//! A module for searching for libraries

use std::path::{Path, PathBuf};
use std::{env, fs};

use rustc_fs_util::try_canonicalize;
use rustc_target::spec::Target;
use smallvec::{SmallVec, smallvec};

use crate::search_paths::{PathKind, SearchPath};

#[derive(Clone)]
pub struct FileSearch {
    cli_search_paths: Vec<SearchPath>,
    tlib_path: SearchPath,
}

impl FileSearch {
    pub fn cli_search_paths<'b>(&'b self, kind: PathKind) -> impl Iterator<Item = &'b SearchPath> {
        self.cli_search_paths.iter().filter(move |sp| sp.kind.matches(kind))
    }

    pub fn search_paths<'b>(&'b self, kind: PathKind) -> impl Iterator<Item = &'b SearchPath> {
        self.cli_search_paths
            .iter()
            .filter(move |sp| sp.kind.matches(kind))
            .chain(std::iter::once(&self.tlib_path))
    }

    pub fn new(cli_search_paths: &[SearchPath], tlib_path: &SearchPath, target: &Target) -> Self {
        let this = FileSearch {
            cli_search_paths: cli_search_paths.to_owned(),
            tlib_path: tlib_path.clone(),
        };
        this.refine(&["lib", &target.staticlib_prefix, &target.dll_prefix])
    }
    // Produce a new file search from this search that has a smaller set of candidates.
    fn refine(mut self, allowed_prefixes: &[&str]) -> FileSearch {
        self.cli_search_paths
            .iter_mut()
            .for_each(|search_paths| search_paths.files.retain(allowed_prefixes));
        self.tlib_path.files.retain(allowed_prefixes);

        self
    }
}

pub fn make_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
    let rustlib_path = rustc_target::relative_target_rustlib_path(sysroot, target_triple);
    sysroot.join(rustlib_path).join("lib")
}

/// Returns a path to the target's `bin` folder within its `rustlib` path in the sysroot. This is
/// where binaries are usually installed, e.g. the self-contained linkers, lld-wrappers, LLVM tools,
/// etc.
pub fn make_target_bin_path(sysroot: &Path, target_triple: &str) -> PathBuf {
    let rustlib_path = rustc_target::relative_target_rustlib_path(sysroot, target_triple);
    sysroot.join(rustlib_path).join("bin")
}

#[cfg(unix)]
fn current_dll_path() -> Result<PathBuf, String> {
    use std::sync::OnceLock;

    // This is somewhat expensive relative to other work when compiling `fn main() {}` as `dladdr`
    // needs to iterate over the symbol table of librustc_driver.so until it finds a match.
    // As such cache this to avoid recomputing if we try to get the sysroot in multiple places.
    static CURRENT_DLL_PATH: OnceLock<Result<PathBuf, String>> = OnceLock::new();
    CURRENT_DLL_PATH
        .get_or_init(|| {
            use std::ffi::{CStr, OsStr};
            use std::os::unix::prelude::*;

            #[cfg(not(target_os = "aix"))]
            unsafe {
                let addr = current_dll_path as usize as *mut _;
                let mut info = std::mem::zeroed();
                if libc::dladdr(addr, &mut info) == 0 {
                    return Err("dladdr failed".into());
                }
                #[cfg(target_os = "cygwin")]
                let fname_ptr = info.dli_fname.as_ptr();
                #[cfg(not(target_os = "cygwin"))]
                let fname_ptr = {
                    assert!(!info.dli_fname.is_null(), "dli_fname cannot be null");
                    info.dli_fname
                };
                let bytes = CStr::from_ptr(fname_ptr).to_bytes();
                let os = OsStr::from_bytes(bytes);
                try_canonicalize(Path::new(os)).map_err(|e| e.to_string())
            }

            #[cfg(target_os = "aix")]
            unsafe {
                // On AIX, the symbol `current_dll_path` references a function descriptor.
                // A function descriptor is consisted of (See https://reviews.llvm.org/D62532)
                // * The address of the entry point of the function.
                // * The TOC base address for the function.
                // * The environment pointer.
                // The function descriptor is in the data section.
                let addr = current_dll_path as u64;
                let mut buffer = vec![std::mem::zeroed::<libc::ld_info>(); 64];
                loop {
                    if libc::loadquery(
                        libc::L_GETINFO,
                        buffer.as_mut_ptr() as *mut u8,
                        (size_of::<libc::ld_info>() * buffer.len()) as u32,
                    ) >= 0
                    {
                        break;
                    } else {
                        if std::io::Error::last_os_error().raw_os_error().unwrap() != libc::ENOMEM {
                            return Err("loadquery failed".into());
                        }
                        buffer.resize(buffer.len() * 2, std::mem::zeroed::<libc::ld_info>());
                    }
                }
                let mut current = buffer.as_mut_ptr() as *mut libc::ld_info;
                loop {
                    let data_base = (*current).ldinfo_dataorg as u64;
                    let data_end = data_base + (*current).ldinfo_datasize;
                    if (data_base..data_end).contains(&addr) {
                        let bytes = CStr::from_ptr(&(*current).ldinfo_filename[0]).to_bytes();
                        let os = OsStr::from_bytes(bytes);
                        return try_canonicalize(Path::new(os)).map_err(|e| e.to_string());
                    }
                    if (*current).ldinfo_next == 0 {
                        break;
                    }
                    current = (current as *mut i8).offset((*current).ldinfo_next as isize)
                        as *mut libc::ld_info;
                }
                return Err(format!("current dll's address {} is not in the load map", addr));
            }
        })
        .clone()
}

#[cfg(windows)]
fn current_dll_path() -> Result<PathBuf, String> {
    use std::ffi::OsString;
    use std::io;
    use std::os::windows::prelude::*;

    use windows::Win32::Foundation::HMODULE;
    use windows::Win32::System::LibraryLoader::{
        GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS, GetModuleFileNameW, GetModuleHandleExW,
    };
    use windows::core::PCWSTR;

    let mut module = HMODULE::default();
    unsafe {
        GetModuleHandleExW(
            GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS,
            PCWSTR(current_dll_path as *mut u16),
            &mut module,
        )
    }
    .map_err(|e| e.to_string())?;

    let mut filename = vec![0; 1024];
    let n = unsafe { GetModuleFileNameW(Some(module), &mut filename) } as usize;
    if n == 0 {
        return Err(format!("GetModuleFileNameW failed: {}", io::Error::last_os_error()));
    }
    if n >= filename.capacity() {
        return Err(format!("our buffer was too small? {}", io::Error::last_os_error()));
    }

    filename.truncate(n);

    let path = try_canonicalize(OsString::from_wide(&filename)).map_err(|e| e.to_string())?;

    // See comments on this target function, but the gist is that
    // gcc chokes on verbatim paths which fs::canonicalize generates
    // so we try to avoid those kinds of paths.
    Ok(rustc_fs_util::fix_windows_verbatim_for_gcc(&path))
}

#[cfg(target_os = "wasi")]
fn current_dll_path() -> Result<PathBuf, String> {
    Err("current_dll_path is not supported on WASI".to_string())
}

pub fn sysroot_with_fallback(sysroot: &Path) -> SmallVec<[PathBuf; 2]> {
    let mut candidates = smallvec![sysroot.to_owned()];
    let default_sysroot = get_or_default_sysroot();
    if default_sysroot != sysroot {
        candidates.push(default_sysroot);
    }
    candidates
}

/// Returns the provided sysroot or calls [`get_or_default_sysroot`] if it's none.
/// Panics if [`get_or_default_sysroot`]  returns an error.
pub fn materialize_sysroot(maybe_sysroot: Option<PathBuf>) -> PathBuf {
    maybe_sysroot.unwrap_or_else(|| get_or_default_sysroot())
}

/// This function checks if sysroot is found using env::args().next(), and if it
/// is not found, finds sysroot from current rustc_driver dll.
pub fn get_or_default_sysroot() -> PathBuf {
    fn default_from_rustc_driver_dll() -> Result<PathBuf, String> {
        let dll = current_dll_path()?;

        // `dll` will be in one of the following two:
        // - compiler's libdir: $sysroot/lib/*.dll
        // - target's libdir: $sysroot/lib/rustlib/$target/lib/*.dll
        //
        // use `parent` twice to chop off the file name and then also the
        // directory containing the dll
        let dir = dll.parent().and_then(|p| p.parent()).ok_or_else(|| {
            format!("Could not move 2 levels upper using `parent()` on {}", dll.display())
        })?;

        // if `dir` points to target's dir, move up to the sysroot
        let mut sysroot_dir = if dir.ends_with(crate::config::host_tuple()) {
            dir.parent() // chop off `$target`
                .and_then(|p| p.parent()) // chop off `rustlib`
                .and_then(|p| p.parent()) // chop off `lib`
                .map(|s| s.to_owned())
                .ok_or_else(|| {
                    format!("Could not move 3 levels upper using `parent()` on {}", dir.display())
                })?
        } else {
            dir.to_owned()
        };

        // On multiarch linux systems, there will be multiarch directory named
        // with the architecture(e.g `x86_64-linux-gnu`) under the `lib` directory.
        // Which cause us to mistakenly end up in the lib directory instead of the sysroot directory.
        if sysroot_dir.ends_with("lib") {
            sysroot_dir =
                sysroot_dir.parent().map(|real_sysroot| real_sysroot.to_owned()).ok_or_else(
                    || format!("Could not move to parent path of {}", sysroot_dir.display()),
                )?
        }

        Ok(sysroot_dir)
    }

    // Use env::args().next() to get the path of the executable without
    // following symlinks/canonicalizing any component. This makes the rustc
    // binary able to locate Rust libraries in systems using content-addressable
    // storage (CAS).
    fn from_env_args_next() -> Option<PathBuf> {
        let mut p = PathBuf::from(env::args_os().next()?);

        // Check if sysroot is found using env::args().next() only if the rustc in argv[0]
        // is a symlink (see #79253). We might want to change/remove it to conform with
        // https://www.gnu.org/prep/standards/standards.html#Finding-Program-Files in the
        // future.
        if fs::read_link(&p).is_err() {
            // Path is not a symbolic link or does not exist.
            return None;
        }

        // Pop off `bin/rustc`, obtaining the suspected sysroot.
        p.pop();
        p.pop();
        // Look for the target rustlib directory in the suspected sysroot.
        let mut rustlib_path = rustc_target::relative_target_rustlib_path(&p, "dummy");
        rustlib_path.pop(); // pop off the dummy target.
        rustlib_path.exists().then_some(p)
    }

    from_env_args_next()
        .unwrap_or_else(|| default_from_rustc_driver_dll().expect("Failed finding sysroot"))
}