debianize-mobilizon/lib/service/formatter/text.ex

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Elixir
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defmodule Mobilizon.Service.Formatter.Text do
@moduledoc """
Helps to format text blocks
Inspired from https://elixirforum.com/t/is-there-are-text-wrapping-library-for-elixir/21733/4
Using the Knuth-Plass Line Wrapping Algorithm https://www.students.cs.ubc.ca/~cs-490/2015W2/lectures/Knuth.pdf
"""
def quote_paragraph(string, max_line_length) do
paragraph(string, max_line_length, "> ")
end
def paragraph(string, max_line_length, prefix \\ "") do
string
|> String.split("\n\n", trim: true)
|> Enum.map_join("\n#{prefix}\n", &subparagraph(&1, max_line_length, prefix))
end
defp subparagraph(string, max_line_length, prefix) do
[word | rest] = String.split(string, ~r/\s+/, trim: true)
rest
|> lines_assemble(max_line_length - String.length(prefix), String.length(word), word, [])
|> Enum.map_join("\n", &"#{prefix}#{&1}")
end
defp lines_assemble([], _, _, line, acc), do: [line | acc] |> Enum.reverse()
defp lines_assemble([word | rest], max, line_length, line, acc) do
if line_length + 1 + String.length(word) > max do
lines_assemble(rest, max, String.length(word), word, [line | acc])
else
lines_assemble(rest, max, line_length + 1 + String.length(word), line <> " " <> word, acc)
end
end
end