ruby 54 lines · 9 steps

Building search-result snippets in Ruby

A class that finds a query match in text and returns a trimmed, highlighted excerpt around it.

Explained by highlit

Intermediate regular-expressions text-processing search string-manipulation

1class SnippetHighlighter
CONTEXT_RADIUS = 60
MAX_TERMS = 8
4 
def initialize(text, query)
  @text = text.to_s
  @terms = extract_terms(query)
end
9 
def call
  return truncated_lead if @terms.empty?
12 
  match = first_match
  return truncated_lead unless match
15 
  window = build_window(match.begin(0), match.end(0))
  highlight(window)
end
19 
private
21 
def extract_terms(query)
  query.to_s.scan(/\w+/).uniq.first(MAX_TERMS).map(&:downcase)
end
25 
def pattern
  @pattern ||= Regexp.union(@terms.map { |t| /#{Regexp.escape(t)}/i })
end
29 
def first_match
  pattern.match(@text)
end
33 
def build_window(match_start, match_end)
  from = [match_start - CONTEXT_RADIUS, 0].max
  to = [match_end + CONTEXT_RADIUS, @text.length].min
37 
  from -= 1 until from.zero? || @text[from - 1] =~ /\s/
  to += 1 until to == @text.length || @text[to] =~ /\s/
40 
  prefix = from.zero? ? "" : "\u2026"
  suffix = to == @text.length ? "" : "\u2026"
  "#{prefix}#{@text[from...to].strip}#{suffix}"
end
45 
def highlight(window)
  window.gsub(pattern) { |m| "<mark>#{m}</mark>" }
end
49 
def truncated_lead
  lead = @text[0, CONTEXT_RADIUS * 2].to_s.strip
  @text.length > lead.length ? "#{lead}\u2026" : lead
end
54end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Clamping offsets with max and min keeps window boundaries safely inside the string.
2Regexp.union with escaped, case-insensitive terms matches any query word in one pass.
3Graceful fallbacks — an empty query or no match — keep a snippet builder from ever returning nothing useful.

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