//! mtgc-server — keeps each user's library so their devices can sync it.
//!
//! The server is deliberately dumb about libraries: it stores one versioned
//! document per user and accepts a write only when the writer names the
//! version it is replacing. All merging happens on the devices (see
//! `mtgc_core::sync::remote`), which is what lets them keep working offline and
//! keeps this side small enough to trust.
//!
//! Sign-in always happens in the browser, on pages this server serves, and
//! ends by handing the app a long-lived token for that one device. Passwords
//! therefore never pass through the app, and the app needs no knowledge of
//! which sign-in methods a server offers.

pub mod auth;
pub mod config;
pub mod db;
mod library;
mod pages;

use std::sync::{Arc, Mutex, MutexGuard};

use axum::http::StatusCode;
use axum::response::{IntoResponse, Response};
use axum::routing::{delete, get, post};
use axum::{Json, Router};
use base64::Engine;
use rusqlite::Connection;
use sha2::{Digest, Sha256};

pub use config::Config;

/// Largest library document accepted. A large collection serialises to a few
/// hundred kilobytes, so this leaves an order of magnitude of headroom while
/// still bounding what one request can make the server hold.
pub const MAX_BODY_BYTES: usize = 16 * 1024 * 1024;

#[derive(Clone)]
pub struct AppState(Arc<Inner>);

pub struct Inner {
    pub config: Config,
    db: Mutex<Connection>,
    pub(crate) local: auth::local::LocalAuth,
    pub(crate) oidc: Option<auth::oidc::Oidc>,
}

impl AppState {
    pub fn new(config: Config, conn: Connection) -> anyhow::Result<Self> {
        let oidc = config.oidc.clone().map(auth::oidc::Oidc::new).transpose()?;
        Ok(Self(Arc::new(Inner {
            config,
            db: Mutex::new(conn),
            local: auth::local::LocalAuth::new(),
            oidc,
        })))
    }

    pub fn config(&self) -> &Config {
        &self.0.config
    }

    /// The database. Never hold this across an `.await`.
    pub fn db(&self) -> MutexGuard<'_, Connection> {
        // A panic while holding the lock leaves nothing half-done that SQLite's
        // own transactions don't already roll back, so carry on.
        self.0.db.lock().unwrap_or_else(|e| e.into_inner())
    }
}

pub fn router(state: AppState) -> Router {
    Router::new()
        .route("/healthz", get(|| async { "ok" }))
        .route("/api/info", get(info))
        .route("/api/library", get(library::get_library).put(library::put_library))
        .route("/api/me", get(auth::me))
        .route("/api/devices/{id}", delete(auth::revoke_device))
        .route("/auth/start", get(auth::start))
        .route("/auth/password", post(auth::local::submit))
        .route("/auth/oidc", get(auth::oidc::begin))
        .route("/auth/callback", get(auth::oidc::callback))
        .route("/auth/token", post(auth::token))
        .route("/auth/logout", post(auth::logout))
        .layer(axum::extract::DefaultBodyLimit::max(MAX_BODY_BYTES))
        .with_state(state)
}

/// Unauthenticated, so the app can check that an address really is an mtgc
/// server before sending the user's browser there.
async fn info(axum::extract::State(state): axum::extract::State<AppState>) -> Json<serde_json::Value> {
    let c = state.config();
    Json(serde_json::json!({
        "server": "mtgc",
        "api": 1,
        "local_auth": c.local_auth,
        "oidc": c.oidc.as_ref().map(|o| o.display_name.clone()),
    }))
}

/// An error answered as `{"error": "..."}` with a status code.
#[derive(Debug)]
pub struct ApiError(pub StatusCode, pub String);

impl ApiError {
    pub fn new(status: StatusCode, msg: impl Into<String>) -> Self {
        Self(status, msg.into())
    }

    pub fn unauthorized() -> Self {
        Self::new(StatusCode::UNAUTHORIZED, "not signed in")
    }
}

impl IntoResponse for ApiError {
    fn into_response(self) -> Response {
        (self.0, Json(serde_json::json!({ "error": self.1 }))).into_response()
    }
}

impl From<rusqlite::Error> for ApiError {
    fn from(e: rusqlite::Error) -> Self {
        tracing::error!("database: {e}");
        Self::new(StatusCode::INTERNAL_SERVER_ERROR, "internal error")
    }
}

pub(crate) fn now() -> i64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_secs() as i64)
        .unwrap_or(0)
}

fn random_bytes<const N: usize>() -> [u8; N] {
    let mut buf = [0u8; N];
    getrandom::fill(&mut buf).expect("the OS random number generator failed");
    buf
}

pub(crate) fn random_hex(bytes: usize) -> String {
    let buf: [u8; 32] = random_bytes();
    hex(&buf[..bytes.min(32)])
}

/// A 256-bit secret, URL-safe.
pub(crate) fn random_token() -> String {
    base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(random_bytes::<32>())
}

/// Tokens and codes are stored only as hashes, so a leaked database can't be
/// used to impersonate a device. SHA-256 rather than a password hash because
/// they are already 256 random bits — there is nothing to brute-force.
pub(crate) fn sha256_hex(s: &str) -> String {
    hex(&Sha256::digest(s.as_bytes()))
}

fn hex(bytes: &[u8]) -> String {
    bytes.iter().map(|b| format!("{b:02x}")).collect()
}