use crate::{obj::{reserved::*, prelude::*}, vm::{consts::ConstPool, inst::Inst, signal::*, Vm}};
use once_cell::sync::Lazy;
use shredder::{GcSafeWrapper, Scan};
use std::{fmt::{Debug, Formatter, self}, io::{self, Write}};

pub type FunLocals = Vec<Sym>;

//
// struct UserFun
//

pub type UserFunRef = ObjRef<UserFun>;

#[derive(Scan)]
pub struct UserFun {
    vtable: Vtable,
    attrs: Attrs,
    // Safe because Vec<Inst> doesn't need to be scanned
    #[shredder(unsafe_skip)]
    code: Vec<Inst>,
    // Safe because this is just an interner that points to symbols, which aren't GC'd
    #[shredder(unsafe_skip)]
    locals: FunLocals,
}

impl UserFun {
    pub fn new_obj(code: Vec<Inst>, locals: FunLocals) -> UserFunRef {
        let obj_ref = ObjRef::new(UserFun {
            vtable: Default::default(), // this is a placeholder for the real vtable
            attrs: Default::default(),
            code,
            locals,
        });

        // XXX replace the vtable before returning, since __call__ member points to the object
        // itself
        {
            write_obj!(let obj = obj_ref);
            obj.vtable = vtable! {
                TY_MEMBER_NAME.sym => USER_FUN_TY.clone(),
                CALL_MEMBER_NAME.sym => obj_ref.clone(),
            };
        }

        obj_ref
    }

    pub fn code(&self) -> &Vec<Inst> {
        &self.code
    }

    pub fn locals(&self) -> &FunLocals {
        &self.locals
    }

    pub fn dump(&self, writer: &mut dyn Write, const_pool: &ConstPool, globals: &FunLocals) -> io::Result<()> {
        fn num_digits(n: usize, radix: usize) -> usize {
            ((n as f64) + 1.0).log(radix as f64).ceil() as usize
        }

        // column widths
        let addr_w = num_digits(self.code().len(), 16).max(4);
        let inst_col = 16 - addr_w;
        let inst_w = 16;

        for (addr, inst) in self.code().iter().enumerate() {
            let (param_val, mut param_name) = match inst {
                Inst::PushSym(sym) | Inst::GetAttr(sym) | Inst::SetAttr(sym) => (
                    sym.index().to_string(),
                    global_sym_lookup(*sym).unwrap().to_string(),
                ),
                Inst::PushConst(hdl) => (
                    hdl.index().to_string(),
                    {
                        let obj_ref = const_pool.get(*hdl);
                        read_obj!(let obj = obj_ref);
                        format!("{:?}", obj)
                    },
                ),
                Inst::LoadLocal(local) => (
                    local.index().to_string(),
                    global_sym_lookup(self.locals()[local.index()]).unwrap().to_string(),
                ),
                Inst::PopLocal(local) => {
                    if let Some(local) = local {
                        let index = local.index();
                        let sym = self.locals()[index];
                        let name = global_sym_lookup(sym).unwrap().to_string();
                        (index.to_string(), name)
                    } else {
                        ("(discarded)".to_string(), String::new())
                    }
                }
                Inst::PopGlobal(global) => {
                    if let Some(global) = global{
                        let index = global.index();
                        let sym = globals[index];
                        let name = global_sym_lookup(sym).unwrap().to_string();
                        (index.to_string(), name)
                    } else {
                        ("(discarded)".to_string(), String::new())
                    }
                }
                Inst::Jump(addr) | Inst::JumpTrue(addr) => (
                    addr.to_string(),
                    String::new(),
                ),
                Inst::Call(argc) => (
                    argc.to_string(),
                    String::new(),
                ),
                _ => (String::new(), String::new()),
            };

            if !param_name.is_empty() {
                param_name = format!("({})", param_name);
            }

            writeln!(
                writer,
                "{:0addr_w$x}{space: >inst_col$}{: <inst_w$}{: <4} {}",
                addr,
                inst.name(),
                param_val,
                param_name,
                space = "",
                addr_w = addr_w,
                inst_w = inst_w,
                inst_col = inst_col,
            )?;
        }
        Ok(())
    }
}

impl_obj!(UserFun);

impl Debug for UserFun {
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        fmt.debug_struct("UserFun")
            .field("attrs", &self.attrs)
            .field("code", &self.code)
            .field("locals", &self.locals)
            .finish()
    }
}

pub static USER_FUN_TY: Lazy<ObjRef<Ty>> = Lazy::new(|| Ty::new_obj(USER_FUN_NAME.sym_ref()));

//
// struct NativeFun
//

pub type NativeFunPtr = Box<dyn (Fn(ObjRef, &mut Vm, Vec<ObjRef>) -> Signal) + Send + Sync>;
pub type NativeFunRef = ObjRef<NativeFun>;

#[derive(Scan)]
pub struct NativeFun {
    vtable: Vtable,
    attrs: Attrs,
    #[shredder(skip)]
    fun: GcSafeWrapper<NativeFunPtr>,
}

//
// impl NativeFun
//

impl NativeFun {
    pub fn new_obj(fun: NativeFunPtr) -> ObjRef<Self> {
        let obj_ref = ObjRef::new(Self {
            vtable: Default::default(),
            attrs: Default::default(),
            fun: GcSafeWrapper::new(fun),
        });


        // XXX replace the vtable before returning, since __call__ member points to the object
        // itself
        {
            write_obj!(let obj = obj_ref);
            obj.vtable = vtable! {
                TY_MEMBER_NAME.sym => NATIVE_FUN_TY.clone(),
                CALL_MEMBER_NAME.sym => obj_ref.clone(),
            };
        }

        obj_ref
    }

    /// Gets the native function that can be invoked.
    pub fn fun(&self) -> &NativeFunPtr {
        &self.fun
    }
}

//
// impl Debug for NativeFun
//

impl Debug for NativeFun {
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        fmt.debug_struct("NativeFun")
            .field("fun", &format!("(function at {:x})", &self.fun as *const _ as usize))
            .field("attrs", &self.attrs)
            .finish()
    }
}

impl_obj!(NativeFun);

pub static NATIVE_FUN_TY: Lazy<ObjRef<Ty>> = Lazy::new(|| Ty::new_obj(NATIVE_FUN_NAME.sym_ref()));

//
// Native function defs
//

// __access__ is what the "dot" operator calls
// __get_attr__ *should* always bypass the __access__ function and get an attribute directly

pub static GET_ATTR_MEMBER_FUN: Lazy<ObjRef<NativeFun>> = Lazy::new(|| {
    NativeFun::new_obj(Box::new(|_caller, _vm, _args| {
        /*
        let sym_ref = vm.pop();
        let obj_ref = vm.pop();
        obj_ref.access()
        */
        todo!("__get_attr__ function")
    }))
});