Class: FractionalIndexer::Midpointer

Inherits:
Object
  • Object
show all
Defined in:
lib/fractional_indexer/midpointer.rb

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.execute(prev_pos = nil, next_pos = nil) ⇒ Object 



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# File 'lib/fractional_indexer/midpointer.rb', line 5

def self.execute(prev_pos = nil, next_pos = nil)
  new.execute(prev_pos, next_pos)
end

Instance Method Details

#execute(prev_pos = nil, next_pos = nil) ⇒ Object 



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# File 'lib/fractional_indexer/midpointer.rb', line 9

def execute(prev_pos = nil, next_pos = nil)
  prev_pos = prev_pos.to_s
  next_pos = next_pos.to_s

  return digits[digits.length / 2] if prev_pos.empty? && next_pos.empty?

  validate_positions!(prev_pos, next_pos)

  unless next_pos.empty?
    n = 0

    # Get a common prefix for prev_pos and next_pos.
    # Also add to the prefix the number of consecutive "0 "s in next_pos.
    # Example:
    #  prev_pos = "123", next_pos = "1230005"
    #  prefix = "123000"
    n += 1 while (prev_pos[n] || digits.first) == next_pos[n]

    return next_pos[0, n] + execute(prev_pos[n..], next_pos[n..]) if n.positive?
  end

  digit_a = prev_pos.empty?   ? 0             : digits.index(prev_pos[0])
  digit_b = next_pos.empty?   ? digits.length : digits.index(next_pos[0])

  if digit_b - digit_a > 1
    mid_digit = ((digit_a + digit_b) / 2.0).round

    return digits[mid_digit]
  end

  if next_pos.length > 1
    next_pos[0]
  else
    digits[digit_a] + execute(prev_pos[1..], nil)
  end
end