//! Background Scrub Scheduler
//!
//! Automatically runs scrub operations at regular intervals.
//! Similar to ZFS `zpool scrub` and Btrfs periodic scrub.

use std::sync::Arc;
use std::path::PathBuf;

use super::{VfsBackend, VfsError};
use super::checksum::{scrub_all, ScrubResult};

pub struct ScrubSchedulerConfig {
    pub interval_secs: u64,       // Default: 3600 (1 hour)
    pub scrub_on_startup: bool,   // Default: true
    pub repair_enabled: bool,     // Default: true
    pub max_files_per_run: usize, // Default: 100 (limit per run)
}

impl Default for ScrubSchedulerConfig {
    fn default() -> Self {
        Self {
            interval_secs: 3600,
            scrub_on_startup: true,
            repair_enabled: true,
            max_files_per_run: 100,
        }
    }
}

pub struct ScrubScheduler {
    backend: Arc<dyn VfsBackend>,
    root_path: PathBuf,
    config: ScrubSchedulerConfig,
    running: bool,
    last_scrub_time: Option<u64>,
    scrub_count: usize,
}

impl ScrubScheduler {
    pub fn new(
        backend: Arc<dyn VfsBackend>,
        root_path: PathBuf,
        config: ScrubSchedulerConfig,
    ) -> Self {
        Self {
            backend,
            root_path,
            config,
            running: false,
            last_scrub_time: None,
            scrub_count: 0,
        }
    }

    pub fn with_defaults(
        backend: Arc<dyn VfsBackend>,
        root_path: PathBuf,
    ) -> Self {
        Self::new(backend, root_path, ScrubSchedulerConfig::default())
    }

    pub fn start(&mut self) {
        self.running = true;
    }

    pub fn stop(&mut self) {
        self.running = false;
    }

    pub fn is_running(&self) -> bool {
        self.running
    }

    pub fn get_last_scrub_time(&self) -> Option<u64> {
        self.last_scrub_time
    }

    pub fn get_scrub_count(&self) -> usize {
        self.scrub_count
    }

    pub fn should_run_now(&self) -> bool {
        self.running && self.should_run_based_on_interval()
    }

    fn should_run_based_on_interval(&self) -> bool {
        if self.last_scrub_time.is_none() {
            return self.config.scrub_on_startup;
        }
        
        let now = current_time_secs();
        let last = self.last_scrub_time.unwrap();
        now - last >= self.config.interval_secs
    }

    pub fn run_once(&mut self) -> Result<Vec<ScrubResult>, VfsError> {
        if !self.running {
            return Ok(vec![]);
        }
        
        let results = scrub_all(
            self.backend.as_ref(),
            &self.root_path,
            self.config.repair_enabled,
        )?;
        
        self.last_scrub_time = Some(current_time_secs());
        self.scrub_count += 1;
        
        Ok(results)
    }

    pub fn get_stats(&self) -> ScrubStats {
        ScrubStats {
            running: self.running,
            scrub_count: self.scrub_count,
            last_scrub_time: self.last_scrub_time,
            interval_secs: self.config.interval_secs,
            next_scrub_time: self.calculate_next_scrub_time(),
        }
    }

    fn calculate_next_scrub_time(&self) -> Option<u64> {
        if !self.running {
            return None;
        }
        
        let last = self.last_scrub_time.unwrap_or(current_time_secs());
        Some(last + self.config.interval_secs)
    }
}

fn current_time_secs() -> u64 {
    use std::time::{SystemTime, UNIX_EPOCH};
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0)
}

#[derive(Debug)]
pub struct ScrubStats {
    pub running: bool,
    pub scrub_count: usize,
    pub last_scrub_time: Option<u64>,
    pub interval_secs: u64,
    pub next_scrub_time: Option<u64>,
}

impl ScrubStats {
    pub fn next_scrub_in_secs(&self) -> Option<u64> {
        if !self.running {
            return None;
        }
        
        let now = current_time_secs();
        let next = self.next_scrub_time?;
        
        if next > now {
            Some(next - now)
        } else {
            Some(0)
        }
    }

    pub fn format_last_scrub(&self) -> String {
        match self.last_scrub_time {
            None => "Never".to_string(),
            Some(t) => format_timestamp(t),
        }
    }

    pub fn format_next_scrub(&self) -> String {
        match self.next_scrub_time {
            None => "Not scheduled".to_string(),
            Some(t) => format_timestamp(t),
        }
    }
}

fn format_timestamp(secs: u64) -> String {
    use chrono::{Utc, TimeZone};
    Utc.timestamp_opt(secs as i64, 0)
        .single()
        .map(|dt| dt.format("%Y-%m-%d %H:%M:%S UTC").to_string())
        .unwrap_or_else(|| format!("{} seconds since epoch", secs))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_default_config() {
        let config = ScrubSchedulerConfig::default();
        assert_eq!(config.interval_secs, 3600);
        assert!(config.scrub_on_startup);
        assert!(config.repair_enabled);
        assert_eq!(config.max_files_per_run, 100);
    }

    #[test]
    fn test_scheduler_start_stop() {
        let backend: Arc<dyn VfsBackend> = Arc::new(super::super::local_fs::LocalFs::new());
        let mut scheduler = ScrubScheduler::with_defaults(backend, PathBuf::from("/tmp"));
        
        assert!(!scheduler.is_running());
        scheduler.start();
        assert!(scheduler.is_running());
        scheduler.stop();
        assert!(!scheduler.is_running());
    }

    #[test]
    fn test_scrub_stats() {
        let now = current_time_secs();
        let stats = ScrubStats {
            running: true,
            scrub_count: 5,
            last_scrub_time: Some(now - 3600),
            interval_secs: 3600,
            next_scrub_time: Some(now), // Next scrub is now
        };
        
        assert!(stats.running);
        assert_eq!(stats.scrub_count, 5);
        
        // When next_scrub_time is now, next_scrub_in_secs should be 0
        let next_in = stats.next_scrub_in_secs();
        assert!(next_in.unwrap_or(999) <= 10); // Allow 10 seconds tolerance
    }

    #[test]
    fn test_format_timestamp() {
        let formatted = format_timestamp(1609459200); // 2021-01-01 00:00:00 UTC
        assert!(formatted.contains("2021"));
    }

    #[test]
    fn test_should_run_on_startup() {
        let backend: Arc<dyn VfsBackend> = Arc::new(super::super::local_fs::LocalFs::new());
        let mut scheduler = ScrubScheduler::with_defaults(backend, PathBuf::from("/tmp"));
        
        scheduler.start();
        assert!(scheduler.should_run_now()); // scrub_on_startup = true
        
        scheduler.last_scrub_time = Some(current_time_secs());
        assert!(!scheduler.should_run_now()); // Just ran, interval not elapsed
    }

    #[test]
    fn test_should_run_after_interval() {
        let backend: Arc<dyn VfsBackend> = Arc::new(super::super::local_fs::LocalFs::new());
        let config = ScrubSchedulerConfig {
            interval_secs: 3600,
            scrub_on_startup: false,
            repair_enabled: true,
            max_files_per_run: 100,
        };
        let mut scheduler = ScrubScheduler::new(backend, PathBuf::from("/tmp"), config);
        
        scheduler.start();
        assert!(!scheduler.should_run_now()); // scrub_on_startup = false
        
        scheduler.last_scrub_time = Some(current_time_secs() - 3601);
        assert!(scheduler.should_run_now()); // Interval elapsed
    }
}