local M = {}

M.init = function()
  -- get tty
  local tty_handle = io.popen('tty')
  if tty_handle == nil then return end
  local tty = tty_handle:read('*a')
  tty_handle:close()
  if tty:find("not a tty") then error('not a tty') end

  M.tty = tty
end

M.update = function()
  if M.tty == nil then return end

  if not M.normal then
    -- get colorscheme Normal highlight
    local normal = vim.api.nvim_get_hl(0, { name = 'Normal', create = false })
    if (normal.bg == nil) then return end
    -- cache old value for use with VimResume
    M.normal = normal
  end

  -- emit CSI to change terminal background to Normal.bg
  os.execute('printf "\\033]11;' .. string.format('#%06x', M.normal.bg) .. '\\007" > ' .. M.tty)

  -- set colorscheme Normal.bg to NONE, making it transparent
  vim.cmd [[hi Normal ctermbg=NONE guibg=NONE]]
end

M.reset = function()
  if M.tty == nil then return end

  os.execute('printf "\\033]111\\007" > ' .. M.tty)
end

M.setup = function(opts)
  opts = opts or {}

  M.init()
  vim.api.nvim_create_autocmd({ 'ColorScheme', 'UIEnter', 'VimResume' }, { callback = M.update })
  vim.api.nvim_create_autocmd({ 'UILeave' }, { callback = M.reset })
end

return M