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use std::ptr::NonNull;

use twizzler_abi::{meta::MetaInfo, object::NULLPAGE_SIZE};

use crate::{
    marker::{BaseType, BaseVersion, ObjSafe},
    object::Object,
};

/// Possible errors from getting a reference to an object's base.
#[derive(Debug)]
pub enum BaseError {
    InvalidTag,
    InvalidVersion(BaseVersion),
}

fn match_tags(_meta: NonNull<MetaInfo>) -> Result<(), BaseError> {
    // TODO
    Ok(())
}

impl<T: BaseType + ObjSafe> Object<T> {
    /// Get a reference to the base of an object. Checks to see if the tags and version information
    /// for the BaseType match.
    pub fn base(&self) -> Result<&T, BaseError> {
        let meta = unsafe { self.meta() };
        match_tags(meta)?;
        Ok(unsafe { self.base_unchecked() })
    }
}

impl<BaseType> Object<BaseType> {
    /// Get a reference to the base of an object, bypassing version and tag checks.
    ///
    /// # Safety
    /// The caller must ensure that the base of the object really is of type BaseType.
    pub unsafe fn base_unchecked(&self) -> &BaseType {
        self.slot
            .raw_lea::<BaseType>(NULLPAGE_SIZE)
            .as_ref()
            .unwrap()
    }

    /// Get a mutable reference to the base of an object, bypassing version and tag checks.
    ///
    /// # Safety
    /// The caller must ensure that the base of the object really is of type BaseType.
    #[allow(clippy::mut_from_ref)]
    pub unsafe fn base_mut_unchecked(&self) -> &mut BaseType {
        self.slot
            .raw_lea_mut::<BaseType>(NULLPAGE_SIZE)
            .as_mut()
            .unwrap()
    }
}