// Trivial tar loader.

use core::mem::{size_of, transmute};
use core::ptr;
use matcha_hal::dprintf;

const EFLASH_START: u32 = 0x44000000;
const EFLASH_END: u32 = 0x45000000;

#[repr(C, packed)]
pub struct TarHeader {
    /* byte offset */
    name: [u8; 100],     /*   0 */
    mode: [u8; 8],       /* 100 */
    uid: [u8; 8],        /* 108 */
    gid: [u8; 8],        /* 116 */
    size: [u8; 12],      /* 124 */
    mtime: [u8; 12],     /* 136 */
    chksum: [u8; 8],     /* 148 */
    typeflag: u8,        /* 156 */
    linkname: [u8; 100], /* 157 */
    magic: [u8; 6],      /* 257 */
    version: [u8; 2],    /* 263 */
    uname: [u8; 32],     /* 265 */
    gname: [u8; 32],     /* 297 */
    devmajor: [u8; 8],   /* 329 */
    devminor: [u8; 8],   /* 337 */
    prefix: [u8; 155],   /* 345 */
    reserved: [u8; 12],  /* 512 */
}

impl Default for TarHeader {
    fn default() -> Self {
        return TarHeader {
            name: [0; 100],
            mode: [0; 8],
            uid: [0; 8],
            gid: [0; 8],
            size: [0; 12],
            mtime: [0; 12],
            chksum: [0; 8],
            typeflag: 0,
            linkname: [0; 100],
            magic: [0; 6],
            version: [0; 2],
            uname: [0; 32],
            gname: [0; 32],
            devmajor: [0; 8],
            devminor: [0; 8],
            prefix: [0; 155],
            reserved: [0; 12],
        };
    }
}

impl TarHeader {
    pub fn from_bytes(b: &[u8]) -> TarHeader {
        unsafe { b.as_ptr().cast::<TarHeader>().read() }
    }

    pub fn has_magic(&self) -> bool {
        self.magic[..5] == *b"ustar"
    }

    pub fn name(&self) -> &str {
        if let Some(len) = self.name.iter().position(|&x| x == 0) {
            core::str::from_utf8(&self.name[..len])
        } else {
            core::str::from_utf8(&self.name)
        }
        .unwrap_or("<invalid>")
    }

    pub fn size(&self) -> u32 {
        parse_octal(&self.size)
    }
}

fn parse_octal(text: &[u8]) -> u32 {
    text.iter()
        .take_while(|&&x| x != 0)
        .fold(0u32, |acc, &x| (acc << 3) + (x as u32 - '0' as u32))
}

pub unsafe fn find_file(name: &str) -> (u32, u32) {
    let mut cursor = EFLASH_START;
    while (cursor + 512) < EFLASH_END {
        let tar_header = &*(cursor as *const TarHeader);
        if !tar_header.has_magic() {
            // Our tar files have the "ustar" magic field; use it
            // to avoid scanning all EFLASH.
            break;
        }
        cursor += size_of::<TarHeader>() as u32;
        let tar_name = tar_header.name();
        let tar_size = tar_header.size();
        if tar_name == name {
            return (cursor, tar_size);
        } else {
            fn roundup(a: u32, b: u32) -> u32 {
                ((a + b - 1) / b) * b
            }
            cursor += roundup(
                tar_size,
                size_of::<TarHeader>() as u32,
            );
        }
    }

    dprintf!("Could not find tar entry for '{}'\n", name);
    return (0, 0);
}

// TODO(sleffler): rethink api, e.g. supply a range for bounds check
pub unsafe fn copy_file(name: &str, offset: u32) -> bool {
    let (cursor, size) = find_file(name);
    if cursor != 0 {
        ptr::copy_nonoverlapping::<u8>(
            transmute(cursor),
            transmute(offset),
            size as usize,
        );
        true
    } else {
        false
    }
}