AirNow

Mathieu 2018-11-18 to 2018-11-28

This GitHub project shares my 2-week experience learning Elixir and applying what I'd learned on a simple project.

1. Read Getting Started, Mix and OTP and Meta Programming. Practiced with the KV example.
2. Analyzed manga_downloadr for a real-world example.
3. Read threads on Elixir Forum to absorbe best practices.
4. Started this project.

Project

• Go to AirNow.gov
• select zip code 95051
• download current and forecast pollution level (Air Quality Index / AQI)
• download current and forecast image
• repeat every minute
• do not save duplicate images (sha256 check)
• store AQI history in memory and on file (DETS)
• offer command-line access
• send e-mail when crossing a * 50 threshold

Objective

• Use Elixir objects: Supervisors, GenServer, Tasks, Mix Tasks, Agents, escript
• Use erlang storage: :ets, :dets
• Use tests: mix test, doctest
• Use web scrape library (Hound), use email library (Swoosh), use HTML parser library (Floki)
• Use minimal try/rescue, let processes fail
• Use function guards and function captures
• Use string formatting (dates)

How I got started

• installed erlang 21.1 (on windows...)
• installed Elixir
• created project on disk

  mix new airnow --module AirNow
  cd airnow
  

• added escript to project and deps (HTTPoison, Floki) to mix.exs

  mix deps.get
  mix compile # asked to install "rebar3"
  

• created cli.ex

  mix escript.build
  escript airnow -z 95051
  

• onwards with development: created workflow.ex, etc.

How to run

• Create and configure config/private.exs (check config/config.exs for details)

• Compile

  mix deps.get
  mix compile
  

• Make sure chromedriver.exe is running in a separate window. Check that it connects successfully

  mix hound
  

• Run the AirNow application once for a given zip code

  mix escript.build && escript airnow -z "95051" -d "d:/Tmp"
  

• Run the AirNow application as a loop, connecting once per minute

  mix loop
  

• Query Air Quality Index(AQI) history from the command line (one number every minute)

  iex -S mix
  AirNow.AQI.aqi_history( "95051" )
  

• Run tests in test/ and inline doctests

  mix test
  

Questions / Comments welcome!