Split reroll-determining to own function

Aids unit testing which is needed for good practice and as we
are seeing bugs creep in around unnecessary rerolls

dice.ts

@@ -259,6 +259,49 @@ class Asphodice extends D10 {
 	 * - dice: Array - final outcome
 	 * - balance: number - +/- of outcomes (successes/failures)
 	 */
+
+	/**
+	 * 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{
+		// 1. if no re-rolls we can finish here
+		if (!(resultDice.includes(this.passCrit) || resultDice.includes(this.failCrit))) {
+			// results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);
+			return false;
+		}
+
+		// count successes and fails
+		let rerollGood = countOccurrencesOfNumber(resultDice, this.passCrit);
+		let rerollBad = countOccurrencesOfNumber(resultDice, this.failCrit);
+
+		// 2. only reroll if they don't cancel each other out
+		if (rerollGood == rerollBad) {
+			// console.log("Good = Bad, no need to reroll");
+			return false;
+			// results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);
+		}
+
+		// 3. If all dice are above/below cutoff we don't need to reroll
+		if (this.allAboveCutOff(resultDice)) {
+			console.log("All above cutoff, auto-success", resultDice);
+			return false;
+		} else if (this.allBelowCutOff(resultDice)) {
+			console.log("All below cutoff, auto-fail", resultDice);
+			return false;
+		}
+
+		// We should re-roll
+		return true;
+
+	}
+
 	roll (numToRoll: number): DiceResult {
 		let results: DiceResult = { total: 0, dice: [] };
 
@@ -266,48 +309,21 @@ class Asphodice extends D10 {
 		for (let i = 0; i < numToRoll; i++) {
 			results.dice.push(randIntMinOne(this.sides));
 		}
-
-		// Check for re-rolls
-		// 1. if no re-rolls we can finish here
-		if (!(results.dice.includes(this.passCrit) || results.dice.includes(this.failCrit))) {
-			// results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);
-			results.reroll = false;
-		} else {
-			// count successes and fails
-			let rerollGood = countOccurrencesOfNumber(results.dice, this.passCrit); 
-			let rerollBad = countOccurrencesOfNumber(results.dice, this.failCrit); 
-			
-			// 2. only reroll if they don't cancel each other out
-			if (rerollGood == rerollBad) {
-				// console.log("Good = Bad, no need to reroll");
-				results.reroll = false;
-				// results.total = results.dice.reduce((acc: number, curr: number) => acc + curr);
-			} 
-			// If all dice are above/below cutoff we don't need to reroll
-			// 3a. Above
-			else if (this.allAboveCutOff(results.dice)) {
-				console.log("All above cutoff, auto-success", results.dice);
-				results.reroll = false;
-		       	} 
-			// 3b. Below
-			else if (this.allBelowCutOff(results.dice)) {
-				console.log("All below cutoff, auto-fail", results.dice);
-				results.reroll = false;
-		       	} 
-			// Reroll
-			else {
-				// Reminder: arr1 = arr2 is a copy by reference!
-				let olddice = results.dice.slice();
-				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;
+		// 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);