//! Hardware video encode (plan §7). Binds FFmpeg (NVENC); never rewrites codecs.
//! Low-latency preset, B-frames off. M0 feeds BGRx CPU frames directly — `*_nvenc`
//! accepts `bgr0` input and converts to YUV on the GPU, so no host-side swscale is
//! needed (dmabuf zero-copy import is deferred; plan §9).

use crate::capture::{CapturedFrame, PixelFormat};
use anyhow::Result;

/// An encoded access unit (one NAL/AU) to hand to `punktfunk_core` for FEC + packetization.
/// `data` is in-band Annex-B (the encoder is opened without a global header), so each
/// keyframe carries its own VPS/SPS/PPS — the bytes are both a playable elementary
/// stream and a self-contained AU for the wire.
pub struct EncodedFrame {
    pub data: Vec<u8>,
    pub pts_ns: u64,
    /// True for IDR/keyframes (sets the SOF/keyframe wire flags).
    pub keyframe: bool,
}

/// Codec selection negotiated with the client.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Codec {
    H264,
    H265,
    Av1,
}

impl Codec {
    /// The FFmpeg NVENC encoder name (selected by name, not codec id — the latter would
    /// pick the software encoder).
    pub fn nvenc_name(self) -> &'static str {
        match self {
            Codec::H264 => "h264_nvenc",
            Codec::H265 => "hevc_nvenc",
            Codec::Av1 => "av1_nvenc",
        }
    }
}

/// A hardware encoder. One per session; runs on the encode thread.
pub trait Encoder: Send {
    fn submit(&mut self, frame: &CapturedFrame) -> Result<()>;
    /// Force the next submitted frame to be an IDR keyframe (e.g. after a client
    /// reference-frame-invalidation request). Default: no-op.
    fn request_keyframe(&mut self) {}
    /// Pull the next encoded AU if one is ready.
    fn poll(&mut self) -> Result<Option<EncodedFrame>>;
    /// Signal end-of-stream. After this, drain the remaining AUs with [`poll`](Self::poll)
    /// until it returns `None` — NVENC buffers frames internally even at `delay=0`.
    fn flush(&mut self) -> Result<()>;
}

impl Codec {
    /// Maximum encodable dimension (px) per side for this codec on NVENC. H.264 tops out at
    /// 4096 (level constraint); HEVC and AV1 allow 8192. Used to reject out-of-range client
    /// modes up front (see [`validate_dimensions`]).
    pub fn max_dimension(self) -> u32 {
        match self {
            Codec::H264 => 4096,
            Codec::H265 | Codec::Av1 => 8192,
        }
    }

    /// The codec's *spec* top level/tier bitrate (bits/s) — the usual boundary at which NVENC
    /// starts rejecting `avcodec_open2` with EINVAL. NOT a hard cap: [`open_video`](crate::encode::
    /// open_video) probes the actual GPU ceiling by stepping DOWN from the requested bitrate only on
    /// EINVAL, and uses this purely as the first step-down candidate (so a card that accepts more —
    /// an RTX 5070 Ti does >1 Gbps HEVC where a 4090 caps at ~800 Mbps — is never clamped to it).
    /// HEVC Level 6.2 High tier = 800 Mbps; H.264 High level 6.2 ≈ 480 Mbps; AV1's levels allow more.
    pub fn max_bitrate_bps(self) -> u64 {
        match self {
            Codec::H264 => 480_000_000,
            Codec::H265 => 800_000_000,
            Codec::Av1 => 1_200_000_000,
        }
    }
}

/// Validate a requested encode resolution before we allocate buffers or open NVENC. Rejects
/// zero/odd-sized and out-of-range modes with a clear error instead of letting buffer math
/// overflow or the encoder open fail with an opaque NVENC code. A client can request any
/// `mode=WxHxFPS`, so this is the gate on attacker/typo-controlled dimensions.
pub fn validate_dimensions(codec: Codec, width: u32, height: u32) -> Result<()> {
    if width == 0 || height == 0 {
        anyhow::bail!("invalid encode resolution {width}x{height}: dimensions must be non-zero");
    }
    // NVENC requires even dimensions for the chroma subsampling it does internally.
    if width % 2 != 0 || height % 2 != 0 {
        anyhow::bail!("invalid encode resolution {width}x{height}: dimensions must be even");
    }
    let max = codec.max_dimension();
    if width > max || height > max {
        anyhow::bail!(
            "{codec:?} max dimension is {max}px; requested {width}x{height} \
             (use HEVC/AV1 above 4096, or lower the client resolution)"
        );
    }
    Ok(())
}

/// Open an NVENC encoder for frames of the given `format` and mode. When `cuda` is true the
/// encoder takes GPU frames (`AV_PIX_FMT_CUDA`) from the zero-copy path; otherwise it takes
/// packed RGB/BGR CPU frames. `format`/`bitrate_bps`/`codec`/mode come from session
/// negotiation; the caller derives `cuda` from the first captured frame's payload.
pub fn open_video(
    codec: Codec,
    format: PixelFormat,
    width: u32,
    height: u32,
    fps: u32,
    bitrate_bps: u64,
    cuda: bool,
) -> Result<Box<dyn Encoder>> {
    validate_dimensions(codec, width, height)?;
    #[cfg(target_os = "linux")]
    {
        // Identify THIS GPU's real max encode bitrate by probing instead of hard-capping every
        // build. NVENC rejects `avcodec_open2` with EINVAL when the bitrate exceeds what any codec
        // level can express, and that ceiling is GPU/driver-specific (an RTX 4090 caps HEVC at
        // ~800 Mbps; an RTX 5070 Ti accepts >1 Gbps). So open at the requested rate first and step
        // down ONLY if this GPU refuses it — each GPU then runs at its own actual maximum, and a
        // capable card is never clamped to a conservative guess. The codec's theoretical level
        // ceiling is just the first step-down candidate (the usual boundary), not a blind cap.
        const MIN_PROBE_BPS: u64 = 50_000_000;
        let mut candidates = vec![bitrate_bps];
        let cap = codec.max_bitrate_bps();
        if cap < bitrate_bps {
            candidates.push(cap);
        }
        let mut b = bitrate_bps.min(cap);
        while b > MIN_PROBE_BPS {
            b = b * 3 / 4;
            candidates.push(b);
        }
        let mut last: Option<anyhow::Error> = None;
        for (i, &b) in candidates.iter().enumerate() {
            match linux::NvencEncoder::open(codec, format, width, height, fps, b, cuda) {
                Ok(enc) => {
                    if i > 0 {
                        tracing::warn!(
                            requested_mbps = bitrate_bps / 1_000_000,
                            opened_mbps = b / 1_000_000,
                            codec = codec.nvenc_name(),
                            "this GPU's NVENC refused the requested bitrate (EINVAL) — opened at the \
                             highest rate it accepts; request AV1 or a lower bitrate for more"
                        );
                    }
                    return Ok(Box::new(enc) as Box<dyn Encoder>);
                }
                // EINVAL = above this GPU's level ceiling → step down. Any other failure (no GPU,
                // bad mode, OOM) is real — surface it rather than masking it with bitrate retries.
                Err(e) if format!("{e:#}").contains("Invalid argument") => last = Some(e),
                Err(e) => return Err(e),
            }
        }
        Err(last.unwrap_or_else(|| anyhow::anyhow!("encoder open failed at every probed bitrate")))
    }
    #[cfg(target_os = "windows")]
    {
        let _ = cuda; // always false on Windows (no Cuda payload)
        let pref = std::env::var("PUNKTFUNK_ENCODER")
            .unwrap_or_default()
            .to_ascii_lowercase();
        if matches!(pref.as_str(), "nvenc" | "hw" | "nvidia") {
            anyhow::bail!(
                "NVENC hardware encode is not yet implemented on Windows — omit PUNKTFUNK_ENCODER \
                 or set it to 'software' to use the openh264 encoder"
            );
        }
        anyhow::ensure!(
            codec == Codec::H264,
            "the Windows software encoder supports H.264 only; client negotiated {codec:?} \
             (request H264, or use a GPU host once NVENC lands)"
        );
        // Software H.264 realistically caps far below the negotiated hardware rates.
        const SW_BITRATE_CEIL: u64 = 100_000_000;
        let enc =
            sw::OpenH264Encoder::open(format, width, height, fps, bitrate_bps.min(SW_BITRATE_CEIL))?;
        Ok(Box::new(enc) as Box<dyn Encoder>)
    }
    #[cfg(not(any(target_os = "linux", target_os = "windows")))]
    {
        let _ = (codec, format, width, height, fps, bitrate_bps, cuda);
        anyhow::bail!("video encode requires Linux or Windows")
    }
}

#[cfg(target_os = "linux")]
mod linux;
#[cfg(target_os = "windows")]
mod sw;

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

    #[test]
    fn rejects_zero_and_odd_dimensions() {
        assert!(validate_dimensions(Codec::H265, 0, 1080).is_err());
        assert!(validate_dimensions(Codec::H265, 1920, 0).is_err());
        assert!(validate_dimensions(Codec::H265, 1921, 1080).is_err()); // odd width
        assert!(validate_dimensions(Codec::H265, 1920, 1081).is_err()); // odd height
    }

    #[test]
    fn h264_capped_at_4096() {
        assert!(validate_dimensions(Codec::H264, 3840, 2160).is_ok()); // 4K fits (width < 4096)
        assert!(validate_dimensions(Codec::H264, 4096, 4096).is_ok()); // exactly at the limit
        assert!(validate_dimensions(Codec::H264, 4098, 2160).is_err());
        assert!(validate_dimensions(Codec::H264, 3840, 4098).is_err());
    }

    #[test]
    fn hevc_and_av1_allow_up_to_8192() {
        for c in [Codec::H265, Codec::Av1] {
            assert!(validate_dimensions(c, 3840, 2160).is_ok());
            assert!(validate_dimensions(c, 7680, 4320).is_ok()); // 8K fits
            assert!(validate_dimensions(c, 8192, 8192).is_ok());
            assert!(validate_dimensions(c, 8194, 4320).is_err());
        }
    }

    #[test]
    fn common_modes_accepted() {
        for c in [Codec::H264, Codec::H265, Codec::Av1] {
            for (w, h) in [(1280, 720), (1920, 1080), (2560, 1440)] {
                assert!(validate_dimensions(c, w, h).is_ok(), "{c:?} {w}x{h}");
            }
        }
    }
}