dice-roller/src/ts/asphodice.ts

const util = require('util');

/**
 * Counts the occurrences of a number in an array of numbers
 *
 * @param inputArray - array of numbers
 * @param checkNumber - number to count occurrences of
 * @returns number of occurrences
 *
 */
function countOccurrencesOfNumber(inputArray: Array<number>, checkNumber: number): number {
        return inputArray.filter(c => c === checkNumber).length;
}

/**
 * Generate a random integer between *1* and `max` (inclusive)
 *
 * @param max - upper bound of random integer to generate
 * @returns random integer
 */
function randIntMinOne(max: number): number {
	return (1 + Math.floor(Math.random() * Math.floor(max)));
}

interface Dice {
	readonly sides: number;
	readonly type: string;
}

export enum Outcomes {
	Success = "Success",
	Fail = "Failure",
	CritSuccess = "Critical Success",
	CritFail = "Critical Failure",
	Other = "Something Else"
}

export interface DiceResult {
	total: number;
	dice: Array<number>;
	olddice?: Array<number>;
	reroll?: boolean;
	outcome?: Outcomes;
	balance?: number;

}

/**
 * Simple d10, implements `roll()`
 */
class D10 implements Dice {
	sides: number = 10;
	type: string = "d10"

	roll(numberToRoll: number): DiceResult {
		let results: DiceResult = { total: 0, dice: [] };
		for (let i = 0; i < numberToRoll; i++) {
			results.dice.push(randIntMinOne(this.sides));
		}

		results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);

		return results;
	}

	[util.inspect.custom](): string {
		return this.type;
	}

	/**
	 * Roll a specified number of dice
	 *
	 * @param numberToRoll - integer number of dice to roll
	 * @returns DiceResult: .total and .dice (individual dice)
	 *
	 * @example Roll 4d10
	 *
	 * ```
	 * D10.roll(4)
	 * { total: 16, dice [ 3, 5, 6, 2] }
	 *
	 */
}

export class Asphodice extends D10 {
	readonly type: string = "asphodice";
	readonly passCrit: number = 10;
	readonly failCrit: number = 1;
	readonly successCutOff: number = 6; // this or larger

	/**
	 * Re-roll the high dice (ie >= 6) for a chance of failure
	 * happens on eg 1
	 *
	 * @remarks
	 * Basically we want to remove a die from the original result,
	 * as long as that die isn't a 10, and is above the
	 * cutoff. So we filter to get rerollCandidates, find the
	 * highest value and get the index of that value in the
	 * original results. We use that to splice() out (remove) that
	 * value and push the rerolled dice onto the modified array
	 *
	 * @param rerollDice
	 * @returns rerollOutcome
	 *
	 * @example Re-roll High Dice on 1
	 * ```
	 * rerollHighDice([8, 1, 1, 4, 7, 10]);
	 * [ 1, 1, 4, 7, 10, 6]
	 * ```
	 *
	 * ## Explanation
	 *
	 * - first filter dice to be not 10 and >= 6 (see {@link Asphodice.successCutOff})
	 * - rerollCandidates are [8, 7]
	 * - max([8, 7] = 8
	 * - indexOf(8) = 0
	 * - rerollResult = 6 (see {@link randIntMinOne()})
	 * - `splice()` replaced dice out of array = [ 1, 1, 4, 7, 10 ]
	 * - `push()` new dice = [ 1, 1, 4, 7, 10, 6]
	 */
	rerollHighDice (rerollDice: Array<number>): Array<number> {
		let rerollCandidates: Array<number> = rerollDice.filter(die => (die < 10 && die >= this.successCutOff));
		let maxValue: number = Math.max(...rerollCandidates);
		let maxIndex = rerollDice.indexOf(maxValue);
		let rerollResult: number = randIntMinOne(this.sides);

		rerollDice.splice(maxIndex, 1);
		rerollDice.push(rerollResult);
		return rerollDice
	}

	/**
	 * Re-roll low dice (ie < 6) for chance of success (ie getting >= 6)
	 *
	 * @remarks
	 *
	 * Generally happens on a 10.
	 *
	 * @see {@link Asphodice.rerollHighDice} for a fuller explanation
	 * for what process in opposite direction
	 */
	rerollLowDice (rerollDice: Array<number>): Array<number> {
		let rerollCandidates: Array<number> = rerollDice.filter(die => (die > 1 && die < this.successCutOff));
		let minValue: number = Math.min(...rerollCandidates);
		let minIndex = rerollDice.indexOf(minValue);
		let rerollResult: number = randIntMinOne(this.sides);

		rerollDice.splice(minIndex, 1);
		rerollDice.push(rerollResult);
		return rerollDice
	}

	/**
	 * Used to determine if all dice are above Asphodice.successCutOff
	 *
	 * @param checkDice - Array of Dice to test
	 *
	 * @see {@link Asphodice.roll} where it is used to determine if
	 * a re-roll can be skipped
	 *
	 * @see {@link allBelowCutOff} also.
	 */
	allAboveCutOff (checkDice: Array<number>): boolean {
		// if filtering those *below* cutoff results in empty set
		// then all must be above cutoff
		return ((checkDice.filter(die => die < this.successCutOff).length == 0));
	}

	/**
	 * Used to determine if all dice are below Asphodice.successCutOff
	 *
	 * @param checkDice - Array of Dice to test
	 *
	 * @see {@link Asphodice.roll} where it is used to determine if
	 * a re-roll can be skipped
	 *
	 * @see {@link allAboveCutOff} also.
	 */
	allBelowCutOff (checkDice: Array<number>): boolean {
		// if filtering those *above or equal to* cutoff results in empty set
		// then all must be below cutoff
		return ((checkDice.filter(die => die >= this.successCutOff).length == 0));
	}

	/**
	 * Determine balance of outcomes - ie successes minus failures
	 *
	 * @remarks
	 *
	 * Success = 1, failure = -1
	 *
	 * Particularly for Asphodice, we aren't terribly concerned with the
	 * numeric sum total of the dice values, we are more concerned with
	 * the overall outcome (see {@link Outcomes}) and for narrative purposes
	 * perhaps the balance of outcomes; for example, 1 success may be
	 * narrated differently than 4 successes.
	 *
	 * **Special note**: This ignores crits! **End special note**
	 *
	 * TODO: Special consideration of a single die roll (?)
	 *
	 * @param resultDice - the final dice after any re-rolls
	 * @returns Single positive/negative number with balance of roll outcomes
	 *
	 * @example Count Outcomes of 5 Dice
	 * ```
	 * countOutcomeBalance([ 7, 4, 4, 9, 1 ])
	 * -1
	 * ```
	 *
	 * - 7 and 9 are above successCutOff → +2
	 * - 4, 4, 1 are below successCutOff → -3
	 */
	countOutcomeBalance (resultDice: Array<number>): number{
		// fun with ternary operators
		return resultDice.reduce(
			(acc: number, curr: number) =>
			{ return (curr < this.successCutOff) ? acc - 1 : acc + 1 },
			0);
			// PS also good practice to supply initialValue (0)
	}

	/**
	 * Determine and return outcome of roll
	 *
	 * @remarks
	 *
	 * Determines outcome as in "Success", "Failure", etc. Assumes that `resultDice` is
	 * the 'final' result after any rerolls.
	 *
	 * @see {@link:countOutcomeBalance}
	 */
	checkOutcome (resultDice: Array<number>): Outcomes{
		// Note: currently, one success = Success, regardless of number of failures
		// TODO: Critical failures, once decided with Mao
		if (this.allBelowCutOff(resultDice)) {
			return Outcomes.Fail;
		} else {
			return Outcomes.Success;
		}
	}

	/**
	 * 'Cancel out' reroll dice
	 *
	 * @remarks
	 *
	 * Helper function.
	 *
	 * **In the context of deciding a reroll only**, the reroll dice can
	 * 'cancel' each other out. The dice themselves remain intact for the
	 * purposes of determining the final outcome.
	 *
	 * @returns Filtered dice
	 */
	cancelRerollDice (resultDice: Array<number>): Array<number> {
		// Naive approach for now:
		// - count 10s and 1s
		// - remove all 10s and 1s from input array
		// - re-add 10s/1s after 'cancelling'
		let tens = 0;
		let ones = 0;

		// count
		for (let die of resultDice) {
			if (die === 10) {
				tens++;
			} else if (die === 1) {
				ones++;
			}
		}

		// remove any reroll dice
		let outputDice = resultDice.filter( die => (die != 1 && die != 10) );

		let balance = tens - ones;

		if (balance < 0) {
			// add balance of ones
			outputDice.push(...Array(Math.abs(balance)).fill(1));
		} else if (balance > 0) {
			// add balance of tens
			outputDice.push(...Array(Math.abs(balance)).fill(10));
		}

		return outputDice;
	}

	/**
	 * Determines if a reroll is needed
	 *
	 * @remarks
	 *
	 * In some cases we don't reroll:
	 *  - reroll dice cancel each other out
	 *  - all are above cutoff (=> auto-success -- NB TODO crits)
	 *  - all below cutoff
	 */
	rerollNeeded(resultDice: Array<number>): boolean{
		// 'Cancel out' matching re-roll dice
		let cancelledDice = this.cancelRerollDice(resultDice);

		// 1. if no re-rolls we can finish here
		if (!(cancelledDice.includes(this.passCrit) || resultDice.includes(this.failCrit))) {
			return false;
		}

		// count successes and fails
		let rerollGood = countOccurrencesOfNumber(cancelledDice, this.passCrit);
		let rerollBad = countOccurrencesOfNumber(cancelledDice, this.failCrit);

		// 2. only reroll if they don't cancel each other out
		if (rerollGood == rerollBad) {
			return false;
		}

		// 3. If all dice are above/below cutoff we don't need to reroll
		if (this.allAboveCutOff(cancelledDice) || this.allBelowCutOff(cancelledDice)) {
			return false;
		}

		// We should re-roll
		return true;

	}

	/**
	 * Roll an Asphodie or Asphodice
	 *
	 * @param numToRoll
	 * @returns a {@link DiceResult} with additional properties:
	 * - reroll: boolean - whether we rerolled
	 * - olddice: Array - original roll
	 * - dice: Array - final outcome
	 * - balance: number - +/- of outcomes (successes/failures)
	 */
	roll (numToRoll: number): DiceResult {
		let results: DiceResult = { total: 0, dice: [] };

		// Initial roll
		for (let i = 0; i < numToRoll; i++) {
			results.dice.push(randIntMinOne(this.sides));
		}
		// Reroll?
		if (this.rerollNeeded(results.dice)) {
			// Reminder: arr1 = arr2 is a copy by reference!
			let olddice = results.dice.slice();
			let rerollGood = countOccurrencesOfNumber(olddice, this.passCrit);
			let rerollBad = countOccurrencesOfNumber(olddice, this.failCrit);
			if (rerollGood > rerollBad) {
				// Re-roll low (<6) dice for chance of success
				results.dice = this.rerollLowDice(results.dice);
			} else {
				// Re-roll high (>=6) dice for chance of failure
				results.dice = this.rerollHighDice(results.dice);
			}
			results.olddice = olddice;
			results.reroll = true;
		}

		results.balance = this.countOutcomeBalance(results.dice);
		results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);

		// Finally, once we're done with rerolls etc, determine outcome
		results.outcome = this.checkOutcome(results.dice);

		return results;
	}
}