// Symphonia

// Copyright (c) 2019-2026 The Project Symphonia Developers.

//

// This Source Code Form is subject to the terms of the Mozilla Public

// License, v. 2.0. If a copy of the MPL was not distributed with this

// file, You can obtain one at https://mozilla.org/MPL/2.0/.

use symphonia_common::xiph::audio::opus;

use symphonia_core::codecs::audio::well_known::CODEC_ID_OPUS;

use symphonia_core::errors::Error;

use symphonia_core::io::BufReader;

use crate::atoms::stsd::AudioSampleEntry;

use crate::atoms::{

    Atom, AtomHeader, AtomIterator, ReadAtom, Result, decode_error, unsupported_error,

};

const OPUS_MAGIC: &[u8] = b"OpusHead";

const OPUS_MAGIC_LEN: usize = OPUS_MAGIC.len();

/// Opus atom.

#[allow(dead_code)]

#[derive(Debug)]

pub struct OpusAtom {

    /// Opus extra data (identification header).

    extra_data: Box<[u8]>,

}

impl Atom for OpusAtom {

    fn read<R: ReadAtom>(reader: &mut AtomIterator<R>, header: &AtomHeader) -> Result<Self> {

        const MIN_OPUS_EXTRA_DATA_SIZE: usize = OPUS_MAGIC_LEN + 11;

        const MAX_OPUS_EXTRA_DATA_SIZE: usize = MIN_OPUS_EXTRA_DATA_SIZE + 257;

        // Offset of the Opus version number in the extra data.

        const OPUS_EXTRADATA_VERSION_OFFSET: usize = OPUS_MAGIC_LEN;

        // The dops atom contains an Opus identification header excluding the OpusHead magic

        // signature. Therefore, the atom data length should be atleast as long as the shortest

        // Opus identification header.

        let data_len = header

            .data_size()

            .ok_or(Error::DecodeError("isomp4 (opus): expected atom size to be known"))?

            as usize;

        if data_len < MIN_OPUS_EXTRA_DATA_SIZE - OPUS_MAGIC_LEN {

            return decode_error("isomp4 (opus): opus identification header too short");

        }

        if data_len > MAX_OPUS_EXTRA_DATA_SIZE - OPUS_MAGIC_LEN {

            return decode_error("isomp4 (opus): opus identification header too large");

        }

        let mut extra_data = vec![0; OPUS_MAGIC_LEN + data_len].into_boxed_slice();

        // The Opus magic is excluded in the atom, but the extra data must start with it.

        extra_data[..OPUS_MAGIC_LEN].copy_from_slice(OPUS_MAGIC);

        // Read the extra data from the atom.

        reader.read_buf_exact(&mut extra_data[OPUS_MAGIC_LEN..])?;

        // Verify the version number is 0.

        if extra_data[OPUS_EXTRADATA_VERSION_OFFSET] != 0 {

            return unsupported_error("isomp4 (opus): unsupported opus version");

        }

        Ok(OpusAtom { extra_data })

    }

}

impl OpusAtom {

    pub fn fill_audio_sample_entry(self, entry: &mut AudioSampleEntry) {

        let mut reader = BufReader::new(&self.extra_data);

        if let Ok(opus_head) = opus::OpusHead::read(&mut reader, 0) {

            entry.channels = Some(opus_head.channels);

            entry.sample_rate = 48_000.0;

        }

        entry.codec_id = CODEC_ID_OPUS;

        entry.extra_data = Some(self.extra_data);

    }

}