Constellations/js/Constellation.js

import generate from Grid.Util;

return {
	random: random
};

function random(size) {
	var indices = Array.from({length: size}).map(function(x, i) {return i;});
	var previousColumn;
	var columns = []
	while(columns.length < 8) {
		previousColumn = pickNextColumn(indices, previousColumn)
		columns.push(previousColumn);
	}
	return generate(size, size, function(cell) {
		return columns[cell.row] == cell.column;
	});
}

function pickNextColumn(columnsLeft, previousColumn) {
	var parts = contiguousParts(columnsLeft);
	if(parts.length == 1 && columnsLeft.length == 4) {
		var candidateColumns = [null, columnsLeft[1], columnsLeft[2], null];
	} else if(parts.length == 2 && columnsLeft.length < 5
		&& Math.min(parts[0].length, parts[1].length) < 2) {
		candidateColumns = parts[0].length == 1 ? [null].concat(parts[1]) : parts[0];
	} else {
		var candidateColumns = columnsLeft;
	}
	candidateColumns = candidateColumns.map(maskAround(previousColumn));
	return columnsLeft.splice(pickIndex(candidateColumns), 1)[0];
}

function maskAround(c0) {
	return function(c1) {
		return Math.abs(c1 - c0) < 2 ? null : c1;
	};
}

function pickIndex(t) {
	var o = {};
	var definedCount = 0;
	for(var i = 0; i < t.length; i++) {
		if(t[i] != undefined) {
			o[definedCount] = i;
			definedCount++;
		}
	}
	return o[Math.floor(definedCount * Math.random())];
}

function contiguousParts(t) {
	var parts = [];
	var current = [];
	for(var i = 0; i < t.length; i++) {
		if(current.length < 1 || t[i] - current[current.length-1] == 1) {
			current.push(t[i]);
		} else {
			parts.push(current);
			current = [t[i]];
		}
	}
	parts.push(current);
	return parts;
}