//! Dump an XBG7 resource's descriptor around each index marker, to see whether a
//! grouped pool carries a declaration PER sub-mesh (the 2026-08-13 mixed-stride
//! finding says it must: n201's four sub-meshes use strides 24/24/24/28 and four
//! different vertex shaders).
//! Usage: desc_dump <container.xpr> <resource>

fn be32(b: &[u8], o: usize) -> u32 {
    u32::from_be_bytes(b[o..o + 4].try_into().unwrap())
}

fn main() {
    let a: Vec<String> = std::env::args().collect();
    let bytes = std::fs::read(&a[1]).unwrap();
    let want = &a[2];
    // Walk the XPR2 directory by hand (the crate's reader is private).
    // 16-byte directory entries at 0x10: type tag, data offset, descriptor size,
    // name offset — all relative to 0x10 (see texture::Xpr2ResourceEntry).
    let num = be32(&bytes, 12) as usize;
    for i in 0..num {
        let e = &bytes[0x10 + i * 16..0x10 + i * 16 + 16];
        let tag = &e[0..4];
        let data_off = be32(e, 4) as usize + 0x10;
        let desc_size = be32(e, 8) as usize;
        let name_off = be32(e, 12) as usize + 0x10;
        if tag != b"XBG7" {
            continue;
        }
        let name = {
            let s = name_off.min(bytes.len());
            let end = bytes[s..].iter().position(|&c| c == 0).unwrap_or(0) + s;
            String::from_utf8_lossy(&bytes[s..end]).to_string()
        };
        if name != *want {
            continue;
        }
        let desc = &bytes[data_off..(data_off + desc_size).min(bytes.len())];
        println!("{name}: descriptor at 0x{data_off:X}, {} bytes", desc.len());
        // markers: a == c*2, c%3==0, vertex count 32 bytes earlier
        let mut rel = 0usize;
        while rel + 8 <= desc.len() {
            let (x, c) = (be32(desc, rel), be32(desc, rel + 4));
            if c >= 3 && c % 3 == 0 && c < 400_000 && x == c * 2 && rel >= 32 {
                let vc = be32(desc, rel - 32);
                if (3..=200_000).contains(&vc) {
                    println!("\n  marker @0x{rel:X}: {vc} verts / {c} indices — declaration triples after it:");
                    let mut r = rel + 8;
                    let mut stride = 0u32;
                    for _ in 0..12 {
                        if r + 12 > desc.len() {
                            break;
                        }
                        let (o, code, usage) = (be32(desc, r), be32(desc, r + 4), be32(desc, r + 8) >> 16);
                        if o == 0x00FF_0000 || code == 0xFFFF_FFFF || o > 0x1000 {
                            println!("    end marker @0x{r:X}: off=0x{o:X} code=0x{code:X}");
                            break;
                        }
                        println!("    off {o:>3}  code 0x{:06X}  usage {usage}", code & 0xFF_FFFF);
                        stride = stride.max(o + 4);
                        r += 12;
                    }
                    println!("    (min stride from element offsets: {stride})");
                    rel += 8;
                    continue;
                }
            }
            rel += 4;
        }
        return;
    }
    eprintln!("resource not found");
}