renderbug/src/task.rs

use std::fmt;

pub trait Task {
    fn tick(&mut self) {}
    fn start(&mut self) {}
    fn stop(&mut self) {}
    fn name(&self) -> &'static str;
}

trait ScheduledState: std::fmt::Debug {
    fn start(self: Box<Self>) -> Box<dyn ScheduledState>;
    fn stop(self: Box<Self>) -> Box<dyn ScheduledState>;
    fn tick(self: Box<Self>, task: &mut dyn Task) -> Box<dyn ScheduledState>;
}

#[derive(Debug)]
struct Starting {}
impl ScheduledState for Starting {
    fn start(self: Box<Self>) -> Box<dyn ScheduledState> {
        self
    }

    fn stop(self: Box<Self>) -> Box<dyn ScheduledState> {
        Box::new(Stopped {})
    }

    fn tick(self: Box<Self>, task: &mut dyn Task) -> Box<dyn ScheduledState> {
        task.start();
        Box::new(Running{})
    }
}

#[derive(Debug)]
struct Running {}
impl ScheduledState for Running {
    fn start(self: Box<Self>) -> Box<dyn ScheduledState> {
        self
    }

    fn stop(self: Box<Self>) -> Box<dyn ScheduledState> {
        Box::new(Stopping {})
    }

    fn tick(self: Box<Self>, task: &mut dyn Task) -> Box<dyn ScheduledState> {
        task.tick();
        self
    }
}

#[derive(Debug)]
struct Stopping {}
impl ScheduledState for Stopping  {
    fn start(self: Box<Self>) -> Box<dyn ScheduledState> {
        Box::new(Running {})
    }

    fn stop(self: Box<Self>) -> Box<dyn ScheduledState> {
        self
    }

    fn tick(self: Box<Self>, task: &mut dyn Task) -> Box<dyn ScheduledState> {
        task.stop();
        Box::new(Stopped {})
    }
}

#[derive(Debug)]
struct Stopped {}
impl ScheduledState for Stopped  {
    fn start(self: Box<Self>) -> Box<dyn ScheduledState> {
        Box::new(Starting {})
    }

    fn stop(self: Box<Self>) -> Box<dyn ScheduledState> {
        self
    }

    fn tick(self: Box<Self>, _task: &mut dyn Task) -> Box<dyn ScheduledState> {
        self
    }
}

struct ScheduledTask {
    state: Option<Box<dyn ScheduledState>>,
    task: Box<dyn Task>
}

impl std::fmt::Debug for ScheduledTask {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ScheduledTask")
            .field("task", &self.task.name())
            .field("state", &self.state)
            .finish()
    }
}

impl ScheduledTask {
    fn new(task: Box<dyn Task>) -> Self {
        ScheduledTask {
            state: Some(Box::new(Starting{})),
            task: task
        }
    }

    fn start(&mut self) {
        if let Some(s) = self.state.take() {
            self.state = Some(s.start());
        }
    }

    fn stop(&mut self) {
        if let Some(s) = self.state.take() {
            self.state = Some(s.stop());
        }
    }

    fn tick(&mut self) {
        if let Some(s) = self.state.take() {
            self.state = Some(s.tick(self.task.as_mut()));
        }
    }
}

pub struct Scheduler {
    tasks: Vec<ScheduledTask>
}

impl Scheduler {
    pub fn new(tasks: Vec<Box<dyn Task>>) -> Self {
        let mut scheduled = Vec::new();
        for task in tasks {
            log::info!("Scheduling task {:?}", task.name());
            scheduled.push(ScheduledTask::new(task));
        }
        Scheduler {
            tasks: scheduled
        }
    }

    pub fn tick(&mut self) {
        for task in &mut self.tasks {
            task.tick();
        }
    }
}