/// File watcher: monitors a directory for new files and auto-ingests them.
/// Drop a CSV, JSON, PDF, or text file → auto-detected → Parquet → queryable.
/// Processed files are moved to a "processed/" subdirectory.

use std::path::{Path, PathBuf};
use std::sync::Arc;
use std::time::Duration;
use tokio::time;

use catalogd::registry::Registry;
use object_store::ObjectStore;

use crate::pipeline;

/// Watch config.
pub struct WatchConfig {
    pub watch_dir: PathBuf,
    pub processed_dir: PathBuf,
    pub failed_dir: PathBuf,
    pub poll_interval: Duration,
}

impl Default for WatchConfig {
    fn default() -> Self {
        Self {
            watch_dir: PathBuf::from("./inbox"),
            processed_dir: PathBuf::from("./inbox/processed"),
            failed_dir: PathBuf::from("./inbox/failed"),
            poll_interval: Duration::from_secs(10),
        }
    }
}

/// Start the file watcher as a background task.
pub fn spawn_watcher(
    config: WatchConfig,
    store: Arc<dyn ObjectStore>,
    registry: Registry,
) -> tokio::task::JoinHandle<()> {
    // Create directories
    std::fs::create_dir_all(&config.watch_dir).ok();
    std::fs::create_dir_all(&config.processed_dir).ok();
    std::fs::create_dir_all(&config.failed_dir).ok();

    tracing::info!("file watcher started: watching {}", config.watch_dir.display());

    tokio::spawn(async move {
        let mut interval = time::interval(config.poll_interval);
        loop {
            interval.tick().await;
            if let Err(e) = process_inbox(&config, &store, &registry).await {
                tracing::error!("watcher error: {e}");
            }
        }
    })
}

/// Scan inbox directory and process any new files.
async fn process_inbox(
    config: &WatchConfig,
    store: &Arc<dyn ObjectStore>,
    registry: &Registry,
) -> Result<(), String> {
    let entries = std::fs::read_dir(&config.watch_dir)
        .map_err(|e| format!("can't read inbox: {e}"))?;

    for entry in entries {
        let entry = match entry {
            Ok(e) => e,
            Err(_) => continue,
        };

        let path = entry.path();

        // Skip directories and hidden files. Bind filename once via
        // let-else so the subsequent use is unwrap-free — previous
        // version relied on a map_or guard above + an .unwrap() here
        // being consistent, which is a fragile invariant.
        if path.is_dir() { continue; }
        let Some(fn_os) = path.file_name() else { continue; };
        let filename = fn_os.to_string_lossy().to_string();
        if filename.starts_with('.') { continue; }
        tracing::info!("watcher: found new file '{}'", filename);

        // Read file
        let content = match std::fs::read(&path) {
            Ok(c) => c,
            Err(e) => {
                tracing::error!("watcher: can't read '{}': {e}", filename);
                move_file(&path, &config.failed_dir.join(&filename));
                continue;
            }
        };

        // Ingest
        match pipeline::ingest_file(&filename, &content, None, store, registry).await {
            Ok(result) => {
                if result.deduplicated {
                    tracing::info!("watcher: '{}' already ingested, skipping", filename);
                } else {
                    tracing::info!("watcher: ingested '{}' → {} ({} rows, {} cols)",
                        filename, result.dataset_name, result.rows, result.columns);
                }
                // Move to processed
                move_file(&path, &config.processed_dir.join(&filename));
            }
            Err(e) => {
                tracing::error!("watcher: failed to ingest '{}': {e}", filename);
                move_file(&path, &config.failed_dir.join(&filename));
            }
        }
    }

    Ok(())
}

fn move_file(from: &Path, to: &Path) {
    if let Err(e) = std::fs::rename(from, to) {
        // rename fails across filesystems, try copy+delete
        if let Err(e2) = std::fs::copy(from, to).and_then(|_| std::fs::remove_file(from)) {
            tracing::warn!("can't move {} → {}: {e}, copy failed: {e2}", from.display(), to.display());
        }
    }
}