_match,
            &method.asset_exclude,
            method.binary.as_deref(),
        )
        .ok_or_else(|| {
            anyhow!(
                "no release asset of '{repo}' matches this platform ({}/{})",
                crate::config::current_platform(),
                std::env::consts::ARCH
            )
        })?;
        app.log
            .info(&format!("selected asset: {} ({})", picked.name, picked.tag));
        (
            picked.url,
            Some(picked.tag.trim_start_matches('v').to_string()),
        )
    } else {
        bail!("binary install requires 'url' or 'repo' (GitHub owner/repo)");
    };

    let names = expected_bin_names(agent, method);
    let bin_name = names
        .first()
        .cloned()
        .unwrap_or_else(|| agent.name.clone());
    let dest_bin = bindir.join(exe_name(&bin_name));

    if app.dry_run() {
        app.log
            .dry(format!("would download {url} and install {}", dest_bin.display()));
        return Ok(InstallOutcome {
            bins: vec![dest_bin],
            version: tag,
        });
    }

    let tmpdir = tempfile::tempdir()?;
    let tmpfile = tmpdir.path().join("download");
    crate::download::download(&url, &tmpfile, method.checksum.as_deref(), true)?;
    if crate::download::extract_archive(&tmpfile, &dist)? {
        let found = crate::download::find_executable(&dist, Some(&bin_name))?;
        std::fs::copy(&found, &dest_bin).with_context(|| {
            format!("cannot copy {} to {}", found.display(), dest_bin.display())
        })?;
        app.log
            .info(&format!("extracted {} -> {}", found.display(), dest_bin.display()));
    } else {
        std::fs::copy(&tmpfile, &dest_bin).with_context(|| {
            format!("cannot copy {} to {}", tmpfile.display(), dest_bin.display())
        })?;
    }
    // Guard against installing something that is not an executable for this
    // platform (wrong architecture, an unextracted archive, ...).
    verify_executable(&dest_bin)?;
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        let _ = std::fs::set_permissions(&dest_bin, std::fs::Permissions::from_mode(0o755));
    }
    let version = detect_version(runner, &dest_bin).or(tag);
    Ok(InstallOutcome {
        bins: vec![dest_bin],
        version,
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn verify_executable_accepts_pe_and_rejects_elf() {
        let dir = tempfile::tempdir().unwrap();
        let pe = dir.path().join("a.exe");
        std::fs::write(&pe, b"MZwhatever").unwrap();
        assert!(verify_executable(&pe).is_ok());
        let elf = dir.path().join("b");
        std::fs::write(&elf, b"ELF").unwrap();
        let err = verify_executable(&elf).unwrap_err();
        assert!(err.to_string().contains("not a"), "{err}");
    }
}

/// Check that the downloaded file is an executable of this platform.
/// Detects the classic Windows "not compatible" (error 216) and Linux
/// "exec format error" failures before the agent is ever started.
fn verify_executable(path: &std::path::Path) -> Result<()> {
    let mut head = [0u8; 4];
    let n = std::fs::File::open(path)
        .and_then(|mut f| std::io::Read::read(&mut f, &mut head))
        .unwrap_or(0);
    #[cfg(windows)]
    let ok = n >= 2 && &head[0..2] == b"MZ";
    #[cfg(target_os = "macos")]
    let ok = (n >= 4 && (&head[0..4] == b"\xcf\xfa\xed\xfe" || &head[0..4] == b"\xfe\xed\xfa\xcf"))
        || (n >= 4 && &head[0..4] == b"\xca\xfe\xba\xbe");
    #[cfg(all(unix, not(target_os = "macos")))]
    let ok = n >= 4 && &head[0..4] == b"\x7fELF";
    if ok {
        return Ok(());
    }
    bail!(
        "downloaded file {} is not a {} executable (magic bytes {:02x?}) — the release asset is probably for another platform or is an installer/archive",
        path.display(),
        std::env::consts::OS,
        &head[..n]
    )
}

/// Latest release tag (without the leading "v").
pub fn latest(
    _app: &App,
    _agent: &AgentDef,
    method: &MethodSpec,
    _runner: &dyn Runner,
) -> Result<Option<String>> {
    let Some(repo) = method.repo.as_deref() else {
        return Ok(None);
    };
    let release = crate::download::latest_release(repo)?;
    Ok(Some(release.tag_name.trim_start_matches('v').to_string()))
}