//! This selects the curve25519_dalek_bits either by default from target_pointer_width or explicitly set

#![deny(clippy::unwrap_used, dead_code)]

#[allow(non_camel_case_types)]
enum DalekBits {
    #[cfg_attr(curve25519_dalek_bits = "64", allow(dead_code))]
    Dalek32,
    #[cfg_attr(curve25519_dalek_bits = "32", allow(dead_code))]
    Dalek64,
}

fn main() {
    #[cfg(curve25519_dalek_bits = "32")]
    let curve25519_dalek_bits = DalekBits::Dalek32;

    #[cfg(curve25519_dalek_bits = "64")]
    let curve25519_dalek_bits = DalekBits::Dalek64;

    #[cfg(all(not(curve25519_dalek_bits = "64"), not(curve25519_dalek_bits = "32")))]
    let curve25519_dalek_bits = deterministic::determine_curve25519_dalek_bits();

    match curve25519_dalek_bits {
        DalekBits::Dalek64 => println!("cargo:rustc-cfg=curve25519_dalek_bits=\"64\""),
        DalekBits::Dalek32 => println!("cargo:rustc-cfg=curve25519_dalek_bits=\"32\""),
    }
}

// Deterministic cfg(curve25519_dalek_bits) when this is not explicitly set.
#[cfg(all(not(curve25519_dalek_bits = "64"), not(curve25519_dalek_bits = "32")))]
mod deterministic {

    use super::*;

    // Standard Cargo TARGET environment variable of triplet is required
    static ERR_MSG_NO_TARGET: &str = "Standard Cargo TARGET environment variable is not set.";

    // Custom Non-Rust standard target platforms require explicit settings.
    static ERR_MSG_NO_PLATFORM: &str = "Unknown Rust target platform.";

    // Error handling when the bits setting cannot be determined
    fn determine_curve25519_dalek_bits_error(cause: &str) -> ! {
        eprintln!("Error: {cause}");
        eprintln!("Please set cfg(curve25519_dalek_bits) explicitly either as 32 or 64.");
        std::process::exit(1)
    }

    // Determine the curve25519_dalek_bits based on Rust standard TARGET triplet
    pub(super) fn determine_curve25519_dalek_bits() -> DalekBits {
        use platforms::target::PointerWidth;

        // TARGET environment is supplied by Cargo
        // https://doc.rust-lang.org/cargo/reference/environment-variables.html
        let target_triplet = match std::env::var("TARGET") {
            Ok(t) => t,
            Err(_) => determine_curve25519_dalek_bits_error(ERR_MSG_NO_TARGET),
        };

        // platforms crate is the source of truth used to determine the platform
        let platform = match platforms::Platform::find(&target_triplet) {
            Some(p) => p,
            None => determine_curve25519_dalek_bits_error(ERR_MSG_NO_PLATFORM),
        };

        #[allow(clippy::match_single_binding)]
        match platform.target_arch {
            //Issues: 449 and 456
            //TODO(Arm): Needs tests + benchmarks to back this up
            //platforms::target::Arch::Arm => DalekBits::Dalek64,
            //TODO(Wasm32): Needs tests + benchmarks to back this up
            //platforms::target::Arch::Wasm32 => DalekBits::Dalek64,
            _ => match platform.target_pointer_width {
                PointerWidth::U64 => DalekBits::Dalek64,
                PointerWidth::U32 => DalekBits::Dalek32,
                // Intended default solely for non-32/64 target pointer widths
                // Otherwise known target platforms only.
                _ => DalekBits::Dalek32,
            },
        }
    }
}