use std::ffi::CString;
use std::io::Cursor;
use std::io::Error as IoError;
use std::io::Read;
use std::num::NonZeroI32;
use std::panic::Location;

use crate::{
    ffi, impl_object, nzi32,
    object::{Call, CallError, FromObject, Object},
    AsLua, LuaError, LuaRead, LuaState, Push, PushGuard, PushInto, PushOne, PushOneInto,
};

/// Wrapper around a `&str`. When pushed, the content will be parsed as Lua code and turned into a
/// function.
///
/// Since pushing this value can fail in case of a parsing error, you must use the `checked_set`
/// method instead of `set`.
///
/// > **Note**: This struct is a wrapper around `LuaCodeFromReader`. There's no advantage in using
/// > it except that it is more convenient. More advanced usages (such as returning a Lua function
/// > from a Rust function) can be done with `LuaCodeFromReader`.
///
/// # Example
///
/// ```no_run
/// let lua = tlua::Lua::new();
/// lua.checked_set("hello", &tlua::LuaCode("return 5")).unwrap();
///
/// let r: i32 = lua.eval("return hello();").unwrap();
/// assert_eq!(r, 5);
/// ```
#[derive(Debug)]
pub struct LuaCode<'a>(pub &'a str);

impl<'c, L> Push<L> for LuaCode<'c>
where
    L: AsLua,
{
    type Err = LuaError;

    #[track_caller]
    #[inline]
    fn push_to_lua(&self, lua: L) -> Result<PushGuard<L>, (LuaError, L)> {
        let reader = Cursor::new(self.0.as_bytes());
        LuaCodeFromReader::new(reader).push_into_lua(lua)
    }
}

impl<'c, L> PushOne<L> for LuaCode<'c> where L: AsLua {}

/// Wrapper around a `Read` object. When pushed, the content will be parsed as Lua code and turned
/// into a function.
///
/// Since pushing this value can fail in case of a reading error or a parsing error, you must use
/// the `checked_set` method instead of `set`.
///
/// # Example: returning a Lua function from a Rust function
///
/// ```no_run
/// use std::io::Cursor;
///
/// let lua = tlua::Lua::new();
///
/// lua.set("call_rust", tlua::function0(|| -> tlua::LuaCodeFromReader<Cursor<String>> {
///     let lua_code = "return 18;";
///     return tlua::LuaCodeFromReader::new(Cursor::new(lua_code.to_owned()));
/// }));
///
/// let r: i32 = lua.eval("local lua_func = call_rust(); return lua_func();").unwrap();
/// assert_eq!(r, 18);
/// ```
#[derive(Debug)]
pub struct LuaCodeFromReader<R> {
    reader: R,
    location: &'static Location<'static>,
}

impl<R> LuaCodeFromReader<R> {
    #[track_caller]
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            location: Location::caller(),
        }
    }
}

impl<L, R> PushInto<L> for LuaCodeFromReader<R>
where
    L: AsLua,
    R: Read,
{
    type Err = LuaError;

    #[inline]
    fn push_into_lua(self, lua: L) -> Result<PushGuard<L>, (LuaError, L)> {
        unsafe {
            struct ReadData<R> {
                reader: R,
                buffer: [u8; 128],
                triggered_error: Option<IoError>,
            }

            let mut read_data = ReadData {
                reader: self.reader,
                buffer: [0; 128],
                triggered_error: None,
            };

            extern "C" fn reader<R>(
                _: LuaState,
                data: *mut libc::c_void,
                size: *mut libc::size_t,
            ) -> *const libc::c_char
            where
                R: Read,
            {
                unsafe {
                    let data: *mut ReadData<R> = data as *mut _;
                    let data: &mut ReadData<R> = &mut *data;

                    if data.triggered_error.is_some() {
                        (*size) = 0;
                        return data.buffer.as_ptr() as *const libc::c_char;
                    }

                    match data.reader.read(&mut data.buffer) {
                        Ok(len) => (*size) = len as libc::size_t,
                        Err(e) => {
                            (*size) = 0;
                            data.triggered_error = Some(e);
                        }
                    };

                    data.buffer.as_ptr() as *const libc::c_char
                }
            }

            let (load_return_value, pushed_value) = {
                let location = format!("=[{}:{}]\0", self.location.file(), self.location.line());
                let location = CString::from_vec_with_nul_unchecked(location.into());
                let code = ffi::lua_load(
                    lua.as_lua(),
                    reader::<R>,
                    &mut read_data as *mut ReadData<_> as *mut _,
                    location.as_ptr(),
                );
                (code, PushGuard::new(lua, 1))
            };

            if read_data.triggered_error.is_some() {
                let error = read_data.triggered_error.unwrap();
                return Err((LuaError::ReadError(error), pushed_value.into_inner()));
            }

            if load_return_value == 0 {
                return Ok(pushed_value);
            }

            let error_msg: String = LuaRead::lua_read(pushed_value.as_lua())
                .expect("can't find error message at the top of the Lua stack");

            if load_return_value == ffi::LUA_ERRMEM {
                panic!("LUA_ERRMEM");
            }

            if load_return_value == ffi::LUA_ERRSYNTAX {
                return Err((LuaError::SyntaxError(error_msg), pushed_value.into_inner()));
            }

            panic!("Unknown error while calling lua_load");
        }
    }
}

impl<L, R> PushOneInto<L> for LuaCodeFromReader<R>
where
    L: AsLua,
    R: Read,
{
}

/// Handle to a function in the Lua context.
///
/// Just like you can read variables as integers and strings, you can also read Lua functions by
/// requesting a `LuaFunction` object. Once you have a `LuaFunction` you can call it with `call()`.
///
/// > **Note**: Passing parameters when calling the function is not yet implemented.
///
/// # Example
///
/// ```no_run
/// let lua = tlua::Lua::new();
/// lua.exec("function foo() return 12 end").unwrap();
///
/// let foo: tlua::LuaFunction<_> = lua.get("foo").unwrap();
/// let result: i32 = foo.call().unwrap();
/// assert_eq!(result, 12);
/// ```
// TODO: example for how to get a LuaFunction as a parameter of a Rust function
#[derive(Debug)]
pub struct LuaFunction<L> {
    inner: Object<L>,
}

impl<L> LuaFunction<L>
where
    L: AsLua,
{
    unsafe fn new(lua: L, index: NonZeroI32) -> Self {
        Self::from_obj(Object::new(lua, index))
    }

    pub fn into_inner(self) -> L {
        self.inner.into_guard()
    }
}

impl_object! { LuaFunction,
    check(lua, index) {
        ffi::lua_isfunction(lua.as_lua(), index.into())
    }
    impl Call,
}

impl<'lua, L> LuaFunction<L>
where
    L: 'lua,
    L: AsLua,
{
    /// Calls the function. Doesn't allow passing parameters.
    ///
    /// TODO: will eventually disappear and get replaced with `call_with_args`
    ///
    /// Returns an error if there is an error while executing the Lua code (eg. a function call
    /// returns an error), or if the requested return type doesn't match the actual return type.
    ///
    /// > **Note**: In order to pass parameters, see `call_with_args` instead.
    #[track_caller]
    #[inline]
    pub fn call<V>(&'lua self) -> Result<V, LuaError>
    where
        V: LuaRead<PushGuard<&'lua L>>,
    {
        Call::call(self)
    }

    /// Calls the function taking ownership of the underlying push guard.
    /// Doesn't allow passing parameters.
    ///
    /// TODO: will eventually disappear and get replaced with `call_with_args`
    ///
    /// Returns an error if there is an error while executing the Lua code (eg. a function call
    /// returns an error), or if the requested return type doesn't match the actual return type.
    ///
    /// > **Note**: In order to pass parameters, see `into_call_with_args`
    /// instead.
    #[track_caller]
    #[inline]
    pub fn into_call<V>(self) -> Result<V, LuaError>
    where
        V: LuaRead<PushGuard<Self>>,
    {
        Call::into_call(self)
    }

    /// Calls the function with parameters.
    ///
    /// TODO: should be eventually be renamed to `call`
    ///
    /// **Note:** this function can return multiple values if `V` is a tuple.
    /// * If the expected number of values is less than the actual, only the
    ///   first few values will be returned.
    /// * If the expected number of values is greater than the actual, the
    ///   function will return an error, unless the excess elements are
    ///   `Option<T>`.
    ///
    /// You can either pass a single value by passing a single value, or multiple parameters by
    /// passing a tuple.
    /// If you pass a tuple, the first element of the tuple will be the first argument, the second
    /// element of the tuple the second argument, and so on.
    ///
    /// Returns an error if there is an error while executing the Lua code (eg. a function call
    /// returns an error), if the requested return type doesn't match the actual return type, or
    /// if we failed to push an argument.
    ///
    /// # Example
    ///
    /// ```no_run
    /// let lua = tlua::Lua::new();
    /// lua.exec("function sub(a, b) return a - b end").unwrap();
    ///
    /// let foo: tlua::LuaFunction<_> = lua.get("sub").unwrap();
    /// let result: i32 = foo.call_with_args((18, 4)).unwrap();
    /// assert_eq!(result, 14);
    /// ```
    ///
    /// # Multiple return values
    ///
    /// ```no_run
    /// let lua = tlua::Lua::new();
    /// lua.exec("function divmod(a, b) return math.floor(a / b), a % b end").unwrap();
    ///
    /// let foo: tlua::LuaFunction<_> = lua.get("divmod").unwrap();
    ///
    /// let first_result: i32 = foo.call_with_args((18, 4)).unwrap();
    /// assert_eq!(first_result, 4);
    ///
    /// let all_result: (i32, i32) = foo.call_with_args((18, 4)).unwrap();
    /// assert_eq!(all_result, (4, 2));
    ///
    /// let excess_results: (i32, i32, Option<i32>) = foo.call_with_args((18, 4)).unwrap();
    /// assert_eq!(excess_results, (4, 2, None));
    /// ```
    #[track_caller]
    #[inline]
    pub fn call_with_args<V, A>(&'lua self, args: A) -> Result<V, CallError<A::Err>>
    where
        A: PushInto<LuaState>,
        V: LuaRead<PushGuard<&'lua L>>,
    {
        Call::call_with(self, args)
    }

    /// Calls the function with parameters taking ownership of the underlying
    /// push guard.
    ///
    /// TODO: should be eventually be renamed to `call`
    ///
    /// **Note:** this function can return multiple values if `V` is a tuple.
    /// * If the expected number of values is less than the actual, only the
    ///   first few values will be returned.
    /// * If the expected number of values is greater than the actual, the
    ///   function will return an error, unless the excess elements are
    ///   `Option<T>`.
    ///
    /// You can either pass a single value by passing a single value, or multiple parameters by
    /// passing a tuple.
    /// If you pass a tuple, the first element of the tuple will be the first argument, the second
    /// element of the tuple the second argument, and so on.
    ///
    /// Returns an error if there is an error while executing the Lua code (eg. a function call
    /// returns an error), if the requested return type doesn't match the actual return type, or
    /// if we failed to push an argument.
    ///
    /// # Example
    ///
    /// ```no_run
    /// let lua = tlua::Lua::new();
    /// lua.exec("function sub(a, b) return a - b end").unwrap();
    ///
    /// let foo: tlua::LuaFunction<_> = lua.get("sub").unwrap();
    /// let result: i32 = foo.into_call_with_args((18, 4)).unwrap();
    /// assert_eq!(result, 14);
    /// ```
    ///
    /// # Multiple return values
    ///
    /// ```no_run
    /// let lua = tlua::Lua::new();
    /// lua.exec("function divmod(a, b) return math.floor(a / b), a % b end").unwrap();
    ///
    /// let foo: tlua::LuaFunction<_> = lua.get("divmod").unwrap();
    ///
    /// let all_result: (i32, i32) = foo.into_call_with_args((18, 4)).unwrap();
    /// assert_eq!(all_result, (4, 2));
    /// ```
    #[track_caller]
    #[inline]
    pub fn into_call_with_args<V, A>(self, args: A) -> Result<V, CallError<A::Err>>
    where
        A: PushInto<LuaState>,
        V: LuaRead<PushGuard<Self>>,
    {
        Call::into_call_with(self, args)
    }
}

impl<L> LuaFunction<PushGuard<L>>
where
    L: AsLua,
{
    /// Builds a new `LuaFunction` from the code of a reader.
    ///
    /// Returns an error if reading from the `Read` object fails or if there is a syntax error in
    /// the code.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use std::io::Cursor;
    ///
    /// let lua = tlua::Lua::new();
    ///
    /// let f = tlua::LuaFunction::load_from_reader(&lua, Cursor::new("return 8")).unwrap();
    /// let ret: i32 = f.call().unwrap();
    /// assert_eq!(ret, 8);
    /// ```
    #[track_caller]
    #[inline]
    pub fn load_from_reader(lua: L, code: impl Read) -> Result<Self, LuaError> {
        match LuaCodeFromReader::new(code).push_into_lua(lua) {
            Ok(pushed) => unsafe { Ok(Self::new(pushed, nzi32!(-1))) },
            Err((err, _)) => Err(err),
        }
    }

    /// Builds a new `LuaFunction` from a raw string.
    ///
    /// > **Note**: This is just a wrapper around `load_from_reader`. There is no advantage in
    /// > using `load` except that it is more convenient.
    // TODO: remove this function? it's only a thin wrapper and it's for a very niche situation
    #[track_caller]
    #[inline(always)]
    pub fn load(lua: L, code: &str) -> Result<Self, LuaError> {
        let reader = Cursor::new(code.as_bytes());
        Self::load_from_reader(lua, reader)
    }
}