use crate::any::Any;
use crate::value::{Value, ValuePtr, ValueType, ValueTypeInfo};
use crate::vm::{Vm, VmError};

mod array;
mod hash_map;
mod object;
mod option;
mod primitive;
mod string;

/// Trait for converting arguments into values.
pub trait IntoArgs {
    /// Encode arguments to the vm.
    ///
    /// # Safety
    ///
    /// This has the ability to encode references into the virtual machine.
    /// The caller must ensure that the virtual machine is cleared with
    /// [clear][Vm::clear] before the references are no longer valid.
    unsafe fn into_args(self, vm: &mut Vm) -> Result<(), VmError>;

    /// The number of arguments.
    fn count() -> usize;
}

/// Trait for converting types into values.
pub trait ReflectValueType: Sized {
    /// Convert into a value type.
    fn value_type() -> ValueType;

    /// Access diagnostical information on the value type.
    fn value_type_info() -> ValueTypeInfo;
}

/// Trait for converting types into values.
pub trait ToValue: Sized {
    /// Convert into a value.
    fn to_value(self, vm: &mut Vm) -> Result<ValuePtr, VmError>;
}

/// Trait for unsafe conversion of value types into values.
pub trait UnsafeToValue {
    /// Convert into a value.
    unsafe fn unsafe_to_value(self, vm: &mut Vm) -> Result<ValuePtr, VmError>;
}

/// Trait for converting from a value.
pub trait FromValue: Sized {
    /// Try to convert to the given type, from the given value.
    fn from_value(value: ValuePtr, vm: &mut Vm) -> Result<Self, VmError>;
}

/// A potentially unsafe conversion for value conversion.
pub trait UnsafeFromValue: Sized {
    /// The output type from the unsafe coercion.
    type Output: 'static;

    /// The raw guard returned.
    ///
    /// Must only be dropped *after* the value returned from this function is
    /// no longer live.
    type Guard: 'static;

    /// Convert the given reference using unsafe assumptions to a value.
    ///
    /// # Safety
    ///
    /// The return value of this function may only be used while a virtual
    /// machine is not being modified.
    ///
    /// You must also make sure that the returned value does not outlive the
    /// guard.
    unsafe fn unsafe_from_value(
        value: ValuePtr,
        vm: &mut Vm,
    ) -> Result<(Self::Output, Self::Guard), VmError>;

    /// Coerce the output of an unsafe from value into the final output type.
    ///
    /// # Safety
    ///
    /// The return value of this function may only be used while a virtual
    /// machine is not being modified.
    ///
    /// You must also make sure that the returned value does not outlive the
    /// guard.
    unsafe fn to_arg(output: Self::Output) -> Self;
}

impl<T> UnsafeFromValue for T
where
    T: 'static + FromValue,
{
    type Output = T;
    type Guard = ();

    unsafe fn unsafe_from_value(
        value: ValuePtr,
        vm: &mut Vm,
    ) -> Result<(Self, Self::Guard), VmError> {
        Ok((T::from_value(value, vm)?, ()))
    }

    unsafe fn to_arg(output: Self::Output) -> Self {
        output
    }
}

impl<T> UnsafeToValue for T
where
    T: ToValue,
{
    unsafe fn unsafe_to_value(self, vm: &mut Vm) -> Result<ValuePtr, VmError> {
        self.to_value(vm)
    }
}

impl FromValue for ValuePtr {
    fn from_value(value: ValuePtr, _: &mut Vm) -> Result<Self, VmError> {
        Ok(value)
    }
}

impl ToValue for ValuePtr {
    fn to_value(self, _vm: &mut Vm) -> Result<ValuePtr, VmError> {
        Ok(self)
    }
}

impl FromValue for Value {
    fn from_value(value: ValuePtr, vm: &mut Vm) -> Result<Self, VmError> {
        vm.value_take(value)
    }
}

impl FromValue for Any {
    fn from_value(value: ValuePtr, vm: &mut Vm) -> Result<Self, VmError> {
        let slot = value.into_external(vm)?;
        vm.external_take_dyn(slot)
    }
}

macro_rules! impl_into_args {
    () => {
        impl_into_args!{@impl 0,}
    };

    ({$ty:ident, $var:ident, $count:expr}, $({$l_ty:ident, $l_var:ident, $l_count:expr},)*) => {
        impl_into_args!{@impl $count, {$ty, $var, $count}, $({$l_ty, $l_var, $l_count},)*}
        impl_into_args!{$({$l_ty, $l_var, $l_count},)*}
    };

    (@impl $count:expr, $({$ty:ident, $var:ident, $ignore_count:expr},)*) => {
        impl<$($ty,)*> IntoArgs for ($($ty,)*)
        where
            $($ty: UnsafeToValue + std::fmt::Debug,)*
        {
            #[allow(unused)]
            unsafe fn into_args(self, vm: &mut Vm) -> Result<(), VmError> {
                let ($($var,)*) = self;
                impl_into_args!(@push vm, [$($var)*]);
                Ok(())
            }

            fn count() -> usize {
                $count
            }
        }
    };

    (@push $vm:expr, [] $($var:ident)*) => {
        $(
            let $var = $var.unsafe_to_value($vm)?;
            $vm.push($var);
        )*
    };

    (@push $vm:expr, [$first:ident $($rest:ident)*] $($var:ident)*) => {
        impl_into_args!(@push $vm, [$($rest)*] $first $($var)*)
    };
}

impl_into_args!(
    {H, h, 8},
    {G, g, 7},
    {F, f, 6},
    {E, e, 5},
    {D, d, 4},
    {C, c, 3},
    {B, b, 2},
    {A, a, 1},
);

macro_rules! impl_from_value_tuple {
    () => {
        impl_from_value_tuple!{@impl 0,}
    };

    ({$ty:ident, $var:ident, $count:expr}, $({$l_ty:ident, $l_var:ident, $l_count:expr},)*) => {
        impl_from_value_tuple!{@impl $count, {$ty, $var, $count}, $({$l_ty, $l_var, $l_count},)*}
        impl_from_value_tuple!{$({$l_ty, $l_var, $l_count},)*}
    };

    (@impl $count:expr, $({$ty:ident, $var:ident, $ignore_count:expr},)*) => {
        impl<$($ty,)*> FromValue for ($($ty,)*)
        where
            $($ty: FromValue,)*
        {
            #[allow(unused)]
            fn from_value(value: ValuePtr, vm: &mut Vm) -> Result<Self, VmError> {
                let array = match value {
                    ValuePtr::Array(slot) => Clone::clone(&*vm.array_ref(slot)?),
                    actual => {
                        let actual = actual.type_info(vm)?;

                        return Err(VmError::ExpectedArray {
                            actual,
                        });
                    }
                };

                if array.len() != $count {
                    return Err(VmError::ExpectedArrayLength {
                        actual: array.len(),
                        expected: $count,
                    });
                }

                #[allow(unused_mut, unused_variables)]
                let mut it = array.iter();

                $(
                    let $var: $ty = match it.next() {
                        Some(value) => <$ty>::from_value(*value, vm)?,
                        None => {
                            return Err(VmError::IterationError);
                        },
                    };
                )*

                Ok(($($var,)*))
            }
        }
    };
}

impl_from_value_tuple!(
    {H, h, 8},
    {G, g, 7},
    {F, f, 6},
    {E, e, 5},
    {D, d, 4},
    {C, c, 3},
    {B, b, 2},
    {A, a, 1},
);