local M = {}

M.exec = function(cmd)
  return io.popen(cmd):read'*l'
end

local function find_sub(s, replacement, pattern, start, special)
  local x1, x2 = s:find(pattern, start, special)
  if x1 then
    return s:sub(1, x1-1) .. replacement .. s:sub(x2+1), x1, x2
  end
  return s
end
-- Only works with prefix comments.
local function get_line_comment()
  local cms = vim.bo.commentstring
  -- This whole pesc dance is a bummer.
  local pattern = '^(%s*)' ..
  (find_sub(vim.pesc((find_sub(cms, '\0', '%s', 1, true))), '(%s*).*', '\0', 1, true))
  local pre_ws, inner_ws = vim.api.nvim_get_current_line():match(pattern)
  if pre_ws then
    return pre_ws .. cms:format('') .. inner_ws
  end
  return ''
end
M.comment = function(str)
  -- add space
  local prefix = vim.bo.commentstring:format(''):gsub('%S$', '%0 ')
  local comment = get_line_comment()
  if comment ~= '' then
    prefix = ''
  end
  return prefix .. str
end

return M