//! [`FsOrchestratorWatcher`] — filesystem driving adapter for the orchestrator
//! protocol (ARCHITECTURE §14.3).
//!
//! An orchestrator agent drops a JSON request under
//! `<project_root>/.ideai/requests/<requester-id>/*.json`. This adapter watches
//! that tree, and for each request file:
//!
//! 1. parses + validates it into a [`domain::OrchestratorCommand`],
//! 2. dispatches it through the application's [`OrchestratorService`] (which calls
//!    the *same* use cases as the UI — IdeA stays the single source of truth for
//!    the agent lifecycle; the orchestrator never spawns a process itself),
//! 3. writes a sibling `<file>.response.json` (`ok` / error),
//! 4. removes the consumed request file.
//!
//! ## notify vs polling
//!
//! We use a **poll loop** as the primary trigger (a tokio interval re-scanning the
//! requests tree) and use [`notify`] purely to *wake* that loop early on a change.
//! Polling is the robust baseline: `notify`'s native back-ends behave
//! inconsistently across the platforms IdeA targets (inotify on Linux, ReadDirectoryChangesW
//! on Windows) and over network/WSL-mounted filesystems where an orchestrator's
//! project root may live. The poll loop guarantees eventual processing regardless;
//! notify just lowers latency. The per-file logic ([`process_request_file`]) is a
//! standalone async fn, unit-tested against a temp dir independently of the watch.

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

use application::OrchestratorService;
use domain::{DomainEvent, OrchestratorRequest, Project};
use serde::{Deserialize, Serialize};
use tokio::sync::mpsc;

/// Subdirectory (under `.ideai/`) the orchestrator drops request files into.
pub const REQUESTS_SUBDIR: &str = "requests";

/// How often the poll loop re-scans the requests tree when idle.
const POLL_INTERVAL_MS: u64 = 500;

/// The JSON response written next to a consumed request file.
///
/// Serialised camelCase to match the DTO convention used across IdeA's wire
/// formats. `ok` is the single boolean an orchestrator polls for; `detail` carries
/// a success summary and `error` the failure reason (mutually exclusive).
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "camelCase")]
pub struct OrchestratorResponse {
    /// Whether IdeA handled the request successfully.
    pub ok: bool,
    /// The action that was attempted (echoed back), when parseable.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub action: Option<String>,
    /// Human-readable success summary (`ok == true`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub detail: Option<String>,
    /// Human-readable failure reason (`ok == false`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub error: Option<String>,
}

impl OrchestratorResponse {
    fn success(action: String, detail: String) -> Self {
        Self {
            ok: true,
            action: Some(action),
            detail: Some(detail),
            error: None,
        }
    }
    fn failure(action: Option<String>, error: String) -> Self {
        Self {
            ok: false,
            action,
            detail: None,
            error: Some(error),
        }
    }
}

/// A running watcher; dropping it stops the background task.
pub struct OrchestratorWatchHandle {
    stop: mpsc::Sender<()>,
}

impl OrchestratorWatchHandle {
    /// Signals the watch loop to stop (best-effort; the task also stops when this
    /// handle is dropped).
    pub fn stop(&self) {
        let _ = self.stop.try_send(());
    }
}

/// Filesystem driving adapter that watches a project's `.ideai/requests/` tree.
pub struct FsOrchestratorWatcher;

impl FsOrchestratorWatcher {
    /// Starts watching `project`'s `.ideai/requests/` tree, dispatching every
    /// request file through `service`. Returns a handle that stops the watch when
    /// dropped (or via [`OrchestratorWatchHandle::stop`]).
    ///
    /// The optional `events` sink (a domain [`EventBus`](domain::ports::EventBus)
    /// publish closure) is invoked with an [`DomainEvent::OrchestratorRequestProcessed`]
    /// after each handled file so the presentation layer can surface orchestration
    /// activity. The actual cell/tab for `spawn_agent` opens off the
    /// [`DomainEvent::AgentLaunched`] the dispatch already publishes.
    ///
    /// Spawns onto the ambient Tokio runtime; never blocks the caller.
    #[must_use]
    pub fn start(
        project: Project,
        service: Arc<OrchestratorService>,
        events: Arc<dyn Fn(DomainEvent) + Send + Sync>,
    ) -> OrchestratorWatchHandle {
        let (stop_tx, mut stop_rx) = mpsc::channel::<()>(1);
        let requests_root = requests_root(&project);

        tokio::spawn(async move {
            // Poll loop. A notify watcher (best-effort) wakes us early; the
            // interval is the robust fallback.
            let (wake_tx, mut wake_rx) = mpsc::channel::<()>(8);
            let _notify_guard = spawn_notify(&requests_root, wake_tx);

            let mut interval =
                tokio::time::interval(std::time::Duration::from_millis(POLL_INTERVAL_MS));
            interval.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);

            loop {
                tokio::select! {
                    _ = stop_rx.recv() => break,
                    _ = interval.tick() => {}
                    _ = wake_rx.recv() => {}
                }
                scan_once(&requests_root, &project, &service, events.as_ref()).await;
            }
        });

        OrchestratorWatchHandle { stop: stop_tx }
    }
}

/// Resolves `<project_root>/.ideai/requests/`.
fn requests_root(project: &Project) -> PathBuf {
    Path::new(project.root.as_str())
        .join(".ideai")
        .join(REQUESTS_SUBDIR)
}

/// Spawns a best-effort `notify` watcher that forwards change notifications to
/// `wake`. Returns the watcher guard (kept alive by the caller); on any error
/// (e.g. the directory does not exist yet) it returns `None` and the poll loop
/// still covers correctness.
fn spawn_notify(root: &Path, wake: mpsc::Sender<()>) -> Option<notify::RecommendedWatcher> {
    use notify::{RecursiveMode, Watcher};

    // The directory may not exist yet; create it so notify has something to watch
    // and orchestrators have a stable drop target. Ignore failures — the poll loop
    // re-creates intent each scan.
    let _ = std::fs::create_dir_all(root);

    let mut watcher = notify::recommended_watcher(move |res: notify::Result<notify::Event>| {
        if res.is_ok() {
            let _ = wake.try_send(());
        }
    })
    .ok()?;
    watcher.watch(root, RecursiveMode::Recursive).ok()?;
    Some(watcher)
}

/// Scans the requests tree once, processing every `*.json` request file that is
/// not itself a `*.response.json`.
async fn scan_once(
    root: &Path,
    project: &Project,
    service: &OrchestratorService,
    publish: &(dyn Fn(DomainEvent) + Send + Sync),
) {
    let Ok(requesters) = std::fs::read_dir(root) else {
        return;
    };
    for requester in requesters.flatten() {
        let dir = requester.path();
        if !dir.is_dir() {
            continue;
        }
        let requester_id = requester.file_name().to_string_lossy().into_owned();
        let Ok(files) = std::fs::read_dir(&dir) else {
            continue;
        };
        for file in files.flatten() {
            let path = file.path();
            if !is_request_file(&path) {
                continue;
            }
            let outcome = process_request_file(&path, project, service).await;
            publish(DomainEvent::OrchestratorRequestProcessed {
                requester_id: requester_id.clone(),
                action: outcome.action.clone().unwrap_or_default(),
                ok: outcome.ok,
            });
        }
    }
}

/// Whether `path` is a request file to process: a `.json` that is not a
/// `.response.json` sibling we wrote ourselves.
fn is_request_file(path: &Path) -> bool {
    let name = path.file_name().and_then(|n| n.to_str()).unwrap_or_default();
    name.ends_with(".json") && !name.ends_with(".response.json")
}

/// Processes a single request file end to end: read → parse/validate → dispatch →
/// write `<file>.response.json` → delete the request file.
///
/// Always writes a response and removes the request (even on error) so a poisoned
/// request can never wedge the loop. Returns the [`OrchestratorResponse`] it wrote
/// (handy for tests and for the change event). Standalone (no watch) so it is
/// unit-testable against a temp directory.
pub async fn process_request_file(
    path: &Path,
    project: &Project,
    service: &OrchestratorService,
) -> OrchestratorResponse {
    let response = dispatch_file(path, project, service).await;
    write_response(path, &response);
    let _ = std::fs::remove_file(path);
    response
}

/// Reads + parses + validates + dispatches a request file, mapping every failure
/// to an [`OrchestratorResponse::failure`].
async fn dispatch_file(
    path: &Path,
    project: &Project,
    service: &OrchestratorService,
) -> OrchestratorResponse {
    let bytes = match std::fs::read(path) {
        Ok(b) => b,
        Err(e) => return OrchestratorResponse::failure(None, format!("read failed: {e}")),
    };
    let request: OrchestratorRequest = match serde_json::from_slice(&bytes) {
        Ok(r) => r,
        Err(e) => return OrchestratorResponse::failure(None, format!("invalid json: {e}")),
    };
    let action = request.action.clone();
    let command = match request.validate() {
        Ok(c) => c,
        Err(e) => return OrchestratorResponse::failure(Some(action), e.to_string()),
    };
    match service.dispatch(project, command).await {
        Ok(out) => OrchestratorResponse::success(action, out.detail),
        Err(e) => OrchestratorResponse::failure(Some(action), e.to_string()),
    }
}

/// Writes the response JSON next to the request file as `<file>.response.json`.
fn write_response(request_path: &Path, response: &OrchestratorResponse) {
    let response_path = response_path_for(request_path);
    if let Ok(json) = serde_json::to_vec_pretty(response) {
        let _ = std::fs::write(response_path, json);
    }
}

/// Derives `<file>.json` → `<file>.json.response.json` so the response is an
/// unambiguous sibling that `is_request_file` skips.
fn response_path_for(request_path: &Path) -> PathBuf {
    let mut name = request_path
        .file_name()
        .map(|n| n.to_string_lossy().into_owned())
        .unwrap_or_default();
    name.push_str(".response.json");
    request_path.with_file_name(name)
}