//! 服务器端 traits。

use super::*;

use std::cell::Cell;
use std::marker::PhantomData;

// FIXME(eddyb) 在 `server.rs` 中生成 `HandleStore` 的定义。
use super::client::HandleStore;

pub trait Types {
    type FreeFunctions: 'static;
    type TokenStream: 'static + Clone;
    type SourceFile: 'static + Clone;
    type Span: 'static + Copy + Eq + Hash;
    type Symbol: 'static;
}

/// 声明以下 traits 之一的关联 fn，添加必要的默认主体。
///
macro_rules! associated_fn {
    (fn drop(&mut self, $arg:ident: $arg_ty:ty)) =>
        (fn drop(&mut self, $arg: $arg_ty) { mem::drop($arg) });

    (fn clone(&mut self, $arg:ident: $arg_ty:ty) -> $ret_ty:ty) =>
        (fn clone(&mut self, $arg: $arg_ty) -> $ret_ty { $arg.clone() });

    ($($item:tt)*) => ($($item)*;)
}

macro_rules! declare_server_traits {
    ($($name:ident {
        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
    }),* $(,)?) => {
        $(pub trait $name: Types {
            $(associated_fn!(fn $method(&mut self, $($arg: $arg_ty),*) $(-> $ret_ty)?);)*
        })*

        pub trait Server: Types $(+ $name)* {
            fn globals(&mut self) -> ExpnGlobals<Self::Span>;

            /// 实习生从 RPC 收到的符号
            fn intern_symbol(ident: &str) -> Self::Symbol;

            /// 恢复符号的字符串值，并使用它调用回调。
            fn with_symbol_string(symbol: &Self::Symbol, f: impl FnOnce(&str));
        }
    }
}
with_api!(Self, self_, declare_server_traits);

pub(super) struct MarkedTypes<S: Types>(S);

impl<S: Server> Server for MarkedTypes<S> {
    fn globals(&mut self) -> ExpnGlobals<Self::Span> {
        <_>::mark(Server::globals(&mut self.0))
    }
    fn intern_symbol(ident: &str) -> Self::Symbol {
        <_>::mark(S::intern_symbol(ident))
    }
    fn with_symbol_string(symbol: &Self::Symbol, f: impl FnOnce(&str)) {
        S::with_symbol_string(symbol.unmark(), f)
    }
}

macro_rules! define_mark_types_impls {
    ($($name:ident {
        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
    }),* $(,)?) => {
        impl<S: Types> Types for MarkedTypes<S> {
            $(type $name = Marked<S::$name, client::$name>;)*
        }

        $(impl<S: $name> $name for MarkedTypes<S> {
            $(fn $method(&mut self, $($arg: $arg_ty),*) $(-> $ret_ty)? {
                <_>::mark($name::$method(&mut self.0, $($arg.unmark()),*))
            })*
        })*
    }
}
with_api!(Self, self_, define_mark_types_impls);

struct Dispatcher<S: Types> {
    handle_store: HandleStore<S>,
    server: S,
}

macro_rules! define_dispatcher_impl {
    ($($name:ident {
        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
    }),* $(,)?) => {
        // FIXME(eddyb) `pub` 仅适用于下面的 `ExecutionStrategy`。
        pub trait DispatcherTrait {
            // HACK(eddyb) 这些是为了让下面的 `Self::$name` 工作。
            $(type $name;)*

            fn dispatch(&mut self, buf: Buffer) -> Buffer;
        }

        impl<S: Server> DispatcherTrait for Dispatcher<MarkedTypes<S>> {
            $(type $name = <MarkedTypes<S> as Types>::$name;)*

            fn dispatch(&mut self, mut buf: Buffer) -> Buffer {
                let Dispatcher { handle_store, server } = self;

                let mut reader = &buf[..];
                match api_tags::Method::decode(&mut reader, &mut ()) {
                    $(api_tags::Method::$name(m) => match m {
                        $(api_tags::$name::$method => {
                            let mut call_method = || {
                                reverse_decode!(reader, handle_store; $($arg: $arg_ty),*);
                                $name::$method(server, $($arg),*)
                            };
                            // HACK(eddyb) 不要在 panic 中使用 `panic::catch_unwind`。
                            // 如果客户端和服务器碰巧使用相同的 `std`，`catch_unwind` 断言 panic 计数器为 0，即使传递给它的闭包没有 panic。
                            //
                            //
                            let r = if thread::panicking() {
                                Ok(call_method())
                            } else {
                                panic::catch_unwind(panic::AssertUnwindSafe(call_method))
                                    .map_err(PanicMessage::from)
                            };

                            buf.clear();
                            r.encode(&mut buf, handle_store);
                        })*
                    }),*
                }
                buf
            }
        }
    }
}
with_api!(Self, self_, define_dispatcher_impl);

pub trait ExecutionStrategy {
    fn run_bridge_and_client(
        &self,
        dispatcher: &mut impl DispatcherTrait,
        input: Buffer,
        run_client: extern "C" fn(BridgeConfig<'_>) -> Buffer,
        force_show_panics: bool,
    ) -> Buffer;
}

thread_local! {
    /// 在使用相同线程执行程序运行 proc 宏时，将设置此标志，强制嵌套 proc 宏调用 (例如
    /// 由于 `TokenStream::expand_expr`) 使用跨线程执行程序运行。
    ///
    /// 这是必需的，因为 proc_macro 客户端中的线程本地状态不处理重新输入，并且在进入嵌套宏时将使所有符号无效。
    ///
    ///
    ///
    static ALREADY_RUNNING_SAME_THREAD: Cell<bool> = Cell::new(false);
}

/// 保持 `ALREADY_RUNNING_SAME_THREAD` (另见其文档) 设置为 `true`，防止同线程重新进入。
///
struct RunningSameThreadGuard(());

impl RunningSameThreadGuard {
    fn new() -> Self {
        let already_running = ALREADY_RUNNING_SAME_THREAD.replace(true);
        assert!(
            !already_running,
            "same-thread nesting (\"reentrance\") of proc macro executions is not supported"
        );
        RunningSameThreadGuard(())
    }
}

impl Drop for RunningSameThreadGuard {
    fn drop(&mut self) {
        ALREADY_RUNNING_SAME_THREAD.set(false);
    }
}

pub struct MaybeCrossThread<P> {
    cross_thread: bool,
    marker: PhantomData<P>,
}

impl<P> MaybeCrossThread<P> {
    pub const fn new(cross_thread: bool) -> Self {
        MaybeCrossThread { cross_thread, marker: PhantomData }
    }
}

impl<P> ExecutionStrategy for MaybeCrossThread<P>
where
    P: MessagePipe<Buffer> + Send + 'static,
{
    fn run_bridge_and_client(
        &self,
        dispatcher: &mut impl DispatcherTrait,
        input: Buffer,
        run_client: extern "C" fn(BridgeConfig<'_>) -> Buffer,
        force_show_panics: bool,
    ) -> Buffer {
        if self.cross_thread || ALREADY_RUNNING_SAME_THREAD.get() {
            <CrossThread<P>>::new().run_bridge_and_client(
                dispatcher,
                input,
                run_client,
                force_show_panics,
            )
        } else {
            SameThread.run_bridge_and_client(dispatcher, input, run_client, force_show_panics)
        }
    }
}

pub struct SameThread;

impl ExecutionStrategy for SameThread {
    fn run_bridge_and_client(
        &self,
        dispatcher: &mut impl DispatcherTrait,
        input: Buffer,
        run_client: extern "C" fn(BridgeConfig<'_>) -> Buffer,
        force_show_panics: bool,
    ) -> Buffer {
        let _guard = RunningSameThreadGuard::new();

        let mut dispatch = |buf| dispatcher.dispatch(buf);

        run_client(BridgeConfig {
            input,
            dispatch: (&mut dispatch).into(),
            force_show_panics,
            _marker: marker::PhantomData,
        })
    }
}

pub struct CrossThread<P>(PhantomData<P>);

impl<P> CrossThread<P> {
    pub const fn new() -> Self {
        CrossThread(PhantomData)
    }
}

impl<P> ExecutionStrategy for CrossThread<P>
where
    P: MessagePipe<Buffer> + Send + 'static,
{
    fn run_bridge_and_client(
        &self,
        dispatcher: &mut impl DispatcherTrait,
        input: Buffer,
        run_client: extern "C" fn(BridgeConfig<'_>) -> Buffer,
        force_show_panics: bool,
    ) -> Buffer {
        let (mut server, mut client) = P::new();

        let join_handle = thread::spawn(move || {
            let mut dispatch = |b: Buffer| -> Buffer {
                client.send(b);
                client.recv().expect("server died while client waiting for reply")
            };

            run_client(BridgeConfig {
                input,
                dispatch: (&mut dispatch).into(),
                force_show_panics,
                _marker: marker::PhantomData,
            })
        });

        while let Some(b) = server.recv() {
            server.send(dispatcher.dispatch(b));
        }

        join_handle.join().unwrap()
    }
}

/// 用于在服务器和客户端线程之间进行通信的消息管道。
pub trait MessagePipe<T>: Sized {
    /// 为消息管道创建一对新端点。
    fn new() -> (Self, Self);

    /// 向此管道的另一个端点发送消息。
    fn send(&mut self, value: T);

    /// 从该管道的另一个端点接收消息。
    ///
    /// 如果管道已经收到其他的结束，则返回 `None`，并且没有收到消息。
    ///
    fn recv(&mut self) -> Option<T>;
}

fn run_server<
    S: Server,
    I: Encode<HandleStore<MarkedTypes<S>>>,
    O: for<'a, 's> DecodeMut<'a, 's, HandleStore<MarkedTypes<S>>>,
>(
    strategy: &impl ExecutionStrategy,
    handle_counters: &'static client::HandleCounters,
    server: S,
    input: I,
    run_client: extern "C" fn(BridgeConfig<'_>) -> Buffer,
    force_show_panics: bool,
) -> Result<O, PanicMessage> {
    let mut dispatcher =
        Dispatcher { handle_store: HandleStore::new(handle_counters), server: MarkedTypes(server) };

    let globals = dispatcher.server.globals();

    let mut buf = Buffer::new();
    (globals, input).encode(&mut buf, &mut dispatcher.handle_store);

    buf = strategy.run_bridge_and_client(&mut dispatcher, buf, run_client, force_show_panics);

    Result::decode(&mut &buf[..], &mut dispatcher.handle_store)
}

impl client::Client<crate::TokenStream, crate::TokenStream> {
    pub fn run<S>(
        &self,
        strategy: &impl ExecutionStrategy,
        server: S,
        input: S::TokenStream,
        force_show_panics: bool,
    ) -> Result<S::TokenStream, PanicMessage>
    where
        S: Server,
        S::TokenStream: Default,
    {
        let client::Client { get_handle_counters, run, _marker } = *self;
        run_server(
            strategy,
            get_handle_counters(),
            server,
            <MarkedTypes<S> as Types>::TokenStream::mark(input),
            run,
            force_show_panics,
        )
        .map(|s| <Option<<MarkedTypes<S> as Types>::TokenStream>>::unmark(s).unwrap_or_default())
    }
}

impl client::Client<(crate::TokenStream, crate::TokenStream), crate::TokenStream> {
    pub fn run<S>(
        &self,
        strategy: &impl ExecutionStrategy,
        server: S,
        input: S::TokenStream,
        input2: S::TokenStream,
        force_show_panics: bool,
    ) -> Result<S::TokenStream, PanicMessage>
    where
        S: Server,
        S::TokenStream: Default,
    {
        let client::Client { get_handle_counters, run, _marker } = *self;
        run_server(
            strategy,
            get_handle_counters(),
            server,
            (
                <MarkedTypes<S> as Types>::TokenStream::mark(input),
                <MarkedTypes<S> as Types>::TokenStream::mark(input2),
            ),
            run,
            force_show_panics,
        )
        .map(|s| <Option<<MarkedTypes<S> as Types>::TokenStream>>::unmark(s).unwrap_or_default())
    }
}