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//! provides functionalities for commands to be executed by the system, such as
//! when the application starts or after the application updates.
//!
use crate::dom::Program;
use crate::dom::{Application, Cmd, Effects};
use wasm_bindgen_futures::spawn_local;

/// Dispatch is a command to be executed by the system.
/// This is returned at the init function of a component and is executed right
/// after instantiation of that component.
/// Dispatch required a DSP object which is the Program as an argument
/// The emit function is called with the program argument.
/// The callback is supplied with the program an is then executed/emitted.
pub struct Dispatch<APP>
where
    APP: Application,
{
    /// the functions that would be executed when this Dispatch is emited
    #[allow(clippy::type_complexity)]
    pub(crate) commands: Vec<Box<dyn FnOnce(Program<APP>)>>,
}

impl<APP> Dispatch<APP>
where
    APP: Application,
{
    /// creates a new Dispatch from a function
    pub fn new<F>(f: F) -> Self
    where
        F: FnOnce(Program<APP>) + 'static,
    {
        Self {
            commands: vec![Box::new(f)],
        }
    }

    /// When you need the runtime to perform couple of commands, you can batch
    /// then together.
    pub fn batch(cmds: impl IntoIterator<Item = Self>) -> Self {
        let mut commands = vec![];
        for cmd in cmds {
            commands.extend(cmd.commands);
        }
        Self { commands }
    }

    /// Add a cmd
    pub fn push(&mut self, cmd: Self) {
        self.append([cmd])
    }

    /// Append more cmd into this cmd and return self
    pub fn append(&mut self, cmds: impl IntoIterator<Item = Self>) {
        for cmd in cmds {
            self.commands.extend(cmd.commands);
        }
    }

    /// Tell the runtime that there are no commands.
    pub fn none() -> Self {
        Dispatch { commands: vec![] }
    }

    /// returns true if commands is empty
    pub fn is_empty(&self) -> bool {
        self.commands.is_empty()
    }

    /// Executes the Dispatch
    pub(crate) fn emit(self, program: Program<APP>) {
        for cb in self.commands {
            let program_clone = program.clone();
            cb(program_clone);
        }
    }

    /// Tell the runtime to execute subsequent update of the App with the message list.
    /// A single call to update the view is then executed thereafter.
    ///
    pub fn batch_msg(msg_list: impl IntoIterator<Item = APP::MSG>) -> Self {
        let msg_list: Vec<APP::MSG> = msg_list.into_iter().collect();
        Dispatch::new(move |mut program| {
            program.dispatch_multiple(msg_list);
        })
    }
}

impl<APP> From<Effects<APP::MSG, ()>> for Dispatch<APP>
where
    APP: Application,
{
    /// Convert Effects that has only follow ups
    fn from(effects: Effects<APP::MSG, ()>) -> Self {
        // we can safely ignore the effects here
        // as there is no content on it.
        let Effects { local, external: _ } = effects;

        Dispatch::batch(local.into_iter().map(Dispatch::from))
    }
}

impl<APP, IN> From<IN> for Dispatch<APP>
where
    APP: Application,
    IN: IntoIterator<Item = Effects<APP::MSG, ()>>,
{
    fn from(effects: IN) -> Self {
        Dispatch::batch(effects.into_iter().map(Dispatch::from))
    }
}

impl<APP> From<Cmd<APP::MSG>> for Dispatch<APP>
where
    APP: Application,
{
    fn from(task: Cmd<APP::MSG>) -> Self {
        Dispatch::new(move |program| {
            for mut command in task.commands.into_iter() {
                let program = program.downgrade();
                spawn_local(async move {
                    let mut program = program.upgrade().expect("upgrade");
                    while let Some(msg) = command.next().await {
                        program.dispatch(msg)
                    }
                });
            }
        })
    }
}