integrations/rust/haskell.rs

use crate::interop::SharedStats;
use libloading::Library;
use std::env;
use std::ffi::{CStr, CString};
use std::fs;
use std::os::raw::{c_char, c_int};
use std::path::{Path, PathBuf};

unsafe extern "C" {
    fn hs_init(argc: *mut c_int, argv: *mut *mut *mut c_char);
    fn hs_exit();
}

type HsComputeStats = unsafe extern "C" fn(c_int, c_int, *mut SharedStats) -> c_int;
type HsMakeMessage = unsafe extern "C" fn(*const c_char, c_int, c_int) -> *mut c_char;
type HsFreeString = unsafe extern "C" fn(*mut c_char);

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct DemoArgs {
    pub name: String,
    pub left: i32,
    pub right: i32,
    pub library_path: Option<String>,
}

pub fn run_haskell_demo(args: &DemoArgs) -> Result<String, String> {
    let library_path = resolve_library_path(args.library_path.as_deref())?;
    let runtime = HaskellRuntime::start()?;

    let output = load_and_run(&library_path, args);

    drop(runtime);
    output
}

struct HaskellRuntime;

impl HaskellRuntime {
    fn start() -> Result<Self, String> {
        let mut argc: c_int = 1;
        let program_name = CString::new("integrations-hs-runtime")
            .map_err(|_| "failed to create runtime program name".to_string())?;
        let mut argv = vec![program_name.as_ptr() as *mut c_char, std::ptr::null_mut()];
        let mut argv_ptr = argv.as_mut_ptr();

        unsafe {
            hs_init(&mut argc, &mut argv_ptr);
        }

        Ok(Self)
    }
}

impl Drop for HaskellRuntime {
    fn drop(&mut self) {
        unsafe {
            hs_exit();
        }
    }
}

fn load_and_run(library_path: &Path, args: &DemoArgs) -> Result<String, String> {
    let library = unsafe { Library::new(library_path) }
        .map_err(|error| format!("failed to load {}: {error}", library_path.display()))?;

    let compute_stats: HsComputeStats = unsafe {
        *library
            .get(b"hs_compute_stats\0")
            .map_err(|error| format!("failed to load hs_compute_stats: {error}"))?
    };
    let make_message: HsMakeMessage = unsafe {
        *library
            .get(b"hs_make_message\0")
            .map_err(|error| format!("failed to load hs_make_message: {error}"))?
    };
    let free_string: HsFreeString = unsafe {
        *library
            .get(b"hs_free_string\0")
            .map_err(|error| format!("failed to load hs_free_string: {error}"))?
    };

    let mut stats = SharedStats::default();
    let status = unsafe { compute_stats(args.left, args.right, &mut stats) };
    if status != 0 {
        return Err(format!("hs_compute_stats returned status {status}"));
    }

    let name = CString::new(args.name.replace('\0', "?"))
        .map_err(|_| "failed to prepare demo name".to_string())?;
    let message_ptr = unsafe { make_message(name.as_ptr(), args.left, args.right) };
    if message_ptr.is_null() {
        return Err("hs_make_message returned a null pointer".to_string());
    }

    let message = unsafe { CStr::from_ptr(message_ptr) }
        .to_string_lossy()
        .into_owned();
    unsafe {
        free_string(message_ptr);
    }

    Ok(format!(
        "Rust -> Haskell demo\nLibrary: {}\nInputs: name={}, left={}, right={}\nStats from Haskell: total={}, product={}, gap={}\nMessage from Haskell: {}",
        library_path.display(),
        args.name,
        args.left,
        args.right,
        stats.total,
        stats.product,
        stats.gap,
        message,
    ))
}

fn resolve_library_path(explicit_path: Option<&str>) -> Result<PathBuf, String> {
    if let Some(path) = explicit_path {
        return Ok(PathBuf::from(path));
    }

    if let Ok(path) = env::var("HASKELL_FOREIGN_LIB") {
        return Ok(PathBuf::from(path));
    }

    let dist_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
        .join("haskell")
        .join("dist-newstyle");
    let mut matches = Vec::new();
    collect_matching_libraries(&dist_dir, &mut matches)?;
    matches.sort();

    matches.into_iter().next().ok_or_else(|| {
        "could not find the Haskell foreign library under haskell/dist-newstyle; run `make haskell-build` first or pass an explicit path".to_string()
    })
}

fn collect_matching_libraries(root: &Path, matches: &mut Vec<PathBuf>) -> Result<(), String> {
    if !root.exists() {
        return Ok(());
    }

    let entries = fs::read_dir(root)
        .map_err(|error| format!("failed to read {}: {error}", root.display()))?;
    for entry in entries {
        let entry = entry.map_err(|error| format!("failed to inspect {}: {error}", root.display()))?;
        let path = entry.path();
        if path.is_dir() {
            collect_matching_libraries(&path, matches)?;
            continue;
        }

        if is_haskell_foreign_library(&path) {
            matches.push(path);
        }
    }

    Ok(())
}

fn is_haskell_foreign_library(path: &Path) -> bool {
    let Some(file_name) = path.file_name().and_then(|value| value.to_str()) else {
        return false;
    };

    let is_library = file_name.ends_with(".so")
        || file_name.ends_with(".dylib")
        || file_name.ends_with(".dll");

    is_library && file_name.contains("interop_hs")
}