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use std::task::Poll;
use std::{fmt, task};

use futures_util::stream::StreamExt;

use crate::actor::{Actor, AsyncContext};
use crate::address::EnvelopeProxy;
use crate::address::{channel, Addr, AddressReceiver, AddressSenderProducer};

#[cfg(feature = "mailbox_assert")]
/// Maximum number of consecutive polls in a loop
const MAX_SYNC_POLLS: u16 = 256;

/// Default address channel capacity
pub const DEFAULT_CAPACITY: usize = 16;

pub struct Mailbox<A>
where
    A: Actor,
    A::Context: AsyncContext<A>,
{
    msgs: AddressReceiver<A>,
}

impl<A> fmt::Debug for Mailbox<A>
where
    A: Actor,
    A::Context: AsyncContext<A>,
{
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_struct("Mailbox")
            .field("capacity", &self.capacity())
            .finish()
    }
}

impl<A> Default for Mailbox<A>
where
    A: Actor,
    A::Context: AsyncContext<A>,
{
    #[inline]
    fn default() -> Self {
        let (_, rx) = channel::channel(DEFAULT_CAPACITY);
        Mailbox { msgs: rx }
    }
}

impl<A> Mailbox<A>
where
    A: Actor,
    A::Context: AsyncContext<A>,
{
    #[inline]
    pub fn new(msgs: AddressReceiver<A>) -> Self {
        Self { msgs }
    }

    pub fn capacity(&self) -> usize {
        self.msgs.capacity()
    }

    pub fn set_capacity(&mut self, cap: usize) {
        self.msgs.set_capacity(cap);
    }

    #[inline]
    pub fn connected(&self) -> bool {
        self.msgs.connected()
    }

    pub fn address(&self) -> Addr<A> {
        Addr::new(self.msgs.sender())
    }

    pub fn sender_producer(&self) -> AddressSenderProducer<A> {
        self.msgs.sender_producer()
    }

    pub fn poll(
        &mut self,
        act: &mut A,
        ctx: &mut A::Context,
        task: &mut task::Context<'_>,
    ) {
        #[cfg(feature = "mailbox_assert")]
        let mut n_polls = 0u16;

        loop {
            let mut not_ready = true;

            // sync messages
            loop {
                if ctx.waiting() {
                    return;
                }

                match self.msgs.poll_next_unpin(task) {
                    Poll::Ready(Some(mut msg)) => {
                        not_ready = false;
                        msg.handle(act, ctx);
                    }
                    Poll::Ready(None) | Poll::Pending => break,
                }

                #[cfg(feature = "mailbox_assert")]
                {
                    n_polls += 1;
                    assert!(n_polls < MAX_SYNC_POLLS, "Too many messages are being processed. Use Self::Context::notify() instead of direct use of address");
                }
            }

            if not_ready {
                return;
            }
        }
    }
}