pub(crate) mod sync;

// NOTE: this module is taken from tokio's tracing span's extensions
//       which is taken from https://github.com/hyperium/http/blob/master/src/extensions.rs

use std::any::Any;
use std::any::TypeId;
use std::collections::HashMap;
use std::fmt;
use std::hash::BuildHasherDefault;
use std::hash::Hasher;

type AnyMap = HashMap<TypeId, Box<dyn Any + Send + Sync>, BuildHasherDefault<IdHasher>>;

// With TypeIds as keys, there's no need to hash them. They are already hashes
// themselves, coming from the compiler. The IdHasher just holds the u64 of
// the TypeId, and then returns it, instead of doing any bit fiddling.
#[derive(Default)]
struct IdHasher(u64);

impl Hasher for IdHasher {
    fn write(&mut self, _: &[u8]) {
        unreachable!("TypeId calls write_u64");
    }

    #[inline]
    fn write_u64(&mut self, id: u64) {
        self.0 = id;
    }

    #[inline]
    fn finish(&self) -> u64 {
        self.0
    }
}

/// A type map of protocol extensions.
///
/// `Extensions` can be used by `Request` and `Response` to store
/// extra data derived from the underlying protocol.
#[derive(Default)]
pub struct Extensions {
    // If extensions are never used, no need to carry around an empty HashMap.
    // That's 3 words. Instead, this is only 1 word.
    map: Option<Box<AnyMap>>,
}

#[allow(unused)]
impl Extensions {
    /// Create an empty `Extensions`.
    #[inline]
    pub(crate) fn new() -> Extensions {
        Extensions { map: None }
    }

    /// Insert a type into this `Extensions`.
    ///
    /// If a extension of this type already existed, it will
    /// be returned.
    pub fn insert<T: Send + Sync + 'static>(&mut self, val: T) -> Option<T> {
        self.map
            .get_or_insert_with(Box::default)
            .insert(TypeId::of::<T>(), Box::new(val))
            .and_then(|boxed| {
                (boxed as Box<dyn Any + 'static>)
                    .downcast()
                    .ok()
                    .map(|boxed| *boxed)
            })
    }

    /// Get a reference to a type previously inserted on this `Extensions`.
    pub fn get<T: Send + Sync + 'static>(&self) -> Option<&T> {
        self.map
            .as_ref()
            .and_then(|map| map.get(&TypeId::of::<T>()))
            .and_then(|boxed| (&**boxed as &(dyn Any + 'static)).downcast_ref())
    }

    /// Get a mutable reference to a type previously inserted on this `Extensions`.
    pub fn get_mut<T: Send + Sync + 'static>(&mut self) -> Option<&mut T> {
        self.map
            .as_mut()
            .and_then(|map| map.get_mut(&TypeId::of::<T>()))
            .and_then(|boxed| (&mut **boxed as &mut (dyn Any + 'static)).downcast_mut())
    }

    /// Get a mutable reference to a type or insert and return the value if it does not exist
    pub fn get_or_default_mut<T: Default + Send + Sync + 'static>(&mut self) -> &mut T {
        let map = self.map.get_or_insert_with(Box::default);
        let value = map
            .entry(TypeId::of::<T>())
            .or_insert_with(|| Box::<T>::default());
        // It should be impossible for the entry to be the wrong type as we don't allow direct access to the map.
        value
            .downcast_mut()
            .expect("default value should be inserted and we should be able to downcast it")
    }

    /// Returns `true` type has been stored in `Extensions`.
    pub fn contains_key<T: Send + Sync + 'static>(&self) -> bool {
        self.map
            .as_ref()
            .map(|map| map.contains_key(&TypeId::of::<T>()))
            .unwrap_or_default()
    }

    /// Remove a type from this `Extensions`.
    ///
    /// If a extension of this type existed, it will be returned.
    pub fn remove<T: Send + Sync + 'static>(&mut self) -> Option<T> {
        self.map
            .as_mut()
            .and_then(|map| map.remove(&TypeId::of::<T>()))
            .and_then(|boxed| {
                (boxed as Box<dyn Any + 'static>)
                    .downcast()
                    .ok()
                    .map(|boxed| *boxed)
            })
    }

    /// Clear the `Extensions` of all inserted extensions.
    #[inline]
    pub fn clear(&mut self) {
        if let Some(ref mut map) = self.map {
            map.clear();
        }
    }

    /// Check whether the extension set is empty or not.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.map.as_ref().is_none_or(|map| map.is_empty())
    }

    /// Get the number of extensions available.
    #[inline]
    pub fn len(&self) -> usize {
        self.map.as_ref().map_or(0, |map| map.len())
    }
}

impl fmt::Debug for Extensions {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Extensions").finish()
    }
}

#[test]
fn test_extensions() {
    #[derive(Debug, PartialEq)]
    struct MyType(i32);

    let mut extensions = Extensions::new();

    extensions.insert(5i32);
    extensions.insert(MyType(10));

    assert_eq!(extensions.get(), Some(&5i32));
    assert_eq!(extensions.get_mut(), Some(&mut 5i32));

    assert_eq!(extensions.remove::<i32>(), Some(5i32));
    assert!(extensions.get::<i32>().is_none());

    assert_eq!(extensions.get::<bool>(), None);
    assert_eq!(extensions.get(), Some(&MyType(10)));
}
