use std::env;
use std::fs::read_dir;
use std::path::{Path, PathBuf};

const AMENT_PREFIX_PATH: &str = "AMENT_PREFIX_PATH";
const ROS_DISTRO: &str = "ROS_DISTRO";
const BINDGEN_WRAPPER: &str = "src/rcl_wrapper.h";

fn get_env_var_or_abort(env_var: &'static str) -> String {
    if let Ok(value) = env::var(env_var) {
        value
    } else {
        panic!(
            "{} environment variable not set - please source ROS 2 installation first.",
            env_var
        );
    }
}

fn main() {
    let ros_distro = if let Ok(value) = env::var(ROS_DISTRO) {
        value
    } else {
        println!(
            "{} environment variable not set - please source ROS 2 installation first.",
            ROS_DISTRO
        );
        return;
    };

    println!("cargo:rustc-cfg=ros_distro=\"{ros_distro}\"");

    let mut builder = bindgen::Builder::default()
        .header(BINDGEN_WRAPPER)
        .derive_copy(false)
        .allowlist_type("rcl_.*")
        .allowlist_type("rmw_.*")
        .allowlist_type("rcutils_.*")
        .allowlist_type("rosidl_.*")
        .allowlist_function("rcl_.*")
        .allowlist_function("rmw_.*")
        .allowlist_function("rcutils_.*")
        .allowlist_function("rosidl_.*")
        .allowlist_var("rcl_.*")
        .allowlist_var("rmw_.*")
        .allowlist_var("rcutils_.*")
        .allowlist_var("rosidl_.*")
        .layout_tests(false)
        .default_enum_style(bindgen::EnumVariation::Rust {
            non_exhaustive: false,
        })
        .parse_callbacks(Box::new(bindgen::CargoCallbacks));

    // Invalidate the built crate whenever this script or the wrapper changes
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rerun-if-changed={BINDGEN_WRAPPER}");

    // #############
    // # ALGORITHM #
    // #############
    //
    // For each prefix in ${AMENT_PREFIX_PATH}:
    // Search through ament index at ${prefix}/share/ament_index/resource_index/packages/ to find packages to include
    // The include root will be located at either:
    // - ${prefix}/include/ (old style)
    // - ${prefix}/include/${package_name} (new style)
    // - ${prefix}/include/CycloneDDS (special case, match for this)
    // End of loop
    // Compiled libraries are always at ${prefix}/lib
    //
    // See REP 122 for more details: https://www.ros.org/reps/rep-0122.html#filesystem-layout

    let ament_prefix_paths = get_env_var_or_abort(AMENT_PREFIX_PATH);
    for ament_prefix_path in ament_prefix_paths.split(':').map(Path::new) {
        // Locate the ament index
        let ament_index = ament_prefix_path.join("share/ament_index/resource_index/packages");
        if !ament_index.is_dir() {
            continue;
        }

        // Old-style include directory
        let include_dir = ament_prefix_path.join("include");

        // Including the old-style packages
        builder = builder.clang_arg(format!("-isystem{}", include_dir.display()));

        // Search for and include new-style-converted package paths
        for dir_entry in read_dir(&ament_index).unwrap().filter_map(|p| p.ok()) {
            let package = dir_entry.file_name();
            let package_include_dir = include_dir.join(&package);

            if package_include_dir.is_dir() {
                let new_style_include_dir = package_include_dir.join(&package);

                // CycloneDDS is a special case - it needs to be included as if it were a new-style path, but
                // doesn't actually have a secondary folder within it called "CycloneDDS"
                // TODO(jhdcs): if this changes in future, remove this check
                if package == "CycloneDDS" || new_style_include_dir.is_dir() {
                    builder =
                        builder.clang_arg(format!("-isystem{}", package_include_dir.display()));
                }
            }
        }

        // Link the native libraries
        let library_path = ament_prefix_path.join("lib");
        println!("cargo:rustc-link-search=native={}", library_path.display());
    }

    println!("cargo:rustc-link-lib=dylib=rcl");
    println!("cargo:rustc-link-lib=dylib=rcl_yaml_param_parser");
    println!("cargo:rustc-link-lib=dylib=rcutils");
    println!("cargo:rustc-link-lib=dylib=rmw");
    println!("cargo:rustc-link-lib=dylib=rmw_implementation");

    let bindings = builder.generate().expect("Unable to generate bindings");

    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
    bindings
        .write_to_file(out_path.join("rcl_bindings_generated.rs"))
        .expect("Couldn't write bindings!");
}