confex-core 0.1.0

use std::{
    ops::{Deref, DerefMut},
    path::PathBuf,
    sync::Arc,
};

use arc_swap::ArcSwap;
use serde::Serialize;

use crate::{
    config::ConfigSchema, deserialize::to_config_value, format::Format, value::ConfigValue,
};

#[cfg(feature = "hot-reload")]
use crate::error::LoadError;

#[derive(Debug)]
pub enum HotReloadError {
    Watch(String),
    Serialize(String),
    Io(std::io::Error),
    /// Failure during the initial config load before the watcher could start.
    Load(crate::error::LoadError),
}

impl std::fmt::Display for HotReloadError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Watch(msg) => write!(f, "failed to set up file watcher: {msg}"),
            Self::Serialize(msg) => write!(f, "failed to serialize config: {msg}"),
            Self::Io(e) => write!(f, "I/O error persisting config: {e}"),
            Self::Load(e) => write!(f, "failed to load initial config: {e}"),
        }
    }
}

impl std::error::Error for HotReloadError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Io(e) => Some(e),
            Self::Load(e) => Some(e),
            _ => None,
        }
    }
}

impl From<std::io::Error> for HotReloadError {
    fn from(e: std::io::Error) -> Self {
        Self::Io(e)
    }
}

impl From<crate::error::LoadError> for HotReloadError {
    fn from(e: crate::error::LoadError) -> Self {
        Self::Load(e)
    }
}

pub(crate) struct FileWriteBack {
    path: PathBuf,
    format: Arc<dyn Format + Send + Sync>,
}

impl FileWriteBack {
    fn persist(&self, value: &ConfigValue) -> Result<(), HotReloadError> {
        let bytes = self
            .format
            .serialize(value)
            .map_err(|e| HotReloadError::Serialize(e.to_string()))?;
        std::fs::write(&self.path, bytes)?;
        Ok(())
    }
}

/// Tuning options for the file watcher.
#[derive(Debug, Clone, Copy)]
pub struct WatchOptions {
    /// Quiet period after the last file event before reloading. Default: 200 ms.
    pub debounce: std::time::Duration,
}

impl Default for WatchOptions {
    fn default() -> Self {
        Self {
            debounce: std::time::Duration::from_millis(200),
        }
    }
}

/// Live, cloneable handle to a loaded config value.
///
/// Reads are lock-free via `ArcSwap`. Writes go through [`WriteGuard`], which
/// atomically updates the in-memory state on drop and optionally persists to
/// the config file (watcher mode only).
///
/// Clone the handle freely — all clones share the same live value.
pub struct ConfigHandle<T> {
    swap: Arc<ArcSwap<T>>,
    write_back: Option<Arc<FileWriteBack>>,
}

impl<T> Clone for ConfigHandle<T> {
    fn clone(&self) -> Self {
        Self {
            swap: Arc::clone(&self.swap),
            write_back: self.write_back.clone(),
        }
    }
}

impl<T: ConfigSchema> From<T> for ConfigHandle<T> {
    fn from(config: T) -> Self {
        Self {
            swap: Arc::new(ArcSwap::from_pointee(config)),
            write_back: None,
        }
    }
}

impl<T: ConfigSchema> ConfigHandle<T> {
    /// Lock-free snapshot of the current config. Equivalent to `Arc::clone` cost.
    #[must_use]
    pub fn read(&self) -> arc_swap::Guard<Arc<T>> {
        self.swap.load()
    }
}

impl<T: ConfigSchema + Clone + Serialize> ConfigHandle<T> {
    /// Write-back mode: no file watcher, but every [`WriteGuard`] drop persists to `path`.
    ///
    /// Use this when you want `config.write()` to auto-save without spinning up a
    /// hot-reload thread.
    #[must_use]
    pub fn write_back(
        initial: T,
        path: impl Into<std::path::PathBuf>,
        format: impl Format + Send + Sync + 'static,
    ) -> Self {
        Self {
            swap: Arc::new(ArcSwap::from_pointee(initial)),
            write_back: Some(Arc::new(FileWriteBack {
                path: path.into(),
                format: Arc::new(format),
            })),
        }
    }

    /// Return a write guard. On drop the guard:
    ///
    /// 1. Serializes the modified value and writes it to the config file (watcher mode).
    /// 2. Atomically swaps it into the `ArcSwap` so all readers see the new value.
    ///
    /// In manual mode only step 2 happens (no file path is stored).
    #[must_use]
    pub fn write(&self) -> WriteGuard<T> {
        let current = self.swap.load();
        WriteGuard {
            value: (**current).clone(),
            swap: Arc::clone(&self.swap),
            write_back: self.write_back.clone(),
        }
    }
}

/// Keeps the file watcher alive. Drop to stop watching.
#[cfg(feature = "hot-reload")]
pub struct WatcherHandle {
    _watcher: notify::RecommendedWatcher,
}

#[cfg(feature = "hot-reload")]
impl<T: ConfigSchema + Clone + Send + Sync + 'static> ConfigHandle<T> {
    /// Watcher mode: watches `path` for external changes and reloads atomically.
    ///
    /// `reload` is called on every detected change after the debounce window.
    /// If it fails the previous config is kept and the error is logged via `tracing`.
    ///
    /// # Errors
    ///
    /// Returns [`HotReloadError::Watch`] if the file watcher cannot be initialised.
    pub fn watch(
        initial: T,
        path: &std::path::Path,
        format: impl Format + Send + Sync + 'static,
        reload: impl Fn() -> Result<T, LoadError> + Send + Sync + 'static,
        options: WatchOptions,
    ) -> Result<(Self, WatcherHandle), HotReloadError> {
        let write_back = Some(Arc::new(FileWriteBack {
            path: path.to_path_buf(),
            format: Arc::new(format),
        }));
        let reload: Arc<dyn Fn() -> Result<T, LoadError> + Send + Sync> = Arc::new(reload);
        Self::spawn_watcher(initial, path, &reload, write_back, options.debounce)
    }

    /// Shared watcher setup used by both file-backed and redb-backed watch modes.
    pub(crate) fn spawn_watcher(
        initial: T,
        watch_path: &std::path::Path,
        reload: &Arc<dyn Fn() -> Result<T, LoadError> + Send + Sync>,
        write_back: Option<Arc<FileWriteBack>>,
        debounce: std::time::Duration,
    ) -> Result<(Self, WatcherHandle), HotReloadError> {
        use notify::{Config, RecursiveMode, Watcher as _};
        use std::sync::mpsc;

        let swap = Arc::new(ArcSwap::from_pointee(initial));
        let swap_bg = Arc::clone(&swap);
        let reload_bg = Arc::clone(reload);

        let (tx, rx) = mpsc::channel::<notify::Result<notify::Event>>();
        let mut watcher = notify::RecommendedWatcher::new(
            move |ev| {
                let _ = tx.send(ev);
            },
            Config::default(),
        )
        .map_err(|e| HotReloadError::Watch(e.to_string()))?;

        watcher
            .watch(watch_path, RecursiveMode::NonRecursive)
            .map_err(|e| HotReloadError::Watch(e.to_string()))?;

        std::thread::Builder::new()
            .name("confex-watcher".into())
            .spawn(move || watcher_loop(&rx, &swap_bg, &reload_bg, debounce))
            .map_err(HotReloadError::Io)?;

        Ok((
            Self { swap, write_back },
            WatcherHandle { _watcher: watcher },
        ))
    }
}

#[cfg(feature = "hot-reload")]
fn watcher_loop<T: Send + Sync + 'static>(
    rx: &std::sync::mpsc::Receiver<notify::Result<notify::Event>>,
    swap: &Arc<ArcSwap<T>>,
    reload: &Arc<dyn Fn() -> Result<T, LoadError> + Send + Sync>,
    debounce: std::time::Duration,
) {
    use std::sync::mpsc::RecvTimeoutError;

    loop {
        // Block until the first event for this change burst.
        match rx.recv() {
            Ok(Ok(_)) => {}
            Ok(Err(e)) => {
                tracing::warn!("watcher error: {e}");
                continue;
            }
            Err(_) => break,
        }
        // Drain additional events within the debounce window.
        loop {
            match rx.recv_timeout(debounce) {
                Ok(_) => {}
                Err(RecvTimeoutError::Timeout) => break,
                Err(RecvTimeoutError::Disconnected) => return,
            }
        }
        match reload() {
            Ok(cfg) => {
                swap.store(Arc::new(cfg));
                tracing::debug!("config hot-reloaded");
            }
            Err(e) => {
                tracing::warn!("hot-reload failed, keeping previous config: {e}");
            }
        }
    }
}

/// Per-source entry for selective hot-reload.
///
/// Only the source whose `watch_paths` match the event path is re-collected;
/// all other entries reuse their cached `ConfigValue`.
#[cfg(feature = "hot-reload")]
pub(crate) struct SelectiveEntry {
    pub(crate) source: std::sync::Arc<dyn crate::source::Source + Send + Sync>,
    pub(crate) cache: std::sync::Mutex<ConfigValue>,
    pub(crate) watch_paths: Vec<std::path::PathBuf>,
}

#[cfg(feature = "hot-reload")]
impl<T: ConfigSchema + Clone + Send + Sync + 'static> ConfigHandle<T> {
    /// Selective-reload watcher: watches all paths declared by watchable sources
    /// and re-collects only the source that actually changed.
    pub(crate) fn spawn_selective_watcher(
        initial: T,
        initial_merged: ConfigValue,
        entries: Vec<SelectiveEntry>,
        strategies: crate::merge::FieldStrategies,
        transform: std::sync::Arc<dyn Fn(ConfigValue) -> Result<T, LoadError> + Send + Sync>,
        debounce: std::time::Duration,
    ) -> Result<(Self, WatcherHandle), HotReloadError> {
        use notify::{Config, RecursiveMode, Watcher as _};
        use std::{collections::HashSet, path::PathBuf, sync::mpsc};

        let swap = std::sync::Arc::new(arc_swap::ArcSwap::from_pointee(initial));
        let swap_bg = std::sync::Arc::clone(&swap);

        let (tx, rx) = mpsc::channel::<notify::Result<notify::Event>>();
        let mut watcher = notify::RecommendedWatcher::new(
            move |ev| {
                let _ = tx.send(ev);
            },
            Config::default(),
        )
        .map_err(|e| HotReloadError::Watch(e.to_string()))?;

        let mut registered: HashSet<PathBuf> = HashSet::new();
        for entry in &entries {
            for path in &entry.watch_paths {
                if registered.insert(path.clone()) {
                    watcher
                        .watch(path, RecursiveMode::NonRecursive)
                        .map_err(|e| HotReloadError::Watch(e.to_string()))?;
                }
            }
        }

        std::thread::Builder::new()
            .name("confex-selective-watcher".into())
            .spawn(move || {
                selective_watcher_loop(
                    rx,
                    swap_bg,
                    entries,
                    initial_merged,
                    strategies,
                    transform,
                    debounce,
                );
            })
            .map_err(HotReloadError::Io)?;

        Ok((
            Self {
                swap,
                write_back: None,
            },
            WatcherHandle { _watcher: watcher },
        ))
    }
}

#[cfg(feature = "hot-reload")]
#[allow(clippy::needless_pass_by_value)]
fn selective_watcher_loop<T: Send + Sync + 'static>(
    rx: std::sync::mpsc::Receiver<notify::Result<notify::Event>>,
    swap: std::sync::Arc<arc_swap::ArcSwap<T>>,
    entries: Vec<SelectiveEntry>,
    mut last_raw: ConfigValue,
    strategies: crate::merge::FieldStrategies,
    transform: std::sync::Arc<dyn Fn(ConfigValue) -> Result<T, LoadError> + Send + Sync>,
    debounce: std::time::Duration,
) {
    use std::{collections::HashSet, path::PathBuf, sync::mpsc::RecvTimeoutError};

    loop {
        let first_ev = match rx.recv() {
            Ok(Ok(ev)) => ev,
            Ok(Err(e)) => {
                tracing::warn!("watcher error: {e}");
                continue;
            }
            Err(_) => break,
        };

        let mut affected: HashSet<PathBuf> = first_ev.paths.into_iter().collect();

        loop {
            match rx.recv_timeout(debounce) {
                Ok(Ok(ev)) => {
                    affected.extend(ev.paths);
                }
                Ok(Err(e)) => tracing::warn!("watcher error: {e}"),
                Err(RecvTimeoutError::Timeout) => break,
                Err(RecvTimeoutError::Disconnected) => return,
            }
        }

        let mut any_updated = false;
        for entry in &entries {
            let matches = entry
                .watch_paths
                .iter()
                .any(|wp| affected.iter().any(|ap| ap == wp || ap.starts_with(wp)));
            if !matches {
                continue;
            }
            match entry.source.collect() {
                Ok(new_cache) => {
                    *entry
                        .cache
                        .lock()
                        .expect("selective-reload cache mutex should never be poisoned") =
                        new_cache;
                    any_updated = true;
                }
                Err(e) => tracing::warn!("failed to re-collect source on change: {e}"),
            }
        }

        if !any_updated {
            continue;
        }

        let mut new_merged = ConfigValue::Table(std::collections::BTreeMap::new());
        for entry in &entries {
            let cache = entry
                .cache
                .lock()
                .expect("selective-reload cache mutex should never be poisoned")
                .clone();
            new_merged = crate::merge::merge(new_merged, cache, strategies);
        }

        // Skip the swap when the merged result is unchanged (self-write suppression).
        if new_merged == last_raw {
            continue;
        }
        last_raw = new_merged.clone();

        match transform(new_merged) {
            Ok(cfg) => {
                swap.store(std::sync::Arc::new(cfg));
                tracing::debug!("config selectively hot-reloaded");
            }
            Err(e) => {
                tracing::warn!("selective hot-reload transform failed, keeping previous: {e}");
            }
        }
    }
}

/// Holds a mutable snapshot of `T`. On drop:
///
/// 1. If a file path is configured, serializes and writes to disk.
/// 2. Atomically swaps the new value into the live handle.
///
/// Disk errors are logged via `tracing::error!`; the in-memory swap always happens.
pub struct WriteGuard<T: ConfigSchema + Clone + Serialize> {
    value: T,
    swap: Arc<ArcSwap<T>>,
    write_back: Option<Arc<FileWriteBack>>,
}

impl<T: ConfigSchema + Clone + Serialize> Deref for WriteGuard<T> {
    type Target = T;
    fn deref(&self) -> &T {
        &self.value
    }
}

impl<T: ConfigSchema + Clone + Serialize> DerefMut for WriteGuard<T> {
    fn deref_mut(&mut self) -> &mut T {
        &mut self.value
    }
}

impl<T: ConfigSchema + Clone + Serialize> Drop for WriteGuard<T> {
    fn drop(&mut self) {
        if let Some(wb) = &self.write_back {
            match to_config_value(&self.value) {
                Ok(cv) => {
                    if let Err(e) = wb.persist(&cv) {
                        tracing::error!("failed to write config to disk: {e}");
                    }
                }
                Err(e) => tracing::error!("failed to serialize config for disk write: {e}"),
            }
        }
        self.swap.store(Arc::new(self.value.clone()));
    }
}

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

    use super::*;
    use crate::{config::ConfigSchema, merge::FieldStrategies};

    #[derive(Debug, Clone, Serialize, Deserialize)]
    struct Cfg {
        value: i64,
    }

    impl ConfigSchema for Cfg {
        const APP_NAME: &'static str = "test";
        const SCHEMA_VERSION: u32 = 1;
        fn field_strategies() -> FieldStrategies {
            &[]
        }
        fn encrypted_fields() -> &'static [&'static str] {
            &[]
        }
    }

    #[test]
    fn read_returns_initial_value() {
        let h = ConfigHandle::from(Cfg { value: 42 });
        assert_eq!(h.read().value, 42);
    }

    #[test]
    fn write_guard_updates_in_memory_on_drop() {
        let h = ConfigHandle::from(Cfg { value: 1 });
        {
            let mut g = h.write();
            (*g).value = 99;
        }
        assert_eq!(h.read().value, 99);
    }

    #[test]
    fn cloned_handle_sees_write() {
        let h = ConfigHandle::from(Cfg { value: 0 });
        let h2 = h.clone();
        {
            let mut g = h.write();
            (*g).value = 7;
        }
        assert_eq!(h2.read().value, 7);
    }

    #[cfg(feature = "hot-reload")]
    #[test]
    fn selective_watcher_only_recollects_changed_source() {
        use crate::{
            config::ConfigLoader,
            format::TomlFormat,
            handle::WatchOptions,
            source::{EnvSource, FileSource},
        };
        use std::{thread, time::Duration};

        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("config.toml");
        std::fs::write(&path, "value = 10\n").unwrap();

        // EnvSource is passive; FileSource is watchable via with_watched_source.
        let (handle, _watcher) = ConfigLoader::<Cfg>::default()
            .with_source(EnvSource::from("CONFEX_TEST_SEL"))
            .with_watched_source(FileSource::new(vec![path.clone()], TomlFormat))
            .watch_auto(WatchOptions::default())
            .unwrap();

        assert_eq!(handle.read().value, 10);

        std::fs::write(&path, "value = 77\n").unwrap();
        thread::sleep(Duration::from_millis(600));

        assert_eq!(handle.read().value, 77);
    }

    #[cfg(feature = "hot-reload")]
    #[test]
    fn watcher_reloads_on_file_change() {
        use crate::{
            format::TomlFormat,
            source::{FileSource, Source},
        };
        use std::{thread, time::Duration};

        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("config.toml");
        std::fs::write(&path, "value = 1\n").unwrap();

        let path_clone = path.clone();
        let (handle, _watcher) = ConfigHandle::watch(
            Cfg { value: 1 },
            &path,
            TomlFormat,
            move || {
                let src = FileSource::new(vec![path_clone.clone()], TomlFormat);
                let cv = src.collect()?;
                Ok(serde::de::Deserialize::deserialize(
                    crate::deserialize::ConfigValueDeserializer(cv),
                )?)
            },
            WatchOptions::default(),
        )
        .unwrap();

        assert_eq!(handle.read().value, 1);

        std::fs::write(&path, "value = 42\n").unwrap();
        // Wait for debounce + watcher to fire.
        thread::sleep(Duration::from_millis(600));

        assert_eq!(handle.read().value, 42);
    }
}