Ruby Weekly Challenge - hashtags

extract_hashtags.rb

# Description:
#
# You start working for a fancy new startup hoping to revolutionize social networking! GASP! They had this great idea that users should be able to specify relevant keywords to their posts using an ingenious idea by prefixing those keywords with the pound sign (#). Your job is to extract those keywords so that they can be used later on for whatever purposes.
#
# Note:
# Pound signs alone do not count, for example: the string "#" would return an empty array.
# If a word is preceded by more than one hashtag, only the last hashtag counts (e.g. "##alot" would return ["alot"])
# Hashtags cannot be within the middle of a word (e.g. "in#line hashtag" returns an empty array)
# Hashtags must precede alphabetical characters (e.g. "#120398" or "#?" are invalid)
#
# Input: String of words, where some words may contain a hashtag.
#
# Output: Array of strings that were prefixed with the hashtag, but do not contain the hashtag.

def extract_hashtags(tweet)
  return [] unless tweet
  tweet.downcase.scan(/\B#+([a-z]*)/i).flatten.reject(&:empty?)
end

extract_hashtags_spec.rb

require_relative '../extract_hashtags'

describe "#extract_hashtags" do
  context "when tweet is nil" do
    it "returns an empty array" do
      expect(extract_hashtags nil).to eql []
    end
  end

  context "when tweet contains valid hashtags" do
    it "returns only valid hashtags" do
      expect(extract_hashtags("#ermigawd #ilovehashtags, like so much!")).to eql %w[ermigawd ilovehashtags]
    end
  end

  context "when tweet contains invalid hashtags" do
    it "returns only valid hashtags" do
      expect(extract_hashtags("#Ermigawd #ilovehashtags, like so much! #123invalidhashtags make me #Sadlaurie. ####validhashtags makes me #happylaurie")).to eql %w[ermigawd ilovehashtags sadlaurie validhashtags happylaurie]
    end

    it "returns an empty array" do
      expect(extract_hashtags("in#line hashtag")).to eql []
    end

    it "returns an empty array" do
      expect(extract_hashtags "#120398" ).to eql []
    end

    it "returns an empty array" do
      expect(extract_hashtags "#?" ).to eql []
    end

    it "returns an empty array" do
      expect(extract_hashtags "#" ).to eql []
    end
  end
end