//! Systemd go-sbot process statistics retrieval functions and associated data types.

use std::{process::Command, str};

use crate::StatsError;

/// go-sbot process statistics.
#[derive(Debug)]
pub struct SbotStat {
    /// Current process state.
    state: String,
    /// Current process memory usage in bytes.
    memory: Option<u32>,
    /// Uptime for the process (if state is `active`).
    uptime: Option<String>,
    /// Downtime for the process (if state is `inactive`).
    downtime: Option<String>,
}

impl SbotStat {
    /// Default builder for `SbotStat`.
    fn default() -> Self {
        Self {
            state: String::new(),
            memory: None,
            uptime: None,
            downtime: None,
        }
    }
}

/// Retrieve statistics for the go-sbot systemd process by querying `systemctl`.
pub fn sbot_stats() -> Result<SbotStat, StatsError> {
    let mut status = SbotStat::default();

    let info_output = Command::new("/usr/bin/systemctl")
        .arg("--user")
        .arg("show")
        .arg("go-sbot.service")
        .arg("--no-page")
        .output()
        .map_err(StatsError::Systemctl)?;

    let service_info = std::str::from_utf8(&info_output.stdout).map_err(StatsError::Utf8String)?;

    for line in service_info.lines() {
        if line.starts_with("ActiveState=") {
            if let Some(state) = line.strip_prefix("ActiveState=") {
                status.state = state.to_string()
            }
        } else if line.starts_with("MemoryCurrent=") {
            if let Some(memory) = line.strip_prefix("MemoryCurrent=") {
                status.memory = memory.parse().ok()
            }
        }
    }

    let status_output = Command::new("/usr/bin/systemctl")
        .arg("--user")
        .arg("status")
        .arg("go-sbot.service")
        .output()
        .unwrap();

    let service_status = str::from_utf8(&status_output.stdout).map_err(StatsError::Utf8String)?;

    // example of the output line we're looking for:
    // `Active: active (running) since Mon 2022-01-24 16:22:51 SAST; 4min 14s ago`

    for line in service_status.lines() {
        if line.contains("Active:") {
            let before_time = line.find(';');
            let after_time = line.find(" ago");
            if let (Some(start), Some(end)) = (before_time, after_time) {
                // extract the uptime / downtime from the `Active: ...` line
                // using the index of ';' + 2 and the index of " ago"
                let time = Some(&line[start + 2..end]);
                // if service is active then the `time` reading is uptime
                if status.state == "active" {
                    status.uptime = time.map(|t| t.to_string())
                // if service is inactive then the `time` reading is downtime
                } else if status.state == "inactive" {
                    status.downtime = time.map(|t| t.to_string())
                }
            }
        }
    }

    Ok(status)
}