Add min/max hit point variants for D&D creatures

A D&D stat block opened for a combatant now offers a Min/Avg/Max toggle below the Hit Points line, deriving both ends from the Hit Dice formula (3d6 + 6 -> 9 / 16 / 24). The switch is applied as a delta, so manual HP edits and damage already taken survive it. Unlike the PF2e weak/elite adjustment this is a convenience tool, not a rules mechanic: nothing but HP changes and the combatant is not renamed. The toggle is hidden when the HP field carries prose instead of a dice pool. Also extracts a SegmentedControl primitive. Game system, theme and the PF2e weak/elite toggle were three hand-rolled copies of the same markup, which is why the D&D toggle first came out chunkier and in the wrong accent color. All four now share one definition, and segments expose aria-pressed instead of signalling the active state by color alone. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-05 17:06:01 +02:00
parent 7b599e9ad9
commit be3778a0c9
22 changed files with 942 additions and 88 deletions
@@ -0,0 +1,58 @@
+/** Which end of a creature's Hit Dice range its max HP is taken from. */
+export type HpVariant = "min" | "max";
+
+export const VALID_HP_VARIANTS: ReadonlySet<string> = new Set(["min", "max"]);
+
+export interface HpRange {
+	/** Every Hit Die rolls a 1 (never below 1 HP). */
+	readonly min: number;
+	/** The statblock's printed average. */
+	readonly average: number;
+	/** Every Hit Die rolls its maximum. */
+	readonly max: number;
+}
+
+/**
+ * Matches a plain Hit Dice pool: "9d8", "3d6 + 6", "2d6 - 2".
+ * Bestiary data uses several dash characters, so hyphen, minus sign, en dash
+ * and em dash all count as a negative modifier.
+ */
+const DICE_FORMULA_REGEX =
+	/^\s*(\d+)\s*[dD]\s*(\d+)\s*(?:([-+−–—])\s*(\d+))?\s*$/;
+
+/**
+ * Derives the min/average/max HP of a creature from its Hit Dice formula.
+ * Returns null when the formula is not a plain dice pool — some sources carry
+ * prose (`hp.special`) or an empty string instead.
+ */
+export function hpRange(
+	hp: Readonly<{ average: number; formula: string }>,
+): HpRange | null {
+	const match = DICE_FORMULA_REGEX.exec(hp.formula);
+	if (!match) return null;
+
+	const count = Number(match[1]);
+	const sides = Number(match[2]);
+	if (count < 1 || sides < 1) return null;
+
+	const modifier =
+		match[4] === undefined
+			? 0
+			: (match[3] === "+" ? 1 : -1) * Number.parseInt(match[4], 10);
+
+	return {
+		min: Math.max(1, count + modifier),
+		average: hp.average,
+		max: Math.max(1, count * sides + modifier),
+	};
+}
+
+/** The HP value a variant selects; undefined means the printed average. */
+export function hpForVariant(
+	range: HpRange,
+	variant: HpVariant | undefined,
+): number {
+	if (variant === "min") return range.min;
+	if (variant === "max") return range.max;
+	return range.average;
+}