use crate::{
    innerlude::{LocalTask, SchedulerMsg},
    scope_context::ScopeContext,
    scopes::ScopeId,
    Task,
};
use std::{
    cell::{Cell, Ref, RefCell},
    collections::VecDeque,
    rc::Rc,
};

thread_local! {
    static RUNTIMES: RefCell<Vec<Rc<Runtime>>> = RefCell::new(vec![]);
}

/// A global runtime that is shared across all scopes that provides the async runtime and context API
pub struct Runtime {
    pub(crate) scope_contexts: RefCell<Vec<Option<ScopeContext>>>,

    // We use this to track the current scope
    pub(crate) scope_stack: RefCell<Vec<ScopeId>>,

    // We use this to track the current task
    pub(crate) current_task: Cell<Option<Task>>,

    pub(crate) rendering: Cell<bool>,

    /// Tasks created with cx.spawn
    pub(crate) tasks: RefCell<slab::Slab<Rc<LocalTask>>>,

    /// Queued tasks that are waiting to be polled
    pub(crate) queued_tasks: Rc<RefCell<VecDeque<Task>>>,

    pub(crate) sender: futures_channel::mpsc::UnboundedSender<SchedulerMsg>,
}

impl Runtime {
    pub(crate) fn new(sender: futures_channel::mpsc::UnboundedSender<SchedulerMsg>) -> Rc<Self> {
        Rc::new(Self {
            sender,
            rendering: Cell::new(true),
            scope_contexts: Default::default(),
            scope_stack: Default::default(),
            current_task: Default::default(),
            tasks: Default::default(),
            queued_tasks: Rc::new(RefCell::new(VecDeque::new())),
        })
    }

    /// Get the current runtime
    pub fn current() -> Option<Rc<Self>> {
        RUNTIMES.with(|stack| stack.borrow().last().cloned())
    }

    /// Create a scope context. This slab is synchronized with the scope slab.
    pub(crate) fn create_context_at(&self, id: ScopeId, context: ScopeContext) {
        let mut contexts = self.scope_contexts.borrow_mut();
        if contexts.len() <= id.0 {
            contexts.resize_with(id.0 + 1, Default::default);
        }
        contexts[id.0] = Some(context);
    }

    pub(crate) fn remove_context(self: &Rc<Self>, id: ScopeId) {
        {
            let borrow = self.scope_contexts.borrow();
            if let Some(scope) = &borrow[id.0] {
                let _runtime_guard = RuntimeGuard::new(self.clone());
                // Manually drop tasks, hooks, and contexts inside of the runtime
                self.on_scope(id, || {
                    // Drop all spawned tasks
                    for id in scope.spawned_tasks.take() {
                        self.remove_task(id);
                    }

                    // Drop all hooks
                    scope.hooks.take();

                    // Drop all contexts
                    scope.shared_contexts.take();
                });
            }
        }
        self.scope_contexts.borrow_mut()[id.0].take();
    }

    /// Get the current scope id
    pub(crate) fn current_scope_id(&self) -> Option<ScopeId> {
        self.scope_stack.borrow().last().copied()
    }

    /// Call this function with the current scope set to the given scope
    ///
    /// Useful in a limited number of scenarios
    pub fn on_scope<O>(&self, id: ScopeId, f: impl FnOnce() -> O) -> O {
        {
            self.scope_stack.borrow_mut().push(id);
        }
        let o = f();
        {
            self.scope_stack.borrow_mut().pop();
        }
        o
    }

    /// Get the context for any scope given its ID
    ///
    /// This is useful for inserting or removing contexts from a scope, or rendering out its root node
    pub(crate) fn get_context(&self, id: ScopeId) -> Option<Ref<'_, ScopeContext>> {
        Ref::filter_map(self.scope_contexts.borrow(), |contexts| {
            contexts.get(id.0).and_then(|f| f.as_ref())
        })
        .ok()
    }

    /// Pushes a new scope onto the stack
    pub(crate) fn push(runtime: Rc<Runtime>) {
        RUNTIMES.with(|stack| stack.borrow_mut().push(runtime));
    }

    /// Pops a scope off the stack
    pub(crate) fn pop() {
        RUNTIMES.with(|stack| stack.borrow_mut().pop());
    }

    /// Runs a function with the current runtime
    pub(crate) fn with<F, R>(f: F) -> Option<R>
    where
        F: FnOnce(&Runtime) -> R,
    {
        RUNTIMES.with(|stack| {
            let stack = stack.borrow();
            stack.last().map(|r| f(r))
        })
    }

    /// Runs a function with the current scope
    pub(crate) fn with_current_scope<F, R>(f: F) -> Option<R>
    where
        F: FnOnce(&ScopeContext) -> R,
    {
        Self::with(|rt| {
            rt.current_scope_id()
                .and_then(|scope| rt.get_context(scope).map(|sc| f(&sc)))
        })
        .flatten()
    }

    /// Runs a function with the current scope
    pub(crate) fn with_scope<F, R>(scope: ScopeId, f: F) -> Option<R>
    where
        F: FnOnce(&ScopeContext) -> R,
    {
        Self::with(|rt| rt.get_context(scope).map(|sc| f(&sc))).flatten()
    }
}

/// A guard for a new runtime. This must be used to override the current runtime when importing components from a dynamic library that has it's own runtime.
///
/// ```rust
/// use dioxus::prelude::*;
///
/// fn main() {
///     let virtual_dom = VirtualDom::new(app);
/// }
///
/// fn app() -> Element {
///     rsx!{ Component { runtime: Runtime::current().unwrap() } }
/// }
///
/// // In a dynamic library
/// #[derive(Props, Clone)]
/// struct ComponentProps {
///    runtime: std::rc::Rc<Runtime>,
/// }
///
/// impl PartialEq for ComponentProps {
///     fn eq(&self, _other: &Self) -> bool {
///         true
///     }
/// }
///
/// fn Component(cx: ComponentProps) -> Element {
///     cx.use_hook(|| RuntimeGuard::new(cx.runtime.clone()));
///
///     rsx! { div {} }
/// }
/// ```
pub struct RuntimeGuard(());

impl RuntimeGuard {
    /// Create a new runtime guard that sets the current Dioxus runtime. The runtime will be reset when the guard is dropped
    pub fn new(runtime: Rc<Runtime>) -> Self {
        Runtime::push(runtime);
        Self(())
    }
}

impl Drop for RuntimeGuard {
    fn drop(&mut self) {
        Runtime::pop();
    }
}