Adding Mod Parsers

Overview

The mod parser converts raw mod strings (e.g., "+10% all stats") into typed Mod objects used by the calculation engine. It uses a template-based system for pattern matching.

When to Use

• Adding support for new mod string patterns
• Extending existing mod types to handle new variants
• Adding new mod types to the engine

Project File Locations

Implementation Checklist

1. Check if Mod Type Exists

Look in src/tli/mod.ts under ModDefinitions. If the mod type doesn't exist, add it:

interface ModDefinitions {
  // ... existing types ...
  NewModType: { value: number; someField: string };
}

2. Add Template in templates.ts

Templates use a DSL for pattern matching:

// Simple template
t("{value:dec%} all stats").output("StatPct", (c) => ({
  value: c.value,
  statModType: "all" as const,
})),

// Template with enum lookup
t("{value:dec%} {statModType:StatWord}")
  .enum("StatWord", StatWordMapping)
  .output("StatPct", (c) => ({ value: c.value, statModType: c.statModType })),

// Template with optional parts (brackets)
t("{value:dec%} [additional] [{modType:DmgModType}] damage").output("DmgPct", (c) => ({
  value: c.value,
  dmgModType: c.modType ?? "global",
  addn: c.additional !== undefined,
})),

// Template outputting multiple mods
t("{value:dec%} attack and cast speed").outputMany([
  spec("AspdPct", (c) => ({ value: c.value, addn: false })),
  spec("CspdPct", (c) => ({ value: c.value, addn: false })),
]),

Template capture types:

Signed vs Unsigned Types:

• Use unsigned (dec%, int) when input does NOT start with + or - (e.g., "8% additional damage applied to Life")
• Use signed (+dec%, +int) when input STARTS with + or - (e.g., "+25% additional damage")
• Signed types will NOT match unsigned inputs, and vice versa

Optional syntax:

• [additional] - Optional literal, sets c.additional?: true
• [{modType:DmgModType}] - Optional capture, sets c.modType?: DmgModType
• (effect|damage) - Alternation (regex-style)

3. Add Enum Mapping (if needed)

If you need custom word → value mapping, add to enums.ts:

// Custom word mappings (input word -> output value)
export const StatWordMapping: Record<string, string> = {
  strength: "str",
  dexterity: "dex",
  intelligence: "int",
};

// Register for validation
registerEnum("StatWord", ["strength", "dexterity", "intelligence"]);

4. Add Handler in offense.ts (if new mod type)

If you added a new mod type, add handling in calculateOffense() or relevant helper:

case "NewModType": {
  // Apply the mod effect
  break;
}

For existing mod types with new variants (like adding statModType: "all"), update existing handlers:

// Before: only handled individual stats
const flat = sumByValue(statMods.filter((m) => m.statModType === statType));

// After: also handles "all"
const flat = sumByValue(
  statMods.filter((m) => m.statModType === statType || m.statModType === "all"),
);

5. Add Tests

Add test cases in src/tli/mod_parser.test.ts:

test("parse percentage all stats", () => {
  const result = parseMod("+10% all stats");
  expect(result).toEqual([
    {
      type: "StatPct",
      statModType: "all",
      value: 10,
    },
  ]);
});

6. Verify

pnpm test src/tli/mod_parser.test.ts
pnpm typecheck
pnpm check

Template Ordering

IMPORTANT: More specific patterns must come before generic ones in allParsers array.

// Good: specific before generic
t("{value:dec%} all stats").output(...),           // Specific
t("{value:dec%} {statModType:StatWord}").output(...), // Generic

// Bad: generic would match first and fail on "all stats"

Examples

Simple Value Parser (Signed)

Input: "+10% all stats" (starts with +)

t("{value:+dec%} all stats").output("StatPct", (c) => ({
  value: c.value,
  statModType: "all" as const,
})),

Simple Value Parser (Unsigned)

Input: "8% additional damage applied to Life" (no sign)

t("{value:dec%} additional damage applied to life").output("DmgPct", (c) => ({
  value: c.value,
  dmgModType: "global" as const,
  addn: true,
})),

Parser with Condition (Signed)

Input: "+40% damage if you have Blocked recently"

t("{value:+dec%} damage if you have blocked recently").output("DmgPct", (c) => ({
  value: c.value,
  dmgModType: "global" as const,
  addn: false,
  cond: "has_blocked_recently" as const,
})),

Parser with Per-Stackable (Signed in "deals" position)

Input: "Deals +1% additional damage to an enemy for every 2 points of Frostbite Rating the enemy has"

Note: The + appears AFTER "deals", so use {value:+dec%}:

t("deals {value:+dec%} additional damage to an enemy for every {amt:int} points of frostbite rating the enemy has")
  .output("DmgPct", (c) => ({
    value: c.value,
    dmgModType: "global" as const,
    addn: true,
    per: { stackable: "frostbite_rating" as const, amt: c.amt },
  })),

Multi-Output Parser (Signed)

Input: "+6% attack and cast speed"

t("{value:+dec%} [additional] attack and cast speed").outputMany([
  spec("AspdPct", (c) => ({ value: c.value, addn: c.additional !== undefined })),
  spec("CspdPct", (c) => ({ value: c.value, addn: c.additional !== undefined })),
]),

Flat Stat Parser (Signed)

Input: "+166 Max Mana"

t("{value:+dec} max mana").output("MaxMana", (c) => ({ value: c.value })),

Common Mistakes

Data Flow

Raw string: "+10% all stats"
    ↓ normalize (lowercase, trim)
"10% all stats"
    ↓ template matching (allParsers)
{ type: "StatPct", value: 10, statModType: "all" }
    ↓ calculateStats() in offense.ts
Applied to str, dex, int calculations