//! This module defines the `ContextProvider` component.

use std::cell::RefCell;

use slab::Slab;

use crate::html::Scope;
use crate::{Callback, Component, Context, Html, Properties};

/// Props for [`ContextProvider`]
#[derive(Debug, Clone, PartialEq, Properties)]
pub struct ContextProviderProps<T: Clone + PartialEq> {
    /// Context value to be passed down
    pub context: T,
    /// Children
    pub children: Html,
}

/// The context provider component.
///
/// Every child (direct or indirect) of this component may access the context value.
/// In order to consume contexts, [`Scope::context`][Scope::context] method is used,
/// In function components the `use_context` hook is used.
#[derive(Debug)]
pub struct ContextProvider<T: Clone + PartialEq + 'static> {
    context: T,
    consumers: RefCell<Slab<Callback<T>>>,
}

/// Owns the connection to a context provider. When dropped, the component will
/// no longer receive updates from the provider.
#[derive(Debug)]
pub struct ContextHandle<T: Clone + PartialEq + 'static> {
    provider: Scope<ContextProvider<T>>,
    key: usize,
}

impl<T: Clone + PartialEq + 'static> Drop for ContextHandle<T> {
    fn drop(&mut self) {
        if let Some(component) = self.provider.get_component() {
            component.consumers.borrow_mut().remove(self.key);
        }
    }
}

impl<T: Clone + PartialEq> ContextProvider<T> {
    /// Add the callback to the subscriber list to be called whenever the context changes.
    /// The consumer is unsubscribed as soon as the callback is dropped.
    pub(crate) fn subscribe_consumer(
        &self,
        callback: Callback<T>,
        scope: Scope<Self>,
    ) -> (T, ContextHandle<T>) {
        let ctx = self.context.clone();
        let key = self.consumers.borrow_mut().insert(callback);

        (
            ctx,
            ContextHandle {
                provider: scope,
                key,
            },
        )
    }

    /// Notify all subscribed consumers and remove dropped consumers from the list.
    fn notify_consumers(&mut self) {
        let consumers: Vec<Callback<T>> = self
            .consumers
            .borrow()
            .iter()
            .map(|(_, v)| v.clone())
            .collect();
        for consumer in consumers {
            consumer.emit(self.context.clone());
        }
    }
}

impl<T: Clone + PartialEq + 'static> Component for ContextProvider<T> {
    type Message = ();
    type Properties = ContextProviderProps<T>;

    fn create(ctx: &Context<Self>) -> Self {
        let props = ctx.props();
        Self {
            context: props.context.clone(),
            consumers: RefCell::new(Slab::new()),
        }
    }

    fn changed(&mut self, ctx: &Context<Self>, old_props: &Self::Properties) -> bool {
        let props = ctx.props();

        let should_render = old_props.children != props.children;

        if self.context != props.context {
            self.context = props.context.clone();
            self.notify_consumers();
        }

        should_render
    }

    fn view(&self, ctx: &Context<Self>) -> Html {
        ctx.props().children.clone()
    }
}