NBS API

-- NoteBlock Song API
-- by MysticT

-- yield to avoid error
local function yield()
    os.queueEvent("fake")
    os.pullEvent("fake")
end

-- read short integer (16-bit) from file
local function readShort(file)
    return file.read() + file.read() * 256
end

-- read integer (32-bit) from file
local function readInt(file)
    return file.read() + file.read() * 256 + file.read() * 65536 + file.read() * 16777216
end

-- read string from file
local function readString(file)
    local s = ""
    local len = readInt(file)
    for i = 1, len do
        local c = file.read()
        if not c then
            break
        end
        s = s..string.char(c)
    end
    return s
end

-- read nbs file header
local function readNBSHeader(file)
    local header = {}
    header.lenght = readShort(file)
    header.height = readShort(file)
    header.name = readString(file)
    if header.name == "" then
        header.name = "Untitled"
    end
    header.author = readString(file)
    if header.author == "" then
        header.author = "Unknown"
    end
    header.original_author = readString(file)
    if header.original_author == "" then
        header.original_author = "Unknown"
    end
    header.description = readString(file)
    header.tempo = readShort(file) / 100
    header.autosave = file.read()
    header.autosave_duration = file.read()
    header.time_signature = file.read()
    header.minutes_spent = readInt(file)
    header.left_clicks = readInt(file)
    header.right_clicks = readInt(file)
    header.blocks_added = readInt(file)
    header.blocks_removed = readInt(file)
    header.filename = readString(file)
    return header
end

-- jump to the next tick in the file
local function nextTick(file, tSong)
    local jump = readShort(file)
    for i = 1, jump - 1 do
        table.insert(tSong, {})
    end
    return jump > 0
end

-- read the notes in a tick
local function readTick(file)
    local t = {}
    local jump = readShort(file)
    while jump > 0 do
        local instrument = file.read() + 1
        if instrument > 5 then
            return nil, "Can't convert custom instruments"
        end
        local note = file.read() - 33
        if note < 0 or note > 24 then
            return nil, "Notes must be in Minecraft's 2 octaves"
        end
        if not t[instrument] then
            t[instrument] = {}
        end
        table.insert(t[instrument], note)
        jump = readShort(file)
    end
    return t
end

-- API functions

-- save a converted song to a file
function saveSong(tSong, sPath)
    local file = fs.open(sPath, "w")
    if file then
        file.write(textutils.serialize(tSong))
        file.close()
        return true
    end
    return false, "Error opening file "..sPath
end

-- load and convert an .nbs file and save it
function load(sPath, bVerbose)
    local file = fs.open(sPath, "rb")
    if file then
        if bVerbose then
            print("Reading header...")
        end
        local tSong = {}
        local header = readNBSHeader(file)
        tSong.name = header.name
        tSong.author = header.author
        tSong.original_author = header.original_author
        tSong.lenght = header.lenght / header.tempo
        tSong.delay = 1 / header.tempo
        if bVerbose then
            print("Reading ticks...")
        end
        while nextTick(file, tSong) do
            local tick, err = readTick(file, tSong)
            if tick then
                table.insert(tSong, tick)
            else
                file.close()
                return nil, err
            end
            yield()
        end
        file.close()
        return tSong
    end
    return nil, "Error opening file "..sPath
end