use std::{any::{Any, TypeId}, marker::PhantomData, sync::{Arc, RwLock}};

use lyra_ecs::Component;
use crate::{loader::LoaderError, lyra_engine};
use uuid::Uuid;

use crate::ResourceStorage;

/// A trait that that each resource type should implement.
pub trait ResourceData: Send + Sync + Any + 'static {
    fn as_any(&self) -> &dyn Any;
    fn as_any_mut(&mut self) -> &mut dyn Any;
    fn type_id(&self) -> TypeId;
}

impl<T: Send + Sync + Any + 'static> ResourceData for T {
    fn as_any(&self) -> &dyn Any {
        self
    }

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

    fn type_id(&self) -> TypeId {
        TypeId::of::<T>()
    }
}

pub enum ResourceState {
    Loading,
    Error(Arc<LoaderError>),
    Ready(Box<dyn ResourceData>),
}

pub struct ResourceDataRef<'a, T> {
    guard: std::sync::RwLockReadGuard<'a, Resource<T>>,
}

impl<'a, T: 'static> std::ops::Deref for ResourceDataRef<'a, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        match &self.guard.state {
            ResourceState::Ready(d) => {
                // for some reason, if I didn't use `.as_ref`, the downcast would fail.
                let d = d.as_ref().as_any();
                d.downcast_ref::<T>().unwrap()
            },
            _ => unreachable!() // ResHandler::data_ref shouldn't allow this to run
        }
    }
}

pub struct Resource<T> {
    pub(crate) version: usize,
    pub(crate) state: ResourceState,
    uuid: Uuid,
    path: Option<String>,
    pub(crate) is_watched: bool,
    _marker: PhantomData<T>,
}

/// A handle to a resource. 
/// 
/// # Note
/// This struct has an inner [`RwLock`] to the resource data, so most methods may be blocking.
/// However, the only times it will be blocking is if another thread is reloading the resource
/// and has a write lock on the data. This means that most of the time, it is not blocking.
#[derive(Component)]
pub struct ResHandle<T: 'static> {
    pub(crate) data: Arc<RwLock<Resource<T>>>,
}

impl<T> Clone for ResHandle<T> {
    fn clone(&self) -> Self {
        Self { data: self.data.clone() }
    }
}

impl<T: ResourceData> ResHandle<T> {
    pub fn new_loading(path: Option<&str>) -> Self {
        let res_version = Resource {
            version: 0,
            path: path.map(str::to_string),
            state: ResourceState::Loading,
            uuid: Uuid::new_v4(),
            is_watched: false,
            _marker: PhantomData::<T>
        };

        Self {
            data: Arc::new(RwLock::new(res_version)),
        }
    }

    /// Create the resource with data, its assumed the state is `Ready`
    pub fn new_ready(path: Option<&str>, data: T) -> Self {
        let res_version = Resource {
            version: 0,
            path: path.map(str::to_string),
            state: ResourceState::Ready(Box::new(data)),
            uuid: Uuid::new_v4(),
            is_watched: false,
            _marker: PhantomData::<T>
        };

        Self {
            data: Arc::new(RwLock::new(res_version)),
        }
    }

    /// Returns a boolean indicating if this resource's path is being watched.
    pub fn is_watched(&self) -> bool {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        d.is_watched
    }

    /// Returns a boolean indicating if this resource is loaded
    pub fn is_loaded(&self) -> bool {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        matches!(d.state, ResourceState::Ready(_))
    }

    /// Returns the current state of the resource.
    /* pub fn state(&self) -> &ResourceState {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        &d.state
    } */

    /// Returns the uuid of the resource.
    pub fn uuid(&self) -> Uuid {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        d.uuid
    }

    pub fn path(&self) -> Option<String> {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        d.path.clone()
    }

    /// Retrieves the current version of the resource. This gets incremented when the resource
    /// is reloaded.
    pub fn version(&self) -> usize {
        let d = self.data.read().expect("Resource mutex was poisoned!");
        d.version
    }

    /// Get a reference to the data in the resource
    pub fn data_ref<'a>(&'a self) -> Option<ResourceDataRef<'a, T>> {
        if self.is_loaded() {
            let d = self.data.read().expect("Resource mutex was poisoned!");
            Some(ResourceDataRef {
                guard: d
            })
        } else {
            None
        }
    }
}

impl<T: Send + Sync + 'static> ResourceStorage for ResHandle<T> {
    fn as_any(&self) -> &dyn Any {
        self
    }

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

    fn as_arc_any(self: Arc<Self>) -> Arc<dyn Any + Send + Sync> {
        self.clone()
    }

    fn as_box_any(self: Box<Self>) -> Box<dyn Any + Send + Sync> {
        self
    }

    fn set_watched(&self, watched: bool) {
        let mut w = self.data.write().unwrap();
        w.is_watched = watched;
    }

    fn version(&self) -> usize {
        self.version()
    }

    fn uuid(&self) -> Uuid {
        self.uuid()
    }

    fn path(&self) -> Option<String> {
        self.path()
    }

    fn is_watched(&self) -> bool {
        self.is_watched()
    }

    fn is_loaded(&self) -> bool {
        self.is_loaded()
    }

    fn set_state(&self, new: ResourceState) {
        let mut d = self.data.write().expect("Resource mutex was poisoned!");
        d.state = new;
    }

    
}