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local gp3 = (function()
  local gp3 = {}

  local dfpwmSecond = 6000
  local pcmSecond = dfpwmSecond * 8
  local padChar = "\0"

  local pcmFormat = string.rep("b", pcmSecond)
  local packedPcmFormat = "c48000"
  local firstFormat = "> c48000 c4"
  local secondFormat = "> s2 H H B s1"
  local checksumFormat = "> I4"
  local firstFormatSize = string.packsize(firstFormat)

  local POLY = 0xEDB88320
  local crc32_table = {}
  for i = 0, 255 do
      local crc = i
      for _ = 1, 8 do
          if bit32.band(crc, 1) ~= 0 then
              crc = bit32.bnot(bit32.rshift(crc, 1), POLY)
          else
              crc = bit32.rshift(crc, 1)
          end
      end
      crc32_table[i] = bit32.band(crc, 0xFFFFFFFF)
  end
  local function crc32(data)
      local sbyte = string.byte
      local band, xor, rshift, bnot = bit32.band, bit32.bxor, bit32.rshift, bit32.bnot
      local crc = 0xFFFFFFFF
      for i = 1, #data do
          local byte = sbyte(data, i)
          local idx = band(xor(crc, byte), 0xFF)
          crc = xor(rshift(crc, 8), crc32_table[idx])
      end
      return bnot(crc) % 0x100000000
  end

  local function unpackPcm(pcm)
      if #pcm < pcmSecond then
          local pad = pcmSecond - #pcm
          pcm = pcm .. string.rep(padChar, pad)
      end

      return { string.unpack(pcmFormat, pcm) }
  end

  local function splitLayout(str)
      local layout = {}
      for ch in str:gmatch("[^|]+") do
          table.insert(layout, ch)
      end
      return layout
  end

  function gp3.decode(packet)
      local output = {
          channels = {},
          layout = {}
      }

      if #packet < firstFormatSize then
          local track = packet:sub(1, pcmSecond)
          return nil, unpackPcm(track)
      end

      local track, checksum, pos = string.unpack(firstFormat, packet)
      local calcChecksum = crc32(track)
      local firstPcm = unpackPcm(track)
      if calcChecksum ~= string.unpack(checksumFormat, checksum) then
          return nil, firstPcm
      end

      local details, total, current, extraChannels, layout, pos = string.unpack(secondFormat, packet:sub(pos))
      output.details = details
      output.totalSeconds = total
      output.currentSeconds = current
      output.channelCount = extraChannels + 1
      output.layout = splitLayout(layout)

      table.insert(output.channels, firstPcm)

      local pos, track = pos, nil
      for i = 1, extraChannels do
          track, pos = string.unpack(packedPcmFormat, packet, pos)
          table.insert(output.channels, unpackPcm(track))
      end

      return output
  end

  return gp3
end)()

local args = {...}
local radio = peripheral.find("radio_tower")

local frequency = tonumber(args[1]) or 5555

radio.setFrequency(frequency)

local pcmSecond = 48000
local formats = {}

formats.pcm = string.rep("b", pcmSecond)
formats.track = "c" .. pcmSecond -- 1 second of PCM
-- big endian, track, crc32, track details, total seconds, current seconds (from 0), extra channels, channels layout
formats.packet = "> " .. formats.track .. " c4 s2 H H B s1"

local speaker = peripheral.find("speaker")
speaker.stop()
local buffer = {}
local tryPlay = true

local function decode(packet)
    local ok, track, details = pcall(function()
        local track, checksum, details, total, current, extraChannels, layout, pos = string.unpack(formats.packet, packet)
        local buffer = { string.unpack(formats.pcm, track) }

        return buffer, details
    end)

    if not ok then
        return nil, track
    end

    return track, details
end

local function submitNext()
    local chunk = table.remove(buffer, 1)
    if chunk then
        speaker.playAudio(chunk)
        tryPlay = false
    end
    if not chunk then
        tryPlay = true
    end
end

local function queue(chunk)
    table.insert(buffer, chunk)
    print(os.clock(), "Buffer Size:", #buffer)
    if tryPlay then
        print("Buffering...")
        if #buffer > 2 then
            submitNext()
        end
    end
end

parallel.waitForAny(function()
    while true do
        local _, _, data = os.pullEvent("radio_message")
        local track, fallback = gp3.decode(data)
        --local buffer, details = decode(data)
        if track then
            queue(track.channels[1])
            print(track.details)
        else
            printError("Could not decode. fallback")
            queue(fallback)
        end
    end
end, function()
    while true do
        os.pullEvent("speaker_audio_empty")
        submitNext()
    end
end)

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