use std::cell::OnceCell;
use std::cell::RefCell;
use std::collections::HashSet;
use std::hash::Hash;
use std::rc::Rc;

use derive_more::{IsVariant, Unwrap};

use super::common as c;
use super::public as p;

use crate::bytecode::OpCodes;
use crate::error::*;
use crate::vm::{Env, VM};

mod attrset;
mod cnst;
mod func;
mod list;
mod primop;
mod string;

pub use attrset::*;
pub use cnst::Const;
pub use func::*;
pub use list::List;
pub use primop::*;

#[derive(Debug, IsVariant, Unwrap, Clone, PartialEq)]
pub enum Value<'vm> {
    Const(Const),
    Thunk(Rc<Thunk<'vm>>),
    ThunkRef(&'vm Thunk<'vm>),
    AttrSet(Rc<AttrSet<'vm>>),
    List(Rc<List<'vm>>),
    Catchable(c::Catchable),
    PrimOp(Rc<PrimOp<'vm>>),
    PartialPrimOp(Rc<PartialPrimOp<'vm>>),
    Func(Rc<Func<'vm>>),
    Builtins,
}

impl Hash for Value<'_> {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        use Value::*;
        std::mem::discriminant(self).hash(state);
        match self {
            Const(x) => x.hash(state),
            Thunk(x) => (x.as_ref() as *const self::Thunk).hash(state),
            ThunkRef(x) => (*x as *const self::Thunk).hash(state),
            AttrSet(x) => (x.as_ref() as *const self::AttrSet).hash(state),
            List(x) => (x.as_ref() as *const self::List).hash(state),
            Catchable(x) => x.hash(state),
            PrimOp(x) => (x.as_ref() as *const self::PrimOp).hash(state),
            PartialPrimOp(x) => (x.as_ref() as *const self::PartialPrimOp).hash(state),
            Func(x) => (x.as_ref() as *const self::Func).hash(state),
            Builtins => (),
        }
    }
}

impl<'vm> Value<'vm> {
    fn eq_impl(&self, other: &Self, vm: &'vm VM<'_>) -> bool {
        use Value::*;
        match (self, other) {
            (Const(a), Const(b)) => a.eq(b),
            (AttrSet(a), AttrSet(b)) => a.eq_impl(b, vm),
            (List(a), List(b)) => a.eq(b),
            (Builtins, AttrSet(attrs)) => attrs.has_attr(vm.new_sym("builtins")),
            (AttrSet(attrs), Builtins) => attrs.has_attr(vm.new_sym("builtins")),
            _ => false,
        }
    }
}

impl Eq for Value<'_> {}

#[derive(Debug, IsVariant, Unwrap, Clone, PartialEq)]
pub enum ValueAsRef<'v, 'vm: 'v> {
    Const(&'v Const),
    Thunk(&'v Thunk<'vm>),
    AttrSet(&'v AttrSet<'vm>),
    List(&'v List<'vm>),
    Catchable(&'v c::Catchable),
    PrimOp(&'v PrimOp<'vm>),
    PartialPrimOp(&'v PartialPrimOp<'vm>),
    Func(&'v Func<'vm>),
}

#[derive(Debug, IsVariant, Unwrap, PartialEq)]
pub enum ValueAsMut<'v, 'vm: 'v> {
    Const(&'v mut Const),
    Thunk(&'v Thunk<'vm>),
    AttrSet(&'v mut AttrSet<'vm>),
    List(&'v mut List<'vm>),
    Catchable(&'v mut c::Catchable),
    PrimOp(&'v mut PrimOp<'vm>),
    PartialPrimOp(&'v mut PartialPrimOp<'vm>),
    Func(&'v Func<'vm>),
}

impl<'v, 'vm: 'v> Value<'vm> {
    pub fn as_ref(&'v self) -> ValueAsRef<'v, 'vm> {
        use Value::*;
        use ValueAsRef as R;
        match self {
            Const(x) => R::Const(x),
            Thunk(x) => R::Thunk(x),
            ThunkRef(x) => R::Thunk(x),
            AttrSet(x) => R::AttrSet(x),
            List(x) => R::List(x),
            Catchable(x) => R::Catchable(x),
            PrimOp(x) => R::PrimOp(x),
            PartialPrimOp(x) => R::PartialPrimOp(x),
            Func(x) => R::Func(x),
            Builtins => unreachable!(),
        }
    }

    pub fn as_mut(&'v mut self) -> ValueAsMut<'v, 'vm> {
        use Value::*;
        use ValueAsMut as M;
        match self {
            Const(x) => M::Const(x),
            Thunk(x) => M::Thunk(x),
            ThunkRef(x) => M::Thunk(x),
            AttrSet(x) => M::AttrSet(Rc::make_mut(x)),
            List(x) => M::List(Rc::make_mut(x)),
            Catchable(x) => M::Catchable(x),
            PrimOp(x) => M::PrimOp(Rc::make_mut(x)),
            PartialPrimOp(x) => M::PartialPrimOp(Rc::make_mut(x)),
            Func(x) => M::Func(x),
            Builtins => unreachable!(),
        }
    }
}

use Value::Const as VmConst;
impl<'vm> Value<'vm> {
    pub fn ok(self) -> Result<Self> {
        Ok(self)
    }

    pub fn typename(&self) -> &'static str {
        use Value::*;
        match self {
            Const(_) => unreachable!(),
            Thunk(_) => "thunk",
            ThunkRef(_) => "thunk",
            AttrSet(_) => "set",
            List(_) => "list",
            Catchable(_) => unreachable!(),
            PrimOp(_) => "lambda",
            PartialPrimOp(_) => "lambda",
            Func(_) => "lambda",
            Builtins => "set",
        }
    }

    pub fn callable(&self) -> bool {
        match self {
            Value::PrimOp(_) | Value::PartialPrimOp(_) | Value::Func(_) => true,
            Value::AttrSet(_) => todo!(),
            _ => false,
        }
    }

    pub fn call(&self, vm: &'vm VM<'_>, args: Vec<Self>) -> Result<Self> {
        use Value::*;
        match self {
            PrimOp(func) => func.call(vm, args),
            PartialPrimOp(func) => func.call(vm, args),
            func @ Value::Func(_) => {
                let mut iter = args.into_iter();
                let mut func = func.clone();
                while let Some(arg) = iter.next() {
                    func = match func {
                        PrimOp(func) => {
                            return func.call(vm, [arg].into_iter().chain(iter).collect());
                        }
                        PartialPrimOp(func) => {
                            return func.call(vm, [arg].into_iter().chain(iter).collect());
                        }
                        Func(func) => func.call(vm, arg)?,
                        _ => todo!(),
                    }
                }
                func.ok()
            }
            x @ Catchable(_) => x.clone().ok(),
            _ => todo!(),
        }
    }

    pub fn not(self) -> Self {
        use Const::*;
        match self {
            VmConst(Bool(bool)) => VmConst(Bool(!bool)),
            x @ Value::Catchable(_) => x,
            _ => todo!(),
        }
    }

    pub fn and(self, other: Self) -> Self {
        use Const::*;
        match (self, other) {
            (VmConst(Bool(a)), VmConst(Bool(b))) => VmConst(Bool(a && b)),
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn or(self, other: Self) -> Self {
        use Const::*;
        match (self, other) {
            (VmConst(Bool(a)), VmConst(Bool(b))) => VmConst(Bool(a || b)),
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn eq(self, other: Self) -> Self {
        use Const::Bool;
        match (self, other) {
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            (s, other) => VmConst(Bool(s == other)),
        }
    }

    pub fn lt(self, other: Self) -> Self {
        use Const::*;
        VmConst(Bool(match (self, other) {
            (VmConst(Int(a)), VmConst(Int(b))) => a < b,
            (VmConst(Int(a)), VmConst(Float(b))) => (a as f64) < b,
            (VmConst(Float(a)), VmConst(Int(b))) => a < b as f64,
            (VmConst(Float(a)), VmConst(Float(b))) => a < b,
            (VmConst(String(a)), VmConst(String(b))) => a < b,
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => return x,
            _ => todo!(),
        }))
    }

    pub fn neg(self) -> Self {
        use Const::*;
        match self {
            VmConst(Int(int)) => VmConst(Int(-int)),
            VmConst(Float(float)) => VmConst(Float(-float)),
            x @ Value::Catchable(_) => x,
            _ => todo!(),
        }
    }

    pub fn add(self, other: Self) -> Self {
        use Const::*;
        match (self, other) {
            (VmConst(Int(a)), VmConst(Int(b))) => VmConst(Int(a + b)),
            (VmConst(Int(a)), VmConst(Float(b))) => VmConst(Float(a as f64 + b)),
            (VmConst(Float(a)), VmConst(Int(b))) => VmConst(Float(a + b as f64)),
            (VmConst(Float(a)), VmConst(Float(b))) => VmConst(Float(a + b)),
            (VmConst(String(a)), VmConst(String(b))) => {
                let mut string = a.clone();
                string.push_str(b.as_str());
                VmConst(String(string))
            }
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn mul(self, other: Self) -> Self {
        use Const::*;
        match (self, other) {
            (VmConst(Int(a)), VmConst(Int(b))) => VmConst(Int(a * b)),
            (VmConst(Int(a)), VmConst(Float(b))) => VmConst(Float(a as f64 * b)),
            (VmConst(Float(a)), VmConst(Int(b))) => VmConst(Float(a * b as f64)),
            (VmConst(Float(a)), VmConst(Float(b))) => VmConst(Float(a * b)),
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn div(self, other: Self) -> Result<Self> {
        use Const::*;
        Ok(match (self, other) {
            (_, VmConst(Int(0))) => return Err(Error::EvalError("division by zero".to_string())),
            (_, VmConst(Float(0.))) => {
                return Err(Error::EvalError("division by zero".to_string()));
            }
            (VmConst(Int(a)), VmConst(Int(b))) => VmConst(Int(a / b)),
            (VmConst(Int(a)), VmConst(Float(b))) => VmConst(Float(a as f64 / b)),
            (VmConst(Float(a)), VmConst(Int(b))) => VmConst(Float(a / b as f64)),
            (VmConst(Float(a)), VmConst(Float(b))) => VmConst(Float(a / b)),
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        })
    }

    pub fn concat_string(&mut self, mut other: Self) -> &mut Self {
        match (self.coerce_to_string(), other.coerce_to_string()) {
            (VmConst(Const::String(a)), VmConst(Const::String(b))) => a.push_str(b.as_str()),
            (_, Value::Catchable(_)) => *self = other,
            (Value::Catchable(_), _) => (),
            _ => todo!(),
        }
        self
    }

    pub fn push(&mut self, elem: Self) -> &mut Self {
        if let Value::List(list) = self {
            Rc::make_mut(list).push(elem);
        } else if let Value::Catchable(_) = self {
        } else if let Value::Catchable(_) = elem {
            *self = elem;
        } else {
            todo!()
        }
        self
    }

    pub fn concat(self, other: Self) -> Self {
        match (self, other) {
            (Value::List(mut a), Value::List(b)) => {
                Rc::make_mut(&mut a).concat(b.as_ref());
                Value::List(a)
            }
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn push_attr(&mut self, sym: usize, val: Self) -> &mut Self {
        if let Value::AttrSet(attrs) = self {
            Rc::make_mut(attrs).push_attr(sym, val)
        } else if let Value::Catchable(_) = self {
        } else if let Value::Catchable(_) = val {
            *self = val
        } else {
            todo!()
        }
        self
    }

    pub fn update(self, other: Self) -> Self {
        match (self, other) {
            (Value::AttrSet(mut a), Value::AttrSet(b)) => {
                Rc::make_mut(&mut a).update(b.as_ref());
                Value::AttrSet(a)
            }
            (x @ Value::Catchable(_), _) | (_, x @ Value::Catchable(_)) => x,
            _ => todo!(),
        }
    }

    pub fn select(&mut self, sym: usize, vm: &'vm VM<'_>) -> Result<&mut Self> {
        let val = match self {
            Value::AttrSet(attrs) => attrs
                .select(sym)
                .ok_or_else(|| Error::EvalError(format!("{} not found", vm.get_sym(sym)))),
            Value::Catchable(_) => return Ok(self),
            _ => Err(Error::EvalError(format!(
                "cannot select from {:?}",
                self.typename()
            ))),
        }?;
        if let Value::Builtins = val {
        } else {
            *self = val;
        }
        Ok(self)
    }

    pub fn select_with_default(&mut self, sym: usize, default: Self) -> Result<&mut Self> {
        let val = match self {
            Value::AttrSet(attrs) => attrs.select(sym).unwrap_or(default),
            Value::Catchable(_) => return Ok(self),
            _ => {
                return Err(Error::EvalError(format!(
                    "cannot select from {:?}",
                    self.typename()
                )));
            }
        };
        if let Value::Builtins = val {
        } else {
            *self = val;
        }
        Ok(self)
    }

    pub fn has_attr(&mut self, sym: usize) -> &mut Self {
        if let Value::AttrSet(attrs) = self {
            let val = VmConst(Const::Bool(attrs.has_attr(sym)));
            *self = val;
        } else if let Value::Catchable(_) = self {
        } else {
            *self = VmConst(Const::Bool(false));
        }
        self
    }

    pub fn coerce_to_string(&mut self) -> &mut Self {
        if let VmConst(Const::String(_)) = self {
        } else if let Value::Catchable(_) = self {
        } else {
            todo!()
        }
        self
    }

    pub fn force(&mut self, vm: &'vm VM<'_>) -> Result<&mut Self> {
        if let Value::Thunk(thunk) = self {
            let value = thunk.force(vm)?;
            *self = value
        } else if let Value::ThunkRef(thunk) = self {
            let value = thunk.force(vm)?;
            *self = value
        }
        Ok(self)
    }

    pub fn force_deep(&mut self, vm: &'vm VM<'_>) -> Result<&mut Self> {
        match self {
            Value::Thunk(thunk) => {
                let mut value = thunk.force(vm)?;
                let _ = value.force_deep(vm)?;
                *self = value;
            }
            Value::ThunkRef(thunk) => {
                let mut value = thunk.force(vm)?;
                let _ = value.force_deep(vm)?;
                *self = value;
            }
            Value::List(list) => Rc::make_mut(list).force_deep(vm)?,
            Value::AttrSet(attrs) => Rc::make_mut(attrs).force_deep(vm)?,
            _ => (),
        }
        Ok(self)
    }

    pub fn to_public(&self, vm: &'vm VM, seen: &mut HashSet<Value<'vm>>) -> p::Value {
        use self::Value::*;
        use p::Value;
        if seen.contains(self) {
            return Value::Repeated;
        }
        seen.insert(self.clone());
        match self {
            AttrSet(attrs) => attrs.to_public(vm, seen),
            List(list) => list.to_public(vm, seen),
            Catchable(catchable) => Value::Catchable(catchable.clone()),
            Const(cnst) => Value::Const(cnst.clone().into()),
            Thunk(_) => Value::Thunk,
            ThunkRef(_) => Value::Thunk,
            PrimOp(primop) => Value::PrimOp(primop.name),
            PartialPrimOp(primop) => Value::PartialPrimOp(primop.name),
            Func(_) => Value::Func,
            Builtins => Value::Repeated,
        }
    }
}

#[derive(Debug, Clone)]
pub struct Thunk<'vm> {
    pub thunk: RefCell<_Thunk<'vm>>,
}

#[derive(Debug, IsVariant, Unwrap, Clone)]
pub enum _Thunk<'vm> {
    Code(&'vm OpCodes, OnceCell<Env<'vm>>),
    SuspendedFrom(*const Thunk<'vm>),
    Value(Value<'vm>),
}

impl<'vm> Thunk<'vm> {
    pub fn new(opcodes: &'vm OpCodes) -> Self {
        Thunk {
            thunk: RefCell::new(_Thunk::Code(opcodes, OnceCell::new())),
        }
    }

    pub fn capture(&self, env: Env<'vm>) {
        if let _Thunk::Code(_, envcell) = &*self.thunk.borrow() {
            envcell.get_or_init(|| env);
        }
    }

    pub fn force(&self, vm: &'vm VM<'_>) -> Result<Value<'vm>> {
        match &*self.thunk.borrow() {
            _Thunk::Value(value) => return Ok(value.clone()),
            _Thunk::SuspendedFrom(from) => {
                return Err(Error::EvalError(format!(
                    "thunk {:p} already suspended from {from:p} (infinite recursion encountered)",
                    self as *const Thunk
                )));
            }
            _Thunk::Code(..) => (),
        }
        let (opcodes, env) = std::mem::replace(
            &mut *self.thunk.borrow_mut(),
            _Thunk::SuspendedFrom(self as *const Thunk),
        )
        .unwrap_code();
        let value = vm.eval(opcodes.iter().copied(), env.get().unwrap().clone())?;
        let _ = std::mem::replace(
            &mut *self.thunk.borrow_mut(),
            _Thunk::Value(value.clone().into()),
        );
        Ok(value)
    }

    pub fn value(&'vm self) -> Option<Value<'vm>> {
        match &*self.thunk.borrow() {
            _Thunk::Value(value) => Some(value.clone()),
            _ => None,
        }
    }
}

impl PartialEq for Thunk<'_> {
    fn eq(&self, _: &Self) -> bool {
        false
    }
}