/// File logger — writes structured log lines alongside the pretty terminal output.
use std::fs::{File, OpenOptions};
use std::io::Write;
use std::sync::{Mutex, OnceLock};

static LOG_FILE: OnceLock<Mutex<File>> = OnceLock::new();
static LOG_PATH: OnceLock<String> = OnceLock::new();

pub fn init() {
    let path = log_path();
    // Create parent dir if needed
    if let Some(parent) = std::path::Path::new(&path).parent() {
        let _ = std::fs::create_dir_all(parent);
    }
    match OpenOptions::new().create(true).append(true).open(&path) {
        Ok(f) => {
            LOG_PATH.set(path.clone()).ok();
            LOG_FILE.set(Mutex::new(f)).ok();
            write_line("INFO", "helios-remote started");
        }
        Err(e) => eprintln!("[logger] Failed to open log file {path}: {e}"),
    }
}

fn log_path() -> String {
    #[cfg(windows)]
    {
        let base = std::env::var("LOCALAPPDATA")
            .unwrap_or_else(|_| "C:\\Temp".to_string());
        format!("{base}\\helios-remote\\helios-remote.log")
    }
    #[cfg(not(windows))]
    {
        "/tmp/helios-remote.log".to_string()
    }
}

pub fn get_log_path() -> String {
    LOG_PATH.get().cloned().unwrap_or_else(log_path)
}

pub fn write_line(level: &str, msg: &str) {
    let now = chrono::Local::now().format("%Y-%m-%d %H:%M:%S");
    let line = format!("{now} [{level:<5}] {msg}\n");
    if let Some(mutex) = LOG_FILE.get() {
        if let Ok(mut f) = mutex.lock() {
            let _ = f.write_all(line.as_bytes());
        }
    }
}

/// Read the last `n` lines from the log file.
pub fn tail(n: u32) -> String {
    let path = get_log_path();
    let content = std::fs::read_to_string(&path).unwrap_or_default();
    let lines: Vec<&str> = content.lines().collect();
    let start = lines.len().saturating_sub(n as usize);
    lines[start..].join("\n")
}