Add 2014 DMG encounter difficulty calculation

Support the 2014 DMG encounter difficulty as an alternative to the 5.5e system behind the existing Rules Edition toggle. The 2014 system uses Easy/Medium/Hard/Deadly thresholds, an encounter multiplier based on monster count, and party size adjustment (×0.5–×5 range). - Extract RulesEdition to its own domain module - Refactor DifficultyTier to abstract numeric values (0–3) - Restructure DifficultyResult with thresholds array - Add 2014 XP thresholds table and encounter multiplier logic - Wire edition from context into difficulty hooks - Edition-aware labels in indicator and breakdown panel - Show multiplier, adjusted XP, and party size note for 2014 - Rename settings label from "Conditions" to "Rules Edition" - Update spec 008 with issue #23 requirements Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-04-04 14:52:23 +02:00
parent 94e1806112
commit 817cfddabc
17 changed files with 892 additions and 257 deletions
--- a/packages/domain/src/encounter-difficulty.ts
+++ b/packages/domain/src/encounter-difficulty.ts
@@ -1,13 +1,23 @@
-export type DifficultyTier = "trivial" | "low" | "moderate" | "high";
+import type { RulesEdition } from "./rules-edition.js";
+
+/** Abstract difficulty severity: 0 = negligible, 3 = maximum. Maps to filled bar count. */
+export type DifficultyTier = 0 | 1 | 2 | 3;
+
+export interface DifficultyThreshold {
+	readonly label: string;
+	readonly value: number;
+}

 export interface DifficultyResult {
 	readonly tier: DifficultyTier;
 	readonly totalMonsterXp: number;
-	readonly partyBudget: {
-		readonly low: number;
-		readonly moderate: number;
-		readonly high: number;
-	};
+	readonly thresholds: readonly DifficultyThreshold[];
+	/** 2014 only: the encounter multiplier applied to base monster XP. */
+	readonly encounterMultiplier: number | undefined;
+	/** 2014 only: monster XP after applying the encounter multiplier. */
+	readonly adjustedXp: number | undefined;
+	/** 2014 only: true when the multiplier was shifted due to party size (<3 or 6+). */
+	readonly partySizeAdjusted: boolean | undefined;
 }

 /** Maps challenge rating strings to XP values (standard 5e). */
@@ -74,6 +84,82 @@ const XP_BUDGET_PER_CHARACTER: Readonly<
 	20: { low: 6400, moderate: 13200, high: 22000 },
 };

+/** Maps character level (1-20) to XP thresholds (2014 DMG). */
+const XP_THRESHOLDS_2014: Readonly<
+	Record<number, { easy: number; medium: number; hard: number; deadly: number }>
+> = {
+	1: { easy: 25, medium: 50, hard: 75, deadly: 100 },
+	2: { easy: 50, medium: 100, hard: 150, deadly: 200 },
+	3: { easy: 75, medium: 150, hard: 225, deadly: 400 },
+	4: { easy: 125, medium: 250, hard: 375, deadly: 500 },
+	5: { easy: 250, medium: 500, hard: 750, deadly: 1100 },
+	6: { easy: 300, medium: 600, hard: 900, deadly: 1400 },
+	7: { easy: 350, medium: 750, hard: 1100, deadly: 1700 },
+	8: { easy: 450, medium: 900, hard: 1400, deadly: 2100 },
+	9: { easy: 550, medium: 1100, hard: 1600, deadly: 2400 },
+	10: { easy: 600, medium: 1200, hard: 1900, deadly: 2800 },
+	11: { easy: 800, medium: 1600, hard: 2400, deadly: 3600 },
+	12: { easy: 1000, medium: 2000, hard: 3000, deadly: 4500 },
+	13: { easy: 1100, medium: 2200, hard: 3400, deadly: 5100 },
+	14: { easy: 1250, medium: 2500, hard: 3800, deadly: 5700 },
+	15: { easy: 1400, medium: 2800, hard: 4300, deadly: 6400 },
+	16: { easy: 1600, medium: 3200, hard: 4800, deadly: 7200 },
+	17: { easy: 2000, medium: 3900, hard: 5900, deadly: 8800 },
+	18: { easy: 2100, medium: 4200, hard: 6300, deadly: 9500 },
+	19: { easy: 2400, medium: 4900, hard: 7300, deadly: 10900 },
+	20: { easy: 2800, medium: 5700, hard: 8500, deadly: 12700 },
+};
+
+/** 2014 encounter multiplier by number of enemy-side monsters. */
+const ENCOUNTER_MULTIPLIER_TABLE: readonly {
+	max: number;
+	multiplier: number;
+}[] = [
+	{ max: 1, multiplier: 1 },
+	{ max: 2, multiplier: 1.5 },
+	{ max: 6, multiplier: 2 },
+	{ max: 10, multiplier: 2.5 },
+	{ max: 14, multiplier: 3 },
+	{ max: Number.POSITIVE_INFINITY, multiplier: 4 },
+];
+
+/**
+ * Multiplier values in ascending order for party size shifting.
+ * Extends beyond the base table: x0.5 (6+ PCs, 1 monster) and x5 (<3 PCs, 15+ monsters)
+ * per 2014 DMG party size adjustment rules.
+ */
+const MULTIPLIER_STEPS = [0.5, 1, 1.5, 2, 2.5, 3, 4, 5] as const;
+
+/** Index into MULTIPLIER_STEPS for each base table entry (before party size adjustment). */
+const BASE_STEP_INDEX = [1, 2, 3, 4, 5, 6] as const;
+
+function getEncounterMultiplier(
+	monsterCount: number,
+	partySize: number,
+): { multiplier: number; partySizeAdjusted: boolean } {
+	const tableIndex = ENCOUNTER_MULTIPLIER_TABLE.findIndex(
+		(entry) => monsterCount <= entry.max,
+	);
+	let stepIndex: number =
+		BASE_STEP_INDEX[
+			tableIndex === -1 ? BASE_STEP_INDEX.length - 1 : tableIndex
+		];
+	let partySizeAdjusted = false;
+
+	if (partySize < 3) {
+		stepIndex = Math.min(stepIndex + 1, MULTIPLIER_STEPS.length - 1);
+		partySizeAdjusted = true;
+	} else if (partySize >= 6) {
+		stepIndex = Math.max(stepIndex - 1, 0);
+		partySizeAdjusted = true;
+	}
+
+	return {
+		multiplier: MULTIPLIER_STEPS[stepIndex] as number,
+		partySizeAdjusted,
+	};
+}
+
 /** All standard 5e challenge rating strings, in ascending order. */
 export const VALID_CR_VALUES: readonly string[] = Object.keys(CR_TO_XP);

@@ -90,14 +176,66 @@ export interface CombatantDescriptor {

 function determineTier(
 	xp: number,
-	low: number,
-	moderate: number,
-	high: number,
+	tierThresholds: readonly number[],
 ): DifficultyTier {
-	if (xp >= high) return "high";
-	if (xp >= moderate) return "moderate";
-	if (xp >= low) return "low";
-	return "trivial";
+	for (let i = tierThresholds.length - 1; i >= 0; i--) {
+		if (xp >= tierThresholds[i]) return (i + 1) as DifficultyTier;
+	}
+	return 0;
+}
+
+function accumulateBudget5_5e(levels: readonly number[]) {
+	const budget = { low: 0, moderate: 0, high: 0 };
+	for (const level of levels) {
+		const b = XP_BUDGET_PER_CHARACTER[level];
+		if (b) {
+			budget.low += b.low;
+			budget.moderate += b.moderate;
+			budget.high += b.high;
+		}
+	}
+	return budget;
+}
+
+function accumulateBudget2014(levels: readonly number[]) {
+	const budget = { easy: 0, medium: 0, hard: 0, deadly: 0 };
+	for (const level of levels) {
+		const b = XP_THRESHOLDS_2014[level];
+		if (b) {
+			budget.easy += b.easy;
+			budget.medium += b.medium;
+			budget.hard += b.hard;
+			budget.deadly += b.deadly;
+		}
+	}
+	return budget;
+}
+
+function scanCombatants(combatants: readonly CombatantDescriptor[]) {
+	let totalMonsterXp = 0;
+	let monsterCount = 0;
+	const partyLevels: number[] = [];
+
+	for (const c of combatants) {
+		if (c.level !== undefined && c.side === "party") {
+			partyLevels.push(c.level);
+		}
+		if (c.cr !== undefined) {
+			const xp = crToXp(c.cr);
+			if (c.side === "enemy") {
+				totalMonsterXp += xp;
+				monsterCount++;
+			} else {
+				totalMonsterXp -= xp;
+			}
+		}
+	}
+
+	return {
+		totalMonsterXp: Math.max(0, totalMonsterXp),
+		monsterCount,
+		partyLevels,
+	};
 }

 /**
@@ -107,41 +245,54 @@ function determineTier(
 */
 export function calculateEncounterDifficulty(
 	combatants: readonly CombatantDescriptor[],
+	edition: RulesEdition,
 ): DifficultyResult {
-	let budgetLow = 0;
-	let budgetModerate = 0;
-	let budgetHigh = 0;
-	let totalMonsterXp = 0;
+	const { totalMonsterXp, monsterCount, partyLevels } =
+		scanCombatants(combatants);

-	for (const c of combatants) {
-		if (c.level !== undefined && c.side === "party") {
-			const budget = XP_BUDGET_PER_CHARACTER[c.level];
-			if (budget) {
-				budgetLow += budget.low;
-				budgetModerate += budget.moderate;
-				budgetHigh += budget.high;
-			}
-		}
-
-		if (c.cr !== undefined) {
-			const xp = crToXp(c.cr);
-			if (c.side === "enemy") {
-				totalMonsterXp += xp;
-			} else {
-				totalMonsterXp -= xp;
-			}
-		}
+	if (edition === "5.5e") {
+		const budget = accumulateBudget5_5e(partyLevels);
+		const thresholds: DifficultyThreshold[] = [
+			{ label: "Low", value: budget.low },
+			{ label: "Moderate", value: budget.moderate },
+			{ label: "High", value: budget.high },
+		];
+		return {
+			tier: determineTier(totalMonsterXp, [
+				budget.low,
+				budget.moderate,
+				budget.high,
+			]),
+			totalMonsterXp,
+			thresholds,
+			encounterMultiplier: undefined,
+			adjustedXp: undefined,
+			partySizeAdjusted: undefined,
+		};
 	}

-	totalMonsterXp = Math.max(0, totalMonsterXp);
+	// 2014 edition
+	const budget = accumulateBudget2014(partyLevels);
+	const { multiplier: encounterMultiplier, partySizeAdjusted } =
+		getEncounterMultiplier(monsterCount, partyLevels.length);
+	const adjustedXp = Math.round(totalMonsterXp * encounterMultiplier);
+	const thresholds: DifficultyThreshold[] = [
+		{ label: "Easy", value: budget.easy },
+		{ label: "Medium", value: budget.medium },
+		{ label: "Hard", value: budget.hard },
+		{ label: "Deadly", value: budget.deadly },
+	];

 	return {
-		tier: determineTier(totalMonsterXp, budgetLow, budgetModerate, budgetHigh),
+		tier: determineTier(adjustedXp, [
+			budget.medium,
+			budget.hard,
+			budget.deadly,
+		]),
 		totalMonsterXp,
-		partyBudget: {
-			low: budgetLow,
-			moderate: budgetModerate,
-			high: budgetHigh,
-		},
+		thresholds,
+		encounterMultiplier,
+		adjustedXp,
+		partySizeAdjusted,
 	};
 }