//! OTP/1 — the opentracker wire protocol.
//!
//! One encrypted UDP datagram per report, no handshake, no connection state. A
//! cold TCP+TLS connection costs roughly ten round trips before the first byte
//! of payload, and a phone that sleeps between reports has a cold connection
//! nearly every time; a single datagram that survives the phone changing IP
//! mid-journey is the entire point of this protocol.
//!
//! This crate is the codec and nothing else: **no I/O, no async, no RNG, no
//! clock.** Nonces and timestamps are passed in by the caller. That is what
//! makes it fuzzable, property-testable, and able to emit reproducible golden
//! vectors — which are the contract the Kotlin implementation is checked
//! against, and the thing that stops a protocol change from silently bricking
//! installed apps.
//!
//! ## Shape of a datagram
//!
//! ```text
//! header[21] || ChaCha20Poly1305(K_dir, nonce, payload, aad = header)
//! ```
//!
//! ## Why there is no replay protection
//!
//! Timestamps are absolute and client-supplied, and the server stores points
//! under `UNIQUE(user_id, ts)` with `ON CONFLICT DO UPDATE`. A replayed
//! datagram therefore carries a timestamp that already exists and collapses
//! into the row already there — replay is idempotent *by construction*. An
//! attacker without the key cannot forge new positions and cannot create
//! duplicate rows, so a counter, a persisted ledger and a replay window would
//! all be state to maintain for no gain.
//!
//! ## Example
//!
//! ```
//! use otproto::{Header, Message, MsgType, Point, kdf, msg::Direction};
//!
//! let token_key = [0x11; 32];
//! let k_up = kdf::derive(&token_key, Direction::Up);
//! let nonce = [0x22; 12]; // in production: 12 fresh random bytes
//!
//! let msg = Message::Loc(vec![Point::new(1_785_000_042, 525_200_080, 134_050_000)]);
//! let datagram = otproto::seal_message(&k_up, 0x1122_3344_5566_7788, nonce, &msg);
//! assert_eq!(datagram.len(), 62);
//!
//! // The server peeks the header to choose a key, then opens.
//! let peeked = Header::peek(&datagram).unwrap();
//! assert_eq!(peeked.msg_type, MsgType::Loc);
//! let (_, back) = otproto::open_message(&k_up, &datagram).unwrap();
//! assert_eq!(back, msg);
//! ```

pub mod error;
pub mod frame;
pub mod kdf;
pub mod msg;
pub mod point;

pub use error::{DecodeError, ValidationError};
pub use frame::{
    HEADER_LEN, Header, MAX_DATAGRAM, MAX_REPLY, MIN_DATAGRAM, REVOKED_DATAGRAM_LEN, TAG_LEN,
    VERSION, datagram_len, fits_reply_budget, may_answer_unverified, open, open_message, seal,
    seal_message,
};
pub use kdf::{KEY_LEN, Key, revocation_key};
pub use msg::{
    Ack, AckFlags, Config, ConfigFlags, ConfigGet, Direction, Hello, HelloFlags, MAX_POINTS,
    Message, MsgType, NONCE_LEN, Nack, NackReason, Nonce, Ping, Pong, Profile, RevokeReason,
    Revoked,
};
pub use point::{Flags as PointFlags, POINT_LEN, Point};