src/BaseCounter.js

import {NotImplementedError} from '@failure-abstraction/error';
import {nlargest} from '@data-structure/heapq';

import counts from './counts.js';

export default function BaseCounter(Map, Dict) {
	const Counter = function (iterable) {
		this.container = new Map();

		if (iterable !== null) this.update(iterable);
	};

	Counter.prototype = new Dict();

	// eslint-disable-next-line no-unused-vars
	Counter.fromkeys = function (seq, value = null) {
		throw new NotImplementedError(
			'Counter.fromkeys() is undefined.  Use Counter(iterable) instead.',
		);
	};

	Counter.prototype.get = function (key) {
		if (this.has(key)) return this.container.get(key);

		return 0;
	};

	Counter.prototype.elements = function* () {
		for (let [key, count] of this) {
			while (count-- > 0) yield key;
		}
	};

	Counter.prototype.increment = function (key, amount = 1) {
		this.set(key, this.get(key) + amount);
	};

	Counter.prototype.decrement = function (key, amount = 1) {
		this.increment(key, -amount);
	};

	Counter.prototype.update = function (iterable) {
		for (const key of iterable) this.increment(key);
	};

	Counter.prototype.add = function (other) {
		for (const [key, count] of other) this.increment(key, count);
	};

	Counter.prototype.subtract = function (other) {
		for (const [key, count] of other) this.decrement(key, count);
	};

	Counter.prototype.most_common = function (n = this.len()) {
		return nlargest(counts, n, this);
	};

	return Counter;
}