//! Service management for GyanDoot — install, remove, and check system services.
//!
//! Supports:
//! - **Linux**: systemd user services (`systemctl --user`)
//! - **macOS**: launchd user agents (`launchctl`)
//!
//! Templates live in the resources/ directory of the repo and are rendered
//! at install time with the actual binary path and home directory.

use std::path::{Path, PathBuf};
use tracing::{info, warn};

use crate::{AgentError, AgentResult};

/// Supported init systems.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum InitSystem {
    Systemd,
    Launchd,
    Unknown,
}

impl InitSystem {
    /// Detect the current init system from the OS.
    pub fn detect() -> Self {
        if cfg!(target_os = "linux") {
            // Check if systemd is available
            if std::process::Command::new("systemctl")
                .arg("--version")
                .output()
                .is_ok()
            {
                Self::Systemd
            } else {
                Self::Unknown
            }
        } else if cfg!(target_os = "macos") {
            Self::Launchd
        } else {
            Self::Unknown
        }
    }

    /// Human-readable name.
    pub fn name(&self) -> &str {
        match self {
            Self::Systemd => "systemd",
            Self::Launchd => "launchd",
            Self::Unknown => "unknown",
        }
    }
}

/// Result of a service status check.
#[derive(Debug, Clone)]
pub struct ServiceStatus {
    pub name: String,
    pub init_system: String,
    pub installed: bool,
    pub running: bool,
    pub enabled: bool,
    pub details: String,
}

/// Install GyanDoot as a system service.
///
/// Detects the init system, renders the appropriate template, installs it,
/// and starts the service.
pub fn install_service() -> AgentResult<ServiceStatus> {
    let init = InitSystem::detect();
    info!("Detected init system: {}", init.name());

    match init {
        InitSystem::Systemd => install_systemd(),
        InitSystem::Launchd => install_launchd(),
        InitSystem::Unknown => Err(AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Unsupported,
            format!(
                "No supported init system detected. Supported: systemd (Linux), launchd (macOS).\n\
                 You can still run GyanDoot manually: `gyandoot run` or `gyandoot serve`"
            ),
        ))),
    }
}

/// Remove the GyanDoot system service (stop + disable + delete).
pub fn remove_service() -> AgentResult<()> {
    let init = InitSystem::detect();
    info!("Detected init system: {}", init.name());

    match init {
        InitSystem::Systemd => remove_systemd(),
        InitSystem::Launchd => remove_launchd(),
        InitSystem::Unknown => Err(AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Unsupported,
            "No supported init system detected.",
        ))),
    }
}

/// Check the status of the GyanDoot service.
pub fn check_service() -> AgentResult<ServiceStatus> {
    let init = InitSystem::detect();
    info!("Detected init system: {}", init.name());

    match init {
        InitSystem::Systemd => check_systemd(),
        InitSystem::Launchd => check_launchd(),
        InitSystem::Unknown => Ok(ServiceStatus {
            name: "gyandoot".to_string(),
            init_system: "unknown".to_string(),
            installed: false,
            running: false,
            enabled: false,
            details: "Unknown init system. Supported: systemd (Linux), launchd (macOS).".to_string(),
        }),
    }
}

// ── systemd ──────────────────────────────────────────────────────────────

/// Get the systemd user service directory.
fn systemd_user_dir() -> PathBuf {
    if let Ok(xdg) = std::env::var("XDG_CONFIG_HOME") {
        PathBuf::from(xdg).join("systemd").join("user")
    } else if let Some(home) = dirs::home_dir() {
        home.join(".config").join("systemd").join("user")
    } else {
        PathBuf::from("/tmp/gyandoot-systemd-user")
    }
}

fn install_systemd() -> AgentResult<ServiceStatus> {
    let home = dirs::home_dir().ok_or_else(|| {
        AgentError::Io(std::io::Error::new(std::io::ErrorKind::NotFound, "Cannot determine home directory"))
    })?;
    let binary = std::env::current_exe().unwrap_or_else(|_| PathBuf::from("gyandoot"));
    let user = std::env::var("USER").unwrap_or_else(|_| "root".to_string());
    let group = std::env::var("USER").unwrap_or_else(|_| "root".to_string());

    let service_dir = systemd_user_dir();
    std::fs::create_dir_all(&service_dir).map_err(|e| {
        AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Other,
            format!("Cannot create systemd user dir {}: {}", service_dir.display(), e),
        ))
    })?;

    let service_path = service_dir.join("gyandoot.service");

    // Render template
    let template = include_str!(concat!(
        env!("CARGO_MANIFEST_DIR"),
        "/../../resources/systemd/gyandoot.service"
    ));

    let rendered = template
        .replace("%BINARY%", &binary.to_string_lossy())
        .replace("%USER%", &user)
        .replace("%GROUP%", &group)
        .replace("%HOME%", &home.to_string_lossy());

    std::fs::write(&service_path, &rendered).map_err(|e| {
        AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Other,
            format!("Cannot write service file {}: {}", service_path.display(), e),
        ))
    })?;

    info!("Wrote systemd service to {}", service_path.display());

    // Reload systemd user daemon
    run_cmd("systemctl", &["--user", "daemon-reload"])?;

    // Enable and start
    run_cmd("systemctl", &["--user", "enable", "gyandoot.service"])?;
    run_cmd("systemctl", &["--user", "start", "gyandoot.service"])?;

    info!("GyanDoot systemd service installed and started");

    check_systemd()
}

fn remove_systemd() -> AgentResult<()> {
    // Stop first
    let _ = run_cmd("systemctl", &["--user", "stop", "gyandoot.service"]);

    // Disable
    let _ = run_cmd("systemctl", &["--user", "disable", "gyandoot.service"]);

    // Remove file
    let service_path = systemd_user_dir().join("gyandoot.service");
    if service_path.exists() {
        std::fs::remove_file(&service_path).map_err(|e| {
            AgentError::Io(std::io::Error::new(
                std::io::ErrorKind::Other,
                format!("Cannot remove {}: {}", service_path.display(), e),
            ))
        })?;
        info!("Removed systemd service file: {}", service_path.display());
    }

    // Reload
    let _ = run_cmd("systemctl", &["--user", "daemon-reload"]);

    Ok(())
}

fn check_systemd() -> AgentResult<ServiceStatus> {
    let mut details = String::new();

    // Check if unit file exists
    let service_path = systemd_user_dir().join("gyandoot.service");
    let installed = service_path.exists();

    let mut running = false;
    let mut enabled = false;

    if installed {
        // Check if running
        if let Ok(out) = run_cmd_for_output("systemctl", &["--user", "is-active", "gyandoot.service"]) {
            running = out.trim() == "active";
            details.push_str(&format!("Active: {}", out.trim()));
        }

        if let Ok(out) = run_cmd_for_output("systemctl", &["--user", "is-enabled", "gyandoot.service"]) {
            enabled = out.trim() == "enabled";
            details.push_str(&format!("\nEnabled: {}", out.trim()));
        }
    } else {
        details = "Not installed".to_string();
    }

    Ok(ServiceStatus {
        name: "gyandoot".to_string(),
        init_system: "systemd".to_string(),
        installed,
        running,
        enabled,
        details,
    })
}

// ── launchd (macOS) ────────────────────────────────────────────────────

fn launchd_plist_path() -> PathBuf {
    if let Some(home) = dirs::home_dir() {
        home.join("Library").join("LaunchAgents").join("com.gyandoot.agent.plist")
    } else {
        PathBuf::from("/tmp/com.gyandoot.agent.plist")
    }
}

fn install_launchd() -> AgentResult<ServiceStatus> {
    let home = dirs::home_dir().ok_or_else(|| {
        AgentError::Io(std::io::Error::new(std::io::ErrorKind::NotFound, "Cannot determine home directory"))
    })?;
    let binary = std::env::current_exe().unwrap_or_else(|_| PathBuf::from("gyandoot"));

    let launch_agents_dir = home.join("Library").join("LaunchAgents");
    std::fs::create_dir_all(&launch_agents_dir).map_err(|e| {
        AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Other,
            format!("Cannot create LaunchAgents dir {}: {}", launch_agents_dir.display(), e),
        ))
    })?;

    let plist_path = launchd_plist_path();

    // Render template
    let template = include_str!(concat!(
        env!("CARGO_MANIFEST_DIR"),
        "/../../resources/launchd/com.gyandoot.agent.plist"
    ));

    let rendered = template
        .replace("%BINARY%", &binary.to_string_lossy())
        .replace("%HOME%", &home.to_string_lossy());

    std::fs::write(&plist_path, &rendered).map_err(|e| {
        AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Other,
            format!("Cannot write plist {}: {}", plist_path.display(), e),
        ))
    })?;

    info!("Wrote launchd plist to {}", plist_path.display());

    // Unload first (in case it was already loaded)
    let _ = run_cmd("launchctl", &["unload", &plist_path.to_string_lossy()]);

    // Load the new plist
    run_cmd("launchctl", &["load", &plist_path.to_string_lossy()])?;

    // Start
    run_cmd("launchctl", &["start", "com.gyandoot.agent"])?;

    info!("GyanDoot launchd agent installed and started");

    check_launchd()
}

fn remove_launchd() -> AgentResult<()> {
    let plist_path = launchd_plist_path();

    // Stop
    let _ = run_cmd("launchctl", &["stop", "com.gyandoot.agent"]);

    // Unload
    if plist_path.exists() {
        let _ = run_cmd("launchctl", &["unload", &plist_path.to_string_lossy()]);
        std::fs::remove_file(&plist_path).map_err(|e| {
            AgentError::Io(std::io::Error::new(
                std::io::ErrorKind::Other,
                format!("Cannot remove plist {}: {}", plist_path.display(), e),
            ))
        })?;
        info!("Removed launchd plist: {}", plist_path.display());
    }

    Ok(())
}

fn check_launchd() -> AgentResult<ServiceStatus> {
    let plist_path = launchd_plist_path();
    let installed = plist_path.exists();

    let mut running = false;
    let mut details = String::new();

    if installed {
        // Check if loaded
        if let Ok(out) = run_cmd_for_output("launchctl", &["list", "com.gyandoot.agent"]) {
            running = !out.contains("PID = 0,") && !out.is_empty();
            details = out;
        }
    } else {
        details = "Not installed".to_string();
    }

    Ok(ServiceStatus {
        name: "com.gyandoot.agent".to_string(),
        init_system: "launchd".to_string(),
        installed,
        running,
        enabled: installed, // launchd agents are "enabled" if loaded
        details,
    })
}

// ── Helpers ─────────────────────────────────────────────────────────────

/// Run a command and return stdout as a String.
fn run_cmd_for_output(cmd: &str, args: &[&str]) -> Result<String, String> {
    let output = std::process::Command::new(cmd)
        .args(args)
        .output()
        .map_err(|e| format!("Failed to execute {}: {}", cmd, e))?;

    let stdout = String::from_utf8_lossy(&output.stdout).to_string();
    let stderr = String::from_utf8_lossy(&output.stderr).to_string();

    if output.status.success() {
        Ok(stdout)
    } else {
        Err(format!("{} failed: {}", cmd, stderr.trim()))
    }
}

/// Run a command and check for success.
fn run_cmd(cmd: &str, args: &[&str]) -> AgentResult<()> {
    let status = std::process::Command::new(cmd)
        .args(args)
        .status()
        .map_err(|e| {
            AgentError::Io(std::io::Error::new(
                std::io::ErrorKind::Other,
                format!("Failed to execute {}: {}", cmd, e),
            ))
        })?;

    if status.success() {
        Ok(())
    } else {
        Err(AgentError::Io(std::io::Error::new(
            std::io::ErrorKind::Other,
            format!("{} exited with status {:?}", cmd, status.code()),
        )))
    }
}