// Copyright (C) 2024-2026 Whiterun LLC
//
// This software is licensed under the GNU Affero General Public License (AGPL), version 3.0 or later.
// A copy of the license can be found in the LICENSE file or at https://www.gnu.org/licenses/agpl-3.0.html

use std::sync::atomic::Ordering;
use std::sync::Arc;

use rocket::http::{ContentType, Status};
use rocket::response::{self, Responder};
use rocket::{get, Request, State};
use serde_json::json;

use crate::IbdState;

/// Custom responder that returns the appropriate status code based on health
pub struct HealthResult {
    healthy: bool,
    body: String,
}

impl<'r> Responder<'r, 'static> for HealthResult {
    fn respond_to(self, _request: &'r Request<'_>) -> response::Result<'static> {
        let status = if self.healthy {
            Status::Ok
        } else {
            Status::ServiceUnavailable
        };

        response::Response::build()
            .status(status)
            .header(ContentType::JSON)
            .sized_body(self.body.len(), std::io::Cursor::new(self.body))
            .ok()
    }
}

/// Health check endpoint for load balancer monitoring.
///
/// Returns HTTP 200 when the indexer is ready to serve requests,
/// or HTTP 503 when initial block download is in progress.
///
/// **Response when healthy (HTTP 200):**
/// ```json
/// {
///     "status": "healthy",
///     "indexed_height": 880000,
///     "chain_tip": 880000,
///     "version": "0.2.0"
/// }
/// ```
///
/// **Response when syncing (HTTP 503):**
/// ```json
/// {
///     "status": "syncing",
///     "indexed_height": 850000,
///     "chain_tip": 880000,
///     "version": "0.2.0"
/// }
/// ```
#[get("/health")]
pub fn health(ibd_state: &State<Arc<IbdState>>) -> HealthResult {
    let is_ready = ibd_state.initial_sync_complete.load(Ordering::Relaxed);
    let indexed_height = ibd_state.current_height.load(Ordering::Relaxed);
    let chain_tip = ibd_state.target_height.load(Ordering::Relaxed);

    let status = if is_ready { "healthy" } else { "syncing" };

    let body = json!({
        "status": status,
        "indexed_height": indexed_height,
        "chain_tip": chain_tip,
        "version": env!("CARGO_PKG_VERSION")
    })
    .to_string();

    HealthResult {
        healthy: is_ready,
        body,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use rocket::http::Status;
    use rocket::local::blocking::Client;
    use rocket::routes;
    use serde_json::Value;
    use std::sync::atomic::AtomicBool;
    use std::sync::atomic::AtomicU64;

    #[test]
    fn test_health_returns_503_during_ibd() {
        let ibd_state = Arc::new(IbdState {
            initial_sync_complete: AtomicBool::new(false),
            current_height: AtomicU64::new(850000),
            target_height: AtomicU64::new(880000),
            serve_during_ibd: false,
        });

        let rocket = rocket::build()
            .manage(ibd_state)
            .mount("/", routes![health]);

        let client = Client::tracked(rocket).expect("valid rocket instance");
        let response = client.get("/health").dispatch();

        assert_eq!(response.status(), Status::ServiceUnavailable);

        let body: Value = serde_json::from_str(&response.into_string().unwrap()).unwrap();
        assert_eq!(body["status"], "syncing");
        assert_eq!(body["indexed_height"], 850000);
        assert_eq!(body["chain_tip"], 880000);
        assert_eq!(body["version"], env!("CARGO_PKG_VERSION"));
    }

    #[test]
    fn test_health_returns_200_when_ready() {
        let ibd_state = Arc::new(IbdState {
            initial_sync_complete: AtomicBool::new(true),
            current_height: AtomicU64::new(880000),
            target_height: AtomicU64::new(880000),
            serve_during_ibd: false,
        });

        let rocket = rocket::build()
            .manage(ibd_state)
            .mount("/", routes![health]);

        let client = Client::tracked(rocket).expect("valid rocket instance");
        let response = client.get("/health").dispatch();

        assert_eq!(response.status(), Status::Ok);

        let body: Value = serde_json::from_str(&response.into_string().unwrap()).unwrap();
        assert_eq!(body["status"], "healthy");
        assert_eq!(body["indexed_height"], 880000);
        assert_eq!(body["chain_tip"], 880000);
        assert_eq!(body["version"], env!("CARGO_PKG_VERSION"));
    }
}