voice-cat/core/src/codec/opus_codec.h

/*
 * codec/opus_codec.h — Opus encode/decode (libopus 1.6).
 *
 * Design: docs/voice.md §3–4. Per-channel AudioConfig (mono/stereo, bitrate, frame size,
 * FEC, DTX, complexity). The server relays Opus payloads unmodified (no transcode).
 */
#ifndef VOICECAT_CODEC_OPUS_CODEC_H
#define VOICECAT_CODEC_OPUS_CODEC_H

#include <cstdint>
#include <vector>

#ifdef VOICECAT_HAS_OPUS
#include <opus/opus.h>
#endif

namespace voicecat::codec {

// Mirrors voicecat::v1::OpusApplication (core/proto/voicecat.proto) without depending on
// generated protobuf headers from this low-level codec module.
enum class OpusApplication {
    Voip     = 0,  // speech, optimized for low-rate intelligibility
    Audio    = 1,  // music/screen-audio, optimized for fidelity
    LowDelay = 2,  // monitoring, minimal algorithmic delay
};

struct OpusParams {
    uint32_t        sample_rate          = 48000;
    uint32_t        bitrate_bps          = 24000;
    uint32_t        frame_ms             = 20;
    bool            stereo               = false;
    bool            fec                  = true;
    bool            dtx                  = false;
    uint32_t        complexity           = 10;
    uint32_t        expected_packet_loss = 0;   // % 0..100
    OpusApplication application           = OpusApplication::Voip;
};

// Returns frame_samples for a given sample_rate + frame_ms.
inline int opus_frame_samples(const OpusParams& p) {
    return static_cast<int>(p.sample_rate / 1000 * p.frame_ms);
}

class OpusEncoder {
   public:
    OpusEncoder() = default;
    ~OpusEncoder() { destroy(); }

    OpusEncoder(const OpusEncoder&)            = delete;
    OpusEncoder& operator=(const OpusEncoder&) = delete;

    // Initialise with the given params. Must be called before encode().
    // Returns true on success; check error_string() on failure.
    bool init(const OpusParams& p);

    // Encode one frame of PCM (frame_ms ms @ sample_rate Hz, mono or stereo).
    // pcm: interleaved int16 samples (frame_samples * channels samples).
    // out_buf: caller-allocated output buffer (recommend >= 4000 bytes).
    // Returns number of bytes written to out_buf, or -1 on error.
    int encode(const int16_t* pcm, int frame_samples, uint8_t* out_buf, int out_cap);

    void destroy();

    bool        valid()        const { return enc_ != nullptr; }
    int         frame_samples()const { return frame_samples_; }
    int         channels()     const { return channels_; }
    const char* error_string() const { return err_; }

   private:
#ifdef VOICECAT_HAS_OPUS
    ::OpusEncoder* enc_ = nullptr;
#else
    void* enc_ = nullptr;
#endif
    int         frame_samples_ = 0;
    int         channels_      = 1;
    const char* err_           = nullptr;
};

class OpusDecoder {
   public:
    OpusDecoder() = default;
    ~OpusDecoder() { destroy(); }

    OpusDecoder(const OpusDecoder&)            = delete;
    OpusDecoder& operator=(const OpusDecoder&) = delete;

    // Initialise. Must be called before decode().
    bool init(const OpusParams& p);

    // Decode one Opus packet into out_pcm (frame_samples * channels int16 samples).
    // opus_data=nullptr, len=0 → PLC (free, always enabled by libopus).
    // fec=true, next valid packet in opus_data → FEC recovery from previous loss.
    // Returns number of samples decoded (= frame_samples), or -1 on error.
    int decode(const uint8_t* opus_data, int len, int16_t* out_pcm, int max_samples,
               bool fec = false);

    void destroy();

    bool        valid()        const { return dec_ != nullptr; }
    int         frame_samples()const { return frame_samples_; }
    int         channels()     const { return channels_; }
    const char* error_string() const { return err_; }

   private:
#ifdef VOICECAT_HAS_OPUS
    ::OpusDecoder* dec_ = nullptr;
#else
    void* dec_ = nullptr;
#endif
    int         frame_samples_ = 0;
    int         channels_      = 1;
    const char* err_           = nullptr;
};

}  // namespace voicecat::codec

#endif  // VOICECAT_CODEC_OPUS_CODEC_H