dvb-si 12.1.0

//! Maximum Bitrate Descriptor — ISO/IEC 13818-1 §2.6.26 (tag 0x0E).
//!
//! Indicates the maximum bitrate of the associated elementary stream
//! in units of 50 bytes/second (§2.6.27).

use super::descriptor_body;
use crate::error::{Error, Result};
use broadcast_common::{Parse, Serialize};

/// Descriptor tag for maximum_bitrate_descriptor.
pub const TAG: u8 = 0x0E;
/// `maximum_bitrate` is a 22-bit uimsbf (units of 50 bytes/s).
const MAXIMUM_BITRATE_BITS: u32 = 22;
const HEADER_LEN: usize = 2;
const BODY_LEN: u8 = 3;
/// Default of the 2-bit `reserved` ahead of `maximum_bitrate` (H.222.0 Table
/// 2-67): clause 2.1 "reserved" = `1` (all 9 editions 07/1995-08/2023, audit
/// §5; confirmed by the TSDuck-compiled oracle PMT).
pub const RESERVED_DEFAULT: u8 = 0b11;
const RESERVED_MASK: u8 = 0x03;

/// Maximum Bitrate Descriptor.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
#[non_exhaustive]
pub struct MaximumBitrateDescriptor {
    /// Maximum bitrate in units of 50 bytes/second.
    pub maximum_bitrate: u32,
    /// `reserved(2)` ahead of `maximum_bitrate` (2 bits, right-aligned).
    /// Captured on parse, re-emitted verbatim;
    /// [`MaximumBitrateDescriptor::new`] uses [`RESERVED_DEFAULT`].
    pub reserved: u8,
}

impl MaximumBitrateDescriptor {
    /// Build with the spec-default reserved bits.
    #[must_use]
    pub const fn new(maximum_bitrate: u32) -> Self {
        Self {
            maximum_bitrate,
            reserved: RESERVED_DEFAULT,
        }
    }
}

impl<'a> Parse<'a> for MaximumBitrateDescriptor {
    type Error = crate::error::Error;

    fn parse(bytes: &'a [u8]) -> Result<Self> {
        let body = descriptor_body(
            bytes,
            TAG,
            "MaximumBitrateDescriptor",
            "unexpected tag for maximum_bitrate_descriptor",
        )?;
        if body.len() != BODY_LEN as usize {
            return Err(Error::InvalidDescriptor {
                tag: TAG,
                reason: "maximum_bitrate_descriptor length must equal 3",
            });
        }
        let maximum_bitrate =
            ((u32::from(body[0]) & 0x3F) << 16) | (u32::from(body[1]) << 8) | u32::from(body[2]);
        Ok(Self {
            maximum_bitrate,
            reserved: body[0] >> 6,
        })
    }
}

impl Serialize for MaximumBitrateDescriptor {
    type Error = crate::error::Error;

    fn serialized_len(&self) -> usize {
        HEADER_LEN + (BODY_LEN as usize)
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        let len = self.serialized_len();
        if buf.len() < len {
            return Err(Error::OutputBufferTooSmall {
                need: len,
                have: buf.len(),
            });
        }
        let mb = broadcast_common::len::fit_bits(
            u64::from(self.maximum_bitrate),
            MAXIMUM_BITRATE_BITS,
            "maximum_bitrate",
        )?;
        buf[0] = TAG;
        buf[1] = BODY_LEN;
        let mb = mb as u32;
        buf[HEADER_LEN] =
            (broadcast_common::len::fit_mask(self.reserved, RESERVED_MASK, "reserved")? << 6)
                | ((mb >> 16) & 0x3F) as u8;
        buf[HEADER_LEN + 1] = ((mb >> 8) & 0xFF) as u8;
        buf[HEADER_LEN + 2] = (mb & 0xFF) as u8;
        Ok(len)
    }
}
impl crate::traits::DescriptorDef<'_> for MaximumBitrateDescriptor {
    const TAG: u8 = TAG;
    const NAME: &'static str = "MAXIMUM_BITRATE";
}

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

    #[test]
    fn parse() {
        let bytes = [
            TAG,
            3,
            0b00_111111,
            0xAB,
            0xCD, // reserved=0, maximum_bitrate=0x3FABCD
        ];
        let d = MaximumBitrateDescriptor::parse(&bytes).unwrap();
        assert_eq!(d.maximum_bitrate, 0x3FABCD);
    }

    #[test]
    fn serialize_round_trip() {
        let d = MaximumBitrateDescriptor::new(0x123456);
        let mut buf = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut buf).unwrap();
        let reparsed = MaximumBitrateDescriptor::parse(&buf).unwrap();
        assert_eq!(d, reparsed);
    }

    #[test]
    fn max_value() {
        let d = MaximumBitrateDescriptor::new(0x3FFFFF); // 22-bit max
        let mut buf = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut buf).unwrap();
        let reparsed = MaximumBitrateDescriptor::parse(&buf).unwrap();
        assert_eq!(reparsed.maximum_bitrate, 0x3FFFFF);
    }

    #[test]
    fn parse_rejects_wrong_tag() {
        let err = MaximumBitrateDescriptor::parse(&[0x0F, 3, 0, 0, 0]).unwrap_err();
        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x0F, .. }));
    }

    #[test]
    fn parse_rejects_wrong_length() {
        let err = MaximumBitrateDescriptor::parse(&[TAG, 2, 0, 0]).unwrap_err();
        assert!(matches!(err, Error::InvalidDescriptor { tag: TAG, .. }));
    }

    #[test]
    fn serialize_rejects_small_buffer() {
        let d = MaximumBitrateDescriptor::new(0);
        let mut tiny = vec![0u8; 2];
        let err = d.serialize_into(&mut tiny).unwrap_err();
        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
    }

    #[test]
    fn serialize_rejects_over_22bit_bitrate() {
        // Pre-fix `(mb >> 16) & 0x3F` silently dropped bits 22..32 (r03-W3).
        let d = MaximumBitrateDescriptor::new(1 << 22);
        let mut buf = vec![0u8; d.serialized_len()];
        assert!(matches!(
            d.serialize_into(&mut buf).unwrap_err(),
            Error::FieldOverflow(_)
        ));
    }

    /// H.222.0 Table 2-67. Parsed reserved bits are preserved (a zero-reserved
    /// sender is no longer normalized to `11`); defaults carry the spec fill.
    #[test]
    fn maximum_bitrate_reserved_preserved() {
        for r in 0u8..=3 {
            let bytes = [TAG, 3, (r << 6) | 0x3F, 0xAB, 0xCD];
            let d = MaximumBitrateDescriptor::parse(&bytes).unwrap();
            assert_eq!(d.reserved, r);
            let mut out = vec![0u8; d.serialized_len()];
            d.serialize_into(&mut out).unwrap();
            assert_eq!(out, bytes);
        }
    }

    #[test]
    fn maximum_bitrate_default_is_spec_value() {
        let d = MaximumBitrateDescriptor::new(0x3FABCD);
        let mut out = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut out).unwrap();
        assert_eq!(out, [TAG, 3, 0xFF, 0xAB, 0xCD]);
    }
}