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Learning Exercise
Elixir's atom type represents a fixed constant. An atom's value is simply its own name. This gives us a type-safe way to interact with data. Atoms can be defined as follows:
# All atoms are preceded with a ':' then follow with alphanumeric snake-cased characters
variable = :an_atom
Atoms are internally represented by an integer in a lookup table, which are set automatically. It is not possible to change this internal value.
Often, we want to write code that can branch based on a condition. While there are many ways to do this in Elixir, one of the simplest ways is using cond/1.
At its simplest, cond follows the first path that evaluates to true with one or more branches:
cond do
x > 10 -> :this_might_be_the_way
y < 7 -> :or_that_might_be_the_way
true -> :this_is_the_default_way
end
If no path evaluates to true, an error is raised by the runtime.
You are running a system that consists of a few applications producing many logs. You want to write a small program that will aggregate those logs and give them labels according to their severity level. All applications in your system use the same log codes, but some of the legacy applications don't support all the codes.
| Log code | Log label | Supported in legacy apps? |
|---|---|---|
| 0 | trace | no |
| 1 | debug | yes |
| 2 | info | yes |
| 3 | warning | yes |
| 4 | error | yes |
| 5 | fatal | no |
| other / not supported | unknown | - |
Implement the LogLevel.to_label/2 function. It should take an integer code and a boolean flag telling you if the log comes from a legacy app, and return the label of a log line as an atom.
Log codes not specified in the table should return an unknown label. Log codes specified in the table as not supported in legacy apps should also return an unknown label if the log came from a legacy app.
LogLevel.to_label(0, false)
# => :trace
LogLevel.to_label(0, true)
# => :unknown
Somebody has to be notified when unexpected things happen.
Implement the LogLevel.alert_recipient/2 function to determine to whom the alert needs to be sent. The function should take an integer code and a boolean flag telling you if the log comes from a legacy app, and return the name of the recipient as an atom.
Use the LogLevel.to_label/2 function from the previous task. If the log label is error or fatal, send the alert to the ops team. If you receive a log with an unknown label from a legacy system, send the alert to the dev1 team, other unknown labels should be sent to the dev2 team. All other log labels can be safely ignored by returning false.
LogLevel.alert_recipient(-1, true)
# => :dev1
LogLevel.alert_recipient(0, false)
# => false
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