Add PF2e encounter difficulty calculation with 5-tier budget system

Implements PF2e encounter difficulty alongside the existing D&D system. PF2e uses creature level vs party level to derive XP, compares against 5-tier budgets (Trivial/Low/Moderate/Severe/Extreme), and adjusts thresholds for party size. The indicator shows 4 bars in PF2e mode. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-04-11 15:24:18 +02:00
parent 064af16f95
commit d9fb271607
14 changed files with 1153 additions and 44 deletions
@@ -2,6 +2,8 @@ import { describe, expect, it } from "vitest";
 import {
 	calculateEncounterDifficulty,
 	crToXp,
+	derivePartyLevel,
+	pf2eCreatureXp,
 } from "../encounter-difficulty.js";

 describe("crToXp", () => {
@@ -386,3 +388,234 @@ describe("calculateEncounterDifficulty — 2014 edition", () => {
 		expect(result.adjustedXp).toBeUndefined();
 	});
 });
+
+/** Helper to build a PF2e enemy-side descriptor with creature level. */
+function pf2eEnemy(creatureLevel: number) {
+	return { creatureLevel, side: "enemy" as const };
+}
+
+/** Helper to build a PF2e party-side creature descriptor. */
+function pf2eAlly(creatureLevel: number) {
+	return { creatureLevel, side: "party" as const };
+}
+
+describe("derivePartyLevel", () => {
+	it("returns 0 for empty array", () => {
+		expect(derivePartyLevel([])).toBe(0);
+	});
+
+	it("returns the level for a single PC", () => {
+		expect(derivePartyLevel([7])).toBe(7);
+	});
+
+	it("returns the unanimous level", () => {
+		expect(derivePartyLevel([5, 5, 5, 5])).toBe(5);
+	});
+
+	it("returns the mode when one level is most common", () => {
+		expect(derivePartyLevel([3, 3, 3, 5])).toBe(3);
+	});
+
+	it("returns rounded average when mode is tied", () => {
+		// 3,3,5,5 → average 4
+		expect(derivePartyLevel([3, 3, 5, 5])).toBe(4);
+	});
+
+	it("returns rounded average when all levels are different", () => {
+		// 2,4,6,8 → average 5
+		expect(derivePartyLevel([2, 4, 6, 8])).toBe(5);
+	});
+
+	it("rounds average to nearest integer", () => {
+		// 1,2 → average 1.5 → rounds to 2
+		expect(derivePartyLevel([1, 2])).toBe(2);
+	});
+});
+
+describe("pf2eCreatureXp", () => {
+	it.each([
+		[-4, 10],
+		[-3, 15],
+		[-2, 20],
+		[-1, 30],
+		[0, 40],
+		[1, 60],
+		[2, 80],
+		[3, 120],
+		[4, 160],
+	])("level diff %i returns %i XP", (diff, expectedXp) => {
+		// partyLevel 5, creatureLevel = 5 + diff
+		expect(pf2eCreatureXp(5 + diff, 5)).toBe(expectedXp);
+	});
+
+	it("clamps level diff below −4 to −4 (10 XP)", () => {
+		expect(pf2eCreatureXp(0, 10)).toBe(10);
+	});
+
+	it("clamps level diff above +4 to +4 (160 XP)", () => {
+		expect(pf2eCreatureXp(15, 5)).toBe(160);
+	});
+});
+
+describe("calculateEncounterDifficulty — pf2e edition", () => {
+	it("returns Trivial (tier 0) for 40 XP with party of 4", () => {
+		// 1 creature at party level = 40 XP, below Low (60)
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(5)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(0);
+		expect(result.totalMonsterXp).toBe(40);
+		expect(result.partyLevel).toBe(5);
+		expect(result.thresholds).toEqual([
+			{ label: "Trivial", value: 40 },
+			{ label: "Low", value: 60 },
+			{ label: "Moderate", value: 80 },
+			{ label: "Severe", value: 120 },
+			{ label: "Extreme", value: 160 },
+		]);
+	});
+
+	it("returns Low (tier 1) for 60 XP", () => {
+		// 1 creature at party level +1 = 60 XP
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(6)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(1);
+		expect(result.totalMonsterXp).toBe(60);
+	});
+
+	it("returns Moderate (tier 2) for 80 XP", () => {
+		// 1 creature at +2 = 80 XP
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(7)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(2);
+		expect(result.totalMonsterXp).toBe(80);
+	});
+
+	it("returns Severe (tier 3) for 120 XP", () => {
+		// 1 creature at +3 = 120 XP
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(8)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(3);
+		expect(result.totalMonsterXp).toBe(120);
+	});
+
+	it("returns Extreme (tier 4) for 160 XP", () => {
+		// 1 creature at +4 = 160 XP
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(9)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(4);
+		expect(result.totalMonsterXp).toBe(160);
+	});
+
+	it("returns tier 0 when XP is below Low threshold", () => {
+		// 1 creature at −4 = 10 XP, Low = 60
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(1)],
+			"pf2e",
+		);
+		expect(result.tier).toBe(0);
+		expect(result.totalMonsterXp).toBe(10);
+	});
+
+	it("adjusts thresholds for 5 PCs (increases by adjustment)", () => {
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), party(5), pf2eEnemy(5)],
+			"pf2e",
+		);
+		expect(result.thresholds).toEqual([
+			{ label: "Trivial", value: 50 },
+			{ label: "Low", value: 75 },
+			{ label: "Moderate", value: 100 },
+			{ label: "Severe", value: 150 },
+			{ label: "Extreme", value: 200 },
+		]);
+	});
+
+	it("adjusts thresholds for 3 PCs (decreases by adjustment)", () => {
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), pf2eEnemy(5)],
+			"pf2e",
+		);
+		expect(result.thresholds).toEqual([
+			{ label: "Trivial", value: 30 },
+			{ label: "Low", value: 45 },
+			{ label: "Moderate", value: 60 },
+			{ label: "Severe", value: 90 },
+			{ label: "Extreme", value: 120 },
+		]);
+	});
+
+	it("floors thresholds at 0 for very small parties", () => {
+		const result = calculateEncounterDifficulty(
+			[party(5), pf2eEnemy(5)],
+			"pf2e",
+		);
+		// 1 PC: adjustment = −3
+		// Trivial: 40 + (−3 * 10) = 10
+		// Low: 60 + (−3 * 15) = 15
+		expect(result.thresholds[0].value).toBe(10);
+		expect(result.thresholds[1].value).toBe(15);
+		expect(result.thresholds[2].value).toBe(20); // 80 − 60
+		expect(result.thresholds[3].value).toBe(30); // 120 − 90
+		expect(result.thresholds[4].value).toBe(40); // 160 − 120
+	});
+
+	it("subtracts XP for party-side creatures", () => {
+		// 2 enemies at party level = 80 XP, 1 ally at party level = 40 XP
+		// Net = 80 − 40 = 40 XP
+		const result = calculateEncounterDifficulty(
+			[
+				party(5),
+				party(5),
+				party(5),
+				party(5),
+				pf2eEnemy(5),
+				pf2eEnemy(5),
+				pf2eAlly(5),
+			],
+			"pf2e",
+		);
+		expect(result.totalMonsterXp).toBe(40);
+	});
+
+	it("floors net creature XP at 0", () => {
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(1), pf2eAlly(9)],
+			"pf2e",
+		);
+		expect(result.totalMonsterXp).toBe(0);
+	});
+
+	it("derives party level using mode", () => {
+		// 3x level 3, 1x level 5 → mode is 3
+		const result = calculateEncounterDifficulty(
+			[party(3), party(3), party(3), party(5), pf2eEnemy(3)],
+			"pf2e",
+		);
+		expect(result.partyLevel).toBe(3);
+	});
+
+	it("has no encounterMultiplier, adjustedXp, or partySizeAdjusted", () => {
+		const result = calculateEncounterDifficulty(
+			[party(5), party(5), party(5), party(5), pf2eEnemy(5)],
+			"pf2e",
+		);
+		expect(result.encounterMultiplier).toBeUndefined();
+		expect(result.adjustedXp).toBeUndefined();
+		expect(result.partySizeAdjusted).toBeUndefined();
+	});
+
+	it("returns partyLevel undefined for D&D editions", () => {
+		const result = calculateEncounterDifficulty([party(1), enemy("1")], "5.5e");
+		expect(result.partyLevel).toBeUndefined();
+	});
+});