ComputerCraft MP3 Player (Pocket Computer)

local width, height = term.getSize()
local Screen = "Main"
local Selection = 0
local Playing = nil
local SongData
local dfpwm = require("cc.audio.dfpwm")
local decoder = dfpwm.make_decoder()
local speaker = peripheral.find("speaker")

function WriteCenter(thing)
    local x, y = term.getCursorPos()
    term.setCursorPos(math.ceil((width/2) - (string.len(thing)/2)) + 1, y)
    term.write(thing)
end

function PlaySong(song)
    local content = http.get(song, nil, true).readAll()
    if not content then
        return false
    end

    SongData = {}
    local pointer = 1
    for i = 1, string.len(content), 16 * 1024 do
        table.insert(SongData, string.sub(content, pointer, i))
        pointer = i+1
    end
    return true
end

fs.makeDir("songs")
function UpdateScreen()
    term.clear()
    paintutils.drawLine(1, 1, width, 1, colors.red)
    WriteCenter("Ender MP3 Player")
    term.setCursorPos(1, 3)
    term.setBackgroundColor(colors.black)
    if Screen == "Main" then
        WriteCenter("[Options]")
        term.setCursorPos(1, 4)
        if Selection == 0 then
            WriteCenter("<Play Music>")
        else
            WriteCenter("Play Music")
        end
        term.setCursorPos(1, 5)
        if Selection == 1 then
            WriteCenter("<Download Music>")
        else
            WriteCenter("Download Music")
        end
    elseif Screen == "PlaySongs" then
        WriteCenter("[Play Songs]")
        local songs = fs.list("songs")
        for a,b in pairs(songs) do
            term.setCursorPos(0, 4+(a-1))
            if Selection == (a-1) then
                WriteCenter("<" .. b .. ">")
            else
                WriteCenter(b)
            end
        end
        term.setCursorPos(0, 4+#songs)
        if Selection == #songs then
            WriteCenter("<Back>")
        else
            WriteCenter("Back")
        end
    elseif Screen == "Song" then
        WriteCenter("[" .. Playing .. "]")
        term.setCursorPos(0, 4)
        WriteCenter("Song may take 5-10")
        term.setCursorPos(0, 5)
        WriteCenter("seconds to load.")
        term.setCursorPos(0, 6)
        WriteCenter("Press [Enter] to stop...")
        term.setCursorPos(0, 8)
    end
end

function Main()
    while true do
        local event, key, isHeld = os.pullEvent("key")
        --print(keys.getName( key ))
        if key == keys.up or key == keys.down then
            if key == keys.up then
                Selection = Selection - 1
            else
                Selection = Selection + 1
            end
            if Screen == "Main" then
                if Selection > 1 then
                    Selection = 0
                elseif Selection < 0 then
                    Selection = 1
                end
            elseif Screen == "PlaySongs" then
                if Selection > #fs.list("songs") then
                    Selection = 0
                elseif Selection < 0 then
                    Selection = #fs.list("songs")
                end
            else
                Selection = 0
            end
        elseif key == keys.enter then
            if Screen == "Main" then
                if Selection == 0 then
                    Screen = "PlaySongs"
                    Selection = 0
                end
            elseif Screen == "PlaySongs" then
                local songs = fs.list("songs")
                if Selection == #songs then
                    Screen = "Main"
                    Selection = 0
                else
                    local songname = songs[Selection+1]
                    local song = fs.open("songs/" .. songname, "r").readLine()
                    if PlaySong(song) then
                        Playing = songname
                    else
                        print("failed to load")
                    end
                    Screen = "Song"
                    Selection = 0
                end
            elseif Screen == "Song" then
                if Selection == 0 then
                    Playing = nil
                    Screen = "PlaySongs"
                    Selection = 0
                end
            end
        end
        UpdateScreen()
    end
end

parallel.waitForAny(Main, function()
    while true do
        if Playing ~= nil then
            for num,chunk in pairs(SongData) do
                UpdateScreen()
                WriteCenter("Chunk #" .. num .. "/" .. #SongData)
                local buffer = decoder(chunk)

                while not speaker.playAudio(buffer) do
                    os.pullEvent("speaker_audio_empty")
                end

                if Playing == nil then
                    break
                end
            end
        else
            sleep(0.1)
        end
    end
end)