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#![feature(offset_to)]

use std::ptr;
use std::rc::Rc;

// These functions are used in macros, so sometimes they will be considered dead.
extern "C" {
    #[allow(dead_code)]
    pub fn emscripten_run_script(s: *const std::os::raw::c_char);
    #[allow(dead_code)]
    pub fn emscripten_run_script_int(s: *const std::os::raw::c_char) -> std::os::raw::c_int;
    #[allow(dead_code)]
    pub fn emscripten_run_script_string(s: *const std::os::raw::c_char) -> *const std::os::raw::c_char;
    
    #[allow(dead_code)]
    pub fn emscripten_asm_const(s: *const std::os::raw::c_char);
    #[allow(dead_code)]
    pub fn emscripten_asm_const_int(s: *const std::os::raw::c_char, ...) -> std::os::raw::c_int;
    #[allow(dead_code)]
    pub fn emscripten_asm_const_double(s: *const std::os::raw::c_char, ...) -> std::os::raw::c_double;
    #[allow(dead_code)]
    pub fn emscripten_pause_main_loop();
    #[allow(dead_code)]
    pub fn emscripten_set_main_loop(m: extern fn(), fps: std::os::raw::c_int, infinite: std::os::raw::c_int);

    pub fn free(p: *mut u8);
}

pub fn string_from_js(ptr: *mut u16) -> String {
    unsafe {
        let size : u32 = *(ptr as *const _ as *const u32);
        let string_slice : &'static [u16] = std::slice::from_raw_parts(ptr, size as usize);
        let result = String::from_utf16_lossy(string_slice);
        free(ptr as *mut _);
        result
    }
}

pub fn js_eval(code: &'static [u8]) {
    unsafe {
        emscripten_asm_const(code as *const _ as *const std::os::raw::c_char);
    }
}

        
#[macro_export]
macro_rules! __js_macro {
    ( $emscr_func:ident, $jscode:expr, $($args:expr),* ) => {
        {
            let jscode : &'static [u8] = concat!($jscode, "\0").as_bytes();
            unsafe {
                $crate::$emscr_func(jscode as *const _ as *const std::os::raw::c_char,
                                    $( $crate::JSObject::from($args).value ),* )
            }
        }
    };
}    

#[macro_export]
macro_rules! js {
    ($jscode:expr $(, $args:expr)*) => {
        __js_macro!(emscripten_asm_const_int, $jscode, $($args),*)
    }
}

#[macro_export]
macro_rules! js_obj {
    ($jscode:expr $(, $args:expr )*) => (
        $crate::JSObject {
            value: __js_macro!(emscripten_asm_const_int, $jscode, $($args),*) as f64,
            jshandle: true,
            refcount: Rc::new(()),
        }
    )
}

#[macro_export]
macro_rules! js_int {
    ($jscode:expr $(, $args:expr )*) => (
        __js_macro!(emscripten_asm_const_int, $jscode, $($args),*)
    )
}

#[macro_export]
macro_rules! js_double {
    ($jscode:expr $(, $args:expr )*) => (
        __js_macro!(emscripten_asm_const_double, $jscode, $($args),*);
    )
}

#[derive(Clone)]
pub struct JSObject {
    pub value: f64,
    pub jshandle: bool,
    pub refcount: Rc<()>,
}

// impl<'a, T> std::convert::From<&'a T> for JSObject
//     where JSObject: std::convert::From<T>, T: Clone {
//     fn from(v: &'a T) -> Self {
//         JSObject::from(v.clone())
//     }
// }

impl<'a> std::convert::From<&'a JSObject> for JSObject {
    fn from(v: &'a JSObject) -> Self {
        JSObject::from(v.clone())
    }
}

impl Drop for JSObject {
    fn drop(&mut self) {
        if self.jshandle && Rc::strong_count(&self.refcount) == 1 {
            let code : &'static [u8] = b"RFRAME.releaseObject($0);\0";
            unsafe {
                emscripten_asm_const_int(code as *const _ as *const std::os::raw::c_char, self.value);
            }
        }
    }
}

impl<T> std::convert::From<Vec<T>> for JSObject
    where JSObject: std::convert::From<T> {
    fn from(v: Vec<T>) -> Self {
        let arr = js_obj!("return RFRAME.storeObject([]);");
        for elem in v {
            let elem_js = JSObject::from(elem);
            let code : &'static [u8] = if elem_js.jshandle {
                b"RFRAME.loadObject($0).push(RFRAME.loadObject($1))\0"
            } else {
                b"RFRAME.loadObject($0).push($1)\0"
            };
            unsafe {
                emscripten_asm_const_int(code as *const _ as *const std::os::raw::c_char,
                                         arr.value, elem_js.value);
            }
        }
        arr
    }
}

macro_rules! __js_from_numeric {
    ( $( $type:ty ),+ ) => (
        $(
            impl std::convert::From<$type> for JSObject {
                fn from(v: $type) -> Self {
                    JSObject {
                        value: v as f64,
                        jshandle: false,
                        refcount: Rc::new(()),
                    }
                }
            }
        )+
    )
}

__js_from_numeric!(isize, usize, i32, u32, i16, u16, i8, u8, f32, f64);

impl<'a> std::convert::From<&'a str> for JSObject {
    fn from(s: &'a str) -> Self { // TODO: This won't work when the pointer can't fit in 31bit int.
        let code : &'static [u8] = b"return RFRAME.storeObject(RFRAME.copyStringFromHeap($0, $1));\0";
        let data : Vec<u16> = s.encode_utf16().collect();
        let data_ptr_as_isize = ptr::null::<u16>().offset_to(data.as_ptr()).unwrap_or(0) * 2;
        unsafe {
            JSObject {
                value: emscripten_asm_const_int(code as *const _ as *const std::os::raw::c_char,
                                                 data_ptr_as_isize, data.len()) as f64,
                jshandle: true,
                refcount: Rc::new(()),
            }
        }
    }
}

impl<'a> std::convert::From<&'a String> for JSObject {
    fn from(s: &'a String) -> Self {
        JSObject::from(s.as_str())
    }
}

impl std::convert::From<String> for JSObject {
    fn from(s: String) -> Self {
        JSObject::from(s.as_str())
    }
}

impl std::convert::From<bool> for JSObject {
    fn from(b: bool) -> Self {
        JSObject {
            value: if b { 1.0 } else { 0.0 },
            jshandle: false,
            refcount: Rc::new(()),
        }
    }
}