use std::{
    boxed::Box,
    future::Future,
    sync::Arc,
    time::Duration,
    pin::Pin,
    task::{Context as FutContext, Poll},
};
use tokio::{
    sync::mpsc::{
        unbounded_channel,
        UnboundedReceiver as Receiver,
        UnboundedSender as Sender,
    },
    time::{Delay, delay_for},
};
use futures::{
    future::BoxFuture,
    stream::{Stream, StreamExt},
};
use crate::{
    client::bridge::gateway::ShardMessenger,
    model::channel::Reaction,
    model::id::UserId,
};

macro_rules! impl_reaction_collector {
    ($($name:ident;)*) => {
        $(
            impl<'a> $name<'a> {
                /// Limits how many messages will attempt to be filtered.
                ///
                /// The filter checks whether the message has been sent
                /// in the right guild, channel, and by the right author.
                pub fn filter_limit(mut self, limit: u32) -> Self {
                    self.filter.as_mut().unwrap().filter_limit = Some(limit);

                    self
                }

                /// Limits how many reactions can be collected.
                ///
                /// A reaction is considered *collected*, if the reaction
                /// passes all the requirements.
                pub fn collect_limit(mut self, limit: u32) -> Self {
                    self.filter.as_mut().unwrap().collect_limit = Some(limit);

                    self
                }

                /// Sets a filter function where reactions passed to the function must
                /// return `true`, otherwise the reaction won't be collected.
                /// This is the last instance to pass for a reaction to count as *collected*.
                ///
                /// This function is intended to be a reaction content filter.
                pub fn filter<F: Fn(&Arc<Reaction>) -> bool + 'static + Send + Sync>(mut self, function: F) -> Self {
                    self.filter.as_mut().unwrap().filter = Some(Arc::new(function));

                    self
                }

                /// Sets the required author ID of a reaction.
                /// If a reaction is not issued by a user with this ID, it won't be received.
                pub fn author_id(mut self, author_id: impl Into<u64>) -> Self {
                    self.filter.as_mut().unwrap().author_id = Some(author_id.into());

                    self
                }

                /// Sets the message on which the reaction must occur.
                /// If a reaction is not on a message with this ID, it won't be received.
                pub fn message_id(mut self, message_id: impl Into<u64>) -> Self {
                    self.filter.as_mut().unwrap().message_id = Some(message_id.into());

                    self
                }

                /// Sets the guild in which the reaction must occur.
                /// If a reaction is not on a message with this ID, it won't be received.
                pub fn guild_id(mut self, guild_id: impl Into<u64>) -> Self {
                    self.filter.as_mut().unwrap().guild_id = Some(guild_id.into());

                    self
                }

                /// Sets the channel on which the reaction must occur.
                /// If a reaction is not on a message with this ID, it won't be received.
                pub fn channel_id(mut self, channel_id: impl Into<u64>) -> Self {
                    self.filter.as_mut().unwrap().channel_id = Some(channel_id.into());

                    self
                }

                /// If set to `true`, added reactions will be collected.
                ///
                /// Set to `true` by default.
                pub fn added(mut self, is_accepted: bool) -> Self {
                    self.filter.as_mut().unwrap().accept_added = is_accepted;

                    self
                }

                /// If set to `true`, removed reactions will be collected.
                ///
                /// Set to `false` by default.
                pub fn removed(mut self, is_accepted: bool) -> Self {
                    self.filter.as_mut().unwrap().accept_removed = is_accepted;

                    self
                }

                /// Sets a `duration` for how long the collector shall receive
                /// reactions.
                pub fn timeout(mut self, duration: Duration) -> Self {
                    self.timeout = Some(delay_for(duration));

                    self
                }
            }
        )*
    }
}

/// Marks whether the reaction has been added or removed.
#[derive(Debug)]
pub enum ReactionAction {
    Added(Arc<Reaction>),
    Removed(Arc<Reaction>),
}

impl ReactionAction {
    pub fn as_inner_ref(&self) -> &Arc<Reaction> {
        match self {
            Self::Added(inner) => inner,
            Self::Removed(inner) => inner,
        }
    }

    pub fn is_added(&self) -> bool {
        if let Self::Added(_) = &self {
            true
        } else {
            false
        }
    }

    pub fn is_removed(&self) -> bool {
        if let Self::Removed(_) = &self {
            true
        } else {
            false
        }
    }
}

/// Filters events on the shard's end and sends them to the collector.
#[derive(Clone, Debug)]
pub struct ReactionFilter {
    filtered: u32,
    collected: u32,
    options: FilterOptions,
    sender: Sender<Arc<ReactionAction>>,
}

impl ReactionFilter {
    /// Creates a new filter
    fn new(options: FilterOptions) -> (Self, Receiver<Arc<ReactionAction>>) {
        let (sender, receiver) = unbounded_channel();

        let filter = Self {
            filtered: 0,
            collected: 0,
            sender,
            options,
        };

        (filter, receiver)
    }

    /// Sends a `reaction` to the consuming collector if the `reaction` conforms
    /// to the constraints and the limits are not reached yet.
    pub(crate) fn send_reaction(&mut self, reaction: &Arc<ReactionAction>) -> bool {
        if self.is_passing_constraints(&reaction) {
            self.collected += 1;

            if self.sender.send(Arc::clone(reaction)).is_err() {
                return false;
            }
        }

        self.filtered += 1;

        self.is_within_limits()
    }

    /// Checks if the `reaction` passes set constraints.
    /// Constraints are optional, as it is possible to limit reactions to
    /// be sent by a specific author or in a specifc guild.
    fn is_passing_constraints(&self, reaction: &Arc<ReactionAction>) -> bool {
        let reaction = match **reaction {
            ReactionAction::Added(ref reaction) => if self.options.accept_added {
                reaction
            } else {
                return false;
            },
            ReactionAction::Removed(ref reaction) => if self.options.accept_removed {
                reaction
            } else {
                return false;
            },
        };

        self.options.guild_id.map_or(true, |id| { Some(id) == reaction.guild_id.map(|g| g.0) })
        && self.options.message_id.map_or(true, |id| { id == reaction.message_id.0 })
        && self.options.channel_id.map_or(true, |id| { id == reaction.channel_id.0 })
        && self.options.author_id.map_or(true, |id| { id == reaction.user_id.unwrap_or(UserId(0)).0 })
        && self.options.filter.as_ref().map_or(true, |f| f(&reaction))
    }


    /// Checks if the filter is within set receive and collect limits.
    /// A reaction is considered *received* even when it does not meet the
    /// constraints.
    fn is_within_limits(&self) -> bool {
        self.options.filter_limit.map_or(true, |limit| { self.filtered < limit })
        && self.options.collect_limit.map_or(true, |limit| { self.collected < limit })
    }
}

#[derive(Clone)]
struct FilterOptions {
    filter_limit: Option<u32>,
    collect_limit: Option<u32>,
    filter: Option<Arc<dyn Fn(&Arc<Reaction>) -> bool + 'static + Send + Sync>>,
    channel_id: Option<u64>,
    guild_id: Option<u64>,
    author_id: Option<u64>,
    message_id: Option<u64>,
    accept_added: bool,
    accept_removed: bool,
}

impl Default for FilterOptions {
    fn default() -> Self {
        Self {
            filter_limit: None,
            collect_limit: None,
            filter: None,
            channel_id: None,
            guild_id: None,
            author_id: None,
            message_id: None,
            accept_added: true,
            accept_removed: false,
        }
    }
}

// Implement the common setters for all reaction collector types.
// This avoids using a trait that the user would need to import in
// order to use any of these methods.
impl_reaction_collector! {
    CollectReaction;
    ReactionCollectorBuilder;
}

pub struct ReactionCollectorBuilder<'a> {
    filter: Option<FilterOptions>,
    shard: Option<ShardMessenger>,
    timeout: Option<Delay>,
    fut: Option<BoxFuture<'a, ReactionCollector>>,
}

impl<'a> ReactionCollectorBuilder<'a> {
    pub fn new(shard_messenger: impl AsRef<ShardMessenger>) -> Self {
        Self {
            filter: Some(FilterOptions::default()),
            shard: Some(shard_messenger.as_ref().clone()),
            timeout: None,
            fut: None,
        }
    }
}

impl<'a> Future for ReactionCollectorBuilder<'a> {
    type Output = ReactionCollector;

    fn poll(mut self: Pin<&mut Self>, ctx: &mut FutContext<'_>) -> Poll<Self::Output> {
        if self.fut.is_none() {
            let shard_messenger = self.shard.take().unwrap();
            let (filter, receiver) = ReactionFilter::new(self.filter.take().unwrap());
            let timeout = self.timeout.take();

            self.fut = Some(Box::pin(async move {
                shard_messenger.set_reaction_filter(filter);

                ReactionCollector {
                    receiver: Box::pin(receiver),
                    timeout: timeout.map(Box::pin),
                }
            }))
        }

        self.fut.as_mut().unwrap().as_mut().poll(ctx)
    }
}

pub struct CollectReaction<'a> {
    filter: Option<FilterOptions>,
    shard: Option<ShardMessenger>,
    timeout: Option<Delay>,
    fut: Option<BoxFuture<'a, Option<Arc<ReactionAction>>>>,
}

impl<'a> CollectReaction<'a> {
    pub fn new(shard_messenger: impl AsRef<ShardMessenger>) -> Self {
        Self {
            filter: Some(FilterOptions::default()),
            shard: Some(shard_messenger.as_ref().clone()),
            timeout: None,
            fut: None,
        }
    }
}

impl<'a> Future for CollectReaction<'a> {
    type Output = Option<Arc<ReactionAction>>;

    fn poll(mut self: Pin<&mut Self>, ctx: &mut FutContext<'_>) -> Poll<Self::Output> {
        if self.fut.is_none() {
            let shard_messenger = self.shard.take().unwrap();
            let (filter, receiver) = ReactionFilter::new(self.filter.take().unwrap());
            let timeout = self.timeout.take();

            self.fut = Some(Box::pin(async move {
                shard_messenger.set_reaction_filter(filter);

                ReactionCollector {
                    receiver: Box::pin(receiver),
                    timeout: timeout.map(Box::pin),
                }.next().await
            }))
        }

        self.fut.as_mut().unwrap().as_mut().poll(ctx)
    }
}

impl std::fmt::Debug for FilterOptions {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ReactionFilter")
            .field("collect_limit", &self.collect_limit)
            .field("filter", &"Option<Arc<dyn Fn(&Arc<Reaction>) -> bool + 'static + Send + Sync>>")
            .field("channel_id", &self.channel_id)
            .field("guild_id", &self.guild_id)
            .field("author_id", &self.author_id)
            .finish()
    }
}

/// A reaction collector receives reactions matching a the given filter for a
/// set duration.
pub struct ReactionCollector {
    receiver: Pin<Box<Receiver<Arc<ReactionAction>>>>,
    timeout: Option<Pin<Box<Delay>>>,
}

impl ReactionCollector {
    /// Stops collecting, this will implicitly be done once the
    /// collector drops.
    /// In case the drop does not appear until later, it is preferred to
    /// stop the collector early.
    pub fn stop(mut self) {
        self.receiver.close();
    }
}

impl Stream for ReactionCollector {
    type Item = Arc<ReactionAction>;
    fn poll_next(mut self: Pin<&mut Self>, ctx: &mut FutContext<'_>) -> Poll<Option<Self::Item>> {
        if let Some(ref mut timeout) = self.timeout {

            match timeout.as_mut().poll(ctx) {
                Poll::Ready(_) => {
                    return Poll::Ready(None);
                },
                Poll::Pending => (),
            }
        }

        self.receiver.as_mut().poll_next(ctx)
    }
}

impl Drop for ReactionCollector {
    fn drop(&mut self) {
        self.receiver.close();
    }
}