[CC API] cfg

-- Configuration API version 2.0

--[[
loads a file into a variable
usage: cfg.load( string file, bool ext )
* "file" determines the file to load
* "ext" if true excludes adding ".cfg" to the end of the filename
returns the file, or "false" and the failure reason ("invalid" or "missing") if it fails
]]
function load( file, ext )
  if not file then
    error( 'Missing expected args' )
    return
  end
  local ext = ext and '' or '.cfg'
  local filename = file .. ext
  if not fs.exists( filename ) then
    return false, 'missing'
  end
  local file = fs.open( filename, 'r' )
  local config = textutils.unserialize( file.readAll() )
  file.close()
  if not config then
    return false, 'invalid'
  end
  return config
end

--[[
loads a file from a variable
usage: cfg.save( string file, table config, bool ext )
* "file" determines the file to save
* "config" is the table to save into the file
* "ext" if true excludes adding ".cfg" to the end of the filename
returns true if suceeds
]]
function save( file, config, ext )
  if not file or not config then
    error( 'Missing expected args' )
    return
  end
  local ext = ext and '' or '.cfg'
  local file = fs.open( file .. ext, 'w' )
  file.write( textutils.serialize( config ) )
  file.close()
  return true
end

--[[
write a value to a config file as a key
usage: cfg.save( string file, any line, any key, bool ext )
* "file" determines the file to save
* "line" is the variable to add to the file
* "key" is the key to write it to
* "ext" if true excludes adding ".cfg" to the end of the filename
returns true if suceeds, or false if the file is invalid
]]
function saveLine( file, line, key, ext )
  if not file or not line or not key then
    error( 'Missing expected args' )
    return
  end
  local config, cfgError = load( file, ext )
  config = config or {}
  if cfgError == 'invalid' then
    return false
  end
  config[key] = line
  save( file, config, ext )
  return true
end