use std::mem;
use std::ptr;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::Instant;

use anyhow::{bail, Result};
use ffmpeg_next as ff;
use ffmpeg_next::ffi;
use ffmpeg_next::packet::Mut as _;

use super::encode_output::{self, FrameOutput, PacketOutput};
use super::hash::hash_sampled_y_plane;
use super::{
    ff_err, BitrateCommand, CpuNv12Frame, EncodeOutcome, ResolutionChange, SwEncodeTiming,
};

pub struct SwEncEncode {
    pub(super) sws_ctx: *mut ffi::SwsContext,
    pub(super) enc_video: ff::codec::encoder::video::Video,
    pub(super) output: Option<FrameOutput>,
    pub(super) yuv_frame: *mut ffi::AVFrame,
    pub(super) last_frame_hash: u64,
    pub(super) frame_count: u64,
    pub(super) starting_timestamp: Option<i64>,
    pub(super) frames_written: bool,
    pub(super) webrtc_disconnected: bool,
    pub(super) webrtc_paused: Option<Arc<AtomicBool>>,
    pub(super) bitrate_rx: crossbeam_channel::Receiver<BitrateCommand>,
    pub(super) resolution_rx: crossbeam_channel::Receiver<ResolutionChange>,
    pub(super) enc_width: u32,
    pub(super) enc_height: u32,
    pub(super) fps: u32,
    pub(super) bitrate: u64,
    pub(super) gop_size: u32,
    /// Set true when WebRTC requests a keyframe. Forces the next frame to
    /// `AV_PICTURE_TYPE_I` and bypasses the dedup hash check. Cleared only
    /// after `avcodec_send_frame` accepts the forced frame.
    pub(super) force_keyframe_pending: bool,
    /// Last per-frame timing snapshot. Reset to `Default` at the start of
    /// every `encode_cpu_frame` call (even on early returns) so stale values
    /// from a previous frame can never leak out.
    pub(super) last_timing: SwEncodeTiming,
    /// Capture time of the frame currently being encoded. Saved from the
    /// input `CpuNv12Frame` so `drain_encoder` can propagate it into the
    /// emitted `EncodedH264Frame` for the frame_age stat (issue #20).
    pub(super) last_capture_time: Option<Instant>,
}

/// WebRTC media clock frequency in Hz. Matches RTP clock for video (RFC 3551).
/// Used as encoder time_base denominator for WebRTC mode (1/90000) so that
/// PTS values directly become RTP timestamps with microsecond precision.
/// MP4 mode keeps 1/fps time_base for file output simplicity.
pub const WEBRTC_RTP_CLOCK_HZ: i128 = 90_000;

// SAFETY: SwEncEncode is moved to a single encode thread and accessed only there
// via &mut self. SwsContext, AVFrame, and AVCodecContext are NOT thread-safe for
// concurrent access but are Send-sound under single-thread exclusive use, which
// the encode worker invariant provides. crossbeam Receiver and Arc<AtomicBool>
// are Send by design.
unsafe impl Send for SwEncEncode {}

impl SwEncEncode {
    pub fn flush(&mut self) -> Result<()> {
        // SAFETY: Sending a null frame flushes the opened software encoder;
        // no frame data is dereferenced. enc_video is exclusively borrowed via &mut self.
        unsafe {
            let ret = ffi::avcodec_send_frame(self.enc_video.as_mut_ptr(), ptr::null());
            if ret < 0 && ret != ffi::AVERROR_EOF {
                bail!("software encoder flush send failed: {}", ff_err(ret));
            }
        }
        let start_ts = self.starting_timestamp.unwrap_or(0);
        let _ = self.drain_encoder(start_ts)?;

        Ok(())
    }

    pub fn take_timing(&mut self) -> SwEncodeTiming {
        mem::take(&mut self.last_timing)
    }

    pub fn encode_cpu_frame(&mut self, frame: &CpuNv12Frame) -> Result<EncodeOutcome> {
        self.last_timing = SwEncodeTiming::default();
        // Save capture_time so drain_encoder can propagate it into the
        // EncodedH264Frame emitted via the WebRTC channel (issue #20).
        self.last_capture_time = Some(frame.capture_time);

        if self.webrtc_disconnected {
            return Ok(EncodeOutcome::SkippedDisconnected);
        }

        // Must drain before the stride check: the import thread emits
        // ResolutionChange before the new (smaller-stride) frame arrives.
        while let Ok(cmd) = self.bitrate_rx.try_recv() {
            match cmd {
                BitrateCommand::UpdateBitrate { target_bps } => {
                    // #23 defensive guardrail: clamp to reasonable max even if policy layer
                    // is bypassed. 50 Mbps is a hard ceiling; primary cap is enforced in
                    // state_portal.rs webrtc_thread_loop via --max-bitrate flag.
                    const ENCODER_BITRATE_HARD_CAP: u64 = 50_000_000;
                    let target_bps = target_bps.min(ENCODER_BITRATE_HARD_CAP);
                    tracing::info!(target_bps, "updating encoder bitrate from BWE feedback");
                    self.bitrate = target_bps;
                    // SAFETY: enc_video is an opened AVCodecContext exclusively owned by &mut self.
                    unsafe {
                        let ctx = self.enc_video.as_mut_ptr();
                        (*ctx).bit_rate = target_bps as i64;
                    }
                }
                BitrateCommand::UpdateResolution { .. } => {}
                BitrateCommand::ForceKeyframe => {
                    self.force_keyframe_pending = true;
                    tracing::debug!("encode thread: ForceKeyframe requested");
                }
            }
        }

        let force_this_frame = self.force_keyframe_pending;

        while let Ok(change) = self.resolution_rx.try_recv() {
            self.recreate_encoder(change.width, change.height)?;
        }

        if frame.y_stride < self.enc_width as usize || frame.uv_stride < self.enc_width as usize {
            bail!("CPU NV12 frame stride is smaller than encoder width");
        }
        if let Some(ref paused) = self.webrtc_paused {
            if paused.load(Ordering::Relaxed) {
                return Ok(EncodeOutcome::SkippedPaused);
            }
        }

        let width = self.enc_width as usize;
        let height = self.enc_height as usize;
        let required_y_len = frame.y_stride * height.saturating_sub(1) + width;
        if frame.y_data.len() < required_y_len {
            bail!("CPU NV12 frame Y plane is smaller than encoder dimensions");
        }

        let frame_index = self.frame_count;
        self.frame_count = self.frame_count.saturating_add(1);
        let current_hash = hash_sampled_y_plane(&frame.y_data, width, height, frame.y_stride);
        let force_gop_frame =
            self.gop_size > 0 && frame_index.is_multiple_of(u64::from(self.gop_size));
        if frame_index > 0
            && !force_gop_frame
            && !force_this_frame
            && current_hash == self.last_frame_hash
        {
            tracing::debug!(frame_index, "skipping duplicate frame");
            self.last_frame_hash = current_hash;
            return Ok(EncodeOutcome::SkippedDuplicate);
        }
        self.last_frame_hash = current_hash;

        let sws_start = Instant::now();
        // SAFETY: yuv_frame is an owned reusable YUV420P frame at the same dimensions as sw_nv12;
        // sws_ctx was created for NV12 -> YUV420P with no resize, so sws_scale only converts format.
        unsafe {
            let ret = ffi::av_frame_make_writable(self.yuv_frame);
            if ret < 0 {
                bail!("av_frame_make_writable failed: {}", ff_err(ret));
            }
            let src_slices = [
                frame.y_data.as_ptr(),
                frame.uv_data.as_ptr(),
                ptr::null(),
                ptr::null(),
            ];
            let src_strides = [frame.y_stride as i32, frame.uv_stride as i32, 0, 0];
            let scaled = ffi::sws_scale(
                self.sws_ctx,
                src_slices.as_ptr(),
                src_strides.as_ptr(),
                0,
                self.enc_height as i32,
                (*self.yuv_frame).data.as_ptr() as *mut *mut u8,
                (*self.yuv_frame).linesize.as_ptr(),
            );
            if scaled < 0 {
                bail!("sws_scale failed for software encoder: {scaled}");
            }
        }
        let sws_us = sws_start.elapsed().as_micros() as u64;

        let pts = frame.pts;
        if self.starting_timestamp.is_none() {
            self.starting_timestamp = Some(pts);
        }
        let start_ts = self.starting_timestamp.unwrap_or(0);

        let enc_start = Instant::now();
        // SAFETY: yuv_frame is initialized, writable, and matches the opened encoder format.
        // pict_type is reset every frame: the AVFrame is reused, so without resetting to NONE
        // a previously-forced I-type would leak into subsequent P-frames. With forced-idr=1
        // set on the encoder, AV_PICTURE_TYPE_I produces a true IDR NALU.
        unsafe {
            (*self.yuv_frame).pts = pts;
            (*self.yuv_frame).pict_type = if force_this_frame {
                ffi::AVPictureType::AV_PICTURE_TYPE_I
            } else {
                ffi::AVPictureType::AV_PICTURE_TYPE_NONE
            };
            let ret = ffi::avcodec_send_frame(self.enc_video.as_mut_ptr(), self.yuv_frame);
            if ret < 0 {
                bail!(
                    "avcodec_send_frame failed for software encoder: {}",
                    ff_err(ret)
                );
            }
        }

        if force_this_frame {
            self.force_keyframe_pending = false;
        }

        let output_bytes = self.drain_encoder(start_ts)?;
        let encode_us = enc_start.elapsed().as_micros() as u64;

        self.last_timing = SwEncodeTiming {
            sws_us,
            encode_us,
            output_bytes,
        };

        Ok(EncodeOutcome::Encoded)
    }

    pub(super) fn write_trailer_if_needed(&mut self) -> Result<()> {
        if self.frames_written {
            if let Some(FrameOutput::Muxer(ref mut octx)) = self.output {
                octx.write_trailer()
                    .map_err(|e| anyhow::anyhow!("Failed to write trailer: {e}"))?;
            }
        }
        Ok(())
    }

    fn drain_encoder(&mut self, start_ts: i64) -> Result<usize> {
        let mut total_bytes = 0usize;
        loop {
            let mut pkt = ff::Packet::empty();
            // SAFETY: enc_video is an open encoder; pkt is writable packet storage.
            let ret = unsafe {
                ffi::avcodec_receive_packet(self.enc_video.as_mut_ptr(), pkt.as_mut_ptr())
            };
            if ret < 0 {
                if ret == ffi::AVERROR(ffi::EAGAIN) || ret == ffi::AVERROR_EOF {
                    break;
                }
                bail!("avcodec_receive_packet failed: {}", ff_err(ret));
            }

            // Count encoded bytes produced before the Muxer/Channel match to
            // avoid branch duplication and handle multi-packet drain correctly.
            // SAFETY: pkt was just filled by a successful avcodec_receive_packet;
            // the size field is valid and initialized.
            let pkt_size = unsafe { (*pkt.as_mut_ptr()).size };
            if pkt_size > 0 {
                total_bytes += pkt_size as usize;
            }

            match self.output {
                Some(FrameOutput::Muxer(ref mut octx)) => {
                    encode_output::write_muxer_packet(
                        &mut pkt,
                        octx,
                        self.enc_video.time_base(),
                        start_ts,
                    )?;
                    self.frames_written = true;
                }
                Some(FrameOutput::Channel(ref tx))
                    if encode_output::send_channel_packet(
                        &mut pkt,
                        tx,
                        start_ts,
                        self.last_capture_time.unwrap_or_else(Instant::now),
                    )? == PacketOutput::Disconnected =>
                {
                    self.webrtc_disconnected = true;
                    break;
                }
                Some(FrameOutput::Channel(_)) => {}
                None => {}
            }
        }
        Ok(total_bytes)
    }
}

impl Drop for SwEncEncode {
    fn drop(&mut self) {
        if !self.sws_ctx.is_null() {
            // SAFETY: sws_ctx is owned by this state and was returned by sws_getContext.
            unsafe { ffi::sws_freeContext(self.sws_ctx) };
            self.sws_ctx = ptr::null_mut();
        }
        if !self.yuv_frame.is_null() {
            // SAFETY: yuv_frame is owned by this state and was allocated by av_frame_alloc.
            unsafe { ffi::av_frame_free(&mut self.yuv_frame) };
        }
    }
}