adding-mod-parsers

name	adding-mod-parsers
description	Use when adding new mod parsers to convert game mod strings to typed Mod objects - guides the template-based parsing pattern (project)

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

Purpose	File Path
Mod type definitions	src/tli/mod.ts
Parser templates	src/tli/mod-parser/templates.ts
Enum registrations	src/tli/mod-parser/enums.ts
Calculation handlers	src/tli/calcs/offense.ts
Tests	src/tli/mod-parser.test.ts

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. Do not add comments to templates.ts - the template string itself is self-documenting.

t("{value:dec%} all stats").output((c) => ({
  type: "StatPct",
  value: c.value,
  statModType: "all",
})),
t("{value:dec%} {statModType:StatWord}")
  .enum("StatWord", StatWordMapping)
  .output((c) => ({ type: "StatPct", value: c.value, statModType: c.statModType })),
t("{value:dec%} [additional] [{modType:DmgModType}] damage").output((c) => ({
  type: "DmgPct",
  value: c.value,
  dmgModType: c.modType ?? "global",
  addn: c.additional !== undefined,
})),
t("{value:dec%} attack and cast speed").outputMany([
  spec((c) => ({ type: "AspdPct", value: c.value, addn: false })),
  spec( ({ : , : c., :  })),
]),

Template capture types:

Type	Matches	Example Input → Output
{name:int}	Unsigned integer	"5" → 5
{name:dec}	Unsigned decimal	"21.5" → 21.5
{name:int%}	Unsigned integer percent	"30%" → 30
{name:dec%}	Unsigned decimal percent	"96%" → 96
{name:+int}	Signed integer (requires + or -)	"+5" → 5, "-3" → -3
{name:+dec}	Signed decimal (requires + or -)	"+21.5" → 21.5
{name:+int%}	Signed integer percent	"+30%" → 30, "-15%" → -15
{name:+dec%}	Signed decimal percent	"+96%" → 96
{name:?int}	Optional-sign integer (matches with or without +/-)	"5" → 5, "+5" → 5, "-3" → -3
{name:?dec}	Optional-sign decimal	"21.5" → 21.5, "+21.5" → 21.5
{name:?int%}

Signed vs Unsigned vs Optional-sign Types:

• Use unsigned (dec%, int) when input NEVER has + or - (e.g., "8% additional damage applied to Life")
• Use signed (+dec%, +int) when input ALWAYS has + or - (e.g., "+25% additional damage")
• Use optional-sign (?dec%, ?int) when input MAY OR MAY NOT have a sign — this avoids needing two separate templates for signed/unsigned variants
• Signed types will NOT match unsigned inputs, and unsigned will NOT match signed inputs
• Prefer ?dec% over two separate dec%/+dec% templates when the same mod can appear with or without a sign

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:

export const StatWordMapping: Record<string, string> = {
  strength: "str",
  dexterity: "dex",
  intelligence: "int",
};

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": {
  break;
}

For existing mod types with new variants (like adding statModType: "all"), update existing handlers to also filter for the new variant:

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((c) => ({
  type: "StatPct",
  value: c.value,
  statModType: "all",
})),

Simple Value Parser (Unsigned)

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

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

Parser with Condition (Signed)

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

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

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((c) => ({
    type: "DmgPct",
    value: c.value,
    dmgModType: "global",
    addn: true,
    per: { stackable: "frostbite_rating", amt: c.amt },
  })),

Multi-Output Parser (Signed)

Input: "+6% attack and cast speed"

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

Flat Stat Parser (Signed)

Input: "+166 Max Mana"

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

Optional-Sign Parser

Input: "12.5% Sealed Mana Compensation for Spirit Magus Skills" OR "+12.5% Sealed Mana Compensation for Spirit Magus Skills"

Use ?dec% when the same mod string can appear with or without a +/- sign, avoiding the need for two separate templates:

t("{value:?dec%} sealed mana compensation for spirit magus skills").output(
  (c) => ({ type: "SealedManaCompPct", value: c.value, addn: false, skillType: "spirit_magus" }),
),

No-Op Parser (Recognized but produces no mods)

Input: "Energy Shield starts to Charge when Blocking"

Use outputNone() when a mod string should be recognized (not flagged as unparsed) but has no effect on calculations:

t("energy shield starts to charge when blocking").outputNone(),

Common Mistakes

Mistake	Fix
Using dec% for input with + prefix	Use +dec% for inputs like "+25% damage", or ?dec% if sign is optional
Using +dec% for input without sign	Use dec% for inputs like "8% damage applied to life", or ?dec% if sign is optional
Two templates for signed/unsigned variants of the same mod	Use ?dec% to match both in a single template
Template doesn't match input case	Templates are matched case-insensitively; input is normalized to lowercase
Missing type field in output mapper	Include type: "ModType" in the returned object — contextual typing from the Mod discriminated union handles narrowing
Handler doesn't account for new variant	Update offense.ts to handle new values (e.g., statModType === "all")
Generic template before specific	Move specific templates earlier in allParsers array

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