dvb-si 12.1.0

//! Metadata STD Descriptor — ISO/IEC 13818-1 §2.6.62, Table 2-91 (tag 0x27).
//!
//! Three 22-bit uimsbf values (stored as u32 with top 10 bits zero),
//! each preceded by 2 reserved bits. Total body: 9 bytes.

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

/// Descriptor tag for Metadata_STD_descriptor.
pub const TAG: u8 = 0x27;
const HEADER_LEN: usize = 2;
const BODY_LEN: u8 = 9;
/// Default of each 2-bit `reserved` ahead of the three 22-bit fields (H.222.0
/// Table 2-91): clause 2.1 "reserved" = `1` (all editions 2006-08/2023, audit
/// §5).
pub const RESERVED_DEFAULT: u8 = 0b11;
const RESERVED_MASK: u8 = 0x03;

/// Metadata STD Descriptor.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[non_exhaustive]
pub struct MetadataStdDescriptor {
    /// metadata_input_leak_rate, 22-bit uimsbf, in units of 400 bits/s.
    pub metadata_input_leak_rate: u32,
    /// metadata_buffer_size, 22-bit uimsbf, in units of 1024 bytes.
    pub metadata_buffer_size: u32,
    /// metadata_output_leak_rate, 22-bit uimsbf, in units of 400 bits/s.
    pub metadata_output_leak_rate: u32,
    /// `reserved(2)` ahead of `metadata_input_leak_rate` (2 bits,
    /// right-aligned). Captured on parse, re-emitted verbatim; defaults to
    /// [`RESERVED_DEFAULT`].
    pub reserved_input_leak_rate: u8,
    /// `reserved(2)` ahead of `metadata_buffer_size` (2 bits, right-aligned).
    /// Captured on parse, re-emitted verbatim; defaults to
    /// [`RESERVED_DEFAULT`].
    pub reserved_buffer_size: u8,
    /// `reserved(2)` ahead of `metadata_output_leak_rate` (2 bits,
    /// right-aligned). Captured on parse, re-emitted verbatim; defaults to
    /// [`RESERVED_DEFAULT`].
    pub reserved_output_leak_rate: u8,
}

impl MetadataStdDescriptor {
    /// Build with the spec-default reserved bits.
    #[must_use]
    pub const fn new(
        metadata_input_leak_rate: u32,
        metadata_buffer_size: u32,
        metadata_output_leak_rate: u32,
    ) -> Self {
        Self {
            metadata_input_leak_rate,
            metadata_buffer_size,
            metadata_output_leak_rate,
            reserved_input_leak_rate: RESERVED_DEFAULT,
            reserved_buffer_size: RESERVED_DEFAULT,
            reserved_output_leak_rate: RESERVED_DEFAULT,
        }
    }
}

/// Extract a 22-bit uimsbf from a 3-byte slice; Table 2-91 puts 2 reserved
/// bits ahead of each 22-bit field (top 2 bits of the first byte), which
/// must be masked off, not folded into the value.
fn read_u22(bytes: &[u8]) -> u32 {
    (((bytes[0] & 0x3F) as u32) << 16) | ((bytes[1] as u32) << 8) | (bytes[2] as u32)
}

/// Write a 22-bit value into a 3-byte slice behind its 2 reserved bits.
fn write_u22(reserved: u8, val: u32, buf: &mut [u8]) -> Result<()> {
    let masked = val & 0x003F_FFFF;
    buf[0] = (broadcast_common::len::fit_mask(reserved, RESERVED_MASK, "reserved")? << 6)
        | ((masked >> 16) & 0x3F) as u8;
    buf[1] = ((masked >> 8) & 0xFF) as u8;
    buf[2] = (masked & 0xFF) as u8;
    Ok(())
}

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

    fn parse(bytes: &'a [u8]) -> Result<Self> {
        let body = descriptor_body(
            bytes,
            TAG,
            "MetadataStdDescriptor",
            "unexpected tag for Metadata_STD_descriptor",
        )?;
        if body.len() != BODY_LEN as usize {
            return Err(Error::InvalidDescriptor {
                tag: TAG,
                reason: "Metadata_STD_descriptor length must equal 9",
            });
        }
        Ok(Self {
            metadata_input_leak_rate: read_u22(&body[0..3]),
            metadata_buffer_size: read_u22(&body[3..6]),
            metadata_output_leak_rate: read_u22(&body[6..9]),
            reserved_input_leak_rate: body[0] >> 6,
            reserved_buffer_size: body[3] >> 6,
            reserved_output_leak_rate: body[6] >> 6,
        })
    }
}

impl Serialize for MetadataStdDescriptor {
    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(),
            });
        }
        // 22-bit fields: `write_u22` masks, so reject a wider value first
        // (audit r03-W3 class).
        broadcast_common::len::fit_bits(
            u64::from(self.metadata_input_leak_rate),
            22,
            "metadata_input_leak_rate",
        )?;
        broadcast_common::len::fit_bits(
            u64::from(self.metadata_buffer_size),
            22,
            "metadata_buffer_size",
        )?;
        broadcast_common::len::fit_bits(
            u64::from(self.metadata_output_leak_rate),
            22,
            "metadata_output_leak_rate",
        )?;
        buf[0] = TAG;
        buf[1] = BODY_LEN;
        write_u22(
            self.reserved_input_leak_rate,
            self.metadata_input_leak_rate,
            &mut buf[HEADER_LEN..HEADER_LEN + 3],
        )?;
        write_u22(
            self.reserved_buffer_size,
            self.metadata_buffer_size,
            &mut buf[HEADER_LEN + 3..HEADER_LEN + 6],
        )?;
        write_u22(
            self.reserved_output_leak_rate,
            self.metadata_output_leak_rate,
            &mut buf[HEADER_LEN + 6..HEADER_LEN + 9],
        )?;
        Ok(len)
    }
}
impl crate::traits::DescriptorDef<'_> for MetadataStdDescriptor {
    const TAG: u8 = TAG;
    const NAME: &'static str = "METADATA_STD";
}

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

    #[test]
    fn parse_extracts_fields() {
        let bytes = [TAG, 9, 0x10, 0x20, 0x30, 0x01, 0x02, 0x03, 0x3F, 0xFF, 0xFF];
        let d = MetadataStdDescriptor::parse(&bytes).unwrap();
        assert_eq!(d.metadata_input_leak_rate, read_u22(&[0x10, 0x20, 0x30]));
        assert_eq!(d.metadata_buffer_size, read_u22(&[0x01, 0x02, 0x03]));
        assert_eq!(d.metadata_output_leak_rate, read_u22(&[0x3F, 0xFF, 0xFF]));
    }

    #[test]
    fn parse_max_values() {
        let bytes = [TAG, 9, 0x3F, 0xFF, 0xFF, 0x3F, 0xFF, 0xFF, 0x3F, 0xFF, 0xFF];
        let d = MetadataStdDescriptor::parse(&bytes).unwrap();
        assert_eq!(d.metadata_input_leak_rate, 0x003F_FFFF);
        assert_eq!(d.metadata_buffer_size, 0x003F_FFFF);
        assert_eq!(d.metadata_output_leak_rate, 0x003F_FFFF);
    }

    #[test]
    fn parse_rejects_wrong_tag() {
        let err = MetadataStdDescriptor::parse(&[0x02, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0]).unwrap_err();
        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x02, .. }));
    }

    #[test]
    fn parse_rejects_wrong_length() {
        let err = MetadataStdDescriptor::parse(&[TAG, 8, 0, 0, 0, 0, 0, 0, 0, 0]).unwrap_err();
        assert!(matches!(err, Error::InvalidDescriptor { .. }));
    }

    #[test]
    fn serialize_round_trip() {
        let d = MetadataStdDescriptor::new(0x000A_BCDE, 0x003F_0000, 0x0000_1234);
        let mut buf = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut buf).unwrap();
        let reparsed = MetadataStdDescriptor::parse(&buf).unwrap();
        assert_eq!(d, reparsed);
    }

    #[test]
    fn serialize_rejects_a_value_wider_than_22_bits() {
        // Used to be masked down silently into a different valid-looking
        // value (audit r03-W3 class).
        for (a, b, c) in [
            (0x0040_0000, 0, 0),
            (0, 0x0040_0000, 0),
            (0, 0, 0x0040_0000),
        ] {
            let d = MetadataStdDescriptor::new(a, b, c);
            let mut buf = vec![0u8; d.serialized_len()];
            assert!(matches!(
                d.serialize_into(&mut buf),
                Err(Error::FieldOverflow(_))
            ));
        }
    }

    #[test]
    fn serialize_round_trip_max_value_and_default_reserved_bits() {
        // The largest 22-bit value round-trips, and the 2 reserved bits ahead
        // of it (Table 2-91) default to 1s when default-constructed, never
        // folded into the value.
        let d = MetadataStdDescriptor::new(0x003F_FFFF, 0x003F_FFFF, 0x003F_FFFF);
        let mut buf = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut buf).unwrap();
        assert_eq!(
            buf[HEADER_LEN] & 0xC0,
            0xC0,
            "reserved bits before leak_rate"
        );
        assert_eq!(
            buf[HEADER_LEN + 3] & 0xC0,
            0xC0,
            "reserved bits before buffer_size"
        );
        assert_eq!(
            buf[HEADER_LEN + 6] & 0xC0,
            0xC0,
            "reserved bits before output_leak_rate"
        );
        let reparsed = MetadataStdDescriptor::parse(&buf).unwrap();
        assert_eq!(reparsed.metadata_input_leak_rate, 0x003F_FFFF);
        assert_eq!(reparsed.metadata_buffer_size, 0x003F_FFFF);
        assert_eq!(reparsed.metadata_output_leak_rate, 0x003F_FFFF);
    }

    /// Regression for issue #1006: a conformant descriptor with reserved
    /// bits set to 1 (`0xC0 00 01 ...`) must decode leak_rate to 1, not
    /// 12,582,913 (the old code folded the reserved bits into the value).
    #[test]
    fn parse_masks_reserved_bits_ahead_of_value() {
        let bytes = [TAG, 9, 0xC0, 0x00, 0x01, 0xC0, 0x00, 0x02, 0xC0, 0x00, 0x03];
        let d = MetadataStdDescriptor::parse(&bytes).unwrap();
        assert_eq!(d.metadata_input_leak_rate, 1);
        assert_eq!(d.metadata_buffer_size, 2);
        assert_eq!(d.metadata_output_leak_rate, 3);
    }

    #[test]
    fn serialize_rejects_small_buffer() {
        let d = MetadataStdDescriptor::new(0, 0, 0);
        let mut tiny = vec![0u8; 8];
        let err = d.serialize_into(&mut tiny).unwrap_err();
        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
    }

    /// H.222.0 Table 2-91. All three reserved(2) regions are preserved
    /// verbatim.
    #[test]
    fn metadata_std_reserved_preserved() {
        for r1 in 0u8..=3 {
            for r2 in 0u8..=3 {
                for r3 in 0u8..=3 {
                    let bytes = [
                        TAG,
                        9,
                        (r1 << 6) | 0x10,
                        0x20,
                        0x30,
                        (r2 << 6) | 0x01,
                        0x02,
                        0x03,
                        (r3 << 6) | 0x3F,
                        0xFF,
                        0xFF,
                    ];
                    let d = MetadataStdDescriptor::parse(&bytes).unwrap();
                    assert_eq!(
                        (
                            d.reserved_input_leak_rate,
                            d.reserved_buffer_size,
                            d.reserved_output_leak_rate
                        ),
                        (r1, r2, r3)
                    );
                    let mut out = vec![0u8; d.serialized_len()];
                    d.serialize_into(&mut out).unwrap();
                    assert_eq!(out, bytes);
                }
            }
        }
    }

    #[test]
    fn metadata_std_default_is_spec_value() {
        let d = MetadataStdDescriptor::new(1, 2, 3);
        let mut out = vec![0u8; d.serialized_len()];
        d.serialize_into(&mut out).unwrap();
        assert_eq!(
            out,
            [TAG, 9, 0xC0, 0x00, 0x01, 0xC0, 0x00, 0x02, 0xC0, 0x00, 0x03]
        );
    }
}