//! M2tsStream — BD transport stream with embedded metadata header.
//!
//! Write: prepends FMKV metadata header, then muxes PES frames into BD-TS.
//! Read: extracts metadata header (or scans PMT), then demuxes BD-TS into PES frames.

use super::{meta, ts};
use crate::disc::{DiscTitle, Stream as DiscStream};
use std::io::{self, Read, Write};

type PesSetup = (
    Vec<u16>,
    Vec<(u16, Box<dyn super::codec::CodecParser>)>,
    Vec<(u16, usize)>,
);

/// Size of initial scan buffer for PMT/stream detection.
const SCAN_SIZE: usize = 1024 * 1024;

enum Mode {
    Write {
        muxer: super::tsmux::TsMuxer<Box<dyn Write + Send>>,
    },
    Read {
        reader: Box<dyn Read + Send>,
    },
}

/// Read as many bytes as possible into buf (multiple read calls if needed).
/// Bounded by buf.len() — caller controls max bytes read.
fn read_fill(r: &mut impl Read, buf: &mut [u8]) -> io::Result<usize> {
    let mut total = 0;
    while total < buf.len() {
        match r.read(&mut buf[total..]) {
            Ok(0) => break,
            Ok(n) => total += n,
            Err(e) if e.kind() == io::ErrorKind::Interrupted => continue,
            Err(e) => return Err(e),
        }
    }
    Ok(total)
}

/// BD transport stream with embedded metadata.
pub struct M2tsStream {
    disc_title: DiscTitle,
    mode: Mode,
    // PES support
    demuxer: Option<ts::TsDemuxer>,
    parsers: Vec<(u16, Box<dyn super::codec::CodecParser>)>,
    pending_frames: std::collections::VecDeque<crate::pes::PesFrame>,
    pid_to_track: Vec<(u16, usize)>,
    pes_eof: bool,
    /// Codec private data per stream (from FMKV header).
    stored_codec_privates: Vec<Option<Vec<u8>>>,
}

impl M2tsStream {
    /// Create for writing PES frames → BD-TS output.
    /// Writes FMKV metadata header, then muxes PES frames into BD transport stream.
    pub fn create(mut writer: impl Write + Send + 'static, title: &DiscTitle) -> io::Result<Self> {
        // Write FMKV metadata header
        if !title.streams.is_empty() {
            let m = meta::M2tsMeta::from_title(title);
            meta::write_header(&mut writer, &m)?;
        }
        let pids: Vec<u16> = title
            .streams
            .iter()
            .map(|s| match s {
                DiscStream::Video(v) => v.pid,
                DiscStream::Audio(a) => a.pid,
                DiscStream::Subtitle(s) => s.pid,
            })
            .collect();
        let boxed: Box<dyn Write + Send> = Box::new(writer);
        let mut muxer = super::tsmux::TsMuxer::new(boxed, &pids);
        for (i, cp) in title.codec_privates.iter().enumerate() {
            if let Some(data) = cp {
                muxer.set_codec_private(i, data.clone());
            }
        }
        Ok(Self {
            disc_title: title.clone(),
            mode: Mode::Write { muxer },
            demuxer: None,
            parsers: Vec::new(),
            pending_frames: std::collections::VecDeque::new(),
            pid_to_track: Vec::new(),
            pes_eof: false,
            stored_codec_privates: Vec::new(),
        })
    }

    fn setup_pes(streams: &[DiscStream]) -> PesSetup {
        let mut pids = Vec::new();
        let mut parsers: Vec<(u16, Box<dyn super::codec::CodecParser>)> = Vec::new();
        let mut pid_to_track = Vec::new();
        for (i, s) in streams.iter().enumerate() {
            let (pid, codec) = match s {
                DiscStream::Video(v) => (v.pid, v.codec),
                DiscStream::Audio(a) => (a.pid, a.codec),
                DiscStream::Subtitle(s) => (s.pid, s.codec),
            };
            pids.push(pid);
            pid_to_track.push((pid, i));
            parsers.push((pid, super::codec::parser_for_codec(codec, None)));
        }
        (pids, parsers, pid_to_track)
    }

    /// Open an M2TS stream for reading. Takes any Read source — file, pipe, socket.
    ///
    /// Tries FMKV metadata header first. Falls back to PMT scan of first 1 MB.
    pub fn open(mut reader: impl Read + Send + 'static) -> io::Result<Self> {
        // Read first chunk — enough for FMKV header or PMT scan
        let mut head = vec![0u8; SCAN_SIZE];
        let head_len = read_fill(&mut reader, &mut head)?;
        head.truncate(head_len);

        // Try FMKV metadata header from the buffered head
        let mut cursor = io::Cursor::new(&head);
        if let Ok(Some(m)) = meta::read_header(&mut cursor) {
            let header_end = cursor.position() as usize;
            let title = m.to_title();
            let (pids, parsers, pid_to_track) = Self::setup_pes(&title.streams);
            // Chain: remaining head bytes + rest of reader
            let remaining_head = &head[header_end..];
            let chain: Box<dyn Read + Send> =
                Box::new(io::Cursor::new(remaining_head.to_vec()).chain(reader));
            return Ok(Self {
                disc_title: title.clone(),
                mode: Mode::Read { reader: chain },
                demuxer: if pids.is_empty() {
                    None
                } else {
                    Some(ts::TsDemuxer::new(&pids))
                },
                parsers,
                pending_frames: std::collections::VecDeque::new(),
                pid_to_track,
                pes_eof: false,
                stored_codec_privates: title.codec_privates,
            });
        }

        // No FMKV header — scan head for PMT
        let streams = ts::scan_streams(&head)
            .ok_or_else(|| -> io::Error { crate::error::Error::NoStreams.into() })?;

        let (pids, parsers, pid_to_track) = Self::setup_pes(&streams);

        // Chain: full head (it's all TS data) + rest of reader
        let chain: Box<dyn Read + Send> = Box::new(io::Cursor::new(head).chain(reader));

        Ok(Self {
            disc_title: DiscTitle {
                duration_secs: 0.0, // unknown without seeking
                streams,
                ..DiscTitle::empty()
            },
            mode: Mode::Read { reader: chain },
            demuxer: if pids.is_empty() {
                None
            } else {
                Some(ts::TsDemuxer::new(&pids))
            },
            parsers,
            pending_frames: std::collections::VecDeque::new(),
            pid_to_track,
            pes_eof: false,
            stored_codec_privates: Vec::new(),
        })
    }
}

impl crate::pes::Stream for M2tsStream {
    fn read(&mut self) -> io::Result<Option<crate::pes::PesFrame>> {
        if let Some(frame) = self.pending_frames.pop_front() {
            return Ok(Some(frame));
        }
        if self.pes_eof {
            return Ok(None);
        }

        loop {
            let reader = match &mut self.mode {
                Mode::Read { reader } => reader,
                _ => return Err(crate::error::Error::StreamWriteOnly.into()),
            };
            let mut buf = vec![0u8; 192 * 1024];
            let n = reader.read(&mut buf)?;
            if n == 0 {
                self.pes_eof = true;
                // Flush demuxer — last PES packet may still be in the assembler
                if let Some(ref mut demuxer) = self.demuxer {
                    for pes in &demuxer.flush() {
                        if let Some((_, track)) =
                            self.pid_to_track.iter().find(|(pid, _)| *pid == pes.pid)
                        {
                            if let Some((_, parser)) =
                                self.parsers.iter_mut().find(|(pid, _)| *pid == pes.pid)
                            {
                                for frame in parser.parse(pes) {
                                    self.pending_frames.push_back(
                                        crate::pes::PesFrame::from_codec_frame(*track, frame),
                                    );
                                }
                            }
                        }
                    }
                }
                return Ok(self.pending_frames.pop_front());
            }

            if let Some(ref mut demuxer) = self.demuxer {
                let packets = demuxer.feed(&buf[..n]);
                for pes in &packets {
                    if let Some((_, track)) =
                        self.pid_to_track.iter().find(|(pid, _)| *pid == pes.pid)
                    {
                        if let Some((_, parser)) =
                            self.parsers.iter_mut().find(|(pid, _)| *pid == pes.pid)
                        {
                            for frame in parser.parse(pes) {
                                self.pending_frames.push_back(
                                    crate::pes::PesFrame::from_codec_frame(*track, frame),
                                );
                            }
                        }
                    }
                }
            }

            if let Some(frame) = self.pending_frames.pop_front() {
                return Ok(Some(frame));
            }
        }
    }

    fn write(&mut self, frame: &crate::pes::PesFrame) -> io::Result<()> {
        match &mut self.mode {
            Mode::Write { muxer } => {
                muxer.write_frame(frame.track, frame.pts, frame.keyframe, &frame.data)
            }
            Mode::Read { .. } => Err(crate::error::Error::StreamReadOnly.into()),
        }
    }

    fn finish(&mut self) -> io::Result<()> {
        match &mut self.mode {
            Mode::Write { muxer } => muxer.finish(),
            Mode::Read { .. } => Ok(()),
        }
    }

    fn info(&self) -> &crate::disc::DiscTitle {
        &self.disc_title
    }

    fn codec_private(&self, track: usize) -> Option<Vec<u8>> {
        // First check stored codec_privates from FMKV header
        if let Some(Some(cp)) = self.stored_codec_privates.get(track) {
            return Some(cp.clone());
        }
        // Fall back to parser-extracted codec_private
        let pid = self
            .pid_to_track
            .iter()
            .find(|(_, idx)| *idx == track)
            .map(|(pid, _)| *pid)?;
        self.parsers
            .iter()
            .find(|(p, _)| *p == pid)
            .and_then(|(_, parser)| parser.codec_private())
    }

    fn headers_ready(&self) -> bool {
        for (idx, s) in self.disc_title.streams.iter().enumerate() {
            if let crate::disc::Stream::Video(v) = s {
                if !v.secondary && self.codec_private(idx).is_none() {
                    return false;
                }
            }
        }
        true
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::disc::{
        Codec, ColorSpace, ContentFormat, DiscTitle, FrameRate, HdrFormat, Resolution,
        Stream as DiscStream, VideoStream,
    };
    use crate::pes::{PesFrame, Stream as PesStreamTrait};

    const VIDEO_PID: u16 = 0x1011;

    fn make_title() -> DiscTitle {
        DiscTitle {
            playlist: String::new(),
            playlist_id: 0,
            duration_secs: 0.0,
            size_bytes: 0,
            clips: Vec::new(),
            streams: vec![DiscStream::Video(VideoStream {
                pid: VIDEO_PID,
                codec: Codec::Hevc,
                resolution: Resolution::R1080p,
                frame_rate: FrameRate::F24,
                hdr: HdrFormat::Sdr,
                color_space: ColorSpace::Bt709,
                secondary: false,
                label: String::new(),
            })],
            chapters: Vec::new(),
            extents: Vec::new(),
            content_format: ContentFormat::BdTs,
            codec_privates: vec![Some({
                // Minimal hvcC with one VPS-like array entry.
                let marker: &[u8] = &[0x40, 0x01, 0x0C, 0x01];
                let mut hvcc = vec![0u8; 22];
                hvcc.push(1); // numArrays
                hvcc.push(32);
                hvcc.extend_from_slice(&1u16.to_be_bytes()); // numNalus
                hvcc.extend_from_slice(&(marker.len() as u16).to_be_bytes());
                hvcc.extend_from_slice(marker);
                hvcc
            })],
        }
    }

    fn fake_idr_pes_data() -> Vec<u8> {
        // 4-byte length prefix + NAL: type 19 (IDR_W_RADL).
        let mut nal = vec![(19u8 << 1) & 0x7E, 0x01];
        for i in 0..200 {
            nal.push((i & 0xFF) as u8);
        }
        let mut out = Vec::with_capacity(4 + nal.len());
        out.extend_from_slice(&(nal.len() as u32).to_be_bytes());
        out.extend_from_slice(&nal);
        out
    }

    /// Writer wrapper that shares an Arc<Mutex<Vec<u8>>> so the test can
    /// inspect the bytes after the muxer drops.
    struct SharedSink(std::sync::Arc<std::sync::Mutex<Vec<u8>>>);
    impl Write for SharedSink {
        fn write(&mut self, b: &[u8]) -> io::Result<usize> {
            self.0.lock().unwrap().extend_from_slice(b);
            Ok(b.len())
        }
        fn flush(&mut self) -> io::Result<()> {
            Ok(())
        }
    }

    #[test]
    fn m2ts_stream_forwards_keyframe_to_rai() {
        let title = make_title();
        let shared = std::sync::Arc::new(std::sync::Mutex::new(Vec::<u8>::new()));
        let sink = SharedSink(shared.clone());
        let mut stream = M2tsStream::create(sink, &title).unwrap();
        let frame = PesFrame {
            track: 0,
            pts: 0,
            keyframe: true,
            data: fake_idr_pes_data(),
        };
        stream.write(&frame).unwrap();
        stream.finish().unwrap();
        drop(stream);

        let buf = shared.lock().unwrap().clone();

        // Skip FMKV metadata header via meta::read_header.
        let mut cursor = std::io::Cursor::new(&buf);
        let _meta = super::meta::read_header(&mut cursor)
            .unwrap()
            .expect("FMKV header present");
        let header_end = cursor.position() as usize;
        let ts_bytes = &buf[header_end..];

        // Find first PUSI packet on VIDEO_PID; verify RAI in AF flags.
        let pkt = ts_bytes
            .chunks(192)
            .find(|p| {
                let h = &p[4..];
                let pid = (((h[1] & 0x1F) as u16) << 8) | h[2] as u16;
                pid == VIDEO_PID && (h[1] & 0x40) != 0
            })
            .expect("video PUSI packet present");
        let h = &pkt[4..];
        let afc = (h[3] >> 4) & 0x03;
        assert!(afc & 0b10 != 0, "AF must be present");
        let af_len = h[4] as usize;
        assert!(af_len >= 1, "AF length must include flags byte");
        let flags = h[5];
        assert_eq!(flags & 0x40, 0x40, "RAI bit set");
    }
}