//! Handles dynamic library loading for proc macro

mod proc_macros;
mod version;

use proc_macro::bridge;
use std::{fmt, fs, io, time::SystemTime};
use temp_dir::TempDir;

use libloading::Library;
use object::Object;
use paths::{Utf8Path, Utf8PathBuf};

use crate::{
    PanicMessage, ProcMacroKind, ProcMacroSrvSpan, dylib::proc_macros::ProcMacros,
    server_impl::TopSubtree,
};

pub(crate) struct Expander {
    inner: ProcMacroLibrary,
    modified_time: SystemTime,
}

impl Expander {
    pub(crate) fn new(
        temp_dir: &TempDir,
        lib: &Utf8Path,
    ) -> Result<Expander, LoadProcMacroDylibError> {
        // Some libraries for dynamic loading require canonicalized path even when it is
        // already absolute
        let lib = lib.canonicalize_utf8()?;
        let modified_time = fs::metadata(&lib).and_then(|it| it.modified())?;

        let path = ensure_file_with_lock_free_access(temp_dir, &lib)?;
        let library = ProcMacroLibrary::open(path.as_ref())?;

        Ok(Expander { inner: library, modified_time })
    }

    pub(crate) fn expand<S: ProcMacroSrvSpan>(
        &self,
        macro_name: &str,
        macro_body: TopSubtree<S>,
        attributes: Option<TopSubtree<S>>,
        def_site: S,
        call_site: S,
        mixed_site: S,
    ) -> Result<TopSubtree<S>, PanicMessage>
    where
        <S::Server as bridge::server::Types>::TokenStream: Default,
    {
        self.inner
            .proc_macros
            .expand(macro_name, macro_body, attributes, def_site, call_site, mixed_site)
    }

    pub(crate) fn list_macros(&self) -> impl Iterator<Item = (&str, ProcMacroKind)> {
        self.inner.proc_macros.list_macros()
    }

    pub(crate) fn modified_time(&self) -> SystemTime {
        self.modified_time
    }
}

#[derive(Debug)]
pub enum LoadProcMacroDylibError {
    Io(io::Error),
    LibLoading(libloading::Error),
    AbiMismatch(String),
}

impl fmt::Display for LoadProcMacroDylibError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Io(e) => e.fmt(f),
            Self::AbiMismatch(v) => {
                use crate::RUSTC_VERSION_STRING;
                write!(f, "mismatched ABI expected: `{RUSTC_VERSION_STRING}`, got `{v}`")
            }
            Self::LibLoading(e) => e.fmt(f),
        }
    }
}

impl From<io::Error> for LoadProcMacroDylibError {
    fn from(e: io::Error) -> Self {
        LoadProcMacroDylibError::Io(e)
    }
}

impl From<libloading::Error> for LoadProcMacroDylibError {
    fn from(e: libloading::Error) -> Self {
        LoadProcMacroDylibError::LibLoading(e)
    }
}

struct ProcMacroLibrary {
    // 'static is actually the lifetime of library, so make sure this drops before _lib
    proc_macros: &'static ProcMacros,
    // Hold on to the library so it doesn't unload
    _lib: Library,
}

impl ProcMacroLibrary {
    fn open(path: &Utf8Path) -> Result<Self, LoadProcMacroDylibError> {
        let file = fs::File::open(path)?;
        #[allow(clippy::undocumented_unsafe_blocks)] // FIXME
        let file = unsafe { memmap2::Mmap::map(&file) }?;
        let obj = object::File::parse(&*file)
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        let version_info = version::read_dylib_info(&obj)?;
        if version_info.version_string != crate::RUSTC_VERSION_STRING {
            return Err(LoadProcMacroDylibError::AbiMismatch(version_info.version_string));
        }

        let symbol_name =
            find_registrar_symbol(&obj).map_err(invalid_data_err)?.ok_or_else(|| {
                invalid_data_err(format!("Cannot find registrar symbol in file {path}"))
            })?;

        // SAFETY: We have verified the validity of the dylib as a proc-macro library
        let lib = unsafe { load_library(path) }.map_err(invalid_data_err)?;
        // SAFETY: We have verified the validity of the dylib as a proc-macro library
        // The 'static lifetime is a lie, it's actually the lifetime of the library but unavoidable
        // due to self-referentiality
        // But we make sure that we do not drop it before the symbol is dropped
        let proc_macros =
            unsafe { lib.get::<&'static &'static ProcMacros>(symbol_name.as_bytes()) };
        match proc_macros {
            Ok(proc_macros) => Ok(ProcMacroLibrary { proc_macros: *proc_macros, _lib: lib }),
            Err(e) => Err(e.into()),
        }
    }
}

fn invalid_data_err(e: impl Into<Box<dyn std::error::Error + Send + Sync>>) -> io::Error {
    io::Error::new(io::ErrorKind::InvalidData, e)
}

fn is_derive_registrar_symbol(symbol: &str) -> bool {
    const NEW_REGISTRAR_SYMBOL: &str = "_rustc_proc_macro_decls_";
    symbol.contains(NEW_REGISTRAR_SYMBOL)
}

fn find_registrar_symbol(obj: &object::File<'_>) -> object::Result<Option<String>> {
    Ok(obj
        .exports()?
        .into_iter()
        .map(|export| export.name())
        .filter_map(|sym| String::from_utf8(sym.into()).ok())
        .find(|sym| is_derive_registrar_symbol(sym))
        .map(|sym| {
            // From MacOS docs:
            // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/dlsym.3.html
            // Unlike other dyld API's, the symbol name passed to dlsym() must NOT be
            // prepended with an underscore.
            if cfg!(target_os = "macos") && sym.starts_with('_') {
                sym[1..].to_owned()
            } else {
                sym
            }
        }))
}

/// Copy the dylib to temp directory to prevent locking in Windows
#[cfg(windows)]
fn ensure_file_with_lock_free_access(
    temp_dir: &TempDir,
    path: &Utf8Path,
) -> io::Result<Utf8PathBuf> {
    use std::collections::hash_map::RandomState;
    use std::hash::{BuildHasher, Hasher};

    if std::env::var("RA_DONT_COPY_PROC_MACRO_DLL").is_ok() {
        return Ok(path.to_path_buf());
    }

    let mut to = Utf8Path::from_path(temp_dir.path()).unwrap().to_owned();

    let file_name = path.file_stem().ok_or_else(|| {
        io::Error::new(io::ErrorKind::InvalidInput, format!("File path is invalid: {path}"))
    })?;

    to.push({
        // Generate a unique number by abusing `HashMap`'s hasher.
        // Maybe this will also "inspire" a libs team member to finally put `rand` in libstd.
        let unique_name = RandomState::new().build_hasher().finish();
        format!("{file_name}-{unique_name}.dll")
    });
    fs::copy(path, &to)?;
    Ok(to)
}

#[cfg(unix)]
fn ensure_file_with_lock_free_access(
    _temp_dir: &TempDir,
    path: &Utf8Path,
) -> io::Result<Utf8PathBuf> {
    Ok(path.to_owned())
}

/// Loads dynamic library in platform dependent manner.
///
/// For unix, you have to use RTLD_DEEPBIND flag to escape problems described
/// [here](https://github.com/fedochet/rust-proc-macro-panic-inside-panic-expample)
/// and [here](https://github.com/rust-lang/rust/issues/60593).
///
/// Usage of RTLD_DEEPBIND
/// [here](https://github.com/fedochet/rust-proc-macro-panic-inside-panic-expample/issues/1)
///
/// It seems that on Windows that behaviour is default, so we do nothing in that case.
///
/// # Safety
///
/// The caller is responsible for ensuring that the path is valid proc-macro library
#[cfg(windows)]
unsafe fn load_library(file: &Utf8Path) -> Result<Library, libloading::Error> {
    // SAFETY: The caller is responsible for ensuring that the path is valid proc-macro library
    unsafe { Library::new(file) }
}

/// Loads dynamic library in platform dependent manner.
///
/// For unix, you have to use RTLD_DEEPBIND flag to escape problems described
/// [here](https://github.com/fedochet/rust-proc-macro-panic-inside-panic-expample)
/// and [here](https://github.com/rust-lang/rust/issues/60593).
///
/// Usage of RTLD_DEEPBIND
/// [here](https://github.com/fedochet/rust-proc-macro-panic-inside-panic-expample/issues/1)
///
/// It seems that on Windows that behaviour is default, so we do nothing in that case.
///
/// # Safety
///
/// The caller is responsible for ensuring that the path is valid proc-macro library
#[cfg(unix)]
unsafe fn load_library(file: &Utf8Path) -> Result<Library, libloading::Error> {
    // not defined by POSIX, different values on mips vs other targets
    #[cfg(target_env = "gnu")]
    use libc::RTLD_DEEPBIND;
    use libloading::os::unix::Library as UnixLibrary;
    // defined by POSIX
    use libloading::os::unix::RTLD_NOW;

    // MUSL and bionic don't have it..
    #[cfg(not(target_env = "gnu"))]
    const RTLD_DEEPBIND: std::os::raw::c_int = 0x0;

    // SAFETY: The caller is responsible for ensuring that the path is valid proc-macro library
    unsafe { UnixLibrary::open(Some(file), RTLD_NOW | RTLD_DEEPBIND).map(|lib| lib.into()) }
}