//! Environment discovery: finding binaries on PATH and detecting available
//! toolchains / package managers on the host system.

use std::path::PathBuf;
use std::process::Command;

/// Rust toolchain availability on the host PATH.
#[derive(Debug, Clone)]
pub struct RustToolchain {
    pub has_rustup: bool,
    pub has_cargo: bool,
}

/// Web / scripting language toolchain availability.
#[derive(Debug, Clone)]
pub struct WebToolchain {
    pub has_npm: bool,
    pub has_go: bool,
    pub has_java: bool,
}

/// General-purpose platform utilities.
#[derive(Debug, Clone)]
pub struct PlatformUtils {
    pub has_curl: bool,
    pub has_tar: bool,
}

/// Pacman and Brew package managers (Arch / macOS).
#[derive(Debug, Clone)]
pub struct PacmanBrew {
    pub has_pacman: bool,
    pub has_brew: bool,
}

/// Apt and DNF package managers (Debian / Fedora).
#[derive(Debug, Clone)]
pub struct AptDnf {
    pub has_apt: bool,
    pub has_dnf: bool,
}

/// Snapshot of the host environment used to decide which install tiers are viable.
///
/// Populated by `detect_env()` once per `provision_all_with_progress()` call so we
/// don't re-shell out for every server. `is_linux` / `is_macos` are
/// computed at startup (compile time would also work, but keeping the
/// shape uniform with the rest of the struct makes the call sites tidy).
#[derive(Debug, Clone)]
pub struct EnvInfo {
    pub rust: RustToolchain,
    pub web: WebToolchain,
    pub platform: PlatformUtils,
    pub pacman_brew: PacmanBrew,
    pub apt_dnf: AptDnf,
    pub is_linux: bool,
    pub is_macos: bool,
}

/// Check whether `binary` exists on PATH by shelling out to `which`.
///
/// Flow: `Command::new("which").arg(binary).output()` → on Unix
///       `which` returns exit 0 + stdout path when found, non-zero
///       otherwise. We return the first stdout line as the `PathBuf`.
///
/// Returns None if `which` itself is missing, fails to spawn, or the
/// binary is not on PATH. We deliberately don't cache this — it's only
/// called during provisioning and the results feed into install-tier
/// gating, which is already cheap.
pub fn which(binary: &str) -> Option<PathBuf> {
    let output = Command::new("which").arg(binary).output().ok()?;
    if !output.status.success() {
        return None;
    }
    let stdout = String::from_utf8_lossy(&output.stdout);
    let first = stdout.lines().next()?.trim();
    if first.is_empty() {
        None
    } else {
        Some(PathBuf::from(first))
    }
}

/// Snapshot the host environment: which toolchains and package managers
/// are available, and what OS we're on.
///
/// Flow: shell out to `which` for each tool in parallel (sequentially,
///       actually — the calls are fast and the ordering doesn't matter)
///       → set `EnvInfo` flags. Linux/macOS are detected via cfg at
///       compile time since `which` won't tell us.
///
/// Edge case: `which` may not exist on Windows; we guard with cfg so
/// this only ever runs on Unix-like targets.
pub fn detect_env() -> EnvInfo {
    EnvInfo {
        rust: RustToolchain {
            has_rustup: which("rustup").is_some(),
            has_cargo: which("cargo").is_some(),
        },
        web: WebToolchain {
            has_npm: which("npm").is_some(),
            has_go: which("go").is_some(),
            has_java: which("java").is_some(),
        },
        platform: PlatformUtils {
            has_curl: which("curl").is_some(),
            has_tar: which("tar").is_some(),
        },
        pacman_brew: PacmanBrew {
            has_pacman: which("pacman").is_some(),
            has_brew: which("brew").is_some(),
        },
        apt_dnf: AptDnf {
            has_apt: which("apt").is_some() || which("apt-get").is_some(),
            has_dnf: which("dnf").is_some(),
        },
        is_linux: cfg!(target_os = "linux"),
        is_macos: cfg!(target_os = "macos"),
    }
}