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use crate::exports::{ExportError, Exportable};
use crate::store::{AsStoreMut, AsStoreRef};
use crate::value::Value;
use crate::vm::VMExtern;
use crate::vm::VMExternGlobal;
use crate::Extern;
use crate::GlobalType;
use crate::Mutability;
use crate::RuntimeError;

#[cfg(feature = "js")]
use crate::js::externals::global as global_impl;
#[cfg(feature = "jsc")]
use crate::jsc::externals::global as global_impl;
#[cfg(feature = "sys")]
use crate::sys::externals::global as global_impl;

/// A WebAssembly `global` instance.
///
/// A global instance is the runtime representation of a global variable.
/// It consists of an individual value and a flag indicating whether it is mutable.
///
/// Spec: <https://webassembly.github.io/spec/core/exec/runtime.html#global-instances>
#[derive(Debug, Clone, PartialEq)]
pub struct Global(pub(crate) global_impl::Global);

impl Global {
    /// Create a new `Global` with the initial value [`Value`].
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmer::{Global, Mutability, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new(&mut store, Value::I32(1));
    ///
    /// assert_eq!(g.get(&mut store), Value::I32(1));
    /// assert_eq!(g.ty(&mut store).mutability, Mutability::Const);
    /// ```
    pub fn new(store: &mut impl AsStoreMut, val: Value) -> Self {
        Self::from_value(store, val, Mutability::Const).unwrap()
    }

    /// Create a mutable `Global` with the initial value [`Value`].
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmer::{Global, Mutability, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new_mut(&mut store, Value::I32(1));
    ///
    /// assert_eq!(g.get(&mut store), Value::I32(1));
    /// assert_eq!(g.ty(&mut store).mutability, Mutability::Var);
    /// ```
    pub fn new_mut(store: &mut impl AsStoreMut, val: Value) -> Self {
        Self::from_value(store, val, Mutability::Var).unwrap()
    }

    /// Create a `Global` with the initial value [`Value`] and the provided [`Mutability`].
    fn from_value(
        store: &mut impl AsStoreMut,
        val: Value,
        mutability: Mutability,
    ) -> Result<Self, RuntimeError> {
        Ok(Self(global_impl::Global::from_value(
            store, val, mutability,
        )?))
    }

    /// Returns the [`GlobalType`] of the `Global`.
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmer::{Global, Mutability, Store, Type, Value, GlobalType};
    /// # let mut store = Store::default();
    /// #
    /// let c = Global::new(&mut store, Value::I32(1));
    /// let v = Global::new_mut(&mut store, Value::I64(1));
    ///
    /// assert_eq!(c.ty(&mut store), GlobalType::new(Type::I32, Mutability::Const));
    /// assert_eq!(v.ty(&mut store), GlobalType::new(Type::I64, Mutability::Var));
    /// ```
    pub fn ty(&self, store: &impl AsStoreRef) -> GlobalType {
        self.0.ty(store)
    }

    /// Retrieves the current value [`Value`] that the Global has.
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmer::{Global, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new(&mut store, Value::I32(1));
    ///
    /// assert_eq!(g.get(&mut store), Value::I32(1));
    /// ```
    pub fn get(&self, store: &mut impl AsStoreMut) -> Value {
        self.0.get(store)
    }

    /// Sets a custom value [`Value`] to the runtime Global.
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmer::{Global, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new_mut(&mut store, Value::I32(1));
    ///
    /// assert_eq!(g.get(&mut store), Value::I32(1));
    ///
    /// g.set(&mut store, Value::I32(2));
    ///
    /// assert_eq!(g.get(&mut store), Value::I32(2));
    /// ```
    ///
    /// # Errors
    ///
    /// Trying to mutate a immutable global will raise an error:
    ///
    /// ```should_panic
    /// # use wasmer::{Global, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new(&mut store, Value::I32(1));
    ///
    /// g.set(&mut store, Value::I32(2)).unwrap();
    /// ```
    ///
    /// Trying to set a value of a incompatible type will raise an error:
    ///
    /// ```should_panic
    /// # use wasmer::{Global, Store, Value};
    /// # let mut store = Store::default();
    /// #
    /// let g = Global::new(&mut store, Value::I32(1));
    ///
    /// // This results in an error: `RuntimeError`.
    /// g.set(&mut store, Value::I64(2)).unwrap();
    /// ```
    pub fn set(&self, store: &mut impl AsStoreMut, val: Value) -> Result<(), RuntimeError> {
        self.0.set(store, val)
    }

    pub(crate) fn from_vm_extern(store: &mut impl AsStoreMut, vm_extern: VMExternGlobal) -> Self {
        Self(global_impl::Global::from_vm_extern(store, vm_extern))
    }

    /// Checks whether this `Global` can be used with the given context.
    pub fn is_from_store(&self, store: &impl AsStoreRef) -> bool {
        self.0.is_from_store(store)
    }

    pub(crate) fn to_vm_extern(&self) -> VMExtern {
        self.0.to_vm_extern()
    }
}

impl std::cmp::Eq for Global {}

impl<'a> Exportable<'a> for Global {
    fn get_self_from_extern(_extern: &'a Extern) -> Result<&'a Self, ExportError> {
        match _extern {
            Extern::Global(global) => Ok(global),
            _ => Err(ExportError::IncompatibleType),
        }
    }
}