//! Read-only build metadata generation for HCIE GUI packages.
//!
//! **Purpose:** Publishes the build number prepared by `scripts/cargo-with-build-id.sh` to every
//! frontend without mutating watched Cargo inputs from inside a build script.
//! **Logic & Workflow:** Uses the wrapper-provided override when present, otherwise reads the
//! canonical repository `build.id`, validates it, and emits synchronized compile-time variables.
//! **Side Effects / Dependencies:** Reads one repository file and writes only Cargo directives.

use std::fs;
use std::io;
use std::path::PathBuf;

/// Reads and validates the canonical or wrapper-provided build identifier.
///
/// **Returns:** The current build ID as `u64`.
/// **Side Effects / Dependencies:** Reads `build.id` when no override is provided.
fn build_id() -> u64 {
    if let Ok(value) = std::env::var("HCIE_BUILD_ID_OVERRIDE") {
        return value
            .parse::<u64>()
            .expect("HCIE_BUILD_ID_OVERRIDE must be an unsigned integer");
    }

    let manifest_dir = PathBuf::from(
        std::env::var_os("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR is required"),
    );
    let canonical = manifest_dir
        .parent()
        .expect("hcie-build-info must live directly under the repository root")
        .join("build.id");
    match fs::read_to_string(&canonical) {
        Ok(value) => value.trim().parse::<u64>().unwrap_or_else(|error| {
            panic!("invalid integer in {}: {error}", canonical.display())
        }),
        Err(error) if error.kind() == io::ErrorKind::NotFound => 0,
        Err(error) => panic!("failed to read {}: {error}", canonical.display()),
    }
}

/// Publishes synchronized build metadata to the library crate.
fn main() {
    let manifest_dir = PathBuf::from(
        std::env::var_os("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR is required"),
    );
    let canonical = manifest_dir
        .parent()
        .expect("hcie-build-info must live directly under the repository root")
        .join("build.id");
    println!("cargo:rerun-if-changed={}", canonical.display());
    println!("cargo:rerun-if-env-changed=HCIE_BUILD_ID_OVERRIDE");

    let build_id = build_id();
    let base_version = std::env::var("CARGO_PKG_VERSION").expect("package version is required");
    println!("cargo:rustc-env=HCIE_BUILD_ID={build_id}");
    println!(
        "cargo:rustc-env=HCIE_BUILD_VERSION={base_version}+build.{build_id}"
    );
}