use super::*;
use std::collections::{HashMap, HashSet};
use std::sync::Arc;
use tokio::sync::{
    RwLock,
    mpsc,
};
use generational_arena::{
    Arena,Index,
};
use futures::prelude::*;

use user::{User, UserID};
use post::{Post, PostID};

mod freeze;
pub use freeze::*;

/// An `Arc<RwLock<T>>` wrapper
type SharedMut<T> = Arc<RwLock<T>>;

/// A shared pointer to a post
pub type SharedPost = SharedMut<Post>;
/// A shared pointer to a user
pub type SharedUser = SharedMut<User>;

#[derive(Debug)]
struct Oneesan
{
    users: Arena<Arc<RwLock<User>>>,
    posts: Arena<Arc<RwLock<Post>>>,

    /// Maps `UserID`s to indexes in the `users` arena.
    users_map: HashMap<UserID, Index>,
    /// Maps `PostID`s to indexies in the `posts` arena.
    posts_map: HashMap<PostID, Index>,

    /// Maps `UserID`s to the user's owned posts in the `posts` arena.
    posts_user_map: HashMap<UserID, MaybeVec<Index>>,
}

#[derive(Debug)]
struct Inner
{
    /// The posts and user state.
    oneesan: RwLock<Oneesan>,
}

/// Contains all posts and users
#[derive(Debug, Clone)]
pub struct State(Arc<Inner>);

impl State
{
    /// Create a new empty state
    pub fn new() -> Self
    {
	Self(Arc::new(
	    Inner {
		oneesan: RwLock::new(Oneesan {
		    users: Arena::new(),
		    posts: Arena::new(),

		    users_map: HashMap::new(),
		    posts_map: HashMap::new(),

		    posts_user_map: HashMap::new(),
		})
	    }
	))
    }

    /// Insert a new user into state.
    ///
    /// # Locks
    /// This function holds the state write lock while performing insertions.
    pub async fn insert_user(&self, user: User) -> SharedUser
    {
	let user_id = *user.id();
	let nuser = Arc::new(RwLock::new(user));
	let mut write = self.0.oneesan.write().await;
	let idx = write.users.insert(Arc::clone(&nuser));
	write.users_map.insert(user_id, idx);
	nuser
    }
    
    /// Insert a new post into state.
    ///
    /// # Locks
    /// This function holds the state write lock while performing insertions.
    pub async fn insert_post(&self, owner: UserID, post: Post) -> SharedPost
    {
	let post_id =*post.post_id();
	let npost = Arc::new(RwLock::new(post));
	let mut write = self.0.oneesan.write().await;
	let idx = write.posts.insert(Arc::clone(&npost));
	write.posts_map.insert(post_id, idx);
	write.posts_user_map.entry(owner).or_insert_with(|| MaybeVec::new()).push(idx);
	npost
    }

    /// Get a shared reference to a user by this ID, if it exists.
    ///
    /// # Locks
    /// This functions holds the state read lock while performing lookups.
    /// # Panics
    /// If the internal ID mappings are invalid
    pub async fn get_user_by_id(&self, id: UserID) -> Option<SharedUser>
    {
	let read = self.0.oneesan.read().await;
	read.users_map.get(&id).map(|&idx| read.users.get(idx).unwrap().clone())
    }
    
    /// Get a shared reference to a post by this ID, if it exists.
    ///
    /// # Locks
    /// This functions holds the state read lock while performing lookups.
    /// # Panics
    /// If the internal ID mappings are invalid
    pub async fn get_post_by_id(&self, id: PostID) -> Option<SharedPost>
    {
	let read = self.0.oneesan.read().await;
	read.posts_map.get(&id).map(|&idx| read.posts.get(idx).unwrap().clone())
    }
    
    /// Consume into a stream that yields all users lazily.
    ///
    /// # Locks
    /// The stream producer holds the Oneesan *read* lock until the stream is consumed or dropped.
    pub fn all_users_stream(self: Arc<Self>) -> impl Stream<Item=SharedUser>
    {
	let (mut tx, rx) = mpsc_channel!(defaults::STATE_STREAM_BUFFER_SIZE);
	tokio::spawn(async move {
	    let onee = self.0.oneesan.read().await;
	    for (_, user) in onee.users.iter()
	    {
		if tx.send(user.clone()).await.is_err() {
		    break;
		}
	    }
	});
	rx
    }

    
    /// Consume into a stream that yields all posts created by this user lazily.
    ///
    /// # Locks
    /// The stream producer holds the Oneesan *read* lock until the stream is consumed or dropped.
    ///
    /// # Panics
    /// The background task will panic and drop the producer if the internal ID mappings are invalid
    pub fn all_posts_by_user_stream(self: Arc<Self>, user: UserID) -> impl Stream<Item=SharedPost>
    {
	let (mut tx, rx) = mpsc_channel!(defaults::STATE_STREAM_BUFFER_SIZE);
	tokio::spawn(async move {
	    let onee = self.0.oneesan.read().await;
	    if let Some(map) = onee.posts_user_map.get(&user) {
		for &post in map.iter()
		{
		    if tx.send(onee.posts.get(post).unwrap().clone()).await.is_err() {
			break;
		    }
		}
	    }
	});
	rx
    }
    
    /// Consume into a stream that yields all posts lazily.
    ///
    /// # Locks
    /// The stream producer holds the Oneesan *read* lock until the stream is consumed or dropped.
    pub fn all_posts_stream(self: Arc<Self>) -> impl Stream<Item=SharedPost>
    {
	let (mut tx, rx) = mpsc_channel!(defaults::STATE_STREAM_BUFFER_SIZE);
	tokio::spawn(async move {
	    let onee = self.0.oneesan.read().await;
	    for (_, post) in onee.posts.iter()
	    {
		if tx.send(post.clone()).await.is_err() {
		    break;
		}
	    }
	});
	rx
    }
    
}