use std::fmt;
use std::sync::{Arc, Mutex};

use crate::executor::Executor;
use crate::model::Model;
use crate::time::{Clock, Scheduler};
use crate::time::{MonotonicTime, SchedulerQueue, TearableAtomicTime};
use crate::util::priority_queue::PriorityQueue;
use crate::util::sync_cell::SyncCell;

use super::{Mailbox, Simulation};

/// Builder for a multi-threaded, discrete-event simulation.
pub struct SimInit {
    executor: Executor,
    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
    time: SyncCell<TearableAtomicTime>,
}

impl SimInit {
    /// Creates a builder for a multithreaded simulation running on all
    /// available logical threads.
    pub fn new() -> Self {
        Self::with_num_threads(num_cpus::get())
    }

    /// Creates a builder for a multithreaded simulation running on the
    /// specified number of threads.
    pub fn with_num_threads(num_threads: usize) -> Self {
        // The current executor's implementation caps the number of thread to 64
        // on 64-bit systems and 32 on 32-bit systems.
        let num_threads = num_threads.min(usize::BITS as usize);

        Self {
            executor: Executor::new(num_threads),
            scheduler_queue: Arc::new(Mutex::new(PriorityQueue::new())),
            time: SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH)),
        }
    }

    /// Adds a model and its mailbox to the simulation bench.
    pub fn add_model<M: Model>(self, model: M, mailbox: Mailbox<M>) -> Self {
        let scheduler_queue = self.scheduler_queue.clone();
        let time = self.time.reader();
        let mut receiver = mailbox.0;

        self.executor.spawn_and_forget(async move {
            let sender = receiver.sender();
            let scheduler = Scheduler::new(sender, scheduler_queue, time);
            let mut model = model.init(&scheduler).await.0;

            while receiver.recv(&mut model, &scheduler).await.is_ok() {}
        });

        self
    }

    /// Builds a simulation initialized at the specified simulation time,
    /// executing the [`Model::init()`](crate::model::Model::init) method on all
    /// model initializers.
    ///
    /// This is equivalent to calling [`SimInit::init_with_clock()`] with a
    /// [`NoClock`](crate::time::NoClock) argument and effectively makes the
    /// simulation run as fast as possible.
    pub fn init(mut self, start_time: MonotonicTime) -> Simulation {
        self.time.write(start_time);
        self.executor.run();

        Simulation::new(self.executor, self.scheduler_queue, self.time)
    }

    /// Builds a simulation synchronized with the provided
    /// [`Clock`](crate::time::Clock) and initialized at the specified
    /// simulation time, executing the
    /// [`Model::init()`](crate::model::Model::init) method on all model
    /// initializers.
    pub fn init_with_clock(
        mut self,
        start_time: MonotonicTime,
        mut clock: impl Clock + 'static,
    ) -> Simulation {
        self.time.write(start_time);
        clock.synchronize(start_time);
        self.executor.run();

        Simulation::with_clock(self.executor, self.scheduler_queue, self.time, clock)
    }
}

impl Default for SimInit {
    fn default() -> Self {
        Self::new()
    }
}

impl fmt::Debug for SimInit {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("SimInit").finish_non_exhaustive()
    }
}