// This module defines unit settings parsing logig
//
// NOTE: ON UNIT PARSING LOGIC
// when parsing a unit in /etc/vigil/units/ we shoul ignore
// ANY broken/bad constructed toml unit configuration file
// without "crashing" logic.
//
// NOTE: ON GENERAL SERVICE LOGGING
// when vigil starts service, it should send out logs to vigil?
// or logs in such init systems are just taking the stdout+stderr
// of service and showing its output? idk 4 now, look into how its supposed to be

use crate::{RUNLEVEL_STATE, log_warning};
use serde::Deserialize;
use std::{
    fs::{read_dir, read_to_string},
    process::{Child, ExitStatus},
    time::Duration,
};

/*
   [info]
   name = "name"
   description = "description"
   version = "version"

   [config]
   exec = "path to exec"
   runlevel =
   restart=always|never

*/

#[derive(Deserialize, PartialEq, Clone)]
enum Restart {
    #[serde(alias = "always")]
    Always,
    #[serde(alias = "never")]
    Never,
}

#[derive(Deserialize, PartialEq, Eq)]
pub enum Runlevel {
    /// The system is shutting down, runlevel int: 0
    Shutdown,
    /// One-user system debug-mode, runlevel int: 1
    OneUser,
    ///  Multi-user CLI (TTY) with no network, runlevel int: 2
    MultiNoNetwork,
    /// Multi-user CLI with network, runlevel int: 3
    MultiNetwork,
    /// Multi-user mode with GUI, runlevel int: 5
    MultiGUINetwork,
    /// Runlevel is not critical for running the service, runlevel int: 4
    Undefined,
    /// System going too reboot, runlevel int: 6
    Reboot,
}

#[allow(dead_code)]
#[derive(Deserialize)]
pub struct ServiceInfo {
    /// Service name
    name: String,
    /// Service description
    description: String,
    /// Service version
    version: String,
}

#[allow(dead_code)]
#[derive(Deserialize)]
pub struct ServiceConfig {
    /// Execution command, like ExecStart in sysd
    exec: String,
    /// Runlevel, like after=*.target
    runlevel: Runlevel,
    /// Restart service: Always|Never
    restart: Restart,
}

/// Main Unit-file struct
#[allow(dead_code)]
#[derive(Deserialize)]
pub struct Unit {
    info: ServiceInfo,
    config: ServiceConfig,
}

#[allow(dead_code)]
impl Restart {
    pub fn as_str(&self) -> &'static str {
        match self {
            Restart::Always => "always",
            Restart::Never => "never",
        }
    }
}

/// Function:
/// 1. starting services declared in `/etc/vigil/units/`
/// 2. checks services for dropping and if ts true to restarting it
/// max restart count: 3
///
/// Based on the global runlevel variable, should be runned as second thread  
// TODO: More logs && better errors processing && fix clippy warnings
pub fn services_mainloop() -> Result<(), Box<dyn std::error::Error + Send>> {
    let unit_list = parse_all_units()?;
    let mut pids: Vec<(Child, String, Restart, u8)> = vec![];

    loop {
        match *RUNLEVEL_STATE.lock().unwrap() {
            Runlevel::Undefined => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::Undefined {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::Reboot => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::Reboot {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::Shutdown => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::Shutdown {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::OneUser => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::OneUser {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::MultiNoNetwork => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::MultiNoNetwork {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::MultiNetwork => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::MultiNetwork {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }

            Runlevel::MultiGUINetwork => {
                for unit in &unit_list {
                    if unit.config.runlevel == Runlevel::MultiGUINetwork {
                        let child = std::process::Command::new(unit.config.exec.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        pids.push((
                            child,
                            unit.config.exec.clone(),
                            unit.config.restart.clone(),
                            0,
                        ));
                    }
                }
            }
        }

        for i in 0..pids.len() {
            match pids[i].0.try_wait() {
                Ok(Some(status)) => {
                    if pids[i].2 == Restart::Always && pids[i].3 < 3 && status.code() != Some(0) {
                        let new_child = std::process::Command::new(pids[i].1.clone())
                            .spawn()
                            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
                        log_warning(&format!(
                            "One of units dropped with Error {};\n Restarting it. Attempt: {}",
                            status,
                            pids[i].3 + 1
                        ));

                        pids.push((
                            new_child,
                            pids[i].1.clone(),
                            pids[i].2.clone(),
                            pids[i].3 + 1,
                        ));
                        pids.remove(i);
                    } else {
                        log_warning(&format!(
                            "Unit {} has reached maximum restart attempts or restart policy is not Always, not restarting.",
                            pids[i].1
                        ));
                        continue;
                    }
                }
                Ok(None) => continue,
                Err(e) => log_warning(&format!("Error occurred while checking services: {}", e)),
            }
        }

        std::thread::sleep(Duration::from_secs(15));
    }
}

fn parse_all_units() -> Result<Vec<Unit>, Box<dyn std::error::Error + Send>> {
    let mut units: Vec<Unit> = Vec::new();

    for unit in read_dir("/etc/vigil/units")
        .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?
    {
        let unit_path = unit
            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?
            .path();
        let unit_str: String = match read_to_string(unit_path) {
            Ok(content) => content,
            Err(e) => {
                log_warning(&format!("Error while reading unit: {}", e));
                continue;
            }
        };

        let deserialized: Result<Unit, _> = toml::from_str(&unit_str);
        match deserialized {
            Ok(unit) => {
                units.push(unit);
            }
            Err(e) => {
                log_warning(&format!("Error while parsing unit: {}", e));
                continue;
            }
        };
    }

    Ok(units)
}