//! Simple in-memory key/value store showing features of axum.
//!
//! Run with:
//!
//! ```not_rust
//! cargo run -p example-key-value-store
//! ```

use axum::{
    body::Bytes,
    error_handling::HandleErrorLayer,
    extract::{DefaultBodyLimit, Path, State},
    handler::Handler,
    http::StatusCode,
    response::IntoResponse,
    routing::{delete, get},
    Router,
};
use std::{
    borrow::Cow,
    collections::HashMap,
    sync::{Arc, RwLock},
    time::Duration,
};
use tower::{BoxError, ServiceBuilder};
use tower_http::{
    compression::CompressionLayer, limit::RequestBodyLimitLayer, trace::TraceLayer,
    validate_request::ValidateRequestHeaderLayer,
};
use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};

#[tokio::main]
async fn main() {
    tracing_subscriber::registry()
        .with(
            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| {
                format!("{}=debug,tower_http=debug", env!("CARGO_CRATE_NAME")).into()
            }),
        )
        .with(tracing_subscriber::fmt::layer())
        .init();

    let shared_state = SharedState::default();

    // Build our application by composing routes
    let app = Router::new()
        .route(
            "/{key}",
            // Add compression to `kv_get`
            get(kv_get.layer(CompressionLayer::new()))
                // But don't compress `kv_set`
                .post_service(
                    kv_set
                        .layer((
                            DefaultBodyLimit::disable(),
                            RequestBodyLimitLayer::new(1024 * 5_000 /* ~5mb */),
                        ))
                        .with_state(Arc::clone(&shared_state)),
                ),
        )
        .route("/keys", get(list_keys))
        // Nest our admin routes under `/admin`
        .nest("/admin", admin_routes())
        // Add middleware to all routes
        .layer(
            ServiceBuilder::new()
                // Handle errors from middleware
                .layer(HandleErrorLayer::new(handle_error))
                .load_shed()
                .concurrency_limit(1024)
                .timeout(Duration::from_secs(10))
                .layer(TraceLayer::new_for_http()),
        )
        .with_state(Arc::clone(&shared_state));

    // Run our app with hyper
    let listener = tokio::net::TcpListener::bind("127.0.0.1:3000")
        .await
        .unwrap();
    tracing::debug!("listening on {}", listener.local_addr().unwrap());
    axum::serve(listener, app).await.unwrap();
}

type SharedState = Arc<RwLock<AppState>>;

#[derive(Default)]
struct AppState {
    db: HashMap<String, Bytes>,
}

async fn kv_get(
    Path(key): Path<String>,
    State(state): State<SharedState>,
) -> Result<Bytes, StatusCode> {
    let db = &state.read().unwrap().db;

    if let Some(value) = db.get(&key) {
        Ok(value.clone())
    } else {
        Err(StatusCode::NOT_FOUND)
    }
}

async fn kv_set(Path(key): Path<String>, State(state): State<SharedState>, bytes: Bytes) {
    state.write().unwrap().db.insert(key, bytes);
}

async fn list_keys(State(state): State<SharedState>) -> String {
    let db = &state.read().unwrap().db;

    db.keys()
        .map(|key| key.to_string())
        .collect::<Vec<String>>()
        .join("\n")
}

fn admin_routes() -> Router<SharedState> {
    async fn delete_all_keys(State(state): State<SharedState>) {
        state.write().unwrap().db.clear();
    }

    async fn remove_key(Path(key): Path<String>, State(state): State<SharedState>) {
        state.write().unwrap().db.remove(&key);
    }

    Router::new()
        .route("/keys", delete(delete_all_keys))
        .route("/key/{key}", delete(remove_key))
        // Require bearer auth for all admin routes
        .layer(ValidateRequestHeaderLayer::bearer("secret-token"))
}

async fn handle_error(error: BoxError) -> impl IntoResponse {
    if error.is::<tower::timeout::error::Elapsed>() {
        return (StatusCode::REQUEST_TIMEOUT, Cow::from("request timed out"));
    }

    if error.is::<tower::load_shed::error::Overloaded>() {
        return (
            StatusCode::SERVICE_UNAVAILABLE,
            Cow::from("service is overloaded, try again later"),
        );
    }

    (
        StatusCode::INTERNAL_SERVER_ERROR,
        Cow::from(format!("Unhandled internal error: {error}")),
    )
}