use std::any::{type_name, Any};
use std::marker::PhantomData;
use std::sync::{Arc, Weak};

use crate::component::storage::Storage as ComponentStorage;
use crate::component::{
    is_optional as component_is_optional,
    Component,
    FromOptional as ComponentFromOptional,
    Id as ComponentId,
    Metadata as ComponentMetadata,
};
use crate::entity::Uid as EntityUid;
use crate::lock::{Lock, ReadGuard};
use crate::system::{ComponentRefMut, Input as SystemInput};
use crate::type_name::TypeName;
use crate::World;

#[derive(Debug)]
pub struct Relationship<Kind, ComponentT: Component>
{
    entity_uid: EntityUid,
    component_storage: Weak<Lock<ComponentStorage>>,
    _pd: PhantomData<(Kind, ComponentT)>,
}

impl<Kind, ComponentT> Relationship<Kind, ComponentT>
where
    ComponentT: Component,
{
    pub fn new(world: &World, entity_uid: EntityUid) -> Self
    {
        Self {
            entity_uid,
            component_storage: Arc::downgrade(&world.data.component_storage),
            _pd: PhantomData,
        }
    }
}

impl<Kind, ComponentT> Component for Relationship<Kind, ComponentT>
where
    Kind: 'static,
    ComponentT: Component,
{
    type Component = Self;
    type RefMut<'component> = Relation<'component, Kind, ComponentT>;

    fn id(&self) -> ComponentId
    {
        ComponentId::of::<Self>()
    }

    fn as_any_mut(&mut self) -> &mut dyn Any
    {
        self
    }

    fn as_any(&self) -> &dyn Any
    {
        self
    }
}

impl<Kind, ComponentT> SystemInput for Relationship<Kind, ComponentT>
where
    Kind: 'static,
    ComponentT: Component,
{
}

impl<Kind, ComponentT: Component> TypeName for Relationship<Kind, ComponentT>
where
    ComponentT: Component,
{
    fn type_name(&self) -> &'static str
    {
        type_name::<Self>()
    }
}

pub struct Relation<'rel_comp, Kind, ComponentT>
where
    Kind: 'static,
    ComponentT: Component,
{
    component_storage_lock: ReadGuard<'static, ComponentStorage>,
    relationship_comp: ComponentRefMut<'rel_comp, Relationship<Kind, ComponentT>>,
    _component_storage: Arc<Lock<ComponentStorage>>,
}

impl<'rel_comp, Kind, ComponentT> ComponentFromOptional<'rel_comp>
    for Relation<'rel_comp, Kind, ComponentT>
where
    ComponentT: Component,
{
    fn from_optional_component(
        optional_component: Option<
            crate::lock::WriteGuard<'rel_comp, Box<dyn Component>>,
        >,
    ) -> Self
    {
        let relationship_comp =
            ComponentRefMut::<Relationship<Kind, ComponentT>>::from_optional_component(
                optional_component,
            );

        let component_storage = relationship_comp
            .component_storage
            .upgrade()
            .expect("World has been dropped");

        let component_storage_lock = component_storage
            .read_nonblock()
            .expect("Failed to aquire read-only component storage lock");

        Self {
            relationship_comp,
            // SAFETY: The component lock is not used for longer than the original
            // lifetime
            component_storage_lock: unsafe { component_storage_lock.upgrade_lifetime() },
            _component_storage: component_storage,
        }
    }
}

impl<'rel_comp, Kind, ComponentT> Relation<'rel_comp, Kind, ComponentT>
where
    ComponentT: Component,
{
    /// Retrieves the related-to component.
    pub fn get(&self) -> Option<ComponentRefMut<'_, ComponentT>>
    {
        let mut archetype_iter =
            self.component_storage_lock
                .find_entities([ComponentMetadata {
                    id: ComponentId::of::<ComponentT>(),
                    is_optional: component_is_optional::<ComponentT>().into(),
                }]);

        let (entity, archetype) = archetype_iter.find_map(|archetype| {
            let Some(entity) = archetype.get_entity(self.relationship_comp.entity_uid)
            else {
                return None;
            };

            Some((entity, archetype))
        })?;

        let component_index =
            archetype.get_index_for_component(&ComponentId::of::<ComponentT>())?;

        let component = ComponentRefMut::new(
            entity
                .get_component(component_index)?
                .component
                .write_nonblock()
                .unwrap_or_else(|_| {
                    panic!(
                        "Failed to aquire read-write lock of component {}",
                        type_name::<ComponentT>()
                    )
                }),
        );

        Some(component)
    }

    /// Changes the related-to entity to the entity with the given UID:
    pub fn set_entity(&mut self, entity_uid: EntityUid)
    {
        self.relationship_comp.entity_uid = entity_uid;
    }
}