#!/usr/bin/env luajit

-- Crappy demo: pushing audio samples with LuaJIT.

local function saw_osc(srate)
    local pos = 0
    return function(freq)
        local signal = pos - 0.25
        pos = math.fmod(pos + (0.5 * freq) / srate, 0.5)
        return signal
    end
end

local function sine_osc(srate)
    local pos = 0
    return function(freq)
        local signal = 0.25 * math.sin(pos * math.pi / srate)
        pos = pos + freq
        return signal
    end
end

local function waveshape(threshold, signal)
    if signal > threshold then
        return 0.1
    else
        return -0.1
    end
end

local function silly_filter()
    local state0 = 0
    local state1 = 0
    return function(cfreq, signal)
        local fa = 1 - cfreq
        local fb = 0.5 * (1 + (1 / fa))
        state0 = state0 * fa + cfreq * (signal + fb * (state0 - state1))
        state1 = fa * state1 + cfreq * state0
        return state1
    end
end

local function eg()
    local time = 0
    local charge = 0
    local state = 0
    local function trigger()
        time = 0
        state = 0
    end
    local function gen(attack, decay, sustain, release)
        local signal = charge
        if state == 0 then
            -- attack
            charge = charge + (1 - charge) * attack
            if 1 - charge < 0.01 then
                state = 1
            end
        elseif state == 1 then
            -- decay
            if decay < 0 then decay = 0 end
            charge = charge * (1 - decay)
            if charge < sustain then
                charge = sustain
                state = 2
            end
        elseif state == 2 then
            -- sustain
            if time > 2400 then
                state = 3
            end
        elseif state == 3 then
            -- release
            charge = charge * (1 - release)
        end
        time = time + 1
        return signal
    end
    return trigger, gen
end

local function delay(len)
    local line = {}
    local pos = 1
    return function(input)
        local signal = line[pos] or 0.0
        line[pos] = input + signal * 0.8
        pos = pos % len + 1
        return signal
    end
end

local notes = {
    110.0,
    130.81278265029931,
    164.81377845643496,
    220.0,
    110.0,
    130.81278265029931,
    164.81377845643496,
    220.0,
    87.307057858250971,
    110.0,
    130.81278265029931,
    164.81377845643496,
    87.307057858250971,
    110.0,
    130.81278265029931,
    164.81377845643496,

    110.0,
    130.81278265029931,
    164.81377845643496,
    220.0,
    110.0,
    130.81278265029931,
    164.81377845643496,
    220.0,
    82.40688922821748,
    110.0,
    130.81278265029931,
    164.81377845643496,
    82.40688922821748,
    110.0,
    130.81278265029931,
    164.81377845643496
}

local up_transpositions = {3, 5, 7}
local down_transpositions = {-5, -7}

local ffi = require "ffi"

ffi.cdef(io.popen("cpp -P /usr/include/alsa/asoundlib.h"):read("*a"))
local alsa = ffi.load "asound"

local function check(err, msg)
    if err < 0 then
        error(msg .. ": " .. ffi.string(alsa.snd_strerror(err)))
    end
end

local handle = ffi.new("snd_pcm_t *[1]")
local hw_params = ffi.new("snd_pcm_hw_params_t *[1]")
local srate = ffi.new("unsigned[1]", 48000)
local dir = ffi.new("int[1]", 0)
check(alsa.snd_pcm_open(handle, "default", alsa.SND_PCM_STREAM_PLAYBACK, 0),
      "Cannot open audio output device")
check(alsa.snd_pcm_hw_params_malloc(hw_params),
      "snd_pcm_hw_params_malloc failed")
check(alsa.snd_pcm_hw_params_any(handle[0], hw_params[0]),
      "snd_pcm_hw_params_any failed")
check(alsa.snd_pcm_hw_params_set_access(
        handle[0], hw_params[0], alsa.SND_PCM_ACCESS_RW_INTERLEAVED),
      "snd_pcm_hw_params_set_access failed")
check(alsa.snd_pcm_hw_params_set_format(
        handle[0], hw_params[0], alsa.SND_PCM_FORMAT_S16),
      "snd_pcm_hw_params_set_format failed")
check(alsa.snd_pcm_hw_params_set_rate_near(
        handle[0], hw_params[0], srate, dir),
      "snd_pcm_hw_params_set_rate_near failed")
check(alsa.snd_pcm_hw_params_set_channels(
        handle[0], hw_params[0], 1),
      "snd_pcm_hw_params_set_channels failed")
check(alsa.snd_pcm_hw_params(handle[0], hw_params[0]),
      "snd_pcm_hw_params failed")
alsa.snd_pcm_hw_params_free(hw_params[0])
check(alsa.snd_pcm_prepare(handle[0]), "snd_pcm_prepare failed")

local pos = 0
local noten = 1
local nsamp = srate[0]/10
local samples = ffi.new("int16_t[?]", nsamp)
local saw_osc_gen = saw_osc(srate[0])
local lfo_gen = sine_osc(srate[0])
local lfo2_gen = sine_osc(srate[0])
local lfo3_gen = sine_osc(srate[0])
local eg_trigger, eg_gen = eg()
local silly_filter_gen = silly_filter()
local de = delay(9000)
local transpose = 0
local transpose_ratio = 2

while true do
    for i = 0, nsamp-1 do
        if pos > 4800 then
            pos = 0
            eg_trigger()
            noten = noten + 1
            if noten > #notes then
                noten = 1
                local threshold = transpose / 48 + 0.5
                local delta
                if math.random() > threshold then
                    delta = up_transpositions[math.random(1, #up_transpositions)]
                else
                    delta = down_transpositions[math.random(1, #down_transpositions)]
                end
                transpose = transpose + delta
                transpose_ratio = math.pow(1.0594630943592953, transpose + 12)
            end
        end
        local saw_out = saw_osc_gen(notes[noten] * transpose_ratio)
        local square_out = waveshape(lfo_gen(0.25) * 0.7, saw_out)
        local mixer_out = 4.0 * saw_out * lfo2_gen(0.12) + 1.2 * square_out
        local eg_out = eg_gen(0.01, 0.00001 + (0.002*(lfo3_gen(0.05)+0.20)), 0.005, 0.0003)
        local vcf_out = silly_filter_gen(eg_out * 0.2 + 0.3, mixer_out * 0.01)
        local vca_out = vcf_out * (math.exp(eg_out)-1) * 5
        local delay_out = vca_out + 0.5 * de(vca_out)
        samples[i] = delay_out * 65000
        pos = pos + 1
    end
    check(alsa.snd_pcm_writei(handle[0], samples, nsamp),
          "snd_pcm_writei failed")
end
check(alsa.snd_pcm_drain(handle[0]),
      "snd_pcm_drain failed")
check(alsa.snd_pcm_close(handle[0]),
      "snd_pcm_close failed")