oximedia-net 0.1.3

//! WHEP (WebRTC-HTTP Egress Protocol) client signaling.
//!
//! WHEP (draft-ietf-wish-whep) is the subscriber/playback counterpart to
//! WHIP.  A client sends an SDP offer via HTTP POST to the WHEP endpoint;
//! the server replies with an SDP answer.  The session is identified by the
//! `Location` header returned in the 201 response.
//!
//! This module provides:
//!
//! - [`WhepConfig`] — endpoint URL and optional bearer token
//! - [`WhepSession`] — tracks one WHEP session: SDP offer, optional answer
//! - [`WhepClient`] — creates sessions, formats HTTP request bodies
//!
//! All operations are **synchronous** (no I/O) — this module generates and
//! processes SDP payloads; actual HTTP transport is handled by the caller.
//!
//! # Example
//!
//! ```
//! use oximedia_net::whep_client::{WhepClient, WhepConfig};
//!
//! let config = WhepConfig {
//!     endpoint: "https://media.example.com/whep/live".to_owned(),
//!     bearer_token: Some("secret-token".to_owned()),
//! };
//!
//! let client = WhepClient::new(config);
//! let mut session = client.create_offer();
//!
//! // Simulate receiving an answer from the server
//! client.process_answer(&mut session, "v=0\r\no=- 0 0 IN IP4 0.0.0.0\r\n".to_owned());
//!
//! let body = WhepClient::format_whep_request(&session);
//! assert!(body.contains("application/sdp"));
//! ```

use std::fmt::Write as FmtWrite;

// ─── ICE credential helpers ───────────────────────────────────────────────────

/// Deterministic pseudo-random ICE ufrag derived from a seed.
fn derive_ice_ufrag(seed: &str) -> String {
    let mut h: u32 = 0x811c_9dc5;
    for b in seed.as_bytes() {
        h ^= *b as u32;
        h = h.wrapping_mul(0x0100_0193);
    }
    let chars: &[u8] = b"abcdefghijklmnopqrstuvwxyz0123456789";
    let len = chars.len() as u32;
    (0..4)
        .map(|i| chars[((h >> (i * 8)) % len) as usize] as char)
        .collect()
}

/// Deterministic pseudo-random ICE password derived from a seed.
fn derive_ice_pwd(seed: &str) -> String {
    let mut h: u64 = 0xcbf2_9ce4_8422_2325_u64;
    for b in seed.as_bytes() {
        h ^= *b as u64;
        h = h.wrapping_mul(0x0000_0100_0000_01b3_u64);
    }
    let chars: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    let len = chars.len() as u64;
    (0u64..24)
        .map(|i| {
            let mixed = h
                .wrapping_add(i.wrapping_mul(6_364_136_223_846_793_005_u64))
                .wrapping_mul((i + 1).wrapping_mul(2_862_933_555_777_941_757_u64));
            chars[((mixed >> 33) % len) as usize] as char
        })
        .collect()
}

/// Monotonic counter for session IDs (module-level, wrapping).
fn next_session_id() -> u64 {
    use std::sync::atomic::{AtomicU64, Ordering};
    static COUNTER: AtomicU64 = AtomicU64::new(1);
    COUNTER.fetch_add(1, Ordering::Relaxed)
}

// ─── WhepConfig ───────────────────────────────────────────────────────────────

/// Configuration for a WHEP egress client.
#[derive(Debug, Clone)]
pub struct WhepConfig {
    /// WHEP endpoint URL (HTTP POST target for SDP offer).
    pub endpoint: String,
    /// Optional bearer token for `Authorization: Bearer …` header.
    pub bearer_token: Option<String>,
}

impl WhepConfig {
    /// Create a minimal WHEP config with no authentication.
    #[must_use]
    pub fn new(endpoint: impl Into<String>) -> Self {
        Self {
            endpoint: endpoint.into(),
            bearer_token: None,
        }
    }

    /// Attach a bearer token.
    #[must_use]
    pub fn with_bearer_token(mut self, token: impl Into<String>) -> Self {
        self.bearer_token = Some(token.into());
        self
    }

    /// Returns the `Authorization` header value if a token is set.
    #[must_use]
    pub fn authorization_header(&self) -> Option<String> {
        self.bearer_token.as_deref().map(|t| format!("Bearer {t}"))
    }
}

// ─── WhepSession ─────────────────────────────────────────────────────────────

/// A single WHEP egress session.
///
/// Carries the SDP offer generated by the client and stores the server's
/// SDP answer once it is received.
#[derive(Debug, Clone)]
pub struct WhepSession {
    /// Unique session identifier (monotonically increasing counter string).
    pub id: String,
    /// The SDP offer body sent to the WHEP server.
    pub sdp_offer: String,
    /// The SDP answer returned by the WHEP server, if available.
    pub sdp_answer: Option<String>,
}

impl WhepSession {
    /// Returns `true` if the server's SDP answer has been received.
    #[must_use]
    pub fn is_answered(&self) -> bool {
        self.sdp_answer.is_some()
    }
}

// ─── WhepClient ───────────────────────────────────────────────────────────────

/// WHEP egress client for generating SDP offers and processing server answers.
///
/// The client is stateless beyond holding the configuration; sessions are
/// independent values that the caller tracks.
pub struct WhepClient {
    config: WhepConfig,
}

impl WhepClient {
    /// Create a new WHEP client with the given configuration.
    #[must_use]
    pub fn new(config: WhepConfig) -> Self {
        Self { config }
    }

    /// Returns a reference to the client configuration.
    #[must_use]
    pub fn config(&self) -> &WhepConfig {
        &self.config
    }

    /// Generate a new WHEP session with a minimal SDP offer.
    ///
    /// The offer includes:
    /// - Session-level ICE credentials
    /// - A video `m=` line with H.264 / PT 96
    /// - An audio `m=` line with Opus / PT 111
    /// - `a=recvonly` direction (the WHEP subscriber receives media)
    ///
    /// Calling this does **not** perform any I/O.
    #[must_use]
    pub fn create_offer(&self) -> WhepSession {
        let seq = next_session_id();
        let id = format!("whep-{seq}");

        let ufrag = derive_ice_ufrag(&id);
        let pwd = derive_ice_pwd(&id);

        let mut sdp = String::with_capacity(512);
        sdp.push_str("v=0\r\n");
        let _ = writeln!(sdp, "o=- {seq} 0 IN IP4 0.0.0.0\r");
        sdp.push_str("s=WHEP Egress\r\n");
        sdp.push_str("t=0 0\r\n");
        let _ = writeln!(sdp, "a=ice-ufrag:{ufrag}\r");
        let _ = writeln!(sdp, "a=ice-pwd:{pwd}\r");
        sdp.push_str(
            "a=fingerprint:sha-256 00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:\
00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00\r\n",
        );
        sdp.push_str("a=setup:actpass\r\n");
        // Video m= line (subscriber → recvonly)
        sdp.push_str("m=video 9 UDP/TLS/RTP/SAVPF 96\r\n");
        sdp.push_str("c=IN IP4 0.0.0.0\r\n");
        sdp.push_str("a=rtpmap:96 H264/90000\r\n");
        sdp.push_str("a=recvonly\r\n");
        sdp.push_str("a=mid:video\r\n");
        // Audio m= line
        sdp.push_str("m=audio 9 UDP/TLS/RTP/SAVPF 111\r\n");
        sdp.push_str("c=IN IP4 0.0.0.0\r\n");
        sdp.push_str("a=rtpmap:111 opus/48000/2\r\n");
        sdp.push_str("a=recvonly\r\n");
        sdp.push_str("a=mid:audio\r\n");

        WhepSession {
            id,
            sdp_offer: sdp,
            sdp_answer: None,
        }
    }

    /// Store the server's SDP answer in an existing session.
    ///
    /// The `session_id` is matched by value; if no match is found the
    /// `sdp_answer` in the returned session is left unset (no panic).
    ///
    /// # Note
    ///
    /// Since `WhepClient` is stateless (it does not hold sessions), the
    /// caller is responsible for looking up the correct [`WhepSession`] by
    /// `session_id` and passing a mutable reference here.
    pub fn process_answer(&self, session: &mut WhepSession, sdp_answer: String) {
        session.sdp_answer = Some(sdp_answer);
    }

    /// Format the HTTP request body and headers for a WHEP POST.
    ///
    /// Returns a string of the form:
    ///
    /// ```text
    /// Content-Type: application/sdp
    /// Accept: application/sdp
    /// [Authorization: Bearer <token>]
    ///
    /// <sdp_offer>
    /// ```
    ///
    /// The caller is responsible for transmitting this over HTTP.
    #[must_use]
    pub fn format_whep_request(session: &WhepSession) -> String {
        let mut out = String::with_capacity(session.sdp_offer.len() + 256);
        out.push_str("Content-Type: application/sdp\r\n");
        out.push_str("Accept: application/sdp\r\n");
        out.push_str("\r\n");
        out.push_str(&session.sdp_offer);
        out
    }

    /// Format the WHEP request with authorization header included.
    ///
    /// Like [`WhepClient::format_whep_request`] but prepends the `Authorization` header
    /// if the client has a bearer token configured.
    #[must_use]
    pub fn format_whep_request_authenticated(&self, session: &WhepSession) -> String {
        let mut out = String::with_capacity(session.sdp_offer.len() + 256);
        if let Some(auth) = self.config.authorization_header() {
            let _ = writeln!(out, "Authorization: {auth}\r");
        }
        out.push_str("Content-Type: application/sdp\r\n");
        out.push_str("Accept: application/sdp\r\n");
        out.push_str("\r\n");
        out.push_str(&session.sdp_offer);
        out
    }
}

// ─── Tests ────────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;

    fn make_client() -> WhepClient {
        WhepClient::new(WhepConfig::new("https://example.com/whep"))
    }

    // 1. WhepConfig::new has no bearer token by default
    #[test]
    fn test_whep_config_no_token() {
        let cfg = WhepConfig::new("https://example.com/whep");
        assert!(cfg.bearer_token.is_none());
        assert!(cfg.authorization_header().is_none());
    }

    // 2. WhepConfig::with_bearer_token sets token
    #[test]
    fn test_whep_config_bearer_token() {
        let cfg = WhepConfig::new("https://example.com/whep").with_bearer_token("tok123");
        assert_eq!(cfg.bearer_token.as_deref(), Some("tok123"));
        assert_eq!(cfg.authorization_header().as_deref(), Some("Bearer tok123"));
    }

    // 3. WhepClient::new stores config
    #[test]
    fn test_whep_client_new() {
        let client = make_client();
        assert_eq!(client.config().endpoint, "https://example.com/whep");
    }

    // 4. create_offer returns session with non-empty id
    #[test]
    fn test_create_offer_session_id() {
        let client = make_client();
        let session = client.create_offer();
        assert!(!session.id.is_empty());
        assert!(session.id.starts_with("whep-"));
    }

    // 5. create_offer SDP starts with v=0
    #[test]
    fn test_create_offer_sdp_starts_v0() {
        let client = make_client();
        let session = client.create_offer();
        assert!(session.sdp_offer.starts_with("v=0"), "SDP must begin v=0");
    }

    // 6. create_offer SDP contains recvonly direction
    #[test]
    fn test_create_offer_recvonly() {
        let client = make_client();
        let session = client.create_offer();
        assert!(
            session.sdp_offer.contains("a=recvonly"),
            "WHEP subscriber must use recvonly"
        );
    }

    // 7. create_offer SDP has video m= line
    #[test]
    fn test_create_offer_video_mline() {
        let client = make_client();
        let session = client.create_offer();
        assert!(session.sdp_offer.contains("m=video"), "must have video m=");
    }

    // 8. create_offer SDP has audio m= line
    #[test]
    fn test_create_offer_audio_mline() {
        let client = make_client();
        let session = client.create_offer();
        assert!(session.sdp_offer.contains("m=audio"), "must have audio m=");
    }

    // 9. sdp_answer is None before process_answer
    #[test]
    fn test_no_answer_initially() {
        let client = make_client();
        let session = client.create_offer();
        assert!(!session.is_answered());
        assert!(session.sdp_answer.is_none());
    }

    // 10. process_answer stores answer
    #[test]
    fn test_process_answer_stores() {
        let client = make_client();
        let mut session = client.create_offer();
        client.process_answer(&mut session, "v=0\r\no=- 0 0 IN IP4 0.0.0.0\r\n".to_owned());
        assert!(session.is_answered());
        assert!(session.sdp_answer.is_some());
    }

    // 11. process_answer stores correct SDP
    #[test]
    fn test_process_answer_content() {
        let client = make_client();
        let mut session = client.create_offer();
        let answer_sdp = "v=0\r\no=- 12345 0 IN IP4 192.168.1.1\r\n".to_owned();
        client.process_answer(&mut session, answer_sdp.clone());
        assert_eq!(session.sdp_answer.as_deref(), Some(answer_sdp.as_str()));
    }

    // 12. format_whep_request contains Content-Type header
    #[test]
    fn test_format_whep_request_content_type() {
        let client = make_client();
        let session = client.create_offer();
        let req = WhepClient::format_whep_request(&session);
        assert!(req.contains("Content-Type: application/sdp"));
    }

    // 13. format_whep_request contains Accept header
    #[test]
    fn test_format_whep_request_accept() {
        let client = make_client();
        let session = client.create_offer();
        let req = WhepClient::format_whep_request(&session);
        assert!(req.contains("Accept: application/sdp"));
    }

    // 14. format_whep_request contains the SDP body
    #[test]
    fn test_format_whep_request_body() {
        let client = make_client();
        let session = client.create_offer();
        let req = WhepClient::format_whep_request(&session);
        assert!(req.contains("v=0"));
        assert!(req.contains("m=video"));
    }

    // 15. format_whep_request_authenticated includes Authorization when token set
    #[test]
    fn test_format_whep_request_authenticated_with_token() {
        let cfg = WhepConfig::new("https://example.com/whep").with_bearer_token("my-token");
        let client = WhepClient::new(cfg);
        let session = client.create_offer();
        let req = client.format_whep_request_authenticated(&session);
        assert!(req.contains("Authorization: Bearer my-token"));
    }

    // 16. format_whep_request_authenticated without token has no Authorization
    #[test]
    fn test_format_whep_request_no_auth_when_no_token() {
        let client = make_client();
        let session = client.create_offer();
        let req = client.format_whep_request_authenticated(&session);
        assert!(!req.contains("Authorization:"));
    }

    // 17. Two successive create_offer calls produce distinct session IDs
    #[test]
    fn test_create_offer_unique_ids() {
        let client = make_client();
        let s1 = client.create_offer();
        let s2 = client.create_offer();
        assert_ne!(s1.id, s2.id);
    }

    // 18. SDP ICE ufrag is present in the offer
    #[test]
    fn test_create_offer_ice_ufrag_present() {
        let client = make_client();
        let session = client.create_offer();
        assert!(session.sdp_offer.contains("a=ice-ufrag:"));
    }

    // 19. SDP ICE pwd is present in the offer
    #[test]
    fn test_create_offer_ice_pwd_present() {
        let client = make_client();
        let session = client.create_offer();
        assert!(session.sdp_offer.contains("a=ice-pwd:"));
    }

    // 20. WhepSession is_answered false → true after process_answer
    #[test]
    fn test_is_answered_transitions() {
        let client = make_client();
        let mut session = client.create_offer();
        assert!(!session.is_answered());
        client.process_answer(&mut session, "v=0\r\n".to_owned());
        assert!(session.is_answered());
    }
}