rune-fs 0.2.0

use nom::{
    combinator::rest,
    number::complete::{be_u16, be_u24, be_u32, be_u8},
};
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};

use crate::{archive::ArchiveRef, error::ReadError};

pub const SECTOR_HEADER_SIZE: usize = 8;
pub const SECTOR_EXPANDED_HEADER_SIZE: usize = 10;
pub const SECTOR_DATA_SIZE: usize = 512;
pub const SECTOR_EXPANDED_DATA_SIZE: usize = 510;
pub const SECTOR_SIZE: usize = SECTOR_HEADER_SIZE + SECTOR_DATA_SIZE;

/// A section of data read from the `Dat2` file.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
pub struct Sector<'a> {
    pub header: SectorHeader,
    pub data_block: &'a [u8],
}

impl<'a> Sector<'a> {
    /// Creates a sector from the given buffer using the header size to correctly initiate
    /// the root sector.
    /// 
    /// # Errors
    /// 
    /// Either a `SectorHeader` couldn't be initiated due to a wrong buffer or 
    /// there are no more bytes after the initial header.
    pub fn new(buffer: &'a [u8], header_size: &SectorHeaderSize) -> crate::Result<Self> {
        let (buffer, header) = SectorHeader::new(buffer, header_size)?;
        let (_, data_block) = rest(buffer)?;

        Ok(Self { header, data_block })
    }
}

/// A section header containing validation and its next sector.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
pub struct SectorHeader {
    pub archive_id: u32,
    pub chunk: usize,
    pub next: usize,
    pub index_id: u8,
}

impl<'a> SectorHeader {
    /// Constructs a sector header from the given buffer.
    /// 
    /// Each sector is guaranteed to have a length of 520 bytes. The header size
    /// will be either 8 or 10 bytes, making the data size either 512 or 510 bytes 
    /// respectively. Only when the archive id exceeds `u16::MAX` will the header size
    /// be expanded (meaning a 10 byte header).
    /// 
    /// # Errors
    /// 
    /// The header buffer needs to be exactly `SectorHeaderSize`, otherwise you will
    /// get a parser error. 
    pub fn new(
        buffer: &'a [u8],
        header_size: &SectorHeaderSize,
    ) -> crate::Result<(&'a [u8], Self)> {
        let (buffer, archive_id) = match header_size {
            SectorHeaderSize::Normal => {
                let (buffer, archive_id) = be_u16(buffer)?;
                (buffer, archive_id as u32)
            }
            SectorHeaderSize::Expanded => be_u32(buffer)?,
        };
        let (buffer, chunk) = be_u16(buffer)?;
        let (buffer, next) = be_u24(buffer)?;
        let (buffer, index_id) = be_u8(buffer)?;

        Ok((
            buffer,
            Self {
                archive_id,
                chunk: chunk as usize,
                next: next as usize,
                index_id,
            },
        ))
    }

    pub const fn validate(
        &self,
        archive_id: u32,
        chunk: usize,
        index_id: u8,
    ) -> Result<(), ReadError> {
        if self.archive_id != archive_id {
            return Err(ReadError::SectorArchiveMismatch(
                self.archive_id,
                archive_id,
            ));
        }

        if self.chunk != chunk {
            return Err(ReadError::SectorChunkMismatch(self.chunk, chunk));
        }

        if self.index_id != index_id {
            return Err(ReadError::SectorIndexMismatch(self.index_id, index_id));
        }

        Ok(())
    }
}

/// Used to convey a sector's header size when parsing from a raw buffer.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
pub enum SectorHeaderSize {
    /// 8 byte header length.
    #[default]
    Normal,
    /// 10 byte header length.
    Expanded,
}

impl From<&ArchiveRef> for SectorHeaderSize {
    fn from(archive: &ArchiveRef) -> Self {
        if archive.id > u16::MAX.into() {
            Self::Expanded
        } else {
            Self::Normal
        }
    }
}

#[test]
fn header_size_normal() -> crate::Result<()> {
    let archive = ArchiveRef {
        id: u16::MAX as u32,
        index_id: 0,
        sector: 0,
        length: 0,
    };
    let header_size = SectorHeaderSize::from(&archive);

    assert_eq!(header_size, SectorHeaderSize::Normal);

    Ok(())
}

#[test]
fn header_size_expanded() -> crate::Result<()> {
    let archive = ArchiveRef {
        id: (u16::MAX as u32) + 1,
        index_id: 0,
        sector: 0,
        length: 0,
    };
    let header_size = SectorHeaderSize::from(&archive);

    assert_eq!(header_size, SectorHeaderSize::Expanded);

    Ok(())
}

#[test]
fn parse_header() -> crate::Result<()> {
    let buffer = &[0, 0, 0, 0, 0, 0, 2, 255];
    let (_, header) = SectorHeader::new(buffer, &SectorHeaderSize::Normal)?;

    assert_eq!(
        header,
        SectorHeader {
            archive_id: 0,
            chunk: 0,
            next: 2,
            index_id: 255
        }
    );

    Ok(())
}

#[test]
fn header_validation() {
    let header = SectorHeader {
        archive_id: 0,
        chunk: 0,
        next: 2,
        index_id: 255,
    };

    assert_eq!(
        header.validate(1, 0, 255),
        Err(ReadError::SectorArchiveMismatch(header.archive_id, 1))
    );
    assert_eq!(
        header.validate(0, 1, 255),
        Err(ReadError::SectorChunkMismatch(header.chunk, 1))
    );
    assert_eq!(
        header.validate(0, 0, 0),
        Err(ReadError::SectorIndexMismatch(header.index_id, 0))
    );
}