/*
 * bytebeat-render.js [Node]
 *
 * Node.JS: Bytebeat generator
 *
 * Note: Calls `ffmpeg` to convert output raw audio to a WAVE file
 *
 * Warning: The current result is quick and dirty. Not for educational or
 * production purposes.
 *
 * TODO: Fix signed bytebeat and floatbeat
 * TODO: Add support for arbitrary (1 <= integer <= 2^32 - 1, because of
 * WAVE/RIFF format limitations) audio bit depth
 * TODO: Do not use FFmpeg, use `pcm.js` or simply write the WAVE/RIFF file
 * headers
 *
 * Author: Intel A80486DX2-66
 * License: Creative Commons Zero 1.0 Universal
 */

const { appendFileSync, unlinkSync, writeFileSync } = require("fs")
const { tmpdir } = require("os")
const { execSync } = require("child_process")
const { basename } = require("path")

let BUFFER_SIZE = 65536 // feel free to change this
const LIGHTNING_MODE = false // disables sequential file write optimization,
//                              feel free to enable this

const SAMPLE_RATE = 8000 // feel free to change this
const SECONDS = 30 // feel free to change this
const CHANNELS = 1 // feel free to change this

const FINAL_SAMPLE_RATE = 44100 // feel free to change this
const FINAL_SAMPLE_RATE_CONVERSION = SAMPLE_RATE / FINAL_SAMPLE_RATE / CHANNELS
const SAMPLES = SECONDS * FINAL_SAMPLE_RATE // feel free to change this
const PRODUCT = SAMPLES * CHANNELS
BUFFER_SIZE = LIGHTNING_MODE ? PRODUCT : BUFFER_SIZE

const TYPE_BYTEBEAT = 0
const TYPE_SIGNED_BYTEBEAT = 1
const TYPE_FLOATBEAT = 2

const SELECTED_TYPE = TYPE_BYTEBEAT // feel free to change this

// for bytebeat
var int = x => Math.floor(x)
var abs = Math.abs
var acos = Math.acos
var acosh = Math.acosh
var asin = Math.asin
var asinh = Math.asinh
var atan = Math.atan
var atanh = Math.atanh
var cbrt = Math.cbrt
var cos = Math.cos
var cosh = Math.cosh
var exp = Math.exp
var floor = Math.floor
var log = Math.log
var log2 = Math.log2
var max = Math.max
var min = Math.min
var PI = Math.PI
var pow = Math.pow
var random = Math.random
var sin = Math.sin
var sinh = Math.sinh
var sqrt = Math.sqrt
var tan = Math.tan
var tanh = Math.tanh

const generateAudio = t => {
	return t&t>>8
}

const clamp = (a, b, c) => max(min(a, c), b)

let lastCorrectSample = 127 // FIXME: guessed value

const constrainValue = sample => {
	if (isNaN(sample) || sample < 0)
		sample = lastCorrectSample
	else
		lastCorrectSample = sample

	switch (SELECTED_TYPE) {
	case TYPE_BYTEBEAT:
		return sample & 255
	case TYPE_SIGNED_BYTEBEAT:
		return ((sample + 127) & 255) - 128
	case TYPE_FLOATBEAT:
		// NOTE: temporary fix copied from a code by lehandsomeguy, see https://
		// www.reddit.com/r/bytebeat/comments/48r00a/floatbeat_test/
		return floor((clamp(sample, -0.9999, 0.9999) * 128) + 128)
	}
}

const random_choice = choices => choices[Math.floor(Math.random() * choices.length)]

const randomFileNameAlphabet =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-"

const generateRandomFilePath = () => {
	let res = tmpdir() + "/" + basename(__filename) + "_"
	for (let i = 0; i < 64; i++)
		res += random_choice(randomFileNameAlphabet)
	return res
}

let t = 0

let filePath = generateRandomFilePath()
writeFileSync(filePath, Buffer.alloc(0))

// the loop of sequential file writing, created to ease load on RAM
const buffer_max = Math.floor((PRODUCT + (BUFFER_SIZE - 1)) / BUFFER_SIZE),
      needTwoBuffers = buffer_max > 1, needSingleBuffer = !needTwoBuffers

let audioData = new Uint8Array(needSingleBuffer ? PRODUCT : BUFFER_SIZE)

for (let seq = 0; seq < buffer_max; seq++) {
	if (needTwoBuffers && (t + BUFFER_SIZE) >= PRODUCT) {
		let calculatedSize = PRODUCT - t
		audioData = new Uint8Array(calculatedSize)
	}

	for (let idx = 0; t < PRODUCT && idx < BUFFER_SIZE; idx++, t++) {
		let sample = generateAudio(t * FINAL_SAMPLE_RATE_CONVERSION)
		if (sample.constructor === Array)
			sample.forEach((sample, index) => {
				audioData[CHANNELS * idx + index] = constrainValue(sample)
			})
		else
			audioData[idx] = constrainValue(sample)
	}

	appendFileSync(filePath, Buffer.from(audioData.buffer))
}

execSync(
	`ffmpeg -f u8 -ar ${FINAL_SAMPLE_RATE} -ac ${CHANNELS} ` +
	`-i ${filePath} output_${+new Date()}.wav`)
unlinkSync(filePath)