Module: FlowChat::TextTruncator

Defined in:
lib/flow_chat/text_truncator.rb

Overview

Shortens text to fit a display cap.

Every renderer that fits a label into a platform's title limit needs this, and so does every choice mapper that has to know exactly what the user is looking at: a mapper that reimplemented the rule separately could drift from what the renderer actually renders, silently reopening the bug this class exists to prevent.

Constant Summary collapse

ELLIPSIS = 
"..."

Class Method Summary collapse

Class Method Details

.number(text, position, cap, measure: :characters) ⇒ Object

Prefixes text with its 1-based position on the rung ("1. ", "10. ", "100. ") and truncates the label to make room, so the combined string never exceeds cap. The prefix's length depends on position, so it has to be computed per choice rather than once for the whole rung: choice 10 loses one more character to its label than choice 1 does.

Every renderer and choice mapper that numbers a choice's on-screen title shares this, for the same reason .truncate is shared: a mapper that reimplemented the prefix-and-truncate rule separately could drift from what the renderer actually renders, silently reopening the bug this class exists to prevent.



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# File 'lib/flow_chat/text_truncator.rb', line 49

def self.number(text, position, cap, measure: :characters)
  prefix = "#{position}. "
  prefix + truncate(text.to_s, cap - size_of(prefix, measure), measure: measure)
end

.truncate(text, length, measure: :characters) ⇒ Object

length is clamped to zero or more before anything else: String#[] with a negative second argument returns nil rather than raising, so a negative length (reachable from #number below, whose prefix can eat more than the whole cap at a small enough cap) would otherwise turn nil + "..." into a NoMethodError deep inside a render.

Below 3 there is no room left for the ellipsis itself - it alone is 3 characters - so a cap that small hard-truncates with no ellipsis rather than returning something longer than the cap it was supposed to respect. measure picks the unit the cap is expressed in. :bytes exists because Meta and Telegram both size these fields in bytes rather than characters - FlowChat::Instagram::Client#measure already draws the same distinction for message bodies, and for the same reason: a character count lets multibyte text through to be rejected by the platform.



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# File 'lib/flow_chat/text_truncator.rb', line 27

def self.truncate(text, length, measure: :characters)
  text = text.to_s
  length = 0 if length.negative?
  return text if size_of(text, measure) <= length

  ellipsis = size_of(ELLIPSIS, measure)
  return cut(text, length, measure) if length < ellipsis

  cut(text, length - ellipsis, measure) + ELLIPSIS
end