#[deny(missing_docs)]
pub mod error_handling;

use libc::c_char;
#[llvm_versions(16.0..=latest)]
use llvm_sys::core::LLVMGetVersion;
use llvm_sys::core::{LLVMCreateMessage, LLVMDisposeMessage};
use llvm_sys::error_handling::LLVMEnablePrettyStackTrace;
use llvm_sys::support::{LLVMLoadLibraryPermanently, LLVMSearchForAddressOfSymbol};

use std::borrow::Cow;
use std::error::Error;
use std::ffi::{CStr, CString};
use std::fmt::{self, Debug, Display, Formatter};
use std::ops::Deref;
use std::path::Path;

/// An owned LLVM String. Also known as a LLVM Message
#[derive(Eq)]
pub struct LLVMString {
    pub(crate) ptr: *const c_char,
}

impl LLVMString {
    pub(crate) unsafe fn new(ptr: *const c_char) -> Self {
        LLVMString { ptr }
    }

    /// This is a convenience method for creating a Rust `String`,
    /// however; it *will* reallocate. `LLVMString` should be used
    /// as much as possible to save memory since it is allocated by
    /// LLVM. It's essentially a `CString` with a custom LLVM
    /// deallocator
    pub fn to_string(&self) -> String {
        (*self).to_string_lossy().into_owned()
    }

    /// This method will allocate a c string through LLVM
    pub(crate) fn create_from_c_str(string: &CStr) -> LLVMString {
        unsafe { LLVMString::new(LLVMCreateMessage(string.as_ptr() as *const _)) }
    }

    /// This method will allocate a c string through LLVM
    pub(crate) fn create_from_str(string: &str) -> LLVMString {
        debug_assert_eq!(string.as_bytes()[string.as_bytes().len() - 1], 0);

        unsafe { LLVMString::new(LLVMCreateMessage(string.as_ptr() as *const _)) }
    }
}

impl Deref for LLVMString {
    type Target = CStr;

    fn deref(&self) -> &Self::Target {
        unsafe { CStr::from_ptr(self.ptr) }
    }
}

impl Debug for LLVMString {
    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
        write!(f, "{:?}", self.deref())
    }
}

impl Display for LLVMString {
    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
        write!(f, "{:?}", self.deref())
    }
}

impl PartialEq for LLVMString {
    fn eq(&self, other: &LLVMString) -> bool {
        **self == **other
    }
}

impl Error for LLVMString {
    fn description(&self) -> &str {
        self.to_str()
            .expect("Could not convert LLVMString to str (likely invalid unicode)")
    }

    fn cause(&self) -> Option<&dyn Error> {
        None
    }
}

impl Drop for LLVMString {
    fn drop(&mut self) {
        unsafe {
            LLVMDisposeMessage(self.ptr as *mut _);
        }
    }
}

// Similar to Cow; however does not provide ability to clone
// since memory is allocated by LLVM. Could use a better name
// too. This is meant to be an internal wrapper only. Maybe
// belongs in a private utils module.
#[derive(Eq)]
pub(crate) enum LLVMStringOrRaw {
    Owned(LLVMString),
    Borrowed(*const c_char),
}

impl LLVMStringOrRaw {
    pub fn as_str(&self) -> &CStr {
        match self {
            LLVMStringOrRaw::Owned(llvm_string) => llvm_string.deref(),
            LLVMStringOrRaw::Borrowed(ptr) => unsafe { CStr::from_ptr(*ptr) },
        }
    }
}

impl PartialEq for LLVMStringOrRaw {
    fn eq(&self, other: &LLVMStringOrRaw) -> bool {
        self.as_str() == other.as_str()
    }
}

/// This function is very unsafe. Any reference to LLVM data after this function is called will likely segfault.
/// Probably only ever useful to call before your program ends. Might not even be absolutely necessary.
pub unsafe fn shutdown_llvm() {
    use llvm_sys::core::LLVMShutdown;

    LLVMShutdown()
}

/// Returns the major, minor, and patch version of the LLVM in use
#[llvm_versions(16.0..=latest)]
pub fn get_llvm_version() -> (u32, u32, u32) {
    let mut major: u32 = 0;
    let mut minor: u32 = 0;
    let mut patch: u32 = 0;

    unsafe { LLVMGetVersion(&mut major, &mut minor, &mut patch) };

    return (major, minor, patch);
}

/// Possible errors that can occur when loading a library
#[derive(thiserror::Error, Debug, PartialEq, Eq, Clone, Copy)]
pub enum LoadLibraryError {
    /// The given path could not be converted to a [`&str`]
    #[error("The given path could not be converted to a `&str`")]
    UnicodeError,
    /// The given path could not be loaded as a library
    #[error("The given path could not be loaded as a library")]
    LoadingError,
}

/// Permanently load the dynamic library at the given `path`.
///
/// It is safe to call this function multiple times for the same library.
pub fn load_library_permanently(path: &Path) -> Result<(), LoadLibraryError> {
    let filename = to_c_str(path.to_str().ok_or(LoadLibraryError::UnicodeError)?);

    let error = unsafe { LLVMLoadLibraryPermanently(filename.as_ptr()) == 1 };
    if error {
        return Err(LoadLibraryError::LoadingError);
    }

    Ok(())
}

#[test]
fn test_load_library_permanently() {
    assert_eq!(
        load_library_permanently(Path::new("missing.dll")),
        Err(LoadLibraryError::LoadingError)
    );
}

/// Permanently loads all the symbols visible inside the current program
pub fn load_visible_symbols() {
    unsafe { LLVMLoadLibraryPermanently(std::ptr::null()) };
}

/// Search through all previously loaded dynamic libraries for `symbol`.
///
/// Returns an address of the symbol, if found
pub fn search_for_address_of_symbol(symbol: &str) -> Option<usize> {
    let symbol = to_c_str(symbol);

    let address = unsafe { LLVMSearchForAddressOfSymbol(symbol.as_ptr()) };
    if address.is_null() {
        return None;
    }
    return Some(address as usize);
}

#[test]
fn test_load_visible_symbols() {
    assert!(search_for_address_of_symbol("malloc").is_none());
    load_visible_symbols();
    assert!(search_for_address_of_symbol("malloc").is_some());
}

/// Determines whether or not LLVM has been configured to run in multithreaded mode. (Inkwell currently does
/// not officially support multithreaded mode)
pub fn is_multithreaded() -> bool {
    use llvm_sys::core::LLVMIsMultithreaded;

    unsafe { LLVMIsMultithreaded() == 1 }
}

pub fn enable_llvm_pretty_stack_trace() {
    unsafe { LLVMEnablePrettyStackTrace() }
}

/// This function takes in a Rust string and either:
///
/// A) Finds a terminating null byte in the Rust string and can reference it directly like a C string.
///
/// B) Finds no null byte and allocates a new C string based on the input Rust string.
pub(crate) fn to_c_str<'s>(mut s: &'s str) -> Cow<'s, CStr> {
    if s.is_empty() {
        s = "\0";
    }

    // Start from the end of the string as it's the most likely place to find a null byte
    if !s.chars().rev().any(|ch| ch == '\0') {
        return Cow::from(CString::new(s).expect("unreachable since null bytes are checked"));
    }

    unsafe { Cow::from(CStr::from_ptr(s.as_ptr() as *const _)) }
}

#[test]
fn test_to_c_str() {
    assert!(matches!(to_c_str("my string"), Cow::Owned(_)));
    assert!(matches!(to_c_str("my string\0"), Cow::Borrowed(_)));
}