'use strict';


const DEFAULT_WEIGHT_MAX = 4;


const graph_proto = {
	connect: function(source, sink, weight) {
		return network_connect(this, source, sink, weight);
	},
};

export function network(input_count, internal_count, output_count, weight_max = 4) {
	const count = input_count + internal_count + output_count;
	const n = Object.create(graph_proto);
	n.input_count = input_count;
	n.output_count = output_count;
	n.adjacency = new Array(count).fill([]);
	n.weight = [];
	return Object.freeze(n);
}


function is_input(n, index) {
	return index < n.input_count;
}
function is_output(n, index) {
	return index >= (n.adjacency.length - n.output_count);
}


function network_connect(n, source, sink, weight) {
	if (is_input(n, sink)) {
		// inputs cannot be sinks
		throw new Error("attempt to use input as sink");
	}
	if (is_output(n, source)) {
		// outputs cannot be sources
		throw new Error("attempt to use output as source");
	}

	const nn = Object.create(graph_proto);
	nn.input_count = n.input_count;
	nn.output_count = n.output_count;
	nn.adjacency = n.adjacency.map((row, i) => {
		if (i === source && i === sink) {
			// self-loop
			return [...row, 2];
		} else if (i === source) {
			return [...row, 1];
		} else if (i === sink) {
			return [...row, -1];
		} else {
			return [...row, 0];
		}
	});
	nn.weight = [...n.weight, weight];

	return Object.freeze(nn);
}