// Copyright (c) 2020-2022  David Sorokin <david.sorokin@gmail.com>, based in Yoshkar-Ola, Russia
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

use std::rc::Rc;
use std::marker::PhantomData;

use crate::simulation;
use crate::simulation::error::*;
use crate::simulation::Point;
use crate::simulation::ref_comp::RefComp;
use crate::simulation::simulation::*;
use crate::simulation::event::*;
use crate::simulation::process::*;
use crate::simulation::strategy::*;
use crate::simulation::resource::*;

/// The queues that gather their statistics when simulating.
pub mod stats;

/// Represents unbounded queues.
pub mod unbounded;

/// A type synonym for the ordinary FIFO queue, also known as the FCFS
/// (First Come - First Serviced) queue.
pub type FCFSQueue<T> = Queue<FCFSStrategy, FCFSStrategy, FCFSStrategy, T>;

/// A type synonym for the ordinary LIFO queue, also known as the LCFS
/// (Last Come - First Serviced) queue.
pub type LCFSQueue<T> = Queue<FCFSStrategy, LCFSStrategy, FCFSStrategy, T>;

/// Represents an optimized bounded queue by using the specified strategies for enqueueing (input), `SI`,
/// internal storing (in memory), `SM`, and dequeueing (output), `SO`, where `T` denotes
/// the type of items stored in the queue.
pub struct Queue<SI, SM, SO, T>
    where SI: QueueStrategy,
          SM: QueueStrategy,
          SO: QueueStrategy
{
    /// The queue capacity.
    max_count: isize,

    /// The enqueue resource.
    enqueue_resource: Rc<Resource<SI>>,

    /// The queue store.
    queue_store: QueueStorageBox<T, SM::Priority>,

    /// The dequeue resource.
    dequeue_resource: Rc<Resource<SO>>,

    /// The queue size.
    count: RefComp<isize>
}

/// Create a new bounded FCFS (a.k.a FIFO) queue by the specified capacity.
#[inline]
pub fn new_fcfs_queue<T>(max_count: isize) -> NewQueue<FCFSStrategy, FCFSStrategy, FCFSStrategy, T>
    where T: 'static
{
    NewQueue {
        enqueue_strategy: FCFSStrategy::Instance,
        storing_strategy: FCFSStrategy::Instance,
        dequeue_strategy: FCFSStrategy::Instance,
        max_count: max_count,
        _phantom: PhantomData
    }
}

/// Create a new bounded LCFS (a.k.a LIFO) queue by the specified capacity.
#[inline]
pub fn new_lcfs_queue<T>(max_count: isize) -> NewQueue<FCFSStrategy, LCFSStrategy, FCFSStrategy, T>
    where T: 'static
{
    NewQueue {
        enqueue_strategy: FCFSStrategy::Instance,
        storing_strategy: LCFSStrategy::Instance,
        dequeue_strategy: FCFSStrategy::Instance,
        max_count: max_count,
        _phantom: PhantomData
    }
}

impl<SI, SM, SO, T> Queue<SI, SM, SO, T>
    where SI: QueueStrategy + Clone + 'static,
          SM: QueueStrategy + Clone + 'static,
          SO: QueueStrategy + Clone + 'static,
          T: Clone + 'static
{
    /// Create a new bounded queue by the specified strategies and capacity.
    #[inline]
    pub fn new(enqueue_strategy: SI,
        storing_strategy: SM,
        dequeue_strategy: SO,
        max_count: isize) -> NewQueue<SI, SM, SO, T>
    {
        NewQueue {
            enqueue_strategy: enqueue_strategy,
            storing_strategy: storing_strategy,
            dequeue_strategy: dequeue_strategy,
            max_count: max_count,
            _phantom: PhantomData
        }
    }

    /// Return the queue capacity, i.e. its maximum size.
    #[inline]
    pub fn max_count(&self) -> isize {
        self.max_count
    }

    /// Test whether the queue is empty.
    #[inline]
    pub fn is_empty(queue: Rc<Self>) -> impl Event<Item = bool> + Clone {
        cons_event(move |p| {
            Result::Ok(queue.count.read_at(p) == 0)
        })
    }

    /// Test whether the queue is full.
    #[inline]
    pub fn is_full(queue: Rc<Self>) -> impl Event<Item = bool> + Clone {
        cons_event(move |p| {
            Result::Ok(queue.count.read_at(p) == queue.max_count)
        })
    }

    /// Return the current queue size.
    #[inline]
    pub fn count(queue: Rc<Self>) -> impl Event<Item = isize> + Clone {
        cons_event(move |p| {
            Result::Ok(queue.count.read_at(p))
        })
    }

    /// Return the load factor: the queue size divided by its capacity, i.e. maximum size.
    #[inline]
    pub fn load_factor(queue: Rc<Self>) -> impl Event<Item = f64> + Clone {
        cons_event(move |p| {
            Result::Ok({
                let x = queue.count.read_at(p);
                let y = queue.max_count;
                (x as f64) / (y as f64)
            })
        })
    }

    /// Dequeue by suspending the process if the queue is empty.
    pub fn dequeue(queue: Rc<Self>) -> impl Process<Item = T> + Clone {
        request_resource(queue.dequeue_resource.clone())
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.dequeue_extract(p)
                })
                .into_process()
            })
    }

    /// Dequeue with output prioerity by suspending the process if the queue is empty.
    pub fn dequeue_with_output_priority(queue: Rc<Self>, po: SO::Priority) -> impl Process<Item = T> + Clone
        where SO::Priority: Clone
    {
        request_resource_with_priority(queue.dequeue_resource.clone(), po)
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.dequeue_extract(p)
                })
                .into_process()
            })
    }

    /// Try to dequeue immediately.
    pub fn try_dequeue(queue: Rc<Self>) -> impl Event<Item = Option<T>> + Clone {
        try_request_resource_within_event(queue.dequeue_resource.clone())
            .flat_map(move |f| {
                if f {
                    cons_event(move |p| {
                        let x = queue.dequeue_extract(p)?;
                        Result::Ok(Some(x))
                    }).into_boxed()
                } else {
                    return_event(None)
                        .into_boxed()
                }
            })
    }

    /// Remove the item from the queue and return a flag indicating
    /// whether the item was found and actually removed.
    pub fn delete(queue: Rc<Self>, item: T) -> impl Event<Item = bool> + Clone
        where T: PartialEq
    {
        let pred = move |x: &T| { *x == item };
        Queue::delete_by(queue, pred)
            .map(|x| { x.is_some() })
    }

    /// Remove the specified item from the queue.
    pub fn delete_(queue: Rc<Self>, item: T) -> impl Event<Item = ()> + Clone
        where T: PartialEq
    {
        let pred = move |x: &T| { *x == item };
        Queue::delete_by(queue, pred)
            .map(|_| ())
    }

    /// Remove an item satisfying the specified predicate and return the item if found.
    pub fn delete_by<F>(queue: Rc<Self>, pred: F) -> impl Event<Item = Option<T>> + Clone
        where F: Fn(&T) -> bool + Clone + 'static
    {
        try_request_resource_within_event(queue.dequeue_resource.clone())
            .flat_map(move |f| {
                if f {
                    cons_event(move |p| {
                        let pred = move |x: &T| { pred(x) };
                        let pred = Rc::new(pred);
                        match queue.queue_store.remove_boxed_by(pred, p) {
                            None => {
                                release_resource_within_event(queue.dequeue_resource.clone())
                                    .call_event(p)?;
                                Result::Ok(None)
                            },
                            Some(i) => {
                                let x = queue.dequeue_post_extract(i, p)?;
                                Result::Ok(Some(x))
                            }
                        }
                    }).into_boxed()
                } else {
                    return_event(None)
                        .into_boxed()
                }
            })
    }

    /// Test whether there is an item satisfying the specified predicate.
    pub fn exists<F>(queue: Rc<Self>, pred: F) -> impl Event<Item = bool> + Clone
        where F: Fn(&T) -> bool + Clone + 'static
    {
        cons_event(move |p| {
            let pred = move |x: &T| { pred(x) };
            let pred = Rc::new(pred);
            Result::Ok(queue.queue_store.exists_boxed(pred, p))
        })
    }

    /// Find an item satisfying the specified predicate.
    pub fn find<F>(queue: Rc<Self>, pred: F) -> impl Event<Item = Option<T>> + Clone
        where F: Fn(&T) -> bool + Clone + 'static,
              T: Clone
    {
        cons_event(move |p| {
            let pred = move |x: &T| { pred(x) };
            let pred = Rc::new(pred);
            Result::Ok(queue.queue_store.find_boxed(pred, p).map(|x| { x.clone() }))
        })
    }

    /// Clear the queue.
    pub fn clear(queue: Rc<Self>) -> impl Event<Item = ()> + Clone {
        cons_event(move |p| {
            loop {
                let x = Queue::try_dequeue(queue.clone()).call_event(p)?;
                match x {
                    None => return Result::Ok(()),
                    Some(_) => {}
                }
            }
        })
    }

    /// Enqueue the item by suspending the process if the queue is full.
    pub fn enqueue(queue: Rc<Self>, item: T) -> impl Process<Item = ()> + Clone {
        request_resource(queue.enqueue_resource.clone())
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.enqueue_store(item, p)
                })
                .into_process()
            })
    }

    /// Enqueue the item with input priority by suspending the process
    /// if the queue is full.
    pub fn enqueue_with_input_priority(queue: Rc<Self>, pi: SI::Priority, item: T) -> impl Process<Item = ()> + Clone
        where SI::Priority: Clone
    {
        request_resource_with_priority(queue.enqueue_resource.clone(), pi)
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.enqueue_store(item, p)
                })
                .into_process()
            })
    }

    /// Enqueue the item with storing priority by suspending the process
    /// if the queue is full.
    pub fn enqueue_with_storing_priority(queue: Rc<Self>, pm: SM::Priority, item: T) -> impl Process<Item = ()> + Clone
        where SM::Priority: Clone
    {
        request_resource(queue.enqueue_resource.clone())
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.enqueue_store_with_priority(pm, item, p)
                })
                .into_process()
            })
    }

    /// Enqueue the item with input and storing priorities by suspending the process
    /// if the queue is full.
    pub fn enqueue_with_input_and_storing_priorities(queue: Rc<Self>, pi: SI::Priority, pm: SM::Priority, item: T) -> impl Process<Item = ()> + Clone
        where SI::Priority: Clone,
              SM::Priority: Clone
    {
        request_resource_with_priority(queue.enqueue_resource.clone(), pi)
            .flat_map(move |()| {
                cons_event(move |p| {
                    queue.enqueue_store_with_priority(pm, item, p)
                })
                .into_process()
            })
    }

    /// Try to enqueue the item. Return `false` within `Event` computation if the queue is full.
    pub fn try_enqueue(queue: Rc<Self>, item: T) -> impl Event<Item = bool> + Clone {
        cons_event(move |p| {
            let x = {
                try_request_resource_within_event(queue.enqueue_resource.clone())
                    .call_event(p)
            }?;
            if x {
                queue.enqueue_store(item, p)?;
                Result::Ok(true)
            } else {
                Result::Ok(false)
            }
        })
    }

    /// Try to enqueue the item with storing priority. Return `false`
    /// within `Event` computation if the queue is full.
    pub fn try_enqueue_with_storing_priority(queue: Rc<Self>, pm: SM::Priority, item: T) -> impl Event<Item = bool> + Clone
        where SM::Priority: Clone
    {
        cons_event(move |p| {
            let x = {
                try_request_resource_within_event(queue.enqueue_resource.clone())
                    .call_event(p)
            }?;
            if x {
                queue.enqueue_store_with_priority(pm, item, p)?;
                Result::Ok(true)
            } else {
                Result::Ok(false)
            }
        })
    }

    /// Extract an item by the dequeue request.
    fn dequeue_extract(&self, p: &Point) -> simulation::Result<T> {
        let i = self.queue_store.pop(p).unwrap();
        self.dequeue_post_extract(i, p)
    }

    /// A post action after extracting the item by the dequeue request.
    fn dequeue_post_extract(&self, i: T, p: &Point) -> simulation::Result<T> {
        let c  = self.count.read_at(p);
        let c2 = c - 1;
        self.count.write_at(c2, p);
        release_resource_within_event(self.enqueue_resource.clone())
            .call_event(p)?;
        Result::Ok(i)
    }

    /// Store the item.
    fn enqueue_store(&self, item: T, p: &Point) -> simulation::Result<()> {
        self.queue_store.push(item, p);
        let c  = self.count.read_at(p);
        let c2 = c + 1;
        self.count.write_at(c2, p);
        release_resource_within_event(self.dequeue_resource.clone())
            .call_event(p)
    }

    /// Store the item with priority.
    fn enqueue_store_with_priority(&self, pm: SM::Priority, item: T, p: &Point) -> simulation::Result<()> {
        self.queue_store.push_with_priority(pm, item, p);
        let c  = self.count.read_at(p);
        let c2 = c + 1;
        self.count.write_at(c2, p);
        release_resource_within_event(self.dequeue_resource.clone())
            .call_event(p)
    }
}

/// Computation that creates a new `Queue`.
#[derive(Clone)]
pub struct NewQueue<SI, SM, SO, T> {

    /// The enqueue strategy.
    enqueue_strategy: SI,

    /// The storing strategy.
    storing_strategy: SM,

    /// The output strategy.
    dequeue_strategy: SO,

    /// The capacity.
    max_count: isize,

    /// To keep the type parameter.
    _phantom: PhantomData<T>
}

impl<SI, SM, SO, T> Event for NewQueue<SI, SM, SO, T>
    where SI: QueueStrategy,
          SM: QueueStrategy,
          SO: QueueStrategy,
          T: Clone + 'static
{
    type Item = Queue<SI, SM, SO, T>;

    #[doc(hidden)]
    #[inline]
    fn call_event(self, p: &Point) -> simulation::Result<Self::Item> {
        let NewQueue { enqueue_strategy, storing_strategy, dequeue_strategy, max_count, _phantom } = self;
        if max_count < 0 {
            let msg = String::from("The queue capacity cannot be actually negative");
            let err = Error::retry(msg);
            Result::Err(err)
        } else {
            let enqueue_resource = {
                Resource::<SI>::new_with_max_count(enqueue_strategy, max_count, Some(max_count))
                    .call_simulation(p.run)?
            };
            let queue_store = storing_strategy.new_storage();
            let dequeue_resource = {
                Resource::<SO>::new_with_max_count(dequeue_strategy, 0, Some(max_count))
                    .call_simulation(p.run)?
            };
            Result::Ok(Queue {
                max_count: max_count,
                enqueue_resource: Rc::new(enqueue_resource),
                queue_store: queue_store,
                dequeue_resource: Rc::new(dequeue_resource),
                count: RefComp::new(0)
            })
        }
    }
}