//! System for running things on an interval.

use std::collections::HashMap;
use std::sync::atomic::{self, AtomicU64};
use std::thread;
use std::time::{Duration, Instant};

use crossbeam::channel::{self, Sender};

/// An ID of a `Interval` hook.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct IntvlHookID(u64);

/// Controls what happens after the hook method is called.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum IntvlHookCtrl {
    /// Continue the hook.
    #[default]
    Continue,
    /// Pause the hook.
    ///
    /// Interval::start(ID) to start hook operation again.
    Pause,
    /// Remove the hook.
    Remove,
}

struct IntvlHook {
    every: Duration,
    last: Option<Instant>,
    delay: Option<Duration>,
    delay_start: Option<Instant>,
    paused: bool,
    method: Box<dyn FnMut(Option<Duration>) -> IntvlHookCtrl + Send + 'static>,
}

enum IntvlEvent {
    Add(IntvlHookID, IntvlHook),
    Pause(IntvlHookID),
    Start(IntvlHookID),
    Remove(IntvlHookID),
}

/// The main struct for the interval system.
///
/// Accessed via `basalt.interval_ref()` or `basalt.interval()`.
pub struct Interval {
    current_id: AtomicU64,
    event_send: Sender<IntvlEvent>,
}

impl Interval {
    pub(crate) fn new() -> Self {
        let (event_send, event_recv) = channel::unbounded();

        let intvl = Self {
            current_id: AtomicU64::new(0),
            event_send,
        };

        thread::spawn(move || {
            let mut hooks: HashMap<IntvlHookID, IntvlHook> = HashMap::new();

            #[cfg(target_os = "windows")]
            unsafe {
                timeBeginPeriod(1);
            }

            loop {
                while let Ok(event) = event_recv.try_recv() {
                    match event {
                        IntvlEvent::Add(id, hook) => {
                            hooks.insert(id, hook);
                        },
                        IntvlEvent::Remove(id) => {
                            hooks.remove(&id);
                        },
                        IntvlEvent::Start(id) => {
                            if let Some(hook) = hooks.get_mut(&id) {
                                hook.paused = false;
                            }
                        },
                        IntvlEvent::Pause(id) => {
                            if let Some(hook) = hooks.get_mut(&id) {
                                hook.paused = true;
                                hook.last = None;
                                hook.delay_start = None;
                            }
                        },
                    }
                }

                let mut remove_hooks = Vec::new();

                for (hook_id, hook) in hooks.iter_mut() {
                    if !hook.paused {
                        if let Some(delay) = &hook.delay {
                            if hook.delay_start.is_none() {
                                hook.delay_start = Some(Instant::now());
                                continue;
                            }

                            if hook.delay_start.as_ref().unwrap().elapsed() < *delay {
                                continue;
                            }
                        }

                        let elapsed = if hook.last.is_none() {
                            let elapsed = hook.last.take().map(|last| last.elapsed());
                            hook.last = Some(Instant::now());
                            elapsed
                        } else if hook.last.as_ref().unwrap().elapsed() < hook.every {
                            continue;
                        } else {
                            let elapsed = hook.last.take().map(|last| last.elapsed());
                            hook.last = Some(Instant::now());
                            elapsed
                        };

                        match (hook.method)(elapsed) {
                            IntvlHookCtrl::Continue => (),
                            IntvlHookCtrl::Pause => {
                                hook.paused = true;
                                hook.last = None;
                                hook.delay_start = None;
                            },
                            IntvlHookCtrl::Remove => {
                                remove_hooks.push(*hook_id);
                            },
                        }
                    }
                }

                for hook_id in remove_hooks {
                    hooks.remove(&hook_id);
                }

                // On Windows this will be 1.48 ms
                thread::sleep(Duration::from_millis(1));
            }
        });

        intvl
    }

    fn add_hook(&self, hook: IntvlHook) -> IntvlHookID {
        let id = IntvlHookID(self.current_id.fetch_add(1, atomic::Ordering::SeqCst));
        self.event_send.send(IntvlEvent::Add(id, hook)).unwrap();
        id
    }

    /// Call the method at provided internval.
    ///
    /// Takes a `Fn(last_call: Option<Duration>) -> IntvlHookCtrl`.
    /// - `last_call`: Duration since the last method was called.
    /// - `delay`: is the duration that has to elapsed after `Interval::start(...)` before
    /// the hook method is called.
    /// - `IntvlHookCtrl`: controls how the hook is handled after the method is called.
    ///
    /// # Notes
    /// - Hooks are paused to begin with. They must be started with `Interval::start(...)`.
    /// - `last_call` will only be `Some` if the method is called continuously. Returning
    /// `InputHookCtrl::Pause` or using `Interval::pause(...)` will cause the next call to
    /// be `None`.
    pub fn do_every<F: FnMut(Option<Duration>) -> IntvlHookCtrl + Send + 'static>(
        &self,
        every: Duration,
        delay: Option<Duration>,
        method: F,
    ) -> IntvlHookID {
        self.add_hook(IntvlHook {
            every,
            last: None,
            delay,
            delay_start: None,
            paused: true,
            method: Box::new(method),
        })
    }

    /// Pause a hook.
    ///
    /// # Notes
    /// - If hook doesn't exist this does nothing.
    pub fn pause(&self, id: IntvlHookID) {
        self.event_send.send(IntvlEvent::Pause(id)).unwrap();
    }

    /// Start a hook.
    ///
    /// # Notes
    /// - If hook doesn't exist this does nothing.
    pub fn start(&self, id: IntvlHookID) {
        self.event_send.send(IntvlEvent::Start(id)).unwrap();
    }

    /// Remove a hook.
    ///
    /// # Notes
    /// - If hook doesn't exist this does nothing.
    pub fn remove(&self, id: IntvlHookID) {
        self.event_send.send(IntvlEvent::Remove(id)).unwrap();
    }
}

#[cfg(target_os = "windows")]
#[link(name = "user32")]
extern "stdcall" {
    fn timeBeginPeriod(uPeriod: u32) -> u32;
}