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//! # JobScheduler
//!
//! A simple cron-like job scheduling library for Rust.
//!
//! ## Usage
//!
//! Be sure to add the job_scheduler crate to your `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! job_scheduler = "*"
//! ```
//!
//! Creating a schedule for a job is done using the `FromStr` impl for the
//! `Schedule` type of the [cron](https://github.com/zslayton/cron) library.
//!
//! The scheduling format is as follows:
//!
//! ```text
//! sec   min   hour   day of month   month   day of week   year
//! *     *     *      *              *       *             *
//! ```
//!
//! Note that the year may be omitted.
//!
//! Comma separated values such as `5,8,10` represent more than one time
//! value. So for example, a schedule of `0 2,14,26 * * * *` would execute
//! on the 2nd, 14th, and 26th minute of every hour.
//!
//! Ranges can be specified with a dash. A schedule of `0 0 * 5-10 * *`
//! would execute once per hour but only on day 5 through 10 of the month.
//!
//! Day of the week can be specified as an abbreviation or the full name.
//! A schedule of `0 0 6 * * Sun,Sat` would execute at 6am on Sunday and
//! Saturday.
//!
//! A simple usage example:
//!
//! ```rust,ignore
//! extern crate job_scheduler;
//! use job_scheduler::{JobScheduler, Job};
//! use std::time::Duration;
//!
//! fn main() {
//!     let mut sched = JobScheduler::new();
//!
//!     sched.add(Job::new("1/10 * * * * *".parse().unwrap(), || {
//!         println!("I get executed every 10 seconds!");
//!     }));
//!
//!     loop {
//!         sched.tick();
//!
//!         std::thread::sleep(Duration::from_millis(500));
//!     }
//! }
//! ```

extern crate chrono;
extern crate cron;

use chrono::DateTime;
use chrono::Utc;
pub use cron::Schedule;


/// A schedulable `Job`.
pub struct Job<'a> {
    schedule: Schedule,
    run: Box<(FnMut() -> ()) + 'a>,
    last_tick: Option<DateTime<Utc>>,
}

impl<'a> Job<'a> {
    /// Create a new job.
    ///
    /// ```rust,ignore
    /// // Run at second 0 of the 15th minute of the 6th, 8th, and 10th hour
    /// // of any day in March and June that is a Friday of the year 2017.
    /// let s: Schedule = "0 15 6,8,10 * Mar,Jun Fri 2017".into().unwrap();
    /// Job::new(s, || println!("I have a complex schedule...") );
    /// ```
    pub fn new<T>(schedule: Schedule, run: T) -> Job<'a>
        where T: 'a,
              T: FnMut() -> ()
    {
        Job {
            schedule,
            run: Box::new(run),

            last_tick: None,
        }
    }

    fn tick(&mut self) {
        let now = Utc::now();
        if self.last_tick.is_none() {
            self.last_tick = Some(now);
            return;
        }
        for event in self.schedule.after(&self.last_tick.unwrap()) {
            if event > now {
                break;
            }

            (self.run)();
        }

        self.last_tick = Some(now);
    }
}

#[derive(Default)]
/// The JobScheduler contains and executes the scheduled jobs.
pub struct JobScheduler<'a> {
    jobs: Vec<Job<'a>>,
}

impl<'a> JobScheduler<'a> {
    /// Create a new `JobScheduler`.
    pub fn new() -> JobScheduler<'a> {
        JobScheduler { jobs: Vec::new() }
    }

    /// Add a job to the `JobScheduler`
    ///
    /// ```rust,ignore
    /// let mut sched = JobScheduler::new();
    /// sched.add(Job::new("1/10 * * * * *".parse().unwrap(), || {
    ///     println!("I get executed every 10 seconds!");
    /// }));
    /// ```
    pub fn add(&mut self, job: Job<'a>) {
        self.jobs.push(job)
    }

    /// The `tick` method increments time for the JobScheduler and executes
    /// any pending jobs. It is recommended to sleep for at least 500
    /// milliseconds between invocations of this method.
    ///
    /// ```rust,ignore
    /// loop {
    ///     sched.tick();
    ///     std::thread::sleep(Duration::from_millis(500));
    /// }
    /// ```
    pub fn tick(&mut self) {
        for mut job in &mut self.jobs {
            job.tick();
        }
    }
}