dwi converter

local note_lookup_table = {
    ['1000'] = '4',    ['0100'] = '2',
    ['0010'] = '8',    ['0001'] = '6',
    ['1100'] = '1',    ['1010'] = '7',
    ['1001'] = 'B',    ['0110'] = 'A',
    ['0101'] = '3',    ['0011'] = '9',
    ['1110'] = '<81>', ['0111'] = '<83>',
    ['1101'] = '<61>', ['1011'] = '<8B>',
    ['1111'] = '<19>', ['0000'] = '0',
}

function string:getFieldContents(field)
    local _, idx = self:find('#' .. field .. ':')
    local str = self:match('%b:;', idx)
    return str:sub(2, #str - 1)
end

local function processMeasure(measure)
    local beat_notes = {''} -- reserve beat_notes[1] for opening tag if necessary
    local note_count = 0
    for note in measure:gmatch('%d%d%d%d') do
        table.insert(beat_notes, note_lookup_table[note])
        table.insert(beat_notes, '') -- for possible note padding
        note_count = note_count + 1
    end

    if note_count == 4 then
        for i=3, 9, 2 do beat_notes[i] = '0' end -- add appropriate note padding
    elseif note_count == 8 then
    elseif note_count == 12 then
        for i=3, 25, 2 do beat_notes[i] = '0' end
        beat_notes[1] = '['; table.insert(beat_notes, ']')
    elseif note_count == 16 then
        beat_notes[1] = '('; table.insert(beat_notes, ')')
    elseif note_count == 24 then
        beat_notes[1] = '['; table.insert(beat_notes, ']')
    elseif note_count == 32 then
        for i=3, 65, 2 do beat_notes[i] = '0' end
        beat_notes[1] = '{'; table.insert(beat_notes, '}')
    elseif note_count == 48 then
        for i=3, 97, 2 do beat_notes[i] = '000' end
        beat_notes[1] = '`'; table.insert(beat_notes, '\'')
    elseif note_count == 64 then
        beat_notes[1] = '{'; table.insert(beat_notes, '}')
    elseif note_count == 96 then
        for i=3, 193, 2 do beat_notes[i] = '0' end
        beat_notes[1] = '`'; table.insert(beat_notes, '\'')
    elseif note_count == 192 then
        beat_notes[1] = '`'; table.insert(beat_notes, '\'')
    else
        return nil -- invalid note count
    end

    return table.concat(beat_notes) .. '\n'
end

local function smToDwi(full_path)
    -- open sm file to read contents into string
    local sm_file
    do
        local tmp = io.open(full_path .. '.sm')
        sm_file = tmp:read('*a')
        tmp:close()
    end

    local changebpm = sm_file:getFieldContents('BPMS')
    local start_bpm
    do -- separate first bpm and bpm changes
        start_bpm = changebpm:match('%d+%.?%d*%s*=%s*(%d+%.?%d*)')
        local _, idx = changebpm:find('%d+%.?%d*%s*=%s*%d+%.?%d*%s*,')
        if idx then
            changebpm = changebpm:sub(idx + 1)
        else
            changebpm = ''
        end
    end

    -- multiply all measures by 4 to convert to beat counts
    local changebpm_str = {}
    if changebpm ~= '' then
        for beat, bpm, comma in changebpm:gmatch('(%d+%.?%d*)%s*(=%s*%d+%.?%d*)(,?)') do
            table.insert(changebpm_str, string.format("%.3f", tonumber(beat) * 4)..bpm)
            if comma ~= '' then table.insert(changebpm_str, ',') end
        end
    end

    -- process common .sm file fields
    local file_contents = {}
    table.insert(file_contents, '#TITLE:'         .. sm_file:getFieldContents('TITLE')                    .. ';\n')
    table.insert(file_contents, '#ARTIST:'        .. sm_file:getFieldContents('ARTIST')                   .. ';\n')
    table.insert(file_contents, '#FILE:'          .. sm_file:getFieldContents('MUSIC')                    .. ';\n')
    table.insert(file_contents, '#BPM:'           .. start_bpm                                            .. ';\n')
    table.insert(file_contents, '#GAP:'           .. tonumber(sm_file:getFieldContents('OFFSET')) * -1000 .. ';\n')
    table.insert(file_contents, '#SAMPLESTART:'   .. sm_file:getFieldContents('SAMPLESTART')              .. ';\n')
    table.insert(file_contents, '#SAMPLELENGTH:'  .. sm_file:getFieldContents('SAMPLELENGTH')             .. ';\n\n')
    if changebpm ~= '' then
        table.insert(file_contents, '#CHANGEBPM:' .. table.concat(changebpm_str)                          .. ';\n')
    end
    table.insert(file_contents, '#SINGLE:MANIAC:1:\n')

    do -- extract start of note data to end of file
        local _, idx = sm_file:find('%d+%.%d+%s*%:', idx)
        sm_file = sm_file:sub(idx + 1)
    end

    for measure in sm_file:gmatch('.-[,;]') do
        table.insert(file_contents, processMeasure(measure))
    end

    -- save converted file
    local dwi_file = io.open(full_path .. '.dwi', 'w')
    dwi_file:write(table.concat(file_contents)..'\n')
    dwi_file:close()
end

smToDwi('test')