//! Check the model is a model and not an LFS pointer.
//!
//! `models/*.onnx` is stored in Git LFS (see `.gitattributes`). A clone made
//! without git-lfs installed, or with `GIT_LFS_SKIP_SMUDGE` set, leaves a
//! ~130-byte text pointer at that path instead of the weights.
//!
//! Without this check `include_bytes!` would happily embed the pointer, the
//! crate would compile, and the failure would surface much later as an opaque
//! ONNX parse error from inside tract — at which point the connection back to
//! a missing `git lfs pull` is not one anybody would make quickly. Failing
//! here costs one file read and turns that into a sentence.

use std::path::Path;

const MODEL: &str = "models/yolo26n-seg.onnx";

fn main() {
    println!("cargo:rerun-if-changed={MODEL}");
    println!("cargo:rerun-if-changed=build.rs");

    // Only the embedded path needs the file present; a build without it is
    // watershed-only by choice and should not be blocked on weights.
    if std::env::var_os("CARGO_FEATURE_EMBEDDED_MODEL").is_none() {
        return;
    }

    let path = Path::new(MODEL);
    let Ok(bytes) = std::fs::read(path) else {
        panic!(
            "\n\n{MODEL} is missing.\n\
             It ships in Git LFS. Run `git lfs install && git lfs pull`, or build \
             with `--no-default-features` for a watershed-only build.\n"
        );
    };

    // ONNX is protobuf, which has no magic number; an LFS pointer is short
    // ASCII beginning with a version URL. Testing for the pointer is the
    // reliable direction — it has a known shape, where "valid protobuf" does
    // not, and this check only has to catch the one failure that actually
    // happens in practice.
    if bytes.starts_with(b"version https://git-lfs") {
        panic!(
            "\n\n{MODEL} is a Git LFS pointer, not the model ({} bytes).\n\
             Run `git lfs install && git lfs pull` to fetch the real file.\n",
            bytes.len()
        );
    }

    // A model that parses as a pointer-sized file is not one either. The real
    // export is ~11 MB; anything under a megabyte is a truncated checkout.
    if bytes.len() < 1_000_000 {
        panic!(
            "\n\n{MODEL} is only {} bytes — expected ~11 MB.\n\
             The checkout looks incomplete; try `git lfs pull`.\n",
            bytes.len()
        );
    }
}