gruggers 0.5.2

use crate::xar::XarHandle;
use crate::mod_api::{ModApi, get_mod_api, get_mod_api_from_text, ModApiError};
use crate::error::GrugError;
use crate::backend::{Backend, ErasedBackend, BytecodeBackend};
use crate::types::{GrugValue, GrugId, GameFnPtr, GrugOnFnId, GrugFileId, GrugEntity, GameFnPtrState};
use crate::xar::Xar;
use crate::ntstring::NTStrPtr;
use crate::arena::Arena;
use crate::nt;
use crate::watcher::{watch_changes, DirChanges};

use gruggers_core::runtime_error::RuntimeError;
pub use gruggers_core::state::State;

use std::marker::PhantomData;
use std::ptr::NonNull;
use std::pin::Pin;
use std::cell::{Cell, RefCell, Ref};
use std::collections::{HashMap, hash_map::Entry};
use std::sync::atomic::{AtomicU64, Ordering};
use std::ffi::{OsString, OsStr};
use std::path::Path;
use std::sync::mpsc::{Receiver, channel};

// /// Called by the 
#[repr(C)]
pub struct RuntimeErrorHandler {
	data: NonNull<()>,
	drop: Option<extern "C" fn(data: Option<NonNull<()>>)>,
	func: Option<for<'b> extern "C" fn(
		data: NonNull<()>, 
		err_kind: u32, 
		reason: NonNull<u8>,
		reason_len: usize, 
		on_fn_name: NonNull<u8>, 
		on_fn_name_len: usize,
		script_path: NonNull<u8>,
		script_path_len: usize,
	)>,
}

const _: () = const {
	assert!(std::mem::size_of::<RuntimeErrorHandler>() == std::mem::size_of::<Option<RuntimeErrorHandler>>());
};

impl RuntimeErrorHandler {
	pub const fn new_default () -> Self {
		Self {
			data: NonNull::dangling(),
			drop: None, 
			func: None
		}
	}

	fn handle_error(&self, kind: RuntimeError, message: &str, on_fn_name: &str, script_path: &OsStr) {
		if let Some(func) = self.func {
			func(
				self.data,
				kind.code(),
				NonNull::from_ref(message).cast::<u8>(),
				message.len(),
				NonNull::from_ref(on_fn_name).cast::<u8>(),
				on_fn_name.len(),
				NonNull::from_ref(script_path).cast::<u8>(),
				script_path.len(),
			)
		} 
	}
}

impl Default for RuntimeErrorHandler {
	fn default() -> Self {
		Self::new_default()
	}
}

impl<F: for<'b> Fn(u32, &'b str, &'b str, &'b str)> From<F> for RuntimeErrorHandler {
	fn from(f: F) -> Self {
		let f = unsafe{NonNull::new_unchecked(Box::into_raw(Box::new(f)))}.cast::<()>();
		extern "C" fn handler<F: for<'a> Fn(u32, &'a str, &'a str, &'a str)> (
			data: NonNull<()>, 
			err_kind: u32, 
			reason: NonNull<u8>,
			reason_len: usize, 
			on_fn_name: NonNull<u8>, 
			on_fn_name_len: usize,
			script_path: NonNull<u8>,
			script_path_len: usize,
		) {
			unsafe{(data.cast::<F>().as_ref())(
				err_kind,
				std::str::from_utf8_unchecked(std::slice::from_raw_parts(reason.as_ptr(), reason_len)),
				std::str::from_utf8_unchecked(std::slice::from_raw_parts(on_fn_name.as_ptr(), on_fn_name_len)),
				std::str::from_utf8_unchecked(std::slice::from_raw_parts(script_path.as_ptr(), script_path_len)),
			)};
		}
		extern "C" fn drop<F>(data: Option<NonNull<()>>) {
			data.map(|x| unsafe{Box::from_raw(x.cast::<F>().as_ptr())});
		}
		Self {
			data: f,
			drop: Some(drop::<F> as extern "C" fn(_)),
			func: Some(handler::<F> as extern "C" fn (_, _, _, _, _, _, _, _)),
		}
	}
}

#[repr(C)]
pub struct GrugInitSettings<'a> {
	_marker: PhantomData<&'a ()>,
	mod_api_path: Option<NonNull<u8>>,
	mod_api_path_len: usize,
	mods_dir_path: Option<NonNull<u8>>,
	mods_dir_path_len: usize,
	runtime_error_handler: Option<RuntimeErrorHandler>,

	backend: Option<ErasedBackend<GrugState>>,
}

const _: () = const {
	unsafe{std::mem::forget(std::mem::MaybeUninit::<GrugInitSettings<'static>>::zeroed().assume_init())};
};

impl<'a> GrugInitSettings<'a> {
	pub const fn new() -> Self {
		Self {
			_marker: PhantomData,
			mod_api_path: None,
			mod_api_path_len: 0,
			mods_dir_path: None,
			mods_dir_path_len: 0,
			runtime_error_handler: None,
			backend: None,
		}
	}

	pub fn set_mods_dir(mut self, dir: &'a str) -> Self {
		if dir.len() == 0 {
			self.mods_dir_path = None;
			self.mods_dir_path_len = 0;
		} else {
			self.mods_dir_path = Some(NonNull::from_ref(dir).cast::<u8>());
			self.mods_dir_path_len = dir.len();
		}
		self
	}

	pub fn set_mod_api_path(mut self, mod_api: &'a str) -> Self {
		if mod_api.len() == 0 {
			self.mod_api_path = None;
			self.mod_api_path_len = 0;
		} else {
			self.mod_api_path = Some(NonNull::from_ref(mod_api).cast::<u8>());
			self.mod_api_path_len = mod_api.len();
		}
		self
	}

	pub fn set_backend<B: Backend>(mut self, backend: B) -> Self {
		self.backend = Some(backend.into());
		self
	}

	pub fn set_runtime_error_handler<F: for<'b> Fn(u32, &'b str, &'b str, &'b str)> (mut self, f: F) -> Self {
		self.runtime_error_handler = Some(f.into());
		self
	}

	pub fn build_state(self) -> Result<GrugState, GrugError> {
		let mod_api_path = unsafe{Self::maybe_nt_or_length(self.mod_api_path, self.mod_api_path_len)}
			.unwrap_or("./mod_api.json");
		let mods_dir_path = unsafe{Self::maybe_nt_or_length(self.mods_dir_path, self.mods_dir_path_len)}
			.unwrap_or("./mods");

		GrugState::new(
			mod_api_path,
			mods_dir_path,
			self.runtime_error_handler.unwrap_or_else(|| RuntimeErrorHandler::new_default()), 
			self.backend.unwrap_or_else(|| BytecodeBackend::new().into())
		)
	}

	unsafe fn maybe_nt_or_length(ptr: Option<NonNull<u8>>, len: usize) -> Option<&'a str> {
		// null terminated
		if let Some(ptr) = ptr {
			if len == 0 {
				let mut i = 0;
				loop {
					if unsafe{ptr.add(i).read()} == b'\0' {
						return Some(
							unsafe{std::str::from_utf8_unchecked(std::slice::from_raw_parts(ptr.as_ptr(), i))}
						)
					}
					i += 1;
				}
			} else {
				Some(
					unsafe{std::str::from_utf8_unchecked(std::slice::from_raw_parts(ptr.as_ptr(), len))}
				)
			}
		} else {None}
	}
}

impl Default for GrugInitSettings<'static> {
	fn default () -> Self {
		Self::new()
	}
}

pub fn default_runtime_error_handler(_err_kind: u32, reason: &str, on_fn_name: &str, script_path: &str) {
	println!("Runtime Error: {} in function {} in script {}", reason, on_fn_name, script_path);
	std::process::exit(1);
}

pub struct GrugState {
	pub(crate) mod_api: ModApi,
	pub(crate) mods_dir_path: OsString,
	next_entity_id: AtomicU64,
	pub(crate) game_functions: HashMap<&'static str, GameFnPtr>,
	pub(crate) runtime_error_handler: RuntimeErrorHandler,

	pub(crate) entities: Xar<GrugEntity>,
	
	// SAFETY: The strings within the `on_functions` field is allocated within
	// `mod_api`. So any reference given out to this field must have the 'self
	// lifetime
	// If a later change makes mod_api mutable, these need to be allocated separately
	// TODO: rename this to `event_functions`
	on_functions: Vec<EventFnEntry<'static>>,
	pub(crate) path_to_script_ids: RefCell<HashMap<OsString, GrugFileId>>,
	next_script_id: AtomicU64,

	pub(crate) backend: ErasedBackend<Self>,
	pub(crate) arenas : RefCell<Vec<Arena>>,
	// pub(crate) backend: Interpreter,
	pub(crate) current_script: Cell<Option<GrugFileId>>,
	pub(crate) current_on_fn_id: Cell<Option<GrugOnFnId>>,
	pub(crate) is_errorring: Cell<bool>,

	pub(crate) changes: Receiver<Result<DirChanges, std::io::Error>>,
}

impl State for GrugState {
	fn set_runtime_error(&self, error: RuntimeError) {
		self.is_errorring.set(true);
		let Some(current_script) = self.current_script.get() else {
			return
		};
		let Some(current_on_fn_id) = self.current_on_fn_id.get() else {
			return
		};
		let current_on_fn_name = self.get_on_fn_name(current_on_fn_id).unwrap();
		let message = format!("{}", error);
		self.runtime_error_handler.handle_error(
			error, 
			&message,
			current_on_fn_name,
			self.get_script_path(current_script).unwrap(),
		);
	}

	fn is_errorring(&self) -> bool {
		self.is_errorring.get()
	}
}

impl GrugState {
	fn new (mod_api_path: impl AsRef<OsStr>, mods_dir_path: impl AsRef<OsStr>, handler: RuntimeErrorHandler, backend: ErasedBackend<Self>) -> Result<Self, GrugError> {
		let mod_api = get_mod_api(mod_api_path.as_ref())?;
		Self::new_inner(mod_api, mods_dir_path, handler, backend)
	}

	pub fn new_from_text (mod_api_text: &str, mods_dir_path: impl AsRef<OsStr>, handler: RuntimeErrorHandler, backend: impl Into<ErasedBackend<Self>>) -> Result<Self, GrugError> {
		let mod_api = get_mod_api_from_text(mod_api_text)?;
		Self::new_inner(mod_api, mods_dir_path, handler, backend.into())
	}

	fn new_inner (mod_api: ModApi, mods_dir_path: impl AsRef<OsStr>, handler: RuntimeErrorHandler, backend: ErasedBackend<Self>) -> Result<Self, GrugError> {
		let mut on_fns = Vec::new();
		let init_globals = nt!("init_globals");
		for (entity_type, entity) in mod_api.entities() {
			on_fns.push(EventFnEntry {
				// SAFETY: All EventFnEntries we give out have a 'self
				// lifetime, which is the same as the 'mod_api lifetime they
				// actually have
				entity_type   : unsafe{entity_type.as_ntstrptr().detach_lifetime()},
				event_fn_name : unsafe{init_globals.as_ntstrptr().detach_lifetime()},
				index      : 0,
			});
			for (i, (event_fn_name, _)) in entity.on_fns.iter().enumerate() {
				on_fns.push(EventFnEntry{
					// SAFETY: All EventFnEntries we give out have a 'self
					// lifetime, which is the same as the 'mod_api lifetime they
					// actually have
					entity_type   : unsafe{entity_type.as_ntstrptr().detach_lifetime()},
					event_fn_name : unsafe{event_fn_name.as_ntstrptr().detach_lifetime()},
					index         : i,
				});
			}
		}

		let (sender, reciever) = channel();
		watch_changes(mods_dir_path.as_ref().to_str().unwrap(), move |changes| sender.send(changes).unwrap()).unwrap();

		Ok(Self {
			mod_api,
			mods_dir_path: OsString::from(mods_dir_path.as_ref()),
			next_entity_id: AtomicU64::new(0),
			game_functions: HashMap::new(),
			runtime_error_handler: handler,
			entities: Xar::new(),
			on_functions: on_fns,
			path_to_script_ids: RefCell::new(HashMap::new()),
			next_script_id: AtomicU64::new(0),
			arenas: RefCell::new(Vec::new()),
			backend: backend.into(),
			current_script: Cell::new(None),
			current_on_fn_id: Cell::new(None),
			is_errorring: Cell::new(false),
			changes: reciever,
		})
	}

	pub fn get_on_fn_id(&self, entity_type: &str, on_fn_name: &str) -> Result<GrugOnFnId, StateError> {
		if !self.mod_api.entities().contains_key(entity_type) {
			return Err(StateError::UnknownEntityType{
				entity_type: String::from(entity_type),
			});
		}
		for (i, on_fn_entry) in self.on_functions.iter().enumerate() {
			if on_fn_entry.entity_type() == entity_type && on_fn_entry.event_fn_name() == on_fn_name {
				return Ok(i as u64)
			}
		}
		Err(StateError::UnknownOnFunction {
			entity_type: String::from(entity_type),
			on_function_name : String::from(on_fn_name ),
		})
	}
	
	pub fn get_on_fn_name(&self, on_fn_id: GrugOnFnId) -> Option<&str> {
		return self.on_functions.get(on_fn_id as usize).map(|entry| entry.event_fn_name())
	}

	pub fn get_on_functions(&self) -> &[EventFnEntry<'_>] {
		&self.on_functions
	}

	pub fn get_entity_on_functions(&self, entity_type: &str) -> Result<&[EventFnEntry<'_>], StateError> {
		if !self.mod_api.entities().contains_key(entity_type) {
			return Err(StateError::UnknownEntityType{
				entity_type: String::from(entity_type),
			});
		}
		let mut start = 0;
		while start != self.on_functions.len() && self.on_functions[start].entity_type() != entity_type {
			start += 1;
		}
		let mut end = start;
		while end != self.on_functions.len() && self.on_functions[end].entity_type() == entity_type {
			end += 1;
		}
		Ok(&self.on_functions[start..end])
	}

	pub unsafe fn register_game_fn(&mut self, name: &'static str, ptr: GameFnPtrState<Self>) -> Result<(), StateError> {
		if !self.mod_api.game_functions().contains_key(name) {
			Err(StateError::UnknownGameFunction{
				game_function_name: name,
			})
		} else {
			match self.game_functions.entry(name) {
				Entry::Occupied(_) => Err(StateError::ReregisteringGameFunction{
					game_function_name: name,
				}),
				Entry::Vacant(x) => {
					x.insert(GameFnPtr::from_ptr(ptr));
					Ok(())
				}
			}
		}
	}

	// Register a dummy function for each game function defined in the mod_api
	// NOTE: This function only exists to allow the cli compiler to function.
	// It is immediate UB to run any grug script created with this grug_state afterwards.
	//
	// You are only allowed to compile scripts from this state.
	pub unsafe fn register_dummies(&mut self) {
		extern "C" fn dummy_host_fn(_state: &GrugState, _arguments: *const GrugValue) -> GrugValue {
			GrugValue{void: ()}
		}

		for (name, _) in self.mod_api.game_functions() {
			self.game_functions.entry(Box::leak(Box::from(name.as_str()))).or_insert(GameFnPtr::from_ptr(dummy_host_fn));
		}
	}
	
	// This should only happen during an error so its okay if its slow
	pub fn get_script_path(&self, script_id: GrugFileId) -> Option<&OsStr> {
		let string = Ref::filter_map(self.path_to_script_ids.borrow(), |inner|
			inner.iter().find(|(_, v)| **v == script_id).map(|x| x.0)

		).ok()?;
		// SAFETY: a path is never replaced once it is inserted into the map;
		let string: &OsStr = unsafe{&*(&**string as *const OsStr)};
		Some(string)
	}

	pub fn all_game_fns_registered(&self) -> Result<(), ModApiError> {
		for game_fn_name in self.mod_api.game_functions().keys() {
			if !self.game_functions.contains_key(game_fn_name.as_str()) {
				Err(ModApiError::GameFnNotProvided{
					game_fn_name: String::from(&**game_fn_name),
				})?;
			}
		}
		Ok(())
	}

	pub(crate) fn get_next_script_id(&self) -> GrugFileId {
		GrugId::new(self.next_script_id.fetch_add(1, Ordering::Relaxed))
	}

	pub fn get_next_entity_id(&self) -> GrugId {
		GrugId::new(self.next_entity_id.fetch_add(1, Ordering::Relaxed))
	}

	/// # Safety
	/// There is no memory safety issue here. 
	/// But this may cause older entities to be replaced 
	/// by newer ones with no warning if the ids start overlapping
	pub unsafe fn set_next_entity_id(&self, next_id: u64) {
		self.next_entity_id.store(next_id, Ordering::Relaxed);
	}

	pub fn create_entity(&self, file_id: GrugFileId) -> Option<GrugEntityHandle<'_>> {
		let old_script   = self.current_script  .get();
		let old_on_fn_id = self.current_on_fn_id.get();
		self.current_script  .set(Some(file_id));
		self.current_on_fn_id.set(Some(0));

		let entity = self.entities.insert(unsafe{GrugEntity::new_uninit(self.get_next_entity_id(), file_id)});
		let entity = unsafe{GrugEntityHandle::new(entity)};
		// SAFETY: Entity is created inside a Xar which does not move elements around. 
		let success = self.backend.init_entity(self, unsafe{Pin::new_unchecked(&entity)});

		self.current_script  .set(old_script);
		self.current_on_fn_id.set(old_on_fn_id);

		if success {
			Some(entity)
		} else {
			unsafe{self.entities.delete(entity.into_inner());}
			None
		}
	}

	pub fn destroy_entity<'a>(&'a self, entity: GrugEntityHandle<'a>) {
		// TODO: Implement Xar::contained_within and perform this check yourself
		if self.entities.is_contained_within(entity.0) {
			self.backend.destroy_entity_data(&*entity);
			// `self.entities.contained_within` returns true so this entity must exist within self
			unsafe{self.entities.delete(entity.into_inner())};
		}
	}

	pub fn clear_entities(&mut self) {
		self.backend.clear_entities();
		self.entities.clear();
	}

	pub fn clear_error(&self) {
		self.is_errorring.set(false);
	}

	fn get_on_fn_index(&self, id: GrugOnFnId) -> usize {
		self.on_functions[id as usize].index
	}
}

impl GrugState {
	/// # SAFETY 
	/// `values` must point to an array of values with length equal to
	/// the number of arguments expected by `function_name`. If there are no arguments, 
	/// `values` may be null
	#[must_use]
	pub unsafe fn call_on_function_raw(&self, entity: &GrugEntity, on_fn_id: GrugOnFnId, values: *const GrugValue) -> bool {
		let old_script   = self.current_script  .get();
		let old_on_fn_id = self.current_on_fn_id.get();
		self.current_script  .set(Some(entity.file_id));
		self.current_on_fn_id.set(Some(on_fn_id));

		let ret_val = unsafe {
			self.backend.call_on_function_raw(self, entity, self.get_on_fn_index(on_fn_id), values)
		};

		self.current_script  .set(old_script);
		self.current_on_fn_id.set(old_on_fn_id);

		ret_val
	}

	#[must_use]
	pub fn call_on_function(&self, entity: &GrugEntity, on_fn_id: GrugOnFnId, values: &[GrugValue]) -> bool {
		let old_script   = self.current_script  .get();
		let old_on_fn_id = self.current_on_fn_id.get();
		self.current_script  .set(Some(entity.file_id));
		self.current_on_fn_id.set(Some(on_fn_id));

		let ret_val = self.backend.call_on_function(self, entity, self.get_on_fn_index(on_fn_id), values);

		self.current_script  .set(old_script);
		self.current_on_fn_id.set(old_on_fn_id);

		ret_val
	}
}

#[derive(Debug)]
pub enum StateError {
	UnknownEntityType{
		entity_type: String
	},
	UnknownOnFunction {
		entity_type: String,
		on_function_name: String,
	},
	UnknownGameFunction {
		game_function_name: &'static str,
	},
	ReregisteringGameFunction {
		game_function_name: &'static str,
	}
}

impl std::fmt::Display for StateError {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		match self {
			Self::UnknownEntityType{
				entity_type,
			} => write!(f, "mod api does not define an entity named {}", entity_type),
			Self::UnknownOnFunction {
				entity_type,
				on_function_name,
			} => write!(f, "'{}' does not contain an on_function named '{}'", entity_type, on_function_name),
			Self::UnknownGameFunction {
				game_function_name,
			} => write!(f, "Game function named '{}' is not found in mod_api.json", game_function_name),
			Self::ReregisteringGameFunction {
				game_function_name,
			} => write!(f, "Game function named '{}' has already been registered", game_function_name),
		}
	}
}

// TODO: This should be moved to gruggers-core
pub struct EventFnEntry<'a> {
	entity_type   : NTStrPtr<'a>,
	event_fn_name : NTStrPtr<'a>,
	pub index      : usize,
}

impl<'a> EventFnEntry<'a> {
	/// Turns the null terminated string representing the entity name into a [`&str`]
	pub fn entity_type(&self) -> &str {
		self.entity_type.to_str()
	}
	/// Turns the null terminated string representing the event function name into a [`&str`]
	pub fn event_fn_name(&self) -> &str {
		self.event_fn_name.to_str()
	}
}

const _: () = const{
	// The C interop with Rust assumes that slice pointers have a layout like this
	// #[repr(C)]
	// struct Slice<T> {
	// 		data: NonNull<T>,
	// 		len : usize,
	// }
	// 
	// The rust compiler currently does not guarantee the layout of slice pointer.
	// These assertions ensure that if the assumption is broken, we get a
	// compile error instead of random crashes
	let x: &[EventFnEntry] = &[];
	unsafe{assert!(x.len() == (&x as *const _ as *const usize).add(1).read());}
};

/// A pointer to a grug entity. Only allows shared access to the data and does
/// not allow copying or cloning. Lifetime of shared borrows are limited to the lifetime of self
#[repr(transparent)]
pub struct GrugEntityHandle<'a>(XarHandle<'a, GrugEntity>);

impl<'a> GrugEntityHandle<'a> {
	/// SAFETY: inner can only be deleted by deleting the returned value
	/// The returned value is allowed to create a shared reference to the data at any time 
	pub unsafe fn new(inner: XarHandle<'a, GrugEntity>) -> Self {
		Self(inner)
	}

	pub fn into_inner(self) -> XarHandle<'a, GrugEntity> {
		self.0
	}
}

impl<'a> AsRef<GrugEntity> for GrugEntityHandle<'a> {
	fn as_ref(&self) -> &GrugEntity {
		unsafe{self.0.get_ref()}
	}
}

impl<'a> std::ops::Deref for GrugEntityHandle<'a> {
	type Target = GrugEntity;
	fn deref(&self) -> &Self::Target {
		unsafe{self.0.get_ref()}
	}
}

#[derive(Debug)]
pub struct FileInfo {
	pub path: Box<Path>,
	pub file_name: Box<OsStr>,
	pub mod_name: Box<OsStr>,
	pub entity_type: Box<str>,
	pub entity_name: Box<OsStr>,
	pub result: Result<GrugFileId, GrugError>,
}