use std::env;
use std::fs::OpenOptions;
#[cfg(not(feature = "hosted"))]
use std::io::Read;
use std::io::Write;
use std::path::PathBuf;

fn out_dir() -> PathBuf { PathBuf::from(env::var_os("OUT_DIR").unwrap()) }

/// Helper macro that returns a constant number of features enabled among specified list.
macro_rules! count_enabled_features {
    ($($feature:literal),*) => {
        {
            let mut enabled_features = 0;
            $(
                enabled_features += cfg!(feature = $feature) as u32;
            )*
            enabled_features
        }
    }
}

/// Helper macro that returns a compile-time error if multiple or none of the
/// features of some category are defined.
///
/// # Example
///
/// Given the following code:
///
/// ```
/// allow_single_feature!("feature-category-name", "a", "b", "c");
/// ```
///
/// These runs fail compilation check:
/// $ cargo check --features a,b # error msg: 'Multiple feature-category-name specified. Only one is allowed.
/// $ cargo check # error msg: 'None of the feature-category-name specified. Pick one.'
///
/// This compiles:
/// $ cargo check --feature a
macro_rules! allow_single_feature {
    ($name:literal, $($feature:literal),*) => {
        const _: () = {
            const MSG_MULTIPLE: &str = concat!("\nMultiple ", $name, " specified. Only one is allowed.");
            const MSG_NONE: &str = concat!("\nNone of the ", $name, " specified. Pick one.");

            match count_enabled_features!($($feature),*) {
                0 => std::panic!("{}", MSG_NONE),
                1 => {}
                2.. => std::panic!("{}", MSG_MULTIPLE),
            }
        };
    }
}

macro_rules! allow_single_target_feature {
    ($($args:tt)+) => {
        allow_single_feature!("targets", $($args)+);
    }
}

#[cfg(feature = "precursor")] // Gitrevs are only relevant for Precursor target
macro_rules! allow_single_gitrev_feature {
    ($($args:tt)+) => {
        allow_single_feature!("gitrevs", $($args)+);
    }
}

fn main() {
    // ------ check that the feature flags are sane -----
    // note on selecting "hosted" mode. An explicit "hosted" flag is provided to clarify
    // the build system's intent. However, in general, most packages prefer to use this idiom:
    //
    // #[cfg(not(target_os = "xous"))]
    //
    // This flag is synonymous with feature = "hosted", and it also makes "hosted" mode the
    // "default" package in the case that the code is being built in CI or in external
    // packages that don't know to configure the "hosted" feature flag.
    //
    // This idiom breaks if Xous ever gets to the point of compiling and running code on
    // its own platform; but generally, if the target binary is running on e.g. windows/linux/non-xous
    // target triples, the user's intent was "hosted" mode.
    //
    // This script retains the use of an explicit "hosted" flag because we want to catch
    // unintentional build system misconfigurations that meant to build for a target other
    // than "hosted", rather than just falling back silently to defaults.
    allow_single_target_feature!(
        "precursor",
        "hosted",
        "renode",
        "atsama5d27",
        "cramium-soc",
        "cramium-fpga"
    );

    #[cfg(feature = "precursor")]
    allow_single_gitrev_feature!("precursor-perflib", "precursor-dvt", "precursor-pvt");

    // ----- select an SVD file based on a specific revision -----
    #[cfg(feature = "precursor-perflib")]
    let svd_filenames = vec!["precursor/soc-perf.svd"];
    #[cfg(feature = "precursor-perflib")]
    let generated_filename = "src/generated/precursor_perf.rs";

    #[cfg(feature = "renode")]
    let svd_filenames = vec!["renode/renode.svd"];
    #[cfg(feature = "renode")]
    let generated_filename = "src/generated/renode.rs";

    #[cfg(feature = "precursor-dvt")]
    let svd_filenames = vec!["precursor/soc-dvt.svd"];
    #[cfg(feature = "precursor-dvt")]
    let generated_filename = "src/generated/precursor_dvt.rs";

    #[cfg(feature = "precursor-pvt")]
    let svd_filenames = vec!["precursor/soc-pvt.svd"];
    #[cfg(feature = "precursor")]
    let generated_filename = "src/generated/precursor_pvt.rs";

    #[cfg(feature = "atsama5d27")]
    let svd_filenames = vec!["atsama5d/ATSAMA5D27.svd"];
    #[cfg(feature = "atsama5d27")]
    let generated_filename = "src/generated/atsama5d27.rs";

    #[cfg(feature = "cramium-soc")]
    let svd_filenames = vec!["cramium/core.svd", "cramium/daric.svd"];
    #[cfg(feature = "cramium-soc")]
    let generated_filename = "src/generated/cramium_soc.rs";

    #[cfg(feature = "cramium-fpga")]
    let svd_filenames = vec!["cramium/soc.svd", "cramium/core.svd", "cramium/daric.svd"];
    #[cfg(feature = "cramium-fpga")]
    let generated_filename = "src/generated/cramium_fpga.rs";

    // ----- control file generation and rebuild sequence -----
    // check and see if the configuration has changed since the last build. This should be
    // passed by the build system (e.g. xtask) if the feature is used.
    //
    // Debug this using:
    //  $env:CARGO_LOG="cargo::core::compiler::fingerprint=info"
    #[cfg(not(feature = "hosted"))]
    {
        let mut svd_files = Vec::new();
        for svd in svd_filenames.iter() {
            let svd_file_path = std::path::Path::new(&svd);
            println!("cargo:rerun-if-changed={}", svd_file_path.canonicalize().unwrap().display());
            svd_files.push(std::fs::File::open(svd_file_path).unwrap());
        }
        // Regenerate the utra file in RAM.
        let mut dest_vec = vec![];
        svd2utra::generate(svd_files, &mut dest_vec).unwrap();

        // If the file exists, check to see if it is different from what we just generated.
        // If not, skip writing the new file.
        // If the file doesn't exist, or if it's different, write out a new utra file.
        let should_write = if let Ok(mut existing_file) = std::fs::File::open(generated_filename) {
            let mut existing_file_contents = vec![];
            existing_file
                .read_to_end(&mut existing_file_contents)
                .expect("couldn't read existing utra generated file");
            existing_file_contents != dest_vec
        } else {
            true
        };
        if should_write {
            let mut dest_file = std::fs::File::create(generated_filename).expect("couldn't open dest file");
            dest_file.write_all(&dest_vec).expect("couldn't write contents to utra file");
        }

        // ----- feedback SVD path to build framework -----
        // pass the computed SVD filename back to the build system, so that we can pass this
        // on to the image creation program. This is necessary so we can extract all the memory
        // regions and create the whitelist of memory pages allowed to the kernel; any page not
        // explicitly used by the hardware model is ineligible for mapping and allocation by any
        // process. This helps to prevent memory aliasing attacks by hardware blocks that partially
        // decode their addresses (this would be in anticipation of potential hardware bugs; ideally
        // this isn't ever a problem).
        let svd_path = out_dir().join("../../SVD_PATH");
        let mut svd_file = OpenOptions::new().create(true).write(true).truncate(true).open(svd_path).unwrap();
        for svd in svd_filenames.iter() {
            writeln!(svd_file, "utralib/{}", svd).unwrap();
        }
    }
    #[cfg(feature = "hosted")]
    {
        let svd_path = out_dir().join("../../SVD_PATH");
        let mut svd_file = OpenOptions::new().create(true).write(true).truncate(true).open(svd_path).unwrap();
        write!(svd_file, "").unwrap(); // there is no SVD file for hosted mode
    }
}