dynpatch-watcher 0.1.0

//! Configuration hot-reloading utilities

use crate::{FileWatcher, Result, WatchError};
use arc_swap::ArcSwap;
use serde::de::DeserializeOwned;
use std::fs;
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};
use tracing::{error, info, warn};

/// Trait for hot-reloadable configuration
pub trait HotConfig: DeserializeOwned + Send + Sync + 'static {
    /// Validate the configuration after loading
    fn validate(&self) -> std::result::Result<(), String> {
        Ok(())
    }
}

/// Configuration watcher that automatically reloads config on file changes
///
/// Features:
/// - Automatic reload on file changes
/// - Debouncing to prevent excessive reloads
/// - Validation before applying
/// - Atomic updates with arc-swap
/// - Error recovery (keeps previous config on failure)
pub struct ConfigWatcher<T: HotConfig> {
    config: Arc<ArcSwap<T>>,
    path: PathBuf,
    _watcher: FileWatcher,
    last_reload: Arc<Mutex<Instant>>,
    debounce_duration: Duration,
}

impl<T: HotConfig> ConfigWatcher<T> {
    /// Create a new config watcher with default debounce duration (500ms)
    pub fn new<P: AsRef<Path>>(path: P) -> Result<Self> {
        Self::with_debounce(path, Duration::from_millis(500))
    }

    /// Create a new config watcher with custom debounce duration
    ///
    /// Debouncing prevents excessive reloads when a file is modified multiple times
    /// in quick succession (common with text editors).
    pub fn with_debounce<P: AsRef<Path>>(path: P, debounce: Duration) -> Result<Self> {
        let path = path.as_ref().to_path_buf();
        let initial_config = Self::load_config(&path)?;
        
        // Validate initial config
        initial_config
            .validate()
            .map_err(|e| WatchError::ParseFailed(format!("Initial config validation failed: {}", e)))?;

        info!("Initial config loaded and validated from: {:?}", path);

        let config = Arc::new(ArcSwap::new(Arc::new(initial_config)));
        let config_clone = config.clone();
        let path_clone = path.clone();
        let last_reload = Arc::new(Mutex::new(Instant::now()));
        let last_reload_clone = last_reload.clone();
        let debounce_clone = debounce;

        let watcher = FileWatcher::new(&path, move |_| {
            // Debounce: check if enough time has passed since last reload
            {
                let mut last = last_reload_clone.lock().unwrap();
                let now = Instant::now();
                if now.duration_since(*last) < debounce_clone {
                    return; // Skip this reload, too soon
                }
                *last = now;
            }

            info!("Config file changed, reloading: {:?}", path_clone);
            
            match Self::load_config(&path_clone) {
                Ok(new_config) => {
                    // Validate before applying
                    if let Err(e) = new_config.validate() {
                        error!("Config validation failed, keeping previous config: {}", e);
                        return;
                    }
                    
                    config_clone.store(Arc::new(new_config));
                    info!("Config reloaded and validated successfully");
                }
                Err(e) => {
                    error!("Failed to reload config (keeping previous): {}", e);
                }
            }
        })?;

        Ok(Self {
            config,
            path,
            _watcher: watcher,
            last_reload,
            debounce_duration: debounce,
        })
    }

    /// Get the current configuration
    pub fn get(&self) -> Arc<T> {
        self.config.load_full()
    }

    /// Manually reload the configuration
    pub fn reload(&self) -> Result<()> {
        let new_config = Self::load_config(&self.path)?;
        new_config
            .validate()
            .map_err(|e| WatchError::ParseFailed(e))?;
        self.config.store(Arc::new(new_config));
        info!("Config manually reloaded");
        Ok(())
    }

    fn load_config(path: &Path) -> Result<T> {
        let content = fs::read_to_string(path)?;
        let extension = path.extension().and_then(|e| e.to_str());

        match extension {
            #[cfg(feature = "json")]
            Some("json") => serde_json::from_str(&content)
                .map_err(|e| WatchError::ParseFailed(e.to_string())),

            #[cfg(feature = "toml")]
            Some("toml") => toml::from_str(&content)
                .map_err(|e| WatchError::ParseFailed(e.to_string())),

            #[cfg(feature = "yaml")]
            Some("yaml") | Some("yml") => serde_yaml::from_str(&content)
                .map_err(|e| WatchError::ParseFailed(e.to_string())),

            _ => Err(WatchError::ParseFailed(format!(
                "Unsupported file extension: {:?}",
                extension
            ))),
        }
    }

    pub fn path(&self) -> &Path {
        &self.path
    }

    /// Get the debounce duration
    pub fn debounce_duration(&self) -> Duration {
        self.debounce_duration
    }

    /// Get the time since last reload
    pub fn time_since_last_reload(&self) -> Duration {
        let last = self.last_reload.lock().unwrap();
        Instant::now().duration_since(*last)
    }
}

/// Watch a configuration file and return a watcher
pub fn watch<T: HotConfig, P: AsRef<Path>>(path: P) -> Result<ConfigWatcher<T>> {
    ConfigWatcher::new(path)
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde::{Deserialize, Serialize};
    use tempfile::Builder;

    #[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
    struct TestConfig {
        value: i32,
        name: String,
    }

    impl HotConfig for TestConfig {}

    #[test]
    #[cfg(feature = "json")]
    fn test_config_watcher_json() {
        let temp = Builder::new()
            .suffix(".json")
            .tempfile()
            .unwrap();
        
        let config = TestConfig {
            value: 42,
            name: "test".to_string(),
        };
        
        std::fs::write(temp.path(), serde_json::to_string(&config).unwrap()).unwrap();

        let watcher = ConfigWatcher::<TestConfig>::new(temp.path()).unwrap();
        let loaded = watcher.get();
        
        assert_eq!(loaded.value, 42);
        assert_eq!(loaded.name, "test");
    }
}