quantum

# Quantum

[Cron](https://en.wikipedia.org/wiki/Cron)-like job scheduler for [Elixir](http://elixir-lang.org/).

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## Setup

To use Quantum in your projects, edit your `mix.exs` file and add Quantum as a dependency:

```elixir
defp deps do
  [{:quantum, ">= 1.5.0"}]
end
```

Then, add Quantum to the list of applications in your `mix.exs` file:

```elixir
def application do
  [applications: [:quantum]]
end
```

## Usage

Configure your cronjobs in your `config/config.exs` like this:

```elixir
config :quantum, cron: [
    # Every minute
    "* * * * *":      {"Heartbeat", :send},
    # Every 15 minutes
    "*/15 * * * *":   fn -> System.cmd("rm", ["/tmp/tmp_"] end,
    # Runs on 18, 20, 22, 0, 2, 4, 6:
    "0 18-6/2 * * *": fn -> :mnesia.backup('/var/backup/mnesia') end,
    # Runs every midnight:
    "@daily":         &Backup.backup/0
]
```

or like this:

```elixir
config :quantum, cron: [
    # Every minute
    "* * * * *": {MyApp.MyModule, :my_method}
]
```

or you can provide module as a string:

```elixir
config :quantum, cron: [
    # Every minute
    "* * * * *": {"MyApp.MyModule", :my_method}
]
```

Or even use cron-like format (useful with
[conform](https://github.com/bitwalker/conform) /
[exrm](https://github.com/bitwalker/exrm) /
[edeliver](https://github.com/boldpoker/edeliver)):
```elixir
config :quantum, cron: [
    # Every minute
    "* * * * * MyApp.MyModule.my_method"
]
```

If you want to add jobs on runtime, this is possible too:

```elixir
Quantum.add_job("1 * * * *", fn -> :ok end)
```

### Named jobs

Job struct:
```elixir
%Quantum.Job{
  name: :job_name, # is set automatically on adding a job
  schedule: "1 * * * *", # required
  task: {MyApp.MyModule, :my_method}, # required
  args: [:a, :b] # optional, default: []
  state: :active, # is used for internal purposes
  nodes: [:node@host] # default: [node()]
}
```

You can define named jobs in your config like this:

```elixir
config :quantum, cron: [
  news_letter: [
    schedule: "@weekly",
    task: "MyApp.NewsLetter.send", # {MyApp.NewsLetter, :send} is supported too
    args: [:whatever]
  ]
]
```

Possible options:
- `schedule` cron schedule, ex: `"@weekly"` or `"1 * * * *"`
- `task` function to be performed, ex: `"MyApp.MyModule.my_method"` or `{MyApp.MyModule, :my_method}`
- `args` arguments list to be passed to `task`
- `nodes` nodes list the task should be run on, default: `[node()]`

So now you can control your jobs behavior on runtime.

Add named jobs on runtime:

```elixir
job_spec = [
  schedule: "1 * * * *",
  task: fn -> :ok end
]
Quantum.add_job(:ok_job, fn -> :ok end)
```

Deactivate job (will not be performed until activation):
```elixir
Quantum.deactivate_job(:ok_job)
Quantum.deactivate_job(:news_letter)
```

Activate inactive job:
```elixir
Quantum.activate_job(:ok_job)
Quantum.activate_job(:news_letter)
```

Find job:
```elixir
Quantum.delete_job(:ok_job)
# {:ok_job, %Quantum.Job{...}}
Quantum.delete_job(:news_letter)
# {:news_letter, %Quantum.Job{...}}
```

Delete job:
```elixir
Quantum.delete_job(:ok_job)
# {:ok_job, %Quantum.Job{...}}
Quantum.delete_job(:news_letter)
# {:news_letter, %Quantum.Job{...}}
```

### Nodes

If you need to run a job on a certain node you can define:

```elixir
config :quantum, cron: [
  news_letter: [
    # your job config
    nodes: [:app1@myhost, "app2@myhost"]
  ]
]
```

**NOTE** If `nodes` is not defined current node is used and a job is performed on all nodes.

### Timezone

Please note that Quantum uses **UTC timezone** and not local timezone by default.

To use local timezone, add the following `timezone` option to your configuration:

```elixir
config :quantum,
  cron: [
    # Your cronjobs
  ],
  timezone: :local
```

### Crontab format

| Field        | Allowed values
| ------------ | --------------
| minute       | 0-59
| hour         | 0-23
| day of month | 1-31
| month        | 1-12 (or names)
| day of week  | 0-6 (0 is Sunday, or use names)

Names can also be used for the `month` and `day of week` fields.
Use the first three letters of the particular day or month (case does not matter).

### Special expressions

Instead of the first five fields, one of these special strings may be used:

| String      | Description
| ----------- | -----------
| `@annually` | Run once a year, same as `"0 0 1 1 *"` or `@yearly`
| `@daily`    | Run once a day, same as `"0 0 * * *"` or `@midnight`
| `@hourly`   | Run once an hour, same as `"0 * * * *"`
| `@midnight` | Run once a day, same as `"0 0 * * *"` or `@daily`
| `@monthly`  | Run once a month, same as `"0 0 1 * *"`
| `@reboot`   | Run once, at startup
| `@weekly`   | Run once a week, same as `"0 0 * * 0"`
| `@yearly`   | Run once a year, same as `"0 0 1 1 *"` or `@annually`

## Contribution

This project uses the [C4.1 process](http://rfc.zeromq.org/spec:22) for all code changes.

> "Everyone, without distinction or discrimination, SHALL have an equal right to become a Contributor under the
terms of this contract."

### tl;dr

1. Check for [open issues](https://github.com/c-rack/quantum-elixir/issues) or [open a new issue](https://github.com/c-rack/quantum-elixir/issues/new) to start a discussion around [a problem](https://www.youtube.com/watch?v=_QF9sFJGJuc).
2. Issues SHALL be named as "Problem: _description of the problem_".
3. Fork the [quantum-elixir repository on GitHub](https://github.com/c-rack/quantum-elixir) to start making your changes
4. If possible, write a test which shows that the problem was solved.
5. Send a pull request.
6. Pull requests SHALL be named as "Solution: _description of your solution_"
7. Your pull request is merged and you are added to the [list of contributors](https://github.com/c-rack/quantum-elixir/graphs/contributors)

## License

[Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)