module FFaker::String

def from_regexp(exp)
  result = +''
  @last_token = nil
  # Drop surrounding /'s and split into characters
  tokens = exp.inspect[1...-1].split(//)
  result << process_token(tokens) until tokens.empty?
  result
end

def generate_range(tokens)
  result = []
  while tokens.any?
    token = tokens.shift
    if token == DASH && tokens.first && result.last
      result += [*result.pop..tokens.shift]
    elsif token == BACKSLASH
      result << special(tokens.shift)
    else
      result << token
    end
  end
  result
end

def generate_token(token, tokens)
  case token
  when /\w/ then
    @last_token = [token]
    token
  when BACKSLASH then
    token = tokens.shift
    @last_token = ['\\', token]
    special(token)
  when '[' then
    set = []
    while (ch = tokens.shift) != ']'
      set << ch
    end
    @last_token = ['['] + set + [']']
    process_token([fetch_sample(generate_range(set))])
  else
    token
  end
end

def process_token(tokens)
  return '' if tokens.empty?
  token = tokens.shift
  case token
  when '?' then
    # TODO: Let ? generate nothing
    '' # We already printed its target
  when '+' then
    tokens.unshift(token) if rand(0..1) == 1 # Leave the `+` on to run again
    process_token(@last_token) # Run the last one at least once
  when '*' then
    tokens.unshift(token) if rand(0..1) == 1 # Leave the `*` on to run again
    return '' if rand(0..1) == 1 # Or maybe do nothing
    process_token(@last_token) # Else run the last one again
  when '{' then
    number = +''
    while (ch = tokens.shift) != '}'
      number << ch
    end
    number = number.to_i - 1
    t = @last_token.dup
    Array.new(number) { process_token(t.dup) }.join
  else
    generate_token token, tokens
  end
end

def special(token)
  case token
  when 'w' then fetch_sample(WORD_CHARS)
  when 'd' then fetch_sample(NUMBERS)
  when 's' then fetch_sample(SPACES)
  when *ESCAPEABLE_CHARS then token
  else
    ''
  end
end