bracket.js

function generateWinnerBracket(playerCounts) {
	let winnerRounds = Math.ceil(Math.log2(playerCounts));
	const seeds = Array.apply(null, {length: playerCounts}).map((x, i) => i + 1);
	const rounds = [];
	const expectedNext = [];
	const expectedBuffer = [];
	for(let seedPower = 1; seedPower <= winnerRounds; seedPower++) {
		const round = {round: winnerRounds - seedPower + 1, matches: []};
		const availableSeeds = [];
		[].push.apply(availableSeeds, seeds.filter(x => x > (1 << (seedPower - 1)) && x <= (1 << seedPower)));
                [].push.apply(availableSeeds, seeds.filter(x => x <= (1 << (seedPower - 1))).slice(-(availableSeeds.length)));
		[].push.apply(expectedNext, expectedNext.splice(0).reduce(function(x, y) {
			if(availableSeeds.indexOf(y) >= 0) {
				x.push(y);
			}
			return x;
		}, []));
		availableSeeds.sort((x, y) => x - y);
		const pairSum = 1 + (1 << (seedPower));
		const matchCount = expectedNext.length || 1 << (seedPower - 1);
		for(let matchNum = 0; matchNum < matchCount; matchNum++) {
			let seedWin, seedLose;
			if (expectedNext.length <= 0) {
				seedWin = availableSeeds.shift();
			} else {
				seedWin = expectedNext.shift();
			}
			seedLose = pairSum - seedWin;
			[seedWin, seedLose].forEach(function(seedValue){
				if(availableSeeds.indexOf(seedValue) >= 0)
					availableSeeds.splice(availableSeeds.indexOf(seedValue), 1);
				expectedBuffer.push(seedValue);
			});
			round.matches.push({matchID: [seedPower, matchNum], pair: [seedWin, seedLose]});
			console.log(seedPower, matchNum, [seedWin, seedLose]);
		}
		[].push.apply(expectedNext, expectedBuffer.splice(0));
		rounds.unshift(round);
	}
	return rounds;
}

function generateDoubleBracket(playerCounts, options){
	options = options || {};
	let winnerRounds = 1;
	let loserRounds = 0;
	if (options.split == "lower") {
		winnerRounds += Math.floor(Math.log2(playerCounts));
		loserRounds += 1;
	} else {
		winnerRounds += Math.ceil(Math.log2(playerCounts));
	}
	loserRounds += 2 * (1 + Math.max(0, winnerRounds - 3));
	const seeds = Array.apply(null, {length: playerCounts}).map((x, i) => i + 1);
	const rounds = [];

	console.log(playerCounts);
	console.log(winnerRounds, "W", loserRounds, "L");
	generateWinnerBracket(playerCounts);
}

generateDoubleBracket(32);
generateDoubleBracket(44, {split: "upper"});
generateDoubleBracket(44, {split: "lower"});