chd 0.3.4

//! Types and methods relating to metadata stored in a CHD file.

use crate::error::{Error, Result};
use crate::make_tag;
use byteorder::{BigEndian, ReadBytesExt};
use std::io::{Cursor, Read, Seek, SeekFrom};

const METADATA_HEADER_SIZE: usize = 16;
use num_derive::FromPrimitive;
use num_traits::FromPrimitive;

/// A list of well-known metadata tags.
#[derive(FromPrimitive, Copy, Clone)]
#[repr(u32)]
pub enum KnownMetadata {
    /// Wildcard for search (0)
    Wildcard = 0,
    /// Hard Disk (`GDDD`)
    HardDisk = make_tag(b"GDDD"),
    /// Hard Disk Identifier (`IDNT`)
    HardDiskIdent = make_tag(b"IDNT"),
    /// Hard Disk Key (`KEY `)
    HardDiskKey = make_tag(b"KEY "),
    /// PCMCIA Card Information (`CIS `)
    PcmciaCIS = make_tag(b"CIS "),
    /// Legacy CD-ROM metadata (`CHCD`)
    CdRomOld = make_tag(b"CHCD"),
    /// CD-ROM track metadata (`CHTR`)
    CdRomTrack = make_tag(b"CHTR"),
    /// CD-ROM track metadata (`CHT2`)
    CdRomTrack2 = make_tag(b"CHT2"),
    /// Legacy GD-ROM metadata (`CHGT`)
    GdRomOld = make_tag(b"CHGT"),
    /// GD-ROM track metadata (`CHGD`)
    GdRomTrack = make_tag(b"CHGD"),
    /// A/V metadata (`AVAV`)
    AudioVideo = make_tag(b"AVAV"),
    /// LaserDisc A/V metadata (`AVLD`)
    AudioVideoLaserDisc = make_tag(b"AVLD"),
}

impl KnownMetadata {
    /// Returns whether a given tag indicates that the CHD contains CDROM data.
    pub fn is_cdrom(tag: u32) -> bool {
        if let Some(tag) = FromPrimitive::from_u32(tag) {
            return matches!(
                tag,
                KnownMetadata::CdRomOld
                    | KnownMetadata::CdRomTrack
                    | KnownMetadata::CdRomTrack2
                    | KnownMetadata::GdRomOld
                    | KnownMetadata::GdRomTrack
            );
        }
        false
    }
}

/// Trait for structs that contain or represent tagged metadata.
pub trait MetadataTag {
    /// Returns the FourCC metatag that this struct represents or refers to.
    fn metatag(&self) -> u32;
}

impl MetadataTag for KnownMetadata {
    fn metatag(&self) -> u32 {
        *self as u32
    }
}

/// A complete CHD metadata entry with contents read into memory.
#[derive(Debug)]
pub struct Metadata {
    /// The FourCC metadata tag.
    pub metatag: u32,
    /// The contents of this metadata entry.
    pub value: Vec<u8>,
    /// The flags of this metadata entry.
    pub flags: u8,
    /// The index of this metadata entry relative to the beginning of the metadata section.
    pub index: u32,
    /// The length of this metadata entry.
    pub length: u32,
}

impl MetadataTag for Metadata {
    fn metatag(&self) -> u32 {
        self.metatag
    }
}

/// A reference to a metadata entry within the CHD file.
#[derive(Clone)]
pub struct MetadataRef {
    offset: u64,
    length: u32,
    flags: u8,
    index: u32,
    metatag: u32,
}

impl MetadataRef {
    fn read_into<F: Read + Seek>(&self, file: &mut F, buf: &mut [u8]) -> Result<()> {
        file.seek(SeekFrom::Start(self.offset + METADATA_HEADER_SIZE as u64))?;
        file.read_exact(buf)?;
        Ok(())
    }

    /// Read the contents of the metadata from the input stream. The `ChdMetadataRef` must have
    /// the same provenance as the input stream for a successful read.
    pub fn read<F: Read + Seek>(&self, file: &mut F) -> Result<Metadata> {
        let mut buf = vec![0u8; self.length as usize];
        self.read_into(file, &mut buf)?;
        Ok(Metadata {
            metatag: self.metatag,
            value: buf,
            flags: self.flags,
            index: self.index,
            length: self.length,
        })
    }
}

impl MetadataTag for MetadataRef {
    #[inline(always)]
    fn metatag(&self) -> u32 {
        self.metatag
    }
}

/// An iterator over references to the metadata entries of a CHD file.
/// If `unstable_lending_iterators` is enabled, metadata can be
/// more ergonomically iterated over with [`MetadataEntries`](crate::iter::MetadataEntries).
pub struct MetadataRefs<'a, F: Read + Seek + 'a> {
    pub(crate) file: &'a mut F,
    curr_offset: u64,
    curr: Option<MetadataRef>,
    // Just use a tuple because we rarely have more than 2 or 3 types of tag.
    indices: Vec<(u32, u32)>,
}

impl<'a, F: Read + Seek + 'a> MetadataRefs<'a, F> {
    pub(crate) fn from_stream(file: &'a mut F, initial_offset: u64) -> Self {
        MetadataRefs {
            file,
            curr_offset: initial_offset,
            curr: None,
            indices: Vec::new(),
        }
    }

    pub(crate) fn dead(file: &'a mut F) -> Self {
        MetadataRefs {
            file,
            curr_offset: 0,
            curr: None,
            indices: Vec::new(),
        }
    }
}

impl<'a, F: Read + Seek + 'a> TryFrom<MetadataRefs<'a, F>> for Vec<Metadata> {
    type Error = Error;

    fn try_from(mut value: MetadataRefs<'a, F>) -> std::result::Result<Self, Self::Error> {
        let metas = &mut value;
        let metas: Vec<_> = metas.collect();
        metas.iter().map(|e| e.read(&mut value.file)).collect()
    }
}

impl<'a, F: Read + Seek + 'a> Iterator for MetadataRefs<'a, F> {
    // really need GATs to do this properly...
    type Item = MetadataRef;

    fn next(&mut self) -> Option<Self::Item> {
        if self.curr_offset == 0 {
            return None;
        }

        fn next_inner<'a, F: Read + Seek + 'a>(s: &mut MetadataRefs<'a, F>) -> Result<MetadataRef> {
            let mut raw_header: [u8; METADATA_HEADER_SIZE] = [0; METADATA_HEADER_SIZE];
            s.file.seek(SeekFrom::Start(s.curr_offset))?;
            let count = s.file.read(&mut raw_header)?;
            if count != METADATA_HEADER_SIZE {
                return Err(Error::MetadataNotFound);
            }
            let mut cursor = Cursor::new(raw_header);
            cursor.seek(SeekFrom::Start(0))?;

            // extract data
            let metatag = cursor.read_u32::<BigEndian>()?;
            let length = cursor.read_u32::<BigEndian>()?;
            let next = cursor.read_u64::<BigEndian>()?;

            let flags = length >> 24;
            // mask off flags
            let length = length & 0x00ffffff;

            let mut index = 0;

            for indice in s.indices.iter_mut() {
                if indice.0 == metatag {
                    index = indice.1;
                    // increment current index
                    indice.1 += 1;
                    break;
                }
            }

            if index == 0 {
                s.indices.push((metatag, 1))
            }

            let new = MetadataRef {
                offset: s.curr_offset,
                length,
                metatag,
                flags: flags as u8,
                index,
            };

            s.curr_offset = next;
            s.curr = Some(new.clone());
            Ok(new)
        }
        next_inner(self).ok()
    }
}