#!/usr/bin/lua
function setup_screen() os.execute("stty cbreak -echo") end
function restore_screen() os.execute("stty -cbreak echo") end
function termout(s) io.stdout:write(s) end
function reset_terminal() termout("\27c") end
function home_cursor() termout("\27[H") end
function read_file(filename)
  return { data = file_contents(filename)
         , filename = filename
         , eobp = eobp
         , kill_line = kill_line
         , redraw = redraw_buf
         , execute = execute
         , save = save
         , backup = backup_buf
         , pos = 0
         , forward = forward_buf
         , delete = delete_in_buf
         , insert = insert_in_buf
         }
end
function file_contents(filename)
  local fd = io.open(filename, "r")
  local data = fd:read("*all")
  fd:close()
  return data
end
function redraw_buf(self)
  reset_terminal()
  termout(string.sub(self.data, 1, self.pos  - 1 ) )--         )
  termout("|")
  termout(string.sub(self.data, self.pos))
end
function execute(self, command)
  if command == "\2" then self:backup()  -- control B
  elseif command == "\6" then self:forward() -- control F
  elseif command == "\127" then self:delete()  -- delete character
  elseif command == "\11" then self:kill_line() -- control K
  else self:insert(command)
  end
end

function kill_line(self)
  while not self:eobp() and string.sub(self.data, self.pos, 1) ~= "\n" do
    self:forward()
    self:delete()
  end
  if not self:eobp() then self:forward(); self:delete() end
end

function eobp(self)
  return self.pos == #(self.data) + 1
end
function save(self)
  local fd = io.open(self.filename, "w")
  fd:write(self.data)
  fd:close()
end
function backup_buf(self)
  if self.pos < 3 then self.pos = 1
  else self.pos = self.pos - 1
  end
end
function forward_buf(self)
  if self.pos > #(self.data) then self.pos = #(self.data) + 1
  else self.pos = self.pos + 1 end
end
function delete_in_buf(self)
  if self.pos > 1 then
    self.data = string.sub(self.data, 1, self.pos - 2) .. string.sub(self.data, self.pos)   
    self.pos = self.pos - 1
     
end end
function insert_in_buf(self, character)
  self.data = string.sub(self.data, 1, self.pos - 1) .. character .. string.sub(self.data, self.pos)


  self.pos = self.pos + 1  



end
function editormain(filename)
  local buf = read_file(filename)
  setup_editor()
  while 1 do
    buf:redraw()
    local command = read_command()
    if command == exit_command then break end
    buf:execute(command)
  end
  buf:save()
end
function read_file(filename)
  return { data = file_contents(filename)
         , filename = filename
         , eobp = eobp
         , kill_line = kill_line
         , redraw = redraw_buf
         , execute = execute
         , save = save
         , backup = backup_buf
         , pos = 0
         , forward = forward_buf
         , delete = delete_in_buf
         , insert = insert_in_buf
         }
end
function setup_editor()
  setup_screen()
  reset_terminal()
end
function read_command() return io.stdin:read(1) end
exit_command = "\24"
local filename = ...
assert(filename)
editormain(filename)
restore_screen()