# File lib/minitest/compress.rb, line 11
def compress orig
  ary = orig

  eswo = ->(a, n, off) { # each_slice_with_offset
    if off.zero? then
      a.each_slice n
    else
      # [ ...off... [...n...] [...n...] ... ]
      front, back = a.take(off), a.drop(off)
      [front].chain back.each_slice n
    end
  }

  3.times do # maybe don't use loop do here?
    index = ary                               # [ a b c b c b c d ]
      .size
      .times                                  # 0...size
      .group_by { |i| ary[i] }                # { a: [0] b: [1 3 5], c: [2 4 6], d: [7] }

    order = index
      .reject { |k, v| v.size == 1 }          # { b: [1 3 5], c: [2 4 6] }
      .sort_by { |k, a1|                      ### sort by max dist + min offset
        d = a1.each_cons(2).sum { |a2, b| b-a2 }
        [-d, a1.first]
      }                                       # b: [1 3 5] c: [2 4 6]

    ranges = order
      .map { |k, a1|                          # [[1..2 3..4] [2..3 4..5]]
        a1
          .each_cons(2)
          .map { |a2, b| a2..b-1 }
      }

    big_ranges = ranges
      .flat_map { |a|                         # [1..2 3..4 2..3 4..5]
        a.sort_by { |r| [-r.size, r.first] }.first 5
      }
      .first(100)

    culprits = big_ranges
      .map { |r|
        eswo[ary, r.size, r.begin]            # [o1 s1 s1 s2 s2]
          .chunk_while { |a, b| a == b }      # [[o1] [s1 s1] [s2 s2]]
          .map { |a| [a.size, a.first] }      # [[1 o1] [2 s1] [2 s2]]
      }
      .select { |chunks|
        chunks.any? { |a| a.first > 1 }       # compressed anything?
      }

    min = culprits
      .min_by { |a| a.flatten.size }          # most compressed

    break unless min

    ary = min.flat_map { |(n, lines)|
      if n > 1 then
        [[n, compress(lines)]]                # [o1 [2 s1] [2 s2]]
      else
        lines
      end
    }
  end

  format = ->(lines) {
    lines.flat_map { |line|
      case line
      when Array then
        n, lines = line
        lines = format[lines]
        [
          " +->> #{n} cycles of #{lines.size} lines:",
          *lines.map { |s| " | #{s}" },
          " +-<<",
        ]
      else
        line
      end
    }
  }

  format[ary]
end