save

function app.saveFile(strFilename, strValue, dir)
    local path = system.pathForFile(strFilename, dir or system.DocumentsDirectory)
    local file = io.open(path, 'w+')
    if file then
       file:write(strValue)
       io.close(file)
    end
end

function app.readFile(strFilename, dir)
    local theFile = strFilename
    local path = system.pathForFile( theFile, dir or system.DocumentsDirectory )
    -- io.open opens a file at path. returns nil if no file found
    local file = io.open( path, 'r')
    if file then
       -- read all contents of file into a string
       local contents = file:read('*a')
       io.close( file )
       return contents
    else
       return ''
    end
end

function app.readJsonFile(strFilename, dir)
    return json.decode(app.readFile(strFilename, dir))
end

function app.saveJsonFile(strFilename, strValue, dir)
   app.saveFile(strFilename, json.encode(strValue), dir)
end